flang/lib/Semantics/resolve-names.cpp

//===-- lib/Semantics/resolve-names.cpp -----------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "resolve-names.h"
#include "assignment.h"
#include "mod-file.h"
#include "pointer-assignment.h"
#include "program-tree.h"
#include "resolve-directives.h"
#include "resolve-names-utils.h"
#include "rewrite-parse-tree.h"
#include "flang/Common/Fortran.h"
#include "flang/Common/default-kinds.h"
#include "flang/Common/indirection.h"
#include "flang/Common/restorer.h"
#include "flang/Evaluate/characteristics.h"
#include "flang/Evaluate/check-expression.h"
#include "flang/Evaluate/common.h"
#include "flang/Evaluate/fold-designator.h"
#include "flang/Evaluate/fold.h"
#include "flang/Evaluate/intrinsics.h"
#include "flang/Evaluate/tools.h"
#include "flang/Evaluate/type.h"
#include "flang/Parser/parse-tree-visitor.h"
#include "flang/Parser/parse-tree.h"
#include "flang/Parser/tools.h"
#include "flang/Semantics/attr.h"
#include "flang/Semantics/expression.h"
#include "flang/Semantics/scope.h"
#include "flang/Semantics/semantics.h"
#include "flang/Semantics/symbol.h"
#include "flang/Semantics/tools.h"
#include "flang/Semantics/type.h"
#include "llvm/Support/raw_ostream.h"
#include <list>
#include <map>
#include <set>
#include <stack>

namespace Fortran::semantics {

using namespace parser::literals;

template <typename T> using Indirection = common::Indirection<T>;
using Message = parser::Message;
using Messages = parser::Messages;
using MessageFixedText = parser::MessageFixedText;
using MessageFormattedText = parser::MessageFormattedText;

class ResolveNamesVisitor;

// ImplicitRules maps initial character of identifier to the DeclTypeSpec
// representing the implicit type; std::nullopt if none.
// It also records the presence of IMPLICIT NONE statements.
// When inheritFromParent is set, defaults come from the parent rules.
class ImplicitRules {
public:
  ImplicitRules(SemanticsContext &context, ImplicitRules *parent)
      : parent_{parent}, context_{context} {
    inheritFromParent_ = parent != nullptr;
  }
  bool isImplicitNoneType() const;
  bool isImplicitNoneExternal() const;
  void set_isImplicitNoneType(bool x) { isImplicitNoneType_ = x; }
  void set_isImplicitNoneExternal(bool x) { isImplicitNoneExternal_ = x; }
  void set_inheritFromParent(bool x) { inheritFromParent_ = x; }
  // Get the implicit type for this name. May be null.
  const DeclTypeSpec *GetType(
      SourceName, bool respectImplicitNone = true) const;
  // Record the implicit type for the range of characters [fromLetter,
  // toLetter].
  void SetTypeMapping(const DeclTypeSpec &type, parser::Location fromLetter,
      parser::Location toLetter);

private:
  static char Incr(char ch);

  ImplicitRules *parent_;
  SemanticsContext &context_;
  bool inheritFromParent_{false}; // look in parent if not specified here
  bool isImplicitNoneType_{
      context_.IsEnabled(common::LanguageFeature::ImplicitNoneTypeAlways)};
  bool isImplicitNoneExternal_{false};
  // map_ contains the mapping between letters and types that were defined
  // by the IMPLICIT statements of the related scope. It does not contain
  // the default Fortran mappings nor the mapping defined in parents.
  std::map<char, common::Reference<const DeclTypeSpec>> map_;

  friend llvm::raw_ostream &operator<<(
      llvm::raw_ostream &, const ImplicitRules &);
  friend void ShowImplicitRule(
      llvm::raw_ostream &, const ImplicitRules &, char);
};

// scope -> implicit rules for that scope
using ImplicitRulesMap = std::map<const Scope *, ImplicitRules>;

// Track statement source locations and save messages.
class MessageHandler {
public:
  MessageHandler() { DIE("MessageHandler: default-constructed"); }
  explicit MessageHandler(SemanticsContext &c) : context_{&c} {}
  Messages &messages() { return context_->messages(); };
  const std::optional<SourceName> &currStmtSource() {
    return context_->location();
  }
  void set_currStmtSource(const std::optional<SourceName> &source) {
    context_->set_location(source);
  }

  // Emit a message associated with the current statement source.
  Message &Say(MessageFixedText &&);
  Message &Say(MessageFormattedText &&);
  // Emit a message about a SourceName
  Message &Say(const SourceName &, MessageFixedText &&);
  // Emit a formatted message associated with a source location.
  template <typename... A>
  Message &Say(const SourceName &source, MessageFixedText &&msg, A &&...args) {
    return context_->Say(source, std::move(msg), std::forward<A>(args)...);
  }

private:
  SemanticsContext *context_;
};

// Inheritance graph for the parse tree visitation classes that follow:
//   BaseVisitor
//   + AttrsVisitor
//   | + DeclTypeSpecVisitor
//   |   + ImplicitRulesVisitor
//   |     + ScopeHandler -----------+--+
//   |       + ModuleVisitor ========|==+
//   |       + InterfaceVisitor      |  |
//   |       +-+ SubprogramVisitor ==|==+
//   + ArraySpecVisitor              |  |
//     + DeclarationVisitor <--------+  |
//       + ConstructVisitor             |
//         + ResolveNamesVisitor <------+

class BaseVisitor {
public:
  BaseVisitor() { DIE("BaseVisitor: default-constructed"); }
  BaseVisitor(
      SemanticsContext &c, ResolveNamesVisitor &v, ImplicitRulesMap &rules)
      : implicitRulesMap_{&rules}, this_{&v}, context_{&c}, messageHandler_{c} {
  }
  template <typename T> void Walk(const T &);

  MessageHandler &messageHandler() { return messageHandler_; }
  const std::optional<SourceName> &currStmtSource() {
    return context_->location();
  }
  SemanticsContext &context() const { return *context_; }
  evaluate::FoldingContext &GetFoldingContext() const {
    return context_->foldingContext();
  }
  bool IsIntrinsic(
      const SourceName &name, std::optional<Symbol::Flag> flag) const {
    if (!flag) {
      return context_->intrinsics().IsIntrinsic(name.ToString());
    } else if (flag == Symbol::Flag::Function) {
      return context_->intrinsics().IsIntrinsicFunction(name.ToString());
    } else if (flag == Symbol::Flag::Subroutine) {
      return context_->intrinsics().IsIntrinsicSubroutine(name.ToString());
    } else {
      DIE("expected Subroutine or Function flag");
    }
  }

  // Make a placeholder symbol for a Name that otherwise wouldn't have one.
  // It is not in any scope and always has MiscDetails.
  void MakePlaceholder(const parser::Name &, MiscDetails::Kind);

  template <typename T> common::IfNoLvalue<T, T> FoldExpr(T &&expr) {
    return evaluate::Fold(GetFoldingContext(), std::move(expr));
  }

  template <typename T> MaybeExpr EvaluateExpr(const T &expr) {
    return FoldExpr(AnalyzeExpr(*context_, expr));
  }

  template <typename T>
  MaybeExpr EvaluateNonPointerInitializer(
      const Symbol &symbol, const T &expr, parser::CharBlock source) {
    if (!context().HasError(symbol)) {
      if (auto maybeExpr{AnalyzeExpr(*context_, expr)}) {
        auto restorer{GetFoldingContext().messages().SetLocation(source)};
        return evaluate::NonPointerInitializationExpr(
            symbol, std::move(*maybeExpr), GetFoldingContext());
      }
    }
    return std::nullopt;
  }

  template <typename T> MaybeIntExpr EvaluateIntExpr(const T &expr) {
    return semantics::EvaluateIntExpr(*context_, expr);
  }

  template <typename T>
  MaybeSubscriptIntExpr EvaluateSubscriptIntExpr(const T &expr) {
    if (MaybeIntExpr maybeIntExpr{EvaluateIntExpr(expr)}) {
      return FoldExpr(evaluate::ConvertToType<evaluate::SubscriptInteger>(
          std::move(*maybeIntExpr)));
    } else {
      return std::nullopt;
    }
  }

  template <typename... A> Message &Say(A &&...args) {
    return messageHandler_.Say(std::forward<A>(args)...);
  }
  template <typename... A>
  Message &Say(
      const parser::Name &name, MessageFixedText &&text, const A &...args) {
    return messageHandler_.Say(name.source, std::move(text), args...);
  }

protected:
  ImplicitRulesMap *implicitRulesMap_{nullptr};

private:
  ResolveNamesVisitor *this_;
  SemanticsContext *context_;
  MessageHandler messageHandler_;
};

// Provide Post methods to collect attributes into a member variable.
class AttrsVisitor : public virtual BaseVisitor {
public:
  bool BeginAttrs(); // always returns true
  Attrs GetAttrs();
  Attrs EndAttrs();
  bool SetPassNameOn(Symbol &);
  void SetBindNameOn(Symbol &);
  void Post(const parser::LanguageBindingSpec &);
  bool Pre(const parser::IntentSpec &);
  bool Pre(const parser::Pass &);

  bool CheckAndSet(Attr);

// Simple case: encountering CLASSNAME causes ATTRNAME to be set.
#define HANDLE_ATTR_CLASS(CLASSNAME, ATTRNAME) \
  bool Pre(const parser::CLASSNAME &) { \
    CheckAndSet(Attr::ATTRNAME); \
    return false; \
  }
  HANDLE_ATTR_CLASS(PrefixSpec::Elemental, ELEMENTAL)
  HANDLE_ATTR_CLASS(PrefixSpec::Impure, IMPURE)
  HANDLE_ATTR_CLASS(PrefixSpec::Module, MODULE)
  HANDLE_ATTR_CLASS(PrefixSpec::Non_Recursive, NON_RECURSIVE)
  HANDLE_ATTR_CLASS(PrefixSpec::Pure, PURE)
  HANDLE_ATTR_CLASS(PrefixSpec::Recursive, RECURSIVE)
  HANDLE_ATTR_CLASS(TypeAttrSpec::BindC, BIND_C)
  HANDLE_ATTR_CLASS(BindAttr::Deferred, DEFERRED)
  HANDLE_ATTR_CLASS(BindAttr::Non_Overridable, NON_OVERRIDABLE)
  HANDLE_ATTR_CLASS(Abstract, ABSTRACT)
  HANDLE_ATTR_CLASS(Allocatable, ALLOCATABLE)
  HANDLE_ATTR_CLASS(Asynchronous, ASYNCHRONOUS)
  HANDLE_ATTR_CLASS(Contiguous, CONTIGUOUS)
  HANDLE_ATTR_CLASS(External, EXTERNAL)
  HANDLE_ATTR_CLASS(Intrinsic, INTRINSIC)
  HANDLE_ATTR_CLASS(NoPass, NOPASS)
  HANDLE_ATTR_CLASS(Optional, OPTIONAL)
  HANDLE_ATTR_CLASS(Parameter, PARAMETER)
  HANDLE_ATTR_CLASS(Pointer, POINTER)
  HANDLE_ATTR_CLASS(Protected, PROTECTED)
  HANDLE_ATTR_CLASS(Save, SAVE)
  HANDLE_ATTR_CLASS(Target, TARGET)
  HANDLE_ATTR_CLASS(Value, VALUE)
  HANDLE_ATTR_CLASS(Volatile, VOLATILE)
#undef HANDLE_ATTR_CLASS

protected:
  std::optional<Attrs> attrs_;

  Attr AccessSpecToAttr(const parser::AccessSpec &x) {
    switch (x.v) {
    case parser::AccessSpec::Kind::Public:
      return Attr::PUBLIC;
    case parser::AccessSpec::Kind::Private:
      return Attr::PRIVATE;
    }
    llvm_unreachable("Switch covers all cases"); // suppress g++ warning
  }
  Attr IntentSpecToAttr(const parser::IntentSpec &x) {
    switch (x.v) {
    case parser::IntentSpec::Intent::In:
      return Attr::INTENT_IN;
    case parser::IntentSpec::Intent::Out:
      return Attr::INTENT_OUT;
    case parser::IntentSpec::Intent::InOut:
      return Attr::INTENT_INOUT;
    }
    llvm_unreachable("Switch covers all cases"); // suppress g++ warning
  }

private:
  bool IsDuplicateAttr(Attr);
  bool HaveAttrConflict(Attr, Attr, Attr);
  bool IsConflictingAttr(Attr);

  MaybeExpr bindName_; // from BIND(C, NAME="...")
  std::optional<SourceName> passName_; // from PASS(...)
};

// Find and create types from declaration-type-spec nodes.
class DeclTypeSpecVisitor : public AttrsVisitor {
public:
  using AttrsVisitor::Post;
  using AttrsVisitor::Pre;
  void Post(const parser::IntrinsicTypeSpec::DoublePrecision &);
  void Post(const parser::IntrinsicTypeSpec::DoubleComplex &);
  void Post(const parser::DeclarationTypeSpec::ClassStar &);
  void Post(const parser::DeclarationTypeSpec::TypeStar &);
  bool Pre(const parser::TypeGuardStmt &);
  void Post(const parser::TypeGuardStmt &);
  void Post(const parser::TypeSpec &);

protected:
  struct State {
    bool expectDeclTypeSpec{false}; // should see decl-type-spec only when true
    const DeclTypeSpec *declTypeSpec{nullptr};
    struct {
      DerivedTypeSpec *type{nullptr};
      DeclTypeSpec::Category category{DeclTypeSpec::TypeDerived};
    } derived;
    bool allowForwardReferenceToDerivedType{false};
  };

  bool allowForwardReferenceToDerivedType() const {
    return state_.allowForwardReferenceToDerivedType;
  }
  void set_allowForwardReferenceToDerivedType(bool yes) {
    state_.allowForwardReferenceToDerivedType = yes;
  }

  // Walk the parse tree of a type spec and return the DeclTypeSpec for it.
  template <typename T>
  const DeclTypeSpec *ProcessTypeSpec(const T &x, bool allowForward = false) {
    auto restorer{common::ScopedSet(state_, State{})};
    set_allowForwardReferenceToDerivedType(allowForward);
    BeginDeclTypeSpec();
    Walk(x);
    const auto *type{GetDeclTypeSpec()};
    EndDeclTypeSpec();
    return type;
  }

  const DeclTypeSpec *GetDeclTypeSpec();
  void BeginDeclTypeSpec();
  void EndDeclTypeSpec();
  void SetDeclTypeSpec(const DeclTypeSpec &);
  void SetDeclTypeSpecCategory(DeclTypeSpec::Category);
  DeclTypeSpec::Category GetDeclTypeSpecCategory() const {
    return state_.derived.category;
  }
  KindExpr GetKindParamExpr(
      TypeCategory, const std::optional<parser::KindSelector> &);
  void CheckForAbstractType(const Symbol &typeSymbol);

private:
  State state_;

  void MakeNumericType(TypeCategory, int kind);
};

// Visit ImplicitStmt and related parse tree nodes and updates implicit rules.
class ImplicitRulesVisitor : public DeclTypeSpecVisitor {
public:
  using DeclTypeSpecVisitor::Post;
  using DeclTypeSpecVisitor::Pre;
  using ImplicitNoneNameSpec = parser::ImplicitStmt::ImplicitNoneNameSpec;

  void Post(const parser::ParameterStmt &);
  bool Pre(const parser::ImplicitStmt &);
  bool Pre(const parser::LetterSpec &);
  bool Pre(const parser::ImplicitSpec &);
  void Post(const parser::ImplicitSpec &);

  const DeclTypeSpec *GetType(
      SourceName name, bool respectImplicitNoneType = true) {
    return implicitRules_->GetType(name, respectImplicitNoneType);
  }
  bool isImplicitNoneType() const {
    return implicitRules_->isImplicitNoneType();
  }
  bool isImplicitNoneType(const Scope &scope) const {
    return implicitRulesMap_->at(&scope).isImplicitNoneType();
  }
  bool isImplicitNoneExternal() const {
    return implicitRules_->isImplicitNoneExternal();
  }
  void set_inheritFromParent(bool x) {
    implicitRules_->set_inheritFromParent(x);
  }

protected:
  void BeginScope(const Scope &);
  void SetScope(const Scope &);

private:
  // implicit rules in effect for current scope
  ImplicitRules *implicitRules_{nullptr};
  std::optional<SourceName> prevImplicit_;
  std::optional<SourceName> prevImplicitNone_;
  std::optional<SourceName> prevImplicitNoneType_;
  std::optional<SourceName> prevParameterStmt_;

  bool HandleImplicitNone(const std::list<ImplicitNoneNameSpec> &nameSpecs);
};

// Track array specifications. They can occur in AttrSpec, EntityDecl,
// ObjectDecl, DimensionStmt, CommonBlockObject, or BasedPointerStmt.
// 1. INTEGER, DIMENSION(10) :: x
// 2. INTEGER :: x(10)
// 3. ALLOCATABLE :: x(:)
// 4. DIMENSION :: x(10)
// 5. COMMON x(10)
// 6. BasedPointerStmt
class ArraySpecVisitor : public virtual BaseVisitor {
public:
  void Post(const parser::ArraySpec &);
  void Post(const parser::ComponentArraySpec &);
  void Post(const parser::CoarraySpec &);
  void Post(const parser::AttrSpec &) { PostAttrSpec(); }
  void Post(const parser::ComponentAttrSpec &) { PostAttrSpec(); }

protected:
  const ArraySpec &arraySpec();
  void set_arraySpec(const ArraySpec arraySpec) { arraySpec_ = arraySpec; }
  const ArraySpec &coarraySpec();
  void BeginArraySpec();
  void EndArraySpec();
  void ClearArraySpec() { arraySpec_.clear(); }
  void ClearCoarraySpec() { coarraySpec_.clear(); }

private:
  // arraySpec_/coarraySpec_ are populated from any ArraySpec/CoarraySpec
  ArraySpec arraySpec_;
  ArraySpec coarraySpec_;
  // When an ArraySpec is under an AttrSpec or ComponentAttrSpec, it is moved
  // into attrArraySpec_
  ArraySpec attrArraySpec_;
  ArraySpec attrCoarraySpec_;

  void PostAttrSpec();
};

// Manage a stack of Scopes
class ScopeHandler : public ImplicitRulesVisitor {
public:
  using ImplicitRulesVisitor::Post;
  using ImplicitRulesVisitor::Pre;

  Scope &currScope() { return DEREF(currScope_); }
  // The enclosing host procedure if current scope is in an internal procedure
  Scope *GetHostProcedure();
  // The innermost enclosing program unit scope, ignoring BLOCK and other
  // construct scopes.
  Scope &InclusiveScope();
  // The enclosing scope, skipping derived types.
  Scope &NonDerivedTypeScope();

  // Create a new scope and push it on the scope stack.
  void PushScope(Scope::Kind kind, Symbol *symbol);
  void PushScope(Scope &scope);
  void PopScope();
  void SetScope(Scope &);

  template <typename T> bool Pre(const parser::Statement<T> &x) {
    messageHandler().set_currStmtSource(x.source);
    currScope_->AddSourceRange(x.source);
    return true;
  }
  template <typename T> void Post(const parser::Statement<T> &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }

  // Special messages: already declared; referencing symbol's declaration;
  // about a type; two names & locations
  void SayAlreadyDeclared(const parser::Name &, Symbol &);
  void SayAlreadyDeclared(const SourceName &, Symbol &);
  void SayAlreadyDeclared(const SourceName &, const SourceName &);
  void SayWithReason(
      const parser::Name &, Symbol &, MessageFixedText &&, MessageFixedText &&);
  void SayWithDecl(const parser::Name &, Symbol &, MessageFixedText &&);
  void SayLocalMustBeVariable(const parser::Name &, Symbol &);
  void SayDerivedType(const SourceName &, MessageFixedText &&, const Scope &);
  void Say2(const SourceName &, MessageFixedText &&, const SourceName &,
      MessageFixedText &&);
  void Say2(
      const SourceName &, MessageFixedText &&, Symbol &, MessageFixedText &&);
  void Say2(
      const parser::Name &, MessageFixedText &&, Symbol &, MessageFixedText &&);

  // Search for symbol by name in current, parent derived type, and
  // containing scopes
  Symbol *FindSymbol(const parser::Name &);
  Symbol *FindSymbol(const Scope &, const parser::Name &);
  // Search for name only in scope, not in enclosing scopes.
  Symbol *FindInScope(const Scope &, const parser::Name &);
  Symbol *FindInScope(const Scope &, const SourceName &);
  template <typename T> Symbol *FindInScope(const T &name) {
    return FindInScope(currScope(), name);
  }
  // Search for name in a derived type scope and its parents.
  Symbol *FindInTypeOrParents(const Scope &, const parser::Name &);
  Symbol *FindInTypeOrParents(const parser::Name &);
  void EraseSymbol(const parser::Name &);
  void EraseSymbol(const Symbol &symbol) { currScope().erase(symbol.name()); }
  // Make a new symbol with the name and attrs of an existing one
  Symbol &CopySymbol(const SourceName &, const Symbol &);

  // Make symbols in the current or named scope
  Symbol &MakeSymbol(Scope &, const SourceName &, Attrs);
  Symbol &MakeSymbol(const SourceName &, Attrs = Attrs{});
  Symbol &MakeSymbol(const parser::Name &, Attrs = Attrs{});
  Symbol &MakeHostAssocSymbol(const parser::Name &, const Symbol &);

  template <typename D>
  common::IfNoLvalue<Symbol &, D> MakeSymbol(
      const parser::Name &name, D &&details) {
    return MakeSymbol(name, Attrs{}, std::move(details));
  }

  template <typename D>
  common::IfNoLvalue<Symbol &, D> MakeSymbol(
      const parser::Name &name, const Attrs &attrs, D &&details) {
    return Resolve(name, MakeSymbol(name.source, attrs, std::move(details)));
  }

  template <typename D>
  common::IfNoLvalue<Symbol &, D> MakeSymbol(
      const SourceName &name, const Attrs &attrs, D &&details) {
    // Note: don't use FindSymbol here. If this is a derived type scope,
    // we want to detect whether the name is already declared as a component.
    auto *symbol{FindInScope(name)};
    if (!symbol) {
      symbol = &MakeSymbol(name, attrs);
      symbol->set_details(std::move(details));
      return *symbol;
    }
    if constexpr (std::is_same_v<DerivedTypeDetails, D>) {
      if (auto *d{symbol->detailsIf<GenericDetails>()}) {
        if (!d->specific()) {
          // derived type with same name as a generic
          auto *derivedType{d->derivedType()};
          if (!derivedType) {
            derivedType =
                &currScope().MakeSymbol(name, attrs, std::move(details));
            d->set_derivedType(*derivedType);
          } else {
            SayAlreadyDeclared(name, *derivedType);
          }
          return *derivedType;
        }
      }
    }
    if (symbol->CanReplaceDetails(details)) {
      // update the existing symbol
      symbol->attrs() |= attrs;
      if constexpr (std::is_same_v<SubprogramDetails, D>) {
        // Dummy argument defined by explicit interface
        details.set_isDummy(IsDummy(*symbol));
      }
      symbol->set_details(std::move(details));
      return *symbol;
    } else if constexpr (std::is_same_v<UnknownDetails, D>) {
      symbol->attrs() |= attrs;
      return *symbol;
    } else {
      if (!CheckPossibleBadForwardRef(*symbol)) {
        SayAlreadyDeclared(name, *symbol);
      }
      // replace the old symbol with a new one with correct details
      EraseSymbol(*symbol);
      auto &result{MakeSymbol(name, attrs, std::move(details))};
      context().SetError(result);
      return result;
    }
  }

  void MakeExternal(Symbol &);

protected:
  // Apply the implicit type rules to this symbol.
  void ApplyImplicitRules(Symbol &, bool allowForwardReference = false);
  bool ImplicitlyTypeForwardRef(Symbol &);
  void AcquireIntrinsicProcedureFlags(Symbol &);
  const DeclTypeSpec *GetImplicitType(
      Symbol &, bool respectImplicitNoneType = true);
  bool ConvertToObjectEntity(Symbol &);
  bool ConvertToProcEntity(Symbol &);

  const DeclTypeSpec &MakeNumericType(
      TypeCategory, const std::optional<parser::KindSelector> &);
  const DeclTypeSpec &MakeLogicalType(
      const std::optional<parser::KindSelector> &);
  void NotePossibleBadForwardRef(const parser::Name &);
  std::optional<SourceName> HadForwardRef(const Symbol &) const;
  bool CheckPossibleBadForwardRef(const Symbol &);

  bool inExecutionPart_{false};
  bool inSpecificationPart_{false};
  bool inEquivalenceStmt_{false};

  // Some information is collected from a specification part for deferred
  // processing in DeclarationPartVisitor functions (e.g., CheckSaveStmts())
  // that are called by ResolveNamesVisitor::FinishSpecificationPart().  Since
  // specification parts can nest (e.g., INTERFACE bodies), the collected
  // information that is not contained in the scope needs to be packaged
  // and restorable.
  struct SpecificationPartState {
    std::set<SourceName> forwardRefs;
    // Collect equivalence sets and process at end of specification part
    std::vector<const std::list<parser::EquivalenceObject> *> equivalenceSets;
    // Names of all common block objects in the scope
    std::set<SourceName> commonBlockObjects;
    // Info about about SAVE statements and attributes in current scope
    struct {
      std::optional<SourceName> saveAll; // "SAVE" without entity list
      std::set<SourceName> entities; // names of entities with save attr
      std::set<SourceName> commons; // names of common blocks with save attr
    } saveInfo;
  } specPartState_;

private:
  Scope *currScope_{nullptr};
};

class ModuleVisitor : public virtual ScopeHandler {
public:
  bool Pre(const parser::AccessStmt &);
  bool Pre(const parser::Only &);
  bool Pre(const parser::Rename::Names &);
  bool Pre(const parser::Rename::Operators &);
  bool Pre(const parser::UseStmt &);
  void Post(const parser::UseStmt &);

  void BeginModule(const parser::Name &, bool isSubmodule);
  bool BeginSubmodule(const parser::Name &, const parser::ParentIdentifier &);
  void ApplyDefaultAccess();
  void AddGenericUse(GenericDetails &, const SourceName &, const Symbol &);
  void ClearUseRenames() { useRenames_.clear(); }
  void ClearUseOnly() { useOnly_.clear(); }

private:
  // The default access spec for this module.
  Attr defaultAccess_{Attr::PUBLIC};
  // The location of the last AccessStmt without access-ids, if any.
  std::optional<SourceName> prevAccessStmt_;
  // The scope of the module during a UseStmt
  Scope *useModuleScope_{nullptr};
  // Names that have appeared in a rename clause of a USE statement
  std::set<std::pair<SourceName, Scope *>> useRenames_;
  // Names that have appeared in an ONLY clause of a USE statement
  std::set<std::pair<SourceName, Scope *>> useOnly_;

  Symbol &SetAccess(const SourceName &, Attr attr, Symbol * = nullptr);
  // A rename in a USE statement: local => use
  struct SymbolRename {
    Symbol *local{nullptr};
    Symbol *use{nullptr};
  };
  // Record a use from useModuleScope_ of use Name/Symbol as local Name/Symbol
  SymbolRename AddUse(const SourceName &localName, const SourceName &useName);
  SymbolRename AddUse(const SourceName &, const SourceName &, Symbol *);
  void DoAddUse(const SourceName &, const SourceName &, Symbol &localSymbol,
      const Symbol &useSymbol);
  void AddUse(const GenericSpecInfo &);
  // If appropriate, erase a previously USE-associated symbol
  void EraseRenamedSymbol(const Symbol &);
  // Record a name appearing in a USE rename clause
  void AddUseRename(const SourceName &name) {
    useRenames_.emplace(std::make_pair(name, useModuleScope_));
  }
  bool IsUseRenamed(const SourceName &name) const {
    return useRenames_.find({name, useModuleScope_}) != useRenames_.end();
  }
  // Record a name appearing in a USE ONLY clause
  void AddUseOnly(const SourceName &name) {
    useOnly_.emplace(std::make_pair(name, useModuleScope_));
  }
  bool IsUseOnly(const SourceName &name) const {
    return useOnly_.find({name, useModuleScope_}) != useOnly_.end();
  }
  Scope *FindModule(const parser::Name &, Scope *ancestor = nullptr);
};

class InterfaceVisitor : public virtual ScopeHandler {
public:
  bool Pre(const parser::InterfaceStmt &);
  void Post(const parser::InterfaceStmt &);
  void Post(const parser::EndInterfaceStmt &);
  bool Pre(const parser::GenericSpec &);
  bool Pre(const parser::ProcedureStmt &);
  bool Pre(const parser::GenericStmt &);
  void Post(const parser::GenericStmt &);

  bool inInterfaceBlock() const;
  bool isGeneric() const;
  bool isAbstract() const;

protected:
  Symbol &GetGenericSymbol() {
    return DEREF(genericInfo_.top().symbol);
  }
  // Add to generic the symbol for the subprogram with the same name
  void CheckGenericProcedures(Symbol &);

private:
  // A new GenericInfo is pushed for each interface block and generic stmt
  struct GenericInfo {
    GenericInfo(bool isInterface, bool isAbstract = false)
        : isInterface{isInterface}, isAbstract{isAbstract} {}
    bool isInterface; // in interface block
    bool isAbstract; // in abstract interface block
    Symbol *symbol{nullptr}; // the generic symbol being defined
  };
  std::stack<GenericInfo> genericInfo_;
  const GenericInfo &GetGenericInfo() const { return genericInfo_.top(); }
  void SetGenericSymbol(Symbol &symbol) { genericInfo_.top().symbol = &symbol; }

  using ProcedureKind = parser::ProcedureStmt::Kind;
  // mapping of generic to its specific proc names and kinds
  std::multimap<Symbol *, std::pair<const parser::Name *, ProcedureKind>>
      specificProcs_;

  void AddSpecificProcs(const std::list<parser::Name> &, ProcedureKind);
  void ResolveSpecificsInGeneric(Symbol &generic);
};

class SubprogramVisitor : public virtual ScopeHandler, public InterfaceVisitor {
public:
  bool HandleStmtFunction(const parser::StmtFunctionStmt &);
  bool Pre(const parser::SubroutineStmt &);
  void Post(const parser::SubroutineStmt &);
  bool Pre(const parser::FunctionStmt &);
  void Post(const parser::FunctionStmt &);
  bool Pre(const parser::EntryStmt &);
  void Post(const parser::EntryStmt &);
  bool Pre(const parser::InterfaceBody::Subroutine &);
  void Post(const parser::InterfaceBody::Subroutine &);
  bool Pre(const parser::InterfaceBody::Function &);
  void Post(const parser::InterfaceBody::Function &);
  bool Pre(const parser::Suffix &);
  bool Pre(const parser::PrefixSpec &);
  void Post(const parser::ImplicitPart &);

  bool BeginSubprogram(
      const parser::Name &, Symbol::Flag, bool hasModulePrefix = false);
  bool BeginMpSubprogram(const parser::Name &);
  void PushBlockDataScope(const parser::Name &);
  void EndSubprogram();

protected:
  // Set when we see a stmt function that is really an array element assignment
  bool badStmtFuncFound_{false};

private:
  // Info about the current function: parse tree of the type in the PrefixSpec;
  // name and symbol of the function result from the Suffix; source location.
  struct {
    const parser::DeclarationTypeSpec *parsedType{nullptr};
    const parser::Name *resultName{nullptr};
    Symbol *resultSymbol{nullptr};
    std::optional<SourceName> source;
  } funcInfo_;

  // Edits an existing symbol created for earlier calls to a subprogram or ENTRY
  // so that it can be replaced by a later definition.
  bool HandlePreviousCalls(const parser::Name &, Symbol &, Symbol::Flag);
  void CheckExtantProc(const parser::Name &, Symbol::Flag);
  // Create a subprogram symbol in the current scope and push a new scope.
  Symbol &PushSubprogramScope(const parser::Name &, Symbol::Flag);
  Symbol *GetSpecificFromGeneric(const parser::Name &);
  SubprogramDetails &PostSubprogramStmt(const parser::Name &);
};

class DeclarationVisitor : public ArraySpecVisitor,
                           public virtual ScopeHandler {
public:
  using ArraySpecVisitor::Post;
  using ScopeHandler::Post;
  using ScopeHandler::Pre;

  bool Pre(const parser::Initialization &);
  void Post(const parser::EntityDecl &);
  void Post(const parser::ObjectDecl &);
  void Post(const parser::PointerDecl &);
  bool Pre(const parser::BindStmt &) { return BeginAttrs(); }
  void Post(const parser::BindStmt &) { EndAttrs(); }
  bool Pre(const parser::BindEntity &);
  bool Pre(const parser::OldParameterStmt &);
  bool Pre(const parser::NamedConstantDef &);
  bool Pre(const parser::NamedConstant &);
  void Post(const parser::EnumDef &);
  bool Pre(const parser::Enumerator &);
  bool Pre(const parser::AccessSpec &);
  bool Pre(const parser::AsynchronousStmt &);
  bool Pre(const parser::ContiguousStmt &);
  bool Pre(const parser::ExternalStmt &);
  bool Pre(const parser::IntentStmt &);
  bool Pre(const parser::IntrinsicStmt &);
  bool Pre(const parser::OptionalStmt &);
  bool Pre(const parser::ProtectedStmt &);
  bool Pre(const parser::ValueStmt &);
  bool Pre(const parser::VolatileStmt &);
  bool Pre(const parser::AllocatableStmt &) {
    objectDeclAttr_ = Attr::ALLOCATABLE;
    return true;
  }
  void Post(const parser::AllocatableStmt &) { objectDeclAttr_ = std::nullopt; }
  bool Pre(const parser::TargetStmt &) {
    objectDeclAttr_ = Attr::TARGET;
    return true;
  }
  void Post(const parser::TargetStmt &) { objectDeclAttr_ = std::nullopt; }
  void Post(const parser::DimensionStmt::Declaration &);
  void Post(const parser::CodimensionDecl &);
  bool Pre(const parser::TypeDeclarationStmt &) { return BeginDecl(); }
  void Post(const parser::TypeDeclarationStmt &);
  void Post(const parser::IntegerTypeSpec &);
  void Post(const parser::IntrinsicTypeSpec::Real &);
  void Post(const parser::IntrinsicTypeSpec::Complex &);
  void Post(const parser::IntrinsicTypeSpec::Logical &);
  void Post(const parser::IntrinsicTypeSpec::Character &);
  void Post(const parser::CharSelector::LengthAndKind &);
  void Post(const parser::CharLength &);
  void Post(const parser::LengthSelector &);
  bool Pre(const parser::KindParam &);
  bool Pre(const parser::DeclarationTypeSpec::Type &);
  void Post(const parser::DeclarationTypeSpec::Type &);
  bool Pre(const parser::DeclarationTypeSpec::Class &);
  void Post(const parser::DeclarationTypeSpec::Class &);
  bool Pre(const parser::DeclarationTypeSpec::Record &);
  void Post(const parser::DerivedTypeSpec &);
  bool Pre(const parser::DerivedTypeDef &);
  bool Pre(const parser::DerivedTypeStmt &);
  void Post(const parser::DerivedTypeStmt &);
  bool Pre(const parser::TypeParamDefStmt &) { return BeginDecl(); }
  void Post(const parser::TypeParamDefStmt &);
  bool Pre(const parser::TypeAttrSpec::Extends &);
  bool Pre(const parser::PrivateStmt &);
  bool Pre(const parser::SequenceStmt &);
  bool Pre(const parser::ComponentDefStmt &) { return BeginDecl(); }
  void Post(const parser::ComponentDefStmt &) { EndDecl(); }
  void Post(const parser::ComponentDecl &);
  bool Pre(const parser::ProcedureDeclarationStmt &);
  void Post(const parser::ProcedureDeclarationStmt &);
  bool Pre(const parser::DataComponentDefStmt &); // returns false
  bool Pre(const parser::ProcComponentDefStmt &);
  void Post(const parser::ProcComponentDefStmt &);
  bool Pre(const parser::ProcPointerInit &);
  void Post(const parser::ProcInterface &);
  void Post(const parser::ProcDecl &);
  bool Pre(const parser::TypeBoundProcedurePart &);
  void Post(const parser::TypeBoundProcedurePart &);
  void Post(const parser::ContainsStmt &);
  bool Pre(const parser::TypeBoundProcBinding &) { return BeginAttrs(); }
  void Post(const parser::TypeBoundProcBinding &) { EndAttrs(); }
  void Post(const parser::TypeBoundProcedureStmt::WithoutInterface &);
  void Post(const parser::TypeBoundProcedureStmt::WithInterface &);
  void Post(const parser::FinalProcedureStmt &);
  bool Pre(const parser::TypeBoundGenericStmt &);
  bool Pre(const parser::AllocateStmt &);
  void Post(const parser::AllocateStmt &);
  bool Pre(const parser::StructureConstructor &);
  bool Pre(const parser::NamelistStmt::Group &);
  bool Pre(const parser::IoControlSpec &);
  bool Pre(const parser::CommonStmt::Block &);
  bool Pre(const parser::CommonBlockObject &);
  void Post(const parser::CommonBlockObject &);
  bool Pre(const parser::EquivalenceStmt &);
  bool Pre(const parser::SaveStmt &);
  bool Pre(const parser::BasedPointerStmt &);

  void PointerInitialization(
      const parser::Name &, const parser::InitialDataTarget &);
  void PointerInitialization(
      const parser::Name &, const parser::ProcPointerInit &);
  void NonPointerInitialization(
      const parser::Name &, const parser::ConstantExpr &);
  void CheckExplicitInterface(const parser::Name &);
  void CheckBindings(const parser::TypeBoundProcedureStmt::WithoutInterface &);

  const parser::Name *ResolveDesignator(const parser::Designator &);

protected:
  bool BeginDecl();
  void EndDecl();
  Symbol &DeclareObjectEntity(const parser::Name &, Attrs = Attrs{});
  // Make sure that there's an entity in an enclosing scope called Name
  Symbol &FindOrDeclareEnclosingEntity(const parser::Name &);
  // Declare a LOCAL/LOCAL_INIT entity. If there isn't a type specified
  // it comes from the entity in the containing scope, or implicit rules.
  // Return pointer to the new symbol, or nullptr on error.
  Symbol *DeclareLocalEntity(const parser::Name &);
  // Declare a statement entity (i.e., an implied DO loop index for
  // a DATA statement or an array constructor).  If there isn't an explict
  // type specified, implicit rules apply. Return pointer to the new symbol,
  // or nullptr on error.
  Symbol *DeclareStatementEntity(const parser::DoVariable &,
      const std::optional<parser::IntegerTypeSpec> &);
  Symbol &MakeCommonBlockSymbol(const parser::Name &);
  Symbol &MakeCommonBlockSymbol(const std::optional<parser::Name> &);
  bool CheckUseError(const parser::Name &);
  void CheckAccessibility(const SourceName &, bool, Symbol &);
  void CheckCommonBlocks();
  void CheckSaveStmts();
  void CheckEquivalenceSets();
  bool CheckNotInBlock(const char *);
  bool NameIsKnownOrIntrinsic(const parser::Name &);

  // Each of these returns a pointer to a resolved Name (i.e. with symbol)
  // or nullptr in case of error.
  const parser::Name *ResolveStructureComponent(
      const parser::StructureComponent &);
  const parser::Name *ResolveDataRef(const parser::DataRef &);
  const parser::Name *ResolveName(const parser::Name &);
  bool PassesSharedLocalityChecks(const parser::Name &name, Symbol &symbol);
  Symbol *NoteInterfaceName(const parser::Name &);
  bool IsUplevelReference(const Symbol &);

  std::optional<SourceName> BeginCheckOnIndexUseInOwnBounds(
      const parser::DoVariable &name) {
    std::optional<SourceName> result{checkIndexUseInOwnBounds_};
    checkIndexUseInOwnBounds_ = name.thing.thing.source;
    return result;
  }
  void EndCheckOnIndexUseInOwnBounds(const std::optional<SourceName> &restore) {
    checkIndexUseInOwnBounds_ = restore;
  }

private:
  // The attribute corresponding to the statement containing an ObjectDecl
  std::optional<Attr> objectDeclAttr_;
  // Info about current character type while walking DeclTypeSpec.
  // Also captures any "*length" specifier on an individual declaration.
  struct {
    std::optional<ParamValue> length;
    std::optional<KindExpr> kind;
  } charInfo_;
  // Info about current derived type while walking DerivedTypeDef
  struct {
    const parser::Name *extends{nullptr}; // EXTENDS(name)
    bool privateComps{false}; // components are private by default
    bool privateBindings{false}; // bindings are private by default
    bool sawContains{false}; // currently processing bindings
    bool sequence{false}; // is a sequence type
    const Symbol *type{nullptr}; // derived type being defined
  } derivedTypeInfo_;
  // In a ProcedureDeclarationStmt or ProcComponentDefStmt, this is
  // the interface name, if any.
  const parser::Name *interfaceName_{nullptr};
  // Map type-bound generic to binding names of its specific bindings
  std::multimap<Symbol *, const parser::Name *> genericBindings_;
  // Info about current ENUM
  struct EnumeratorState {
    // Enum value must hold inside a C_INT (7.6.2).
    std::optional<int> value{0};
  } enumerationState_;
  // Set for OldParameterStmt processing
  bool inOldStyleParameterStmt_{false};
  // Set when walking DATA & array constructor implied DO loop bounds
  // to warn about use of the implied DO intex therein.
  std::optional<SourceName> checkIndexUseInOwnBounds_;

  bool HandleAttributeStmt(Attr, const std::list<parser::Name> &);
  Symbol &HandleAttributeStmt(Attr, const parser::Name &);
  Symbol &DeclareUnknownEntity(const parser::Name &, Attrs);
  Symbol &DeclareProcEntity(const parser::Name &, Attrs, const ProcInterface &);
  void SetType(const parser::Name &, const DeclTypeSpec &);
  std::optional<DerivedTypeSpec> ResolveDerivedType(const parser::Name &);
  std::optional<DerivedTypeSpec> ResolveExtendsType(
      const parser::Name &, const parser::Name *);
  Symbol *MakeTypeSymbol(const SourceName &, Details &&);
  Symbol *MakeTypeSymbol(const parser::Name &, Details &&);
  bool OkToAddComponent(const parser::Name &, const Symbol * = nullptr);
  ParamValue GetParamValue(
      const parser::TypeParamValue &, common::TypeParamAttr attr);
  void CheckCommonBlockDerivedType(const SourceName &, const Symbol &);
  std::optional<MessageFixedText> CheckSaveAttr(const Symbol &);
  Attrs HandleSaveName(const SourceName &, Attrs);
  void AddSaveName(std::set<SourceName> &, const SourceName &);
  void SetSaveAttr(Symbol &);
  bool HandleUnrestrictedSpecificIntrinsicFunction(const parser::Name &);
  const parser::Name *FindComponent(const parser::Name *, const parser::Name &);
  void Initialization(const parser::Name &, const parser::Initialization &,
      bool inComponentDecl);
  bool PassesLocalityChecks(const parser::Name &name, Symbol &symbol);
  bool CheckForHostAssociatedImplicit(const parser::Name &);

  // Declare an object or procedure entity.
  // T is one of: EntityDetails, ObjectEntityDetails, ProcEntityDetails
  template <typename T>
  Symbol &DeclareEntity(const parser::Name &name, Attrs attrs) {
    Symbol &symbol{MakeSymbol(name, attrs)};
    if (context().HasError(symbol) || symbol.has<T>()) {
      return symbol; // OK or error already reported
    } else if (symbol.has<UnknownDetails>()) {
      symbol.set_details(T{});
      return symbol;
    } else if (auto *details{symbol.detailsIf<EntityDetails>()}) {
      symbol.set_details(T{std::move(*details)});
      return symbol;
    } else if (std::is_same_v<EntityDetails, T> &&
        (symbol.has<ObjectEntityDetails>() ||
            symbol.has<ProcEntityDetails>())) {
      return symbol; // OK
    } else if (auto *details{symbol.detailsIf<UseDetails>()}) {
      Say(name.source,
          "'%s' is use-associated from module '%s' and cannot be re-declared"_err_en_US,
          name.source, GetUsedModule(*details).name());
    } else if (auto *details{symbol.detailsIf<SubprogramNameDetails>()}) {
      if (details->kind() == SubprogramKind::Module) {
        Say2(name,
            "Declaration of '%s' conflicts with its use as module procedure"_err_en_US,
            symbol, "Module procedure definition"_en_US);
      } else if (details->kind() == SubprogramKind::Internal) {
        Say2(name,
            "Declaration of '%s' conflicts with its use as internal procedure"_err_en_US,
            symbol, "Internal procedure definition"_en_US);
      } else {
        DIE("unexpected kind");
      }
    } else if (std::is_same_v<ObjectEntityDetails, T> &&
        symbol.has<ProcEntityDetails>()) {
      SayWithDecl(
          name, symbol, "'%s' is already declared as a procedure"_err_en_US);
    } else if (std::is_same_v<ProcEntityDetails, T> &&
        symbol.has<ObjectEntityDetails>()) {
      if (InCommonBlock(symbol)) {
        SayWithDecl(name, symbol,
            "'%s' may not be a procedure as it is in a COMMON block"_err_en_US);
      } else {
        SayWithDecl(
            name, symbol, "'%s' is already declared as an object"_err_en_US);
      }
    } else if (!CheckPossibleBadForwardRef(symbol)) {
      SayAlreadyDeclared(name, symbol);
    }
    context().SetError(symbol);
    return symbol;
  }
  bool HasCycle(const Symbol &, const ProcInterface &);
};

// Resolve construct entities and statement entities.
// Check that construct names don't conflict with other names.
class ConstructVisitor : public virtual DeclarationVisitor {
public:
  bool Pre(const parser::ConcurrentHeader &);
  bool Pre(const parser::LocalitySpec::Local &);
  bool Pre(const parser::LocalitySpec::LocalInit &);
  bool Pre(const parser::LocalitySpec::Shared &);
  bool Pre(const parser::AcSpec &);
  bool Pre(const parser::AcImpliedDo &);
  bool Pre(const parser::DataImpliedDo &);
  bool Pre(const parser::DataIDoObject &);
  bool Pre(const parser::DataStmtObject &);
  bool Pre(const parser::DataStmtValue &);
  bool Pre(const parser::DoConstruct &);
  void Post(const parser::DoConstruct &);
  bool Pre(const parser::ForallConstruct &);
  void Post(const parser::ForallConstruct &);
  bool Pre(const parser::ForallStmt &);
  void Post(const parser::ForallStmt &);
  bool Pre(const parser::BlockStmt &);
  bool Pre(const parser::EndBlockStmt &);
  void Post(const parser::Selector &);
  void Post(const parser::AssociateStmt &);
  void Post(const parser::EndAssociateStmt &);
  bool Pre(const parser::Association &);
  void Post(const parser::SelectTypeStmt &);
  void Post(const parser::SelectRankStmt &);
  bool Pre(const parser::SelectTypeConstruct &);
  void Post(const parser::SelectTypeConstruct &);
  bool Pre(const parser::SelectTypeConstruct::TypeCase &);
  void Post(const parser::SelectTypeConstruct::TypeCase &);
  // Creates Block scopes with neither symbol name nor symbol details.
  bool Pre(const parser::SelectRankConstruct::RankCase &);
  void Post(const parser::SelectRankConstruct::RankCase &);
  void Post(const parser::TypeGuardStmt::Guard &);
  void Post(const parser::SelectRankCaseStmt::Rank &);
  bool Pre(const parser::ChangeTeamStmt &);
  void Post(const parser::EndChangeTeamStmt &);
  void Post(const parser::CoarrayAssociation &);

  // Definitions of construct names
  bool Pre(const parser::WhereConstructStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::ForallConstructStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::CriticalStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::LabelDoStmt &) {
    return false; // error recovery
  }
  bool Pre(const parser::NonLabelDoStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::IfThenStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::SelectCaseStmt &x) { return CheckDef(x.t); }
  bool Pre(const parser::SelectRankConstruct &);
  void Post(const parser::SelectRankConstruct &);
  bool Pre(const parser::SelectRankStmt &x) {
    return CheckDef(std::get<0>(x.t));
  }
  bool Pre(const parser::SelectTypeStmt &x) {
    return CheckDef(std::get<0>(x.t));
  }

  // References to construct names
  void Post(const parser::MaskedElsewhereStmt &x) { CheckRef(x.t); }
  void Post(const parser::ElsewhereStmt &x) { CheckRef(x.v); }
  void Post(const parser::EndWhereStmt &x) { CheckRef(x.v); }
  void Post(const parser::EndForallStmt &x) { CheckRef(x.v); }
  void Post(const parser::EndCriticalStmt &x) { CheckRef(x.v); }
  void Post(const parser::EndDoStmt &x) { CheckRef(x.v); }
  void Post(const parser::ElseIfStmt &x) { CheckRef(x.t); }
  void Post(const parser::ElseStmt &x) { CheckRef(x.v); }
  void Post(const parser::EndIfStmt &x) { CheckRef(x.v); }
  void Post(const parser::CaseStmt &x) { CheckRef(x.t); }
  void Post(const parser::EndSelectStmt &x) { CheckRef(x.v); }
  void Post(const parser::SelectRankCaseStmt &x) { CheckRef(x.t); }
  void Post(const parser::TypeGuardStmt &x) { CheckRef(x.t); }
  void Post(const parser::CycleStmt &x) { CheckRef(x.v); }
  void Post(const parser::ExitStmt &x) { CheckRef(x.v); }

private:
  // R1105 selector -> expr | variable
  // expr is set in either case unless there were errors
  struct Selector {
    Selector() {}
    Selector(const SourceName &source, MaybeExpr &&expr)
        : source{source}, expr{std::move(expr)} {}
    operator bool() const { return expr.has_value(); }
    parser::CharBlock source;
    MaybeExpr expr;
  };
  // association -> [associate-name =>] selector
  struct Association {
    const parser::Name *name{nullptr};
    Selector selector;
  };
  std::vector<Association> associationStack_;
  Association *currentAssociation_{nullptr};

  template <typename T> bool CheckDef(const T &t) {
    return CheckDef(std::get<std::optional<parser::Name>>(t));
  }
  template <typename T> void CheckRef(const T &t) {
    CheckRef(std::get<std::optional<parser::Name>>(t));
  }
  bool CheckDef(const std::optional<parser::Name> &);
  void CheckRef(const std::optional<parser::Name> &);
  const DeclTypeSpec &ToDeclTypeSpec(evaluate::DynamicType &&);
  const DeclTypeSpec &ToDeclTypeSpec(
      evaluate::DynamicType &&, MaybeSubscriptIntExpr &&length);
  Symbol *MakeAssocEntity();
  void SetTypeFromAssociation(Symbol &);
  void SetAttrsFromAssociation(Symbol &);
  Selector ResolveSelector(const parser::Selector &);
  void ResolveIndexName(const parser::ConcurrentControl &control);
  void SetCurrentAssociation(std::size_t n);
  Association &GetCurrentAssociation();
  void PushAssociation();
  void PopAssociation(std::size_t count = 1);
};

// Create scopes for OpenACC constructs
class AccVisitor : public virtual DeclarationVisitor {
public:
  void AddAccSourceRange(const parser::CharBlock &);

  static bool NeedsScope(const parser::OpenACCBlockConstruct &);

  bool Pre(const parser::OpenACCBlockConstruct &);
  void Post(const parser::OpenACCBlockConstruct &);
  bool Pre(const parser::AccBeginBlockDirective &x) {
    AddAccSourceRange(x.source);
    return true;
  }
  void Post(const parser::AccBeginBlockDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
  bool Pre(const parser::AccEndBlockDirective &x) {
    AddAccSourceRange(x.source);
    return true;
  }
  void Post(const parser::AccEndBlockDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
  bool Pre(const parser::AccBeginLoopDirective &x) {
    AddAccSourceRange(x.source);
    return true;
  }
  void Post(const parser::AccBeginLoopDirective &x) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
};

bool AccVisitor::NeedsScope(const parser::OpenACCBlockConstruct &x) {
  const auto &beginBlockDir{std::get<parser::AccBeginBlockDirective>(x.t)};
  const auto &beginDir{std::get<parser::AccBlockDirective>(beginBlockDir.t)};
  switch (beginDir.v) {
  case llvm::acc::Directive::ACCD_data:
  case llvm::acc::Directive::ACCD_host_data:
  case llvm::acc::Directive::ACCD_kernels:
  case llvm::acc::Directive::ACCD_parallel:
  case llvm::acc::Directive::ACCD_serial:
    return true;
  default:
    return false;
  }
}

void AccVisitor::AddAccSourceRange(const parser::CharBlock &source) {
  messageHandler().set_currStmtSource(source);
  currScope().AddSourceRange(source);
}

bool AccVisitor::Pre(const parser::OpenACCBlockConstruct &x) {
  if (NeedsScope(x)) {
    PushScope(Scope::Kind::Block, nullptr);
  }
  return true;
}

void AccVisitor::Post(const parser::OpenACCBlockConstruct &x) {
  if (NeedsScope(x)) {
    PopScope();
  }
}

// Create scopes for OpenMP constructs
class OmpVisitor : public virtual DeclarationVisitor {
public:
  void AddOmpSourceRange(const parser::CharBlock &);

  static bool NeedsScope(const parser::OpenMPBlockConstruct &);

  bool Pre(const parser::OpenMPBlockConstruct &);
  void Post(const parser::OpenMPBlockConstruct &);
  bool Pre(const parser::OmpBeginBlockDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpBeginBlockDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
  bool Pre(const parser::OmpEndBlockDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpEndBlockDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }

  bool Pre(const parser::OpenMPLoopConstruct &) {
    PushScope(Scope::Kind::Block, nullptr);
    return true;
  }
  void Post(const parser::OpenMPLoopConstruct &) { PopScope(); }
  bool Pre(const parser::OmpBeginLoopDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpBeginLoopDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
  bool Pre(const parser::OmpEndLoopDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpEndLoopDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }

  bool Pre(const parser::OpenMPSectionsConstruct &) {
    PushScope(Scope::Kind::Block, nullptr);
    return true;
  }
  void Post(const parser::OpenMPSectionsConstruct &) { PopScope(); }
  bool Pre(const parser::OmpBeginSectionsDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpBeginSectionsDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
  bool Pre(const parser::OmpEndSectionsDirective &x) {
    AddOmpSourceRange(x.source);
    return true;
  }
  void Post(const parser::OmpEndSectionsDirective &) {
    messageHandler().set_currStmtSource(std::nullopt);
  }
};

bool OmpVisitor::NeedsScope(const parser::OpenMPBlockConstruct &x) {
  const auto &beginBlockDir{std::get<parser::OmpBeginBlockDirective>(x.t)};
  const auto &beginDir{std::get<parser::OmpBlockDirective>(beginBlockDir.t)};
  switch (beginDir.v) {
  case llvm::omp::Directive::OMPD_target_data:
  case llvm::omp::Directive::OMPD_master:
  case llvm::omp::Directive::OMPD_ordered:
  case llvm::omp::Directive::OMPD_taskgroup:
    return false;
  default:
    return true;
  }
}

void OmpVisitor::AddOmpSourceRange(const parser::CharBlock &source) {
  messageHandler().set_currStmtSource(source);
  currScope().AddSourceRange(source);
}

bool OmpVisitor::Pre(const parser::OpenMPBlockConstruct &x) {
  if (NeedsScope(x)) {
    PushScope(Scope::Kind::Block, nullptr);
  }
  return true;
}

void OmpVisitor::Post(const parser::OpenMPBlockConstruct &x) {
  if (NeedsScope(x)) {
    PopScope();
  }
}

// Walk the parse tree and resolve names to symbols.
class ResolveNamesVisitor : public virtual ScopeHandler,
                            public ModuleVisitor,
                            public SubprogramVisitor,
                            public ConstructVisitor,
                            public OmpVisitor,
                            public AccVisitor {
public:
  using AccVisitor::Post;
  using AccVisitor::Pre;
  using ArraySpecVisitor::Post;
  using ConstructVisitor::Post;
  using ConstructVisitor::Pre;
  using DeclarationVisitor::Post;
  using DeclarationVisitor::Pre;
  using ImplicitRulesVisitor::Post;
  using ImplicitRulesVisitor::Pre;
  using InterfaceVisitor::Post;
  using InterfaceVisitor::Pre;
  using ModuleVisitor::Post;
  using ModuleVisitor::Pre;
  using OmpVisitor::Post;
  using OmpVisitor::Pre;
  using ScopeHandler::Post;
  using ScopeHandler::Pre;
  using SubprogramVisitor::Post;
  using SubprogramVisitor::Pre;

  ResolveNamesVisitor(SemanticsContext &context, ImplicitRulesMap &rules)
      : BaseVisitor{context, *this, rules} {
    PushScope(context.globalScope());
  }

  // Default action for a parse tree node is to visit children.
  template <typename T> bool Pre(const T &) { return true; }
  template <typename T> void Post(const T &) {}

  bool Pre(const parser::SpecificationPart &);
  void Post(const parser::Program &);
  bool Pre(const parser::ImplicitStmt &);
  void Post(const parser::PointerObject &);
  void Post(const parser::AllocateObject &);
  bool Pre(const parser::PointerAssignmentStmt &);
  void Post(const parser::Designator &);
  template <typename A, typename B>
  void Post(const parser::LoopBounds<A, B> &x) {
    ResolveName(*parser::Unwrap<parser::Name>(x.name));
  }
  void Post(const parser::ProcComponentRef &);
  bool Pre(const parser::FunctionReference &);
  bool Pre(const parser::CallStmt &);
  bool Pre(const parser::ImportStmt &);
  void Post(const parser::TypeGuardStmt &);
  bool Pre(const parser::StmtFunctionStmt &);
  bool Pre(const parser::DefinedOpName &);
  bool Pre(const parser::ProgramUnit &);
  void Post(const parser::AssignStmt &);
  void Post(const parser::AssignedGotoStmt &);

  // These nodes should never be reached: they are handled in ProgramUnit
  bool Pre(const parser::MainProgram &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::FunctionSubprogram &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::SubroutineSubprogram &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::SeparateModuleSubprogram &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::Module &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::Submodule &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }
  bool Pre(const parser::BlockData &) {
    llvm_unreachable("This node is handled in ProgramUnit");
  }

  void NoteExecutablePartCall(Symbol::Flag, const parser::Call &);

  friend void ResolveSpecificationParts(SemanticsContext &, const Symbol &);

private:
  // Kind of procedure we are expecting to see in a ProcedureDesignator
  std::optional<Symbol::Flag> expectedProcFlag_;
  std::optional<SourceName> prevImportStmt_;

  void PreSpecificationConstruct(const parser::SpecificationConstruct &);
  void CreateCommonBlockSymbols(const parser::CommonStmt &);
  void CreateGeneric(const parser::GenericSpec &);
  void FinishSpecificationPart(const std::list<parser::DeclarationConstruct> &);
  void AnalyzeStmtFunctionStmt(const parser::StmtFunctionStmt &);
  void CheckImports();
  void CheckImport(const SourceName &, const SourceName &);
  void HandleCall(Symbol::Flag, const parser::Call &);
  void HandleProcedureName(Symbol::Flag, const parser::Name &);
  bool CheckImplicitNoneExternal(const SourceName &, const Symbol &);
  bool SetProcFlag(const parser::Name &, Symbol &, Symbol::Flag);
  void ResolveSpecificationParts(ProgramTree &);
  void AddSubpNames(ProgramTree &);
  bool BeginScopeForNode(const ProgramTree &);
  void FinishSpecificationParts(const ProgramTree &);
  void FinishDerivedTypeInstantiation(Scope &);
  void ResolveExecutionParts(const ProgramTree &);
};

// ImplicitRules implementation

bool ImplicitRules::isImplicitNoneType() const {
  if (isImplicitNoneType_) {
    return true;
  } else if (map_.empty() && inheritFromParent_) {
    return parent_->isImplicitNoneType();
  } else {
    return false; // default if not specified
  }
}

bool ImplicitRules::isImplicitNoneExternal() const {
  if (isImplicitNoneExternal_) {
    return true;
  } else if (inheritFromParent_) {
    return parent_->isImplicitNoneExternal();
  } else {
    return false; // default if not specified
  }
}

const DeclTypeSpec *ImplicitRules::GetType(
    SourceName name, bool respectImplicitNoneType) const {
  char ch{name.begin()[0]};
  if (isImplicitNoneType_ && respectImplicitNoneType) {
    return nullptr;
  } else if (auto it{map_.find(ch)}; it != map_.end()) {
    return &*it->second;
  } else if (inheritFromParent_) {
    return parent_->GetType(name, respectImplicitNoneType);
  } else if (ch >= 'i' && ch <= 'n') {
    return &context_.MakeNumericType(TypeCategory::Integer);
  } else if (ch >= 'a' && ch <= 'z') {
    return &context_.MakeNumericType(TypeCategory::Real);
  } else {
    return nullptr;
  }
}

void ImplicitRules::SetTypeMapping(const DeclTypeSpec &type,
    parser::Location fromLetter, parser::Location toLetter) {
  for (char ch = *fromLetter; ch; ch = ImplicitRules::Incr(ch)) {
    auto res{map_.emplace(ch, type)};
    if (!res.second) {
      context_.Say(parser::CharBlock{fromLetter},
          "More than one implicit type specified for '%c'"_err_en_US, ch);
    }
    if (ch == *toLetter) {
      break;
    }
  }
}

// Return the next char after ch in a way that works for ASCII or EBCDIC.
// Return '\0' for the char after 'z'.
char ImplicitRules::Incr(char ch) {
  switch (ch) {
  case 'i':
    return 'j';
  case 'r':
    return 's';
  case 'z':
    return '\0';
  default:
    return ch + 1;
  }
}

llvm::raw_ostream &operator<<(
    llvm::raw_ostream &o, const ImplicitRules &implicitRules) {
  o << "ImplicitRules:\n";
  for (char ch = 'a'; ch; ch = ImplicitRules::Incr(ch)) {
    ShowImplicitRule(o, implicitRules, ch);
  }
  ShowImplicitRule(o, implicitRules, '_');
  ShowImplicitRule(o, implicitRules, '$');
  ShowImplicitRule(o, implicitRules, '@');
  return o;
}
void ShowImplicitRule(
    llvm::raw_ostream &o, const ImplicitRules &implicitRules, char ch) {
  auto it{implicitRules.map_.find(ch)};
  if (it != implicitRules.map_.end()) {
    o << "  " << ch << ": " << *it->second << '\n';
  }
}

template <typename T> void BaseVisitor::Walk(const T &x) {
  parser::Walk(x, *this_);
}

void BaseVisitor::MakePlaceholder(
    const parser::Name &name, MiscDetails::Kind kind) {
  if (!name.symbol) {
    name.symbol = &context_->globalScope().MakeSymbol(
        name.source, Attrs{}, MiscDetails{kind});
  }
}

// AttrsVisitor implementation

bool AttrsVisitor::BeginAttrs() {
  CHECK(!attrs_);
  attrs_ = std::make_optional<Attrs>();
  return true;
}
Attrs AttrsVisitor::GetAttrs() {
  CHECK(attrs_);
  return *attrs_;
}
Attrs AttrsVisitor::EndAttrs() {
  Attrs result{GetAttrs()};
  attrs_.reset();
  passName_ = std::nullopt;
  bindName_.reset();
  return result;
}

bool AttrsVisitor::SetPassNameOn(Symbol &symbol) {
  if (!passName_) {
    return false;
  }
  std::visit(common::visitors{
                 [&](ProcEntityDetails &x) { x.set_passName(*passName_); },
                 [&](ProcBindingDetails &x) { x.set_passName(*passName_); },
                 [](auto &) { common::die("unexpected pass name"); },
             },
      symbol.details());
  return true;
}

void AttrsVisitor::SetBindNameOn(Symbol &symbol) {
  if (!attrs_ || !attrs_->test(Attr::BIND_C)) {
    return;
  }
  std::optional<std::string> label{
      evaluate::GetScalarConstantValue<evaluate::Ascii>(bindName_)};
  // 18.9.2(2): discard leading and trailing blanks, ignore if all blank
  if (label) {
    auto first{label->find_first_not_of(" ")};
    if (first == std::string::npos) {
      // Empty NAME= means no binding at all (18.10.2p2)
      Say(currStmtSource().value(), "Blank binding label ignored"_en_US);
      return;
    }
    auto last{label->find_last_not_of(" ")};
    label = label->substr(first, last - first + 1);
  } else {
    label = parser::ToLowerCaseLetters(symbol.name().ToString());
  }
  symbol.SetBindName(std::move(*label));
}

void AttrsVisitor::Post(const parser::LanguageBindingSpec &x) {
  CHECK(attrs_);
  if (CheckAndSet(Attr::BIND_C)) {
    if (x.v) {
      bindName_ = EvaluateExpr(*x.v);
    }
  }
}
bool AttrsVisitor::Pre(const parser::IntentSpec &x) {
  CHECK(attrs_);
  CheckAndSet(IntentSpecToAttr(x));
  return false;
}
bool AttrsVisitor::Pre(const parser::Pass &x) {
  if (CheckAndSet(Attr::PASS)) {
    if (x.v) {
      passName_ = x.v->source;
      MakePlaceholder(*x.v, MiscDetails::Kind::PassName);
    }
  }
  return false;
}

// C730, C743, C755, C778, C1543 say no attribute or prefix repetitions
bool AttrsVisitor::IsDuplicateAttr(Attr attrName) {
  if (attrs_->test(attrName)) {
    Say(currStmtSource().value(),
        "Attribute '%s' cannot be used more than once"_en_US,
        AttrToString(attrName));
    return true;
  }
  return false;
}

// See if attrName violates a constraint cause by a conflict.  attr1 and attr2
// name attributes that cannot be used on the same declaration
bool AttrsVisitor::HaveAttrConflict(Attr attrName, Attr attr1, Attr attr2) {
  if ((attrName == attr1 && attrs_->test(attr2)) ||
      (attrName == attr2 && attrs_->test(attr1))) {
    Say(currStmtSource().value(),
        "Attributes '%s' and '%s' conflict with each other"_err_en_US,
        AttrToString(attr1), AttrToString(attr2));
    return true;
  }
  return false;
}
// C759, C1543
bool AttrsVisitor::IsConflictingAttr(Attr attrName) {
  return HaveAttrConflict(attrName, Attr::INTENT_IN, Attr::INTENT_INOUT) ||
      HaveAttrConflict(attrName, Attr::INTENT_IN, Attr::INTENT_OUT) ||
      HaveAttrConflict(attrName, Attr::INTENT_INOUT, Attr::INTENT_OUT) ||
      HaveAttrConflict(attrName, Attr::PASS, Attr::NOPASS) || // C781
      HaveAttrConflict(attrName, Attr::PURE, Attr::IMPURE) ||
      HaveAttrConflict(attrName, Attr::PUBLIC, Attr::PRIVATE) ||
      HaveAttrConflict(attrName, Attr::RECURSIVE, Attr::NON_RECURSIVE);
}
bool AttrsVisitor::CheckAndSet(Attr attrName) {
  CHECK(attrs_);
  if (IsConflictingAttr(attrName) || IsDuplicateAttr(attrName)) {
    return false;
  }
  attrs_->set(attrName);
  return true;
}

// DeclTypeSpecVisitor implementation

const DeclTypeSpec *DeclTypeSpecVisitor::GetDeclTypeSpec() {
  return state_.declTypeSpec;
}

void DeclTypeSpecVisitor::BeginDeclTypeSpec() {
  CHECK(!state_.expectDeclTypeSpec);
  CHECK(!state_.declTypeSpec);
  state_.expectDeclTypeSpec = true;
}
void DeclTypeSpecVisitor::EndDeclTypeSpec() {
  CHECK(state_.expectDeclTypeSpec);
  state_ = {};
}

void DeclTypeSpecVisitor::SetDeclTypeSpecCategory(
    DeclTypeSpec::Category category) {
  CHECK(state_.expectDeclTypeSpec);
  state_.derived.category = category;
}

bool DeclTypeSpecVisitor::Pre(const parser::TypeGuardStmt &) {
  BeginDeclTypeSpec();
  return true;
}
void DeclTypeSpecVisitor::Post(const parser::TypeGuardStmt &) {
  EndDeclTypeSpec();
}

void DeclTypeSpecVisitor::Post(const parser::TypeSpec &typeSpec) {
  // Record the resolved DeclTypeSpec in the parse tree for use by
  // expression semantics if the DeclTypeSpec is a valid TypeSpec.
  // The grammar ensures that it's an intrinsic or derived type spec,
  // not TYPE(*) or CLASS(*) or CLASS(T).
  if (const DeclTypeSpec * spec{state_.declTypeSpec}) {
    switch (spec->category()) {
    case DeclTypeSpec::Numeric:
    case DeclTypeSpec::Logical:
    case DeclTypeSpec::Character:
      typeSpec.declTypeSpec = spec;
      break;
    case DeclTypeSpec::TypeDerived:
      if (const DerivedTypeSpec * derived{spec->AsDerived()}) {
        CheckForAbstractType(derived->typeSymbol()); // C703
        typeSpec.declTypeSpec = spec;
      }
      break;
    default:
      CRASH_NO_CASE;
    }
  }
}

void DeclTypeSpecVisitor::Post(
    const parser::IntrinsicTypeSpec::DoublePrecision &) {
  MakeNumericType(TypeCategory::Real, context().doublePrecisionKind());
}
void DeclTypeSpecVisitor::Post(
    const parser::IntrinsicTypeSpec::DoubleComplex &) {
  MakeNumericType(TypeCategory::Complex, context().doublePrecisionKind());
}
void DeclTypeSpecVisitor::MakeNumericType(TypeCategory category, int kind) {
  SetDeclTypeSpec(context().MakeNumericType(category, kind));
}

void DeclTypeSpecVisitor::CheckForAbstractType(const Symbol &typeSymbol) {
  if (typeSymbol.attrs().test(Attr::ABSTRACT)) {
    Say("ABSTRACT derived type may not be used here"_err_en_US);
  }
}

void DeclTypeSpecVisitor::Post(const parser::DeclarationTypeSpec::ClassStar &) {
  SetDeclTypeSpec(context().globalScope().MakeClassStarType());
}
void DeclTypeSpecVisitor::Post(const parser::DeclarationTypeSpec::TypeStar &) {
  SetDeclTypeSpec(context().globalScope().MakeTypeStarType());
}

// Check that we're expecting to see a DeclTypeSpec (and haven't seen one yet)
// and save it in state_.declTypeSpec.
void DeclTypeSpecVisitor::SetDeclTypeSpec(const DeclTypeSpec &declTypeSpec) {
  CHECK(state_.expectDeclTypeSpec);
  CHECK(!state_.declTypeSpec);
  state_.declTypeSpec = &declTypeSpec;
}

KindExpr DeclTypeSpecVisitor::GetKindParamExpr(
    TypeCategory category, const std::optional<parser::KindSelector> &kind) {
  return AnalyzeKindSelector(context(), category, kind);
}

// MessageHandler implementation

Message &MessageHandler::Say(MessageFixedText &&msg) {
  return context_->Say(currStmtSource().value(), std::move(msg));
}
Message &MessageHandler::Say(MessageFormattedText &&msg) {
  return context_->Say(currStmtSource().value(), std::move(msg));
}
Message &MessageHandler::Say(const SourceName &name, MessageFixedText &&msg) {
  return Say(name, std::move(msg), name);
}

// ImplicitRulesVisitor implementation

void ImplicitRulesVisitor::Post(const parser::ParameterStmt &) {
  prevParameterStmt_ = currStmtSource();
}

bool ImplicitRulesVisitor::Pre(const parser::ImplicitStmt &x) {
  bool result{
      std::visit(common::visitors{
                     [&](const std::list<ImplicitNoneNameSpec> &y) {
                       return HandleImplicitNone(y);
                     },
                     [&](const std::list<parser::ImplicitSpec> &) {
                       if (prevImplicitNoneType_) {
                         Say("IMPLICIT statement after IMPLICIT NONE or "
                             "IMPLICIT NONE(TYPE) statement"_err_en_US);
                         return false;
                       }
                       implicitRules_->set_isImplicitNoneType(false);
                       return true;
                     },
                 },
          x.u)};
  prevImplicit_ = currStmtSource();
  return result;
}

bool ImplicitRulesVisitor::Pre(const parser::LetterSpec &x) {
  auto loLoc{std::get<parser::Location>(x.t)};
  auto hiLoc{loLoc};
  if (auto hiLocOpt{std::get<std::optional<parser::Location>>(x.t)}) {
    hiLoc = *hiLocOpt;
    if (*hiLoc < *loLoc) {
      Say(hiLoc, "'%s' does not follow '%s' alphabetically"_err_en_US,
          std::string(hiLoc, 1), std::string(loLoc, 1));
      return false;
    }
  }
  implicitRules_->SetTypeMapping(*GetDeclTypeSpec(), loLoc, hiLoc);
  return false;
}

bool ImplicitRulesVisitor::Pre(const parser::ImplicitSpec &) {
  BeginDeclTypeSpec();
  set_allowForwardReferenceToDerivedType(true);
  return true;
}

void ImplicitRulesVisitor::Post(const parser::ImplicitSpec &) {
  EndDeclTypeSpec();
}

void ImplicitRulesVisitor::SetScope(const Scope &scope) {
  implicitRules_ = &DEREF(implicitRulesMap_).at(&scope);
  prevImplicit_ = std::nullopt;
  prevImplicitNone_ = std::nullopt;
  prevImplicitNoneType_ = std::nullopt;
  prevParameterStmt_ = std::nullopt;
}
void ImplicitRulesVisitor::BeginScope(const Scope &scope) {
  // find or create implicit rules for this scope
  DEREF(implicitRulesMap_).try_emplace(&scope, context(), implicitRules_);
  SetScope(scope);
}

// TODO: for all of these errors, reference previous statement too
bool ImplicitRulesVisitor::HandleImplicitNone(
    const std::list<ImplicitNoneNameSpec> &nameSpecs) {
  if (prevImplicitNone_) {
    Say("More than one IMPLICIT NONE statement"_err_en_US);
    Say(*prevImplicitNone_, "Previous IMPLICIT NONE statement"_en_US);
    return false;
  }
  if (prevParameterStmt_) {
    Say("IMPLICIT NONE statement after PARAMETER statement"_err_en_US);
    return false;
  }
  prevImplicitNone_ = currStmtSource();
  bool implicitNoneTypeNever{
      context().IsEnabled(common::LanguageFeature::ImplicitNoneTypeNever)};
  if (nameSpecs.empty()) {
    if (!implicitNoneTypeNever) {
      prevImplicitNoneType_ = currStmtSource();
      implicitRules_->set_isImplicitNoneType(true);
      if (prevImplicit_) {
        Say("IMPLICIT NONE statement after IMPLICIT statement"_err_en_US);
        return false;
      }
    }
  } else {
    int sawType{0};
    int sawExternal{0};
    for (const auto noneSpec : nameSpecs) {
      switch (noneSpec) {
      case ImplicitNoneNameSpec::External:
        implicitRules_->set_isImplicitNoneExternal(true);
        ++sawExternal;
        break;
      case ImplicitNoneNameSpec::Type:
        if (!implicitNoneTypeNever) {
          prevImplicitNoneType_ = currStmtSource();
          implicitRules_->set_isImplicitNoneType(true);
          if (prevImplicit_) {
            Say("IMPLICIT NONE(TYPE) after IMPLICIT statement"_err_en_US);
            return false;
          }
          ++sawType;
        }
        break;
      }
    }
    if (sawType > 1) {
      Say("TYPE specified more than once in IMPLICIT NONE statement"_err_en_US);
      return false;
    }
    if (sawExternal > 1) {
      Say("EXTERNAL specified more than once in IMPLICIT NONE statement"_err_en_US);
      return false;
    }
  }
  return true;
}

// ArraySpecVisitor implementation

void ArraySpecVisitor::Post(const parser::ArraySpec &x) {
  CHECK(arraySpec_.empty());
  arraySpec_ = AnalyzeArraySpec(context(), x);
}
void ArraySpecVisitor::Post(const parser::ComponentArraySpec &x) {
  CHECK(arraySpec_.empty());
  arraySpec_ = AnalyzeArraySpec(context(), x);
}
void ArraySpecVisitor::Post(const parser::CoarraySpec &x) {
  CHECK(coarraySpec_.empty());
  coarraySpec_ = AnalyzeCoarraySpec(context(), x);
}

const ArraySpec &ArraySpecVisitor::arraySpec() {
  return !arraySpec_.empty() ? arraySpec_ : attrArraySpec_;
}
const ArraySpec &ArraySpecVisitor::coarraySpec() {
  return !coarraySpec_.empty() ? coarraySpec_ : attrCoarraySpec_;
}
void ArraySpecVisitor::BeginArraySpec() {
  CHECK(arraySpec_.empty());
  CHECK(coarraySpec_.empty());
  CHECK(attrArraySpec_.empty());
  CHECK(attrCoarraySpec_.empty());
}
void ArraySpecVisitor::EndArraySpec() {
  CHECK(arraySpec_.empty());
  CHECK(coarraySpec_.empty());
  attrArraySpec_.clear();
  attrCoarraySpec_.clear();
}
void ArraySpecVisitor::PostAttrSpec() {
  // Save dimension/codimension from attrs so we can process array/coarray-spec
  // on the entity-decl
  if (!arraySpec_.empty()) {
    if (attrArraySpec_.empty()) {
      attrArraySpec_ = arraySpec_;
      arraySpec_.clear();
    } else {
      Say(currStmtSource().value(),
          "Attribute 'DIMENSION' cannot be used more than once"_err_en_US);
    }
  }
  if (!coarraySpec_.empty()) {
    if (attrCoarraySpec_.empty()) {
      attrCoarraySpec_ = coarraySpec_;
      coarraySpec_.clear();
    } else {
      Say(currStmtSource().value(),
          "Attribute 'CODIMENSION' cannot be used more than once"_err_en_US);
    }
  }
}

// ScopeHandler implementation

void ScopeHandler::SayAlreadyDeclared(const parser::Name &name, Symbol &prev) {
  SayAlreadyDeclared(name.source, prev);
}
void ScopeHandler::SayAlreadyDeclared(const SourceName &name, Symbol &prev) {
  if (context().HasError(prev)) {
    // don't report another error about prev
  } else {
    if (const auto *details{prev.detailsIf<UseDetails>()}) {
      Say(name, "'%s' is already declared in this scoping unit"_err_en_US)
          .Attach(details->location(),
              "It is use-associated with '%s' in module '%s'"_err_en_US,
              details->symbol().name(), GetUsedModule(*details).name());
    } else {
      SayAlreadyDeclared(name, prev.name());
    }
    context().SetError(prev);
  }
}
void ScopeHandler::SayAlreadyDeclared(
    const SourceName &name1, const SourceName &name2) {
  if (name1.begin() < name2.begin()) {
    SayAlreadyDeclared(name2, name1);
  } else {
    Say(name1, "'%s' is already declared in this scoping unit"_err_en_US)
        .Attach(name2, "Previous declaration of '%s'"_en_US, name2);
  }
}

void ScopeHandler::SayWithReason(const parser::Name &name, Symbol &symbol,
    MessageFixedText &&msg1, MessageFixedText &&msg2) {
  Say2(name, std::move(msg1), symbol, std::move(msg2));
  context().SetError(symbol, msg1.isFatal());
}

void ScopeHandler::SayWithDecl(
    const parser::Name &name, Symbol &symbol, MessageFixedText &&msg) {
  SayWithReason(name, symbol, std::move(msg),
      symbol.test(Symbol::Flag::Implicit) ? "Implicit declaration of '%s'"_en_US
                                          : "Declaration of '%s'"_en_US);
}

void ScopeHandler::SayLocalMustBeVariable(
    const parser::Name &name, Symbol &symbol) {
  SayWithDecl(name, symbol,
      "The name '%s' must be a variable to appear"
      " in a locality-spec"_err_en_US);
}

void ScopeHandler::SayDerivedType(
    const SourceName &name, MessageFixedText &&msg, const Scope &type) {
  const Symbol &typeSymbol{DEREF(type.GetSymbol())};
  Say(name, std::move(msg), name, typeSymbol.name())
      .Attach(typeSymbol.name(), "Declaration of derived type '%s'"_en_US,
          typeSymbol.name());
}
void ScopeHandler::Say2(const SourceName &name1, MessageFixedText &&msg1,
    const SourceName &name2, MessageFixedText &&msg2) {
  Say(name1, std::move(msg1)).Attach(name2, std::move(msg2), name2);
}
void ScopeHandler::Say2(const SourceName &name, MessageFixedText &&msg1,
    Symbol &symbol, MessageFixedText &&msg2) {
  Say2(name, std::move(msg1), symbol.name(), std::move(msg2));
  context().SetError(symbol, msg1.isFatal());
}
void ScopeHandler::Say2(const parser::Name &name, MessageFixedText &&msg1,
    Symbol &symbol, MessageFixedText &&msg2) {
  Say2(name.source, std::move(msg1), symbol.name(), std::move(msg2));
  context().SetError(symbol, msg1.isFatal());
}

// This is essentially GetProgramUnitContaining(), but it can return
// a mutable Scope &, it ignores statement functions, and it fails
// gracefully for error recovery (returning the original Scope).
template <typename T> static T &GetInclusiveScope(T &scope) {
  for (T *s{&scope}; !s->IsGlobal(); s = &s->parent()) {
    switch (s->kind()) {
    case Scope::Kind::Module:
    case Scope::Kind::MainProgram:
    case Scope::Kind::Subprogram:
    case Scope::Kind::BlockData:
      if (!s->IsStmtFunction()) {
        return *s;
      }
      break;
    default:;
    }
  }
  return scope;
}

Scope &ScopeHandler::InclusiveScope() { return GetInclusiveScope(currScope()); }

Scope *ScopeHandler::GetHostProcedure() {
  Scope &parent{InclusiveScope().parent()};
  switch (parent.kind()) {
  case Scope::Kind::Subprogram:
    return &parent;
  case Scope::Kind::MainProgram:
    return &parent;
  default:
    return nullptr;
  }
}

Scope &ScopeHandler::NonDerivedTypeScope() {
  return currScope_->IsDerivedType() ? currScope_->parent() : *currScope_;
}

void ScopeHandler::PushScope(Scope::Kind kind, Symbol *symbol) {
  PushScope(currScope().MakeScope(kind, symbol));
}
void ScopeHandler::PushScope(Scope &scope) {
  currScope_ = &scope;
  auto kind{currScope_->kind()};
  if (kind != Scope::Kind::Block) {
    BeginScope(scope);
  }
  // The name of a module or submodule cannot be "used" in its scope,
  // as we read 19.3.1(2), so we allow the name to be used as a local
  // identifier in the module or submodule too.  Same with programs
  // (14.1(3)) and BLOCK DATA.
  if (!currScope_->IsDerivedType() && kind != Scope::Kind::Module &&
      kind != Scope::Kind::MainProgram && kind != Scope::Kind::BlockData) {
    if (auto *symbol{scope.symbol()}) {
      // Create a dummy symbol so we can't create another one with the same
      // name. It might already be there if we previously pushed the scope.
      if (!FindInScope(scope, symbol->name())) {
        auto &newSymbol{MakeSymbol(symbol->name())};
        if (kind == Scope::Kind::Subprogram) {
          // Allow for recursive references.  If this symbol is a function
          // without an explicit RESULT(), this new symbol will be discarded
          // and replaced with an object of the same name.
          newSymbol.set_details(HostAssocDetails{*symbol});
        } else {
          newSymbol.set_details(MiscDetails{MiscDetails::Kind::ScopeName});
        }
      }
    }
  }
}
void ScopeHandler::PopScope() {
  // Entities that are not yet classified as objects or procedures are now
  // assumed to be objects.
  // TODO: Statement functions
  for (auto &pair : currScope()) {
    ConvertToObjectEntity(*pair.second);
  }
  SetScope(currScope_->parent());
}
void ScopeHandler::SetScope(Scope &scope) {
  currScope_ = &scope;
  ImplicitRulesVisitor::SetScope(InclusiveScope());
}

Symbol *ScopeHandler::FindSymbol(const parser::Name &name) {
  return FindSymbol(currScope(), name);
}
Symbol *ScopeHandler::FindSymbol(const Scope &scope, const parser::Name &name) {
  if (scope.IsDerivedType()) {
    if (Symbol * symbol{scope.FindComponent(name.source)}) {
      if (!symbol->has<ProcBindingDetails>() &&
          !symbol->test(Symbol::Flag::ParentComp)) {
        return Resolve(name, symbol);
      }
    }
    return FindSymbol(scope.parent(), name);
  } else {
    // In EQUIVALENCE statements only resolve names in the local scope, see
    // 19.5.1.4, paragraph 2, item (10)
    return Resolve(name,
        inEquivalenceStmt_ ? FindInScope(scope, name)
                           : scope.FindSymbol(name.source));
  }
}

Symbol &ScopeHandler::MakeSymbol(
    Scope &scope, const SourceName &name, Attrs attrs) {
  if (Symbol * symbol{FindInScope(scope, name)}) {
    symbol->attrs() |= attrs;
    return *symbol;
  } else {
    const auto pair{scope.try_emplace(name, attrs, UnknownDetails{})};
    CHECK(pair.second); // name was not found, so must be able to add
    return *pair.first->second;
  }
}
Symbol &ScopeHandler::MakeSymbol(const SourceName &name, Attrs attrs) {
  return MakeSymbol(currScope(), name, attrs);
}
Symbol &ScopeHandler::MakeSymbol(const parser::Name &name, Attrs attrs) {
  return Resolve(name, MakeSymbol(name.source, attrs));
}
Symbol &ScopeHandler::MakeHostAssocSymbol(
    const parser::Name &name, const Symbol &hostSymbol) {
  Symbol &symbol{*NonDerivedTypeScope()
                      .try_emplace(name.source, HostAssocDetails{hostSymbol})
                      .first->second};
  name.symbol = &symbol;
  symbol.attrs() = hostSymbol.attrs(); // TODO: except PRIVATE, PUBLIC?
  symbol.flags() = hostSymbol.flags();
  return symbol;
}
Symbol &ScopeHandler::CopySymbol(const SourceName &name, const Symbol &symbol) {
  CHECK(!FindInScope(name));
  return MakeSymbol(currScope(), name, symbol.attrs());
}

// Look for name only in scope, not in enclosing scopes.
Symbol *ScopeHandler::FindInScope(
    const Scope &scope, const parser::Name &name) {
  return Resolve(name, FindInScope(scope, name.source));
}
Symbol *ScopeHandler::FindInScope(const Scope &scope, const SourceName &name) {
  // all variants of names, e.g. "operator(.ne.)" for "operator(/=)"
  for (const std::string &n : GetAllNames(context(), name)) {
    auto it{scope.find(SourceName{n})};
    if (it != scope.end()) {
      return &*it->second;
    }
  }
  return nullptr;
}

// Find a component or type parameter by name in a derived type or its parents.
Symbol *ScopeHandler::FindInTypeOrParents(
    const Scope &scope, const parser::Name &name) {
  return Resolve(name, scope.FindComponent(name.source));
}
Symbol *ScopeHandler::FindInTypeOrParents(const parser::Name &name) {
  return FindInTypeOrParents(currScope(), name);
}

void ScopeHandler::EraseSymbol(const parser::Name &name) {
  currScope().erase(name.source);
  name.symbol = nullptr;
}

static bool NeedsType(const Symbol &symbol) {
  return !symbol.GetType() &&
      std::visit(common::visitors{
                     [](const EntityDetails &) { return true; },
                     [](const ObjectEntityDetails &) { return true; },
                     [](const AssocEntityDetails &) { return true; },
                     [&](const ProcEntityDetails &p) {
                       return symbol.test(Symbol::Flag::Function) &&
                           !symbol.attrs().test(Attr::INTRINSIC) &&
                           !p.interface().type() && !p.interface().symbol();
                     },
                     [](const auto &) { return false; },
                 },
          symbol.details());
}

void ScopeHandler::ApplyImplicitRules(
    Symbol &symbol, bool allowForwardReference) {
  if (context().HasError(symbol) || !NeedsType(symbol)) {
    return;
  }
  if (const DeclTypeSpec * type{GetImplicitType(symbol)}) {
    symbol.set(Symbol::Flag::Implicit);
    symbol.SetType(*type);
    return;
  }
  if (symbol.has<ProcEntityDetails>() && !symbol.attrs().test(Attr::EXTERNAL)) {
    std::optional<Symbol::Flag> functionOrSubroutineFlag;
    if (symbol.test(Symbol::Flag::Function)) {
      functionOrSubroutineFlag = Symbol::Flag::Function;
    } else if (symbol.test(Symbol::Flag::Subroutine)) {
      functionOrSubroutineFlag = Symbol::Flag::Subroutine;
    }
    if (IsIntrinsic(symbol.name(), functionOrSubroutineFlag)) {
      // type will be determined in expression semantics
      AcquireIntrinsicProcedureFlags(symbol);
      return;
    }
  }
  if (allowForwardReference && ImplicitlyTypeForwardRef(symbol)) {
    return;
  }
  if (!context().HasError(symbol)) {
    Say(symbol.name(), "No explicit type declared for '%s'"_err_en_US);
    context().SetError(symbol);
  }
}

// Extension: Allow forward references to scalar integer dummy arguments
// to appear in specification expressions under IMPLICIT NONE(TYPE) when
// what would otherwise have been their implicit type is default INTEGER.
bool ScopeHandler::ImplicitlyTypeForwardRef(Symbol &symbol) {
  if (!inSpecificationPart_ || context().HasError(symbol) || !IsDummy(symbol) ||
      symbol.Rank() != 0 ||
      !context().languageFeatures().IsEnabled(
          common::LanguageFeature::ForwardRefDummyImplicitNone)) {
    return false;
  }
  const DeclTypeSpec *type{
      GetImplicitType(symbol, false /*ignore IMPLICIT NONE*/)};
  if (!type || !type->IsNumeric(TypeCategory::Integer)) {
    return false;
  }
  auto kind{evaluate::ToInt64(type->numericTypeSpec().kind())};
  if (!kind || *kind != context().GetDefaultKind(TypeCategory::Integer)) {
    return false;
  }
  if (!ConvertToObjectEntity(symbol)) {
    return false;
  }
  // TODO: check no INTENT(OUT)?
  if (context().languageFeatures().ShouldWarn(
          common::LanguageFeature::ForwardRefDummyImplicitNone)) {
    Say(symbol.name(),
        "Dummy argument '%s' was used without being explicitly typed"_en_US,
        symbol.name());
  }
  symbol.set(Symbol::Flag::Implicit);
  symbol.SetType(*type);
  return true;
}

// Ensure that the symbol for an intrinsic procedure is marked with
// the INTRINSIC attribute.  Also set PURE &/or ELEMENTAL as
// appropriate.
void ScopeHandler::AcquireIntrinsicProcedureFlags(Symbol &symbol) {
  symbol.attrs().set(Attr::INTRINSIC);
  switch (context().intrinsics().GetIntrinsicClass(symbol.name().ToString())) {
  case evaluate::IntrinsicClass::elementalFunction:
  case evaluate::IntrinsicClass::elementalSubroutine:
    symbol.attrs().set(Attr::ELEMENTAL);
    symbol.attrs().set(Attr::PURE);
    break;
  case evaluate::IntrinsicClass::impureSubroutine:
    break;
  default:
    symbol.attrs().set(Attr::PURE);
  }
}

const DeclTypeSpec *ScopeHandler::GetImplicitType(
    Symbol &symbol, bool respectImplicitNoneType) {
  const Scope *scope{&symbol.owner()};
  if (scope->IsGlobal()) {
    scope = &currScope();
  }
  scope = &GetInclusiveScope(*scope);
  const auto *type{implicitRulesMap_->at(scope).GetType(
      symbol.name(), respectImplicitNoneType)};
  if (type) {
    if (const DerivedTypeSpec * derived{type->AsDerived()}) {
      // Resolve any forward-referenced derived type; a quick no-op else.
      auto &instantiatable{*const_cast<DerivedTypeSpec *>(derived)};
      instantiatable.Instantiate(currScope());
    }
  }
  return type;
}

// Convert symbol to be a ObjectEntity or return false if it can't be.
bool ScopeHandler::ConvertToObjectEntity(Symbol &symbol) {
  if (symbol.has<ObjectEntityDetails>()) {
    // nothing to do
  } else if (symbol.has<UnknownDetails>()) {
    symbol.set_details(ObjectEntityDetails{});
  } else if (auto *details{symbol.detailsIf<EntityDetails>()}) {
    symbol.set_details(ObjectEntityDetails{std::move(*details)});
  } else if (auto *useDetails{symbol.detailsIf<UseDetails>()}) {
    return useDetails->symbol().has<ObjectEntityDetails>();
  } else {
    return false;
  }
  return true;
}
// Convert symbol to be a ProcEntity or return false if it can't be.
bool ScopeHandler::ConvertToProcEntity(Symbol &symbol) {
  if (symbol.has<ProcEntityDetails>()) {
    // nothing to do
  } else if (symbol.has<UnknownDetails>()) {
    symbol.set_details(ProcEntityDetails{});
  } else if (auto *details{symbol.detailsIf<EntityDetails>()}) {
    symbol.set_details(ProcEntityDetails{std::move(*details)});
    if (symbol.GetType() && !symbol.test(Symbol::Flag::Implicit)) {
      CHECK(!symbol.test(Symbol::Flag::Subroutine));
      symbol.set(Symbol::Flag::Function);
    }
  } else {
    return false;
  }
  return true;
}

const DeclTypeSpec &ScopeHandler::MakeNumericType(
    TypeCategory category, const std::optional<parser::KindSelector> &kind) {
  KindExpr value{GetKindParamExpr(category, kind)};
  if (auto known{evaluate::ToInt64(value)}) {
    return context().MakeNumericType(category, static_cast<int>(*known));
  } else {
    return currScope_->MakeNumericType(category, std::move(value));
  }
}

const DeclTypeSpec &ScopeHandler::MakeLogicalType(
    const std::optional<parser::KindSelector> &kind) {
  KindExpr value{GetKindParamExpr(TypeCategory::Logical, kind)};
  if (auto known{evaluate::ToInt64(value)}) {
    return context().MakeLogicalType(static_cast<int>(*known));
  } else {
    return currScope_->MakeLogicalType(std::move(value));
  }
}

void ScopeHandler::NotePossibleBadForwardRef(const parser::Name &name) {
  if (inSpecificationPart_ && name.symbol) {
    auto kind{currScope().kind()};
    if ((kind == Scope::Kind::Subprogram && !currScope().IsStmtFunction()) ||
        kind == Scope::Kind::Block) {
      bool isHostAssociated{&name.symbol->owner() == &currScope()
              ? name.symbol->has<HostAssocDetails>()
              : name.symbol->owner().Contains(currScope())};
      if (isHostAssociated) {
        specPartState_.forwardRefs.insert(name.source);
      }
    }
  }
}

std::optional<SourceName> ScopeHandler::HadForwardRef(
    const Symbol &symbol) const {
  auto iter{specPartState_.forwardRefs.find(symbol.name())};
  if (iter != specPartState_.forwardRefs.end()) {
    return *iter;
  }
  return std::nullopt;
}

bool ScopeHandler::CheckPossibleBadForwardRef(const Symbol &symbol) {
  if (!context().HasError(symbol)) {
    if (auto fwdRef{HadForwardRef(symbol)}) {
      const Symbol *outer{symbol.owner().FindSymbol(symbol.name())};
      if (outer && symbol.has<UseDetails>() &&
          &symbol.GetUltimate() == &outer->GetUltimate()) {
        // e.g. IMPORT of host's USE association
        return false;
      }
      Say(*fwdRef,
          "Forward reference to '%s' is not allowed in the same specification part"_err_en_US,
          *fwdRef)
          .Attach(symbol.name(), "Later declaration of '%s'"_en_US, *fwdRef);
      context().SetError(symbol);
      return true;
    }
    if (IsDummy(symbol) && isImplicitNoneType() &&
        symbol.test(Symbol::Flag::Implicit) && !context().HasError(symbol)) {
      // Dummy was implicitly typed despite IMPLICIT NONE(TYPE) in
      // ApplyImplicitRules() due to use in a specification expression,
      // and no explicit type declaration appeared later.
      Say(symbol.name(),
          "No explicit type declared for dummy argument '%s'"_err_en_US);
      context().SetError(symbol);
      return true;
    }
  }
  return false;
}

void ScopeHandler::MakeExternal(Symbol &symbol) {
  if (!symbol.attrs().test(Attr::EXTERNAL)) {
    symbol.attrs().set(Attr::EXTERNAL);
    if (symbol.attrs().test(Attr::INTRINSIC)) { // C840
      Say(symbol.name(),
          "Symbol '%s' cannot have both EXTERNAL and INTRINSIC attributes"_err_en_US,
          symbol.name());
    }
  }
}

// ModuleVisitor implementation

bool ModuleVisitor::Pre(const parser::Only &x) {
  std::visit(common::visitors{
                 [&](const Indirection<parser::GenericSpec> &generic) {
                   GenericSpecInfo genericSpecInfo{generic.value()};
                   AddUseOnly(genericSpecInfo.symbolName());
                   AddUse(genericSpecInfo);
                 },
                 [&](const parser::Name &name) {
                   AddUseOnly(name.source);
                   Resolve(name, AddUse(name.source, name.source).use);
                 },
                 [&](const parser::Rename &rename) { Walk(rename); },
             },
      x.u);
  return false;
}

bool ModuleVisitor::Pre(const parser::Rename::Names &x) {
  const auto &localName{std::get<0>(x.t)};
  const auto &useName{std::get<1>(x.t)};
  AddUseRename(useName.source);
  SymbolRename rename{AddUse(localName.source, useName.source)};
  if (rename.use) {
    EraseRenamedSymbol(*rename.use);
  }
  Resolve(useName, rename.use);
  Resolve(localName, rename.local);
  return false;
}
bool ModuleVisitor::Pre(const parser::Rename::Operators &x) {
  const parser::DefinedOpName &local{std::get<0>(x.t)};
  const parser::DefinedOpName &use{std::get<1>(x.t)};
  GenericSpecInfo localInfo{local};
  GenericSpecInfo useInfo{use};
  if (IsIntrinsicOperator(context(), local.v.source)) {
    Say(local.v,
        "Intrinsic operator '%s' may not be used as a defined operator"_err_en_US);
  } else if (IsLogicalConstant(context(), local.v.source)) {
    Say(local.v,
        "Logical constant '%s' may not be used as a defined operator"_err_en_US);
  } else {
    SymbolRename rename{AddUse(localInfo.symbolName(), useInfo.symbolName())};
    if (rename.use) {
      EraseRenamedSymbol(*rename.use);
    }
    useInfo.Resolve(rename.use);
    localInfo.Resolve(rename.local);
  }
  return false;
}

// Set useModuleScope_ to the Scope of the module being used.
bool ModuleVisitor::Pre(const parser::UseStmt &x) {
  useModuleScope_ = FindModule(x.moduleName);
  if (!useModuleScope_) {
    return false;
  }
  // use the name from this source file
  useModuleScope_->symbol()->ReplaceName(x.moduleName.source);
  return true;
}

void ModuleVisitor::Post(const parser::UseStmt &x) {
  if (const auto *list{std::get_if<std::list<parser::Rename>>(&x.u)}) {
    // Not a use-only: collect the names that were used in renames,
    // then add a use for each public name that was not renamed.
    std::set<SourceName> useNames;
    for (const auto &rename : *list) {
      std::visit(common::visitors{
                     [&](const parser::Rename::Names &names) {
                       useNames.insert(std::get<1>(names.t).source);
                     },
                     [&](const parser::Rename::Operators &ops) {
                       useNames.insert(std::get<1>(ops.t).v.source);
                     },
                 },
          rename.u);
    }
    for (const auto &[name, symbol] : *useModuleScope_) {
      if (symbol->attrs().test(Attr::PUBLIC) && !IsUseRenamed(symbol->name()) &&
          (!symbol->attrs().test(Attr::INTRINSIC) ||
              symbol->has<UseDetails>()) &&
          !symbol->has<MiscDetails>() && useNames.count(name) == 0) {
        SourceName location{x.moduleName.source};
        if