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//===-- lib/Parser/prescan.h ------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Defines a fast Fortran source prescanning phase that implements some
// character-level features of the language that can be inefficient to
// support directly in a backtracking parser. This phase handles Fortran
// line continuation, comment removal, card image margins, padding out
// fixed form character literals on truncated card images, file
// inclusion, and driving the Fortran source preprocessor.
#include "token-sequence.h"
#include "flang/Common/Fortran-features.h"
#include "flang/Parser/characters.h"
#include "flang/Parser/message.h"
#include "flang/Parser/provenance.h"
#include <bitset>
#include <optional>
#include <string>
#include <unordered_set>
namespace Fortran::parser {
class Messages;
class Preprocessor;
class Prescanner {
Prescanner(Messages &, CookedSource &, Preprocessor &,
Prescanner(const Prescanner &);
const AllSources &allSources() const { return allSources_; }
AllSources &allSources() { return allSources_; }
const Messages &messages() const { return messages_; }
Messages &messages() { return messages_; }
const Preprocessor &preprocessor() const { return preprocessor_; }
Preprocessor &preprocessor() { return preprocessor_; }
Prescanner &set_fixedForm(bool yes) {
inFixedForm_ = yes;
return *this;
Prescanner &set_encoding(Encoding code) {
encoding_ = code;
return *this;
Prescanner &set_fixedFormColumnLimit(int limit) {
fixedFormColumnLimit_ = limit;
return *this;
Prescanner &AddCompilerDirectiveSentinel(const std::string &);
void Prescan(ProvenanceRange);
void Statement();
void NextLine();
// Callbacks for use by Preprocessor.
bool IsAtEnd() const { return nextLine_ >= limit_; }
bool IsNextLinePreprocessorDirective() const;
TokenSequence TokenizePreprocessorDirective();
Provenance GetCurrentProvenance() const { return GetProvenance(at_); }
template <typename... A> Message &Say(A &&...a) {
return messages_.Say(std::forward<A>(a)...);
struct LineClassification {
enum class Kind {
IncludeDirective, // #include
DefinitionDirective, // #define & #undef
IncludeLine, // Fortran INCLUDE
LineClassification(Kind k, std::size_t po = 0, const char *s = nullptr)
: kind{k}, payloadOffset{po}, sentinel{s} {}
LineClassification(LineClassification &&) = default;
Kind kind;
std::size_t payloadOffset; // byte offset of content
const char *sentinel; // if it's a compiler directive
void BeginSourceLine(const char *at) {
at_ = at;
column_ = 1;
tabInCurrentLine_ = false;
void BeginSourceLineAndAdvance() {
void BeginStatementAndAdvance() {
slashInCurrentStatement_ = false;
preventHollerith_ = false;
delimiterNesting_ = 0;
Provenance GetProvenance(const char *sourceChar) const {
return startProvenance_ + (sourceChar - start_);
ProvenanceRange GetProvenanceRange(
const char *first, const char *afterLast) const {
std::size_t bytes = afterLast - first;
return {startProvenance_ + (first - start_), bytes};
void EmitChar(TokenSequence &tokens, char ch) {
tokens.PutNextTokenChar(ch, GetCurrentProvenance());
void EmitInsertedChar(TokenSequence &tokens, char ch) {
Provenance provenance{allSources_.CompilerInsertionProvenance(ch)};
tokens.PutNextTokenChar(ch, provenance);
char EmitCharAndAdvance(TokenSequence &tokens, char ch) {
EmitChar(tokens, ch);
return *at_;
bool InCompilerDirective() const { return directiveSentinel_ != nullptr; }
bool InFixedFormSource() const {
return inFixedForm_ && !inPreprocessorDirective_ && !InCompilerDirective();
bool IsCComment(const char *p) const {
return p[0] == '/' && p[1] == '*' &&
(inPreprocessorDirective_ ||
(!inCharLiteral_ &&
void LabelField(TokenSequence &);
void EnforceStupidEndStatementRules(const TokenSequence &);
void SkipToEndOfLine();
bool MustSkipToEndOfLine() const;
void NextChar();
void SkipToNextSignificantCharacter();
void SkipCComments();
void SkipSpaces();
static const char *SkipWhiteSpace(const char *);
const char *SkipWhiteSpaceAndCComments(const char *) const;
const char *SkipCComment(const char *) const;
bool NextToken(TokenSequence &);
bool ExponentAndKind(TokenSequence &);
void QuotedCharacterLiteral(TokenSequence &, const char *start);
void Hollerith(TokenSequence &, int count, const char *start);
bool PadOutCharacterLiteral(TokenSequence &);
bool SkipCommentLine(bool afterAmpersand);
bool IsFixedFormCommentLine(const char *) const;
const char *IsFreeFormComment(const char *) const;
std::optional<std::size_t> IsIncludeLine(const char *) const;
void FortranInclude(const char *quote);
const char *IsPreprocessorDirectiveLine(const char *) const;
const char *FixedFormContinuationLine(bool mightNeedSpace);
const char *FreeFormContinuationLine(bool ampersand);
bool IsImplicitContinuation() const;
bool FixedFormContinuation(bool mightNeedSpace);
bool FreeFormContinuation();
bool Continuation(bool mightNeedFixedFormSpace);
std::optional<LineClassification> IsFixedFormCompilerDirectiveLine(
const char *) const;
std::optional<LineClassification> IsFreeFormCompilerDirectiveLine(
const char *) const;
const char *IsCompilerDirectiveSentinel(const char *) const;
LineClassification ClassifyLine(const char *) const;
void SourceFormChange(std::string &&);
Messages &messages_;
CookedSource &cooked_;
Preprocessor &preprocessor_;
AllSources &allSources_;
common::LanguageFeatureControl features_;
bool inFixedForm_{false};
int fixedFormColumnLimit_{72};
Encoding encoding_{Encoding::UTF_8};
int delimiterNesting_{0};
int prescannerNesting_{0};
Provenance startProvenance_;
const char *start_{nullptr}; // beginning of current source file content
const char *limit_{nullptr}; // first address after end of current source
const char *nextLine_{nullptr}; // next line to process; <= limit_
const char *directiveSentinel_{nullptr}; // current compiler directive
// This data members are state for processing the source line containing
// "at_", which goes to up to the newline character before "nextLine_".
const char *at_{nullptr}; // next character to process; < nextLine_
int column_{1}; // card image column position of next character
bool tabInCurrentLine_{false};
bool slashInCurrentStatement_{false};
bool preventHollerith_{false}; // CHARACTER*4HIMOM not Hollerith
bool inCharLiteral_{false};
bool inPreprocessorDirective_{false};
// In some edge cases of compiler directive continuation lines, it
// is necessary to treat the line break as a space character by
// setting this flag, which is cleared by EmitChar().
bool insertASpace_{false};
// When a free form continuation marker (&) appears at the end of a line
// before a INCLUDE or #include, we delete it and omit the newline, so
// that the first line of the included file is truly a continuation of
// the line before. Also used when the & appears at the end of the last
// line in an include file.
bool omitNewline_{false};
bool skipLeadingAmpersand_{false};
const Provenance spaceProvenance_{
allSources_.CompilerInsertionProvenance(' ')};
const Provenance backslashProvenance_{
// To avoid probing the set of active compiler directive sentinel strings
// on every comment line, they're checked first with a cheap Bloom filter.
static const int prime1{1019}, prime2{1021};
std::bitset<prime2> compilerDirectiveBloomFilter_; // 128 bytes
std::unordered_set<std::string> compilerDirectiveSentinels_;
} // namespace Fortran::parser