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//===--- MultiwayPathsCoveredCheck.cpp - clang-tidy------------------------===//
// 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
#include "MultiwayPathsCoveredCheck.h"
#include "clang/AST/ASTContext.h"
#include <limits>
using namespace clang::ast_matchers;
namespace clang {
namespace tidy {
namespace hicpp {
void MultiwayPathsCoveredCheck::storeOptions(
ClangTidyOptions::OptionMap &Opts) {, "WarnOnMissingElse", WarnOnMissingElse);
void MultiwayPathsCoveredCheck::registerMatchers(MatchFinder *Finder) {
// Match on switch statements that have either a bit-field or
// an integer condition. The ordering in 'anyOf()' is
// important because the last condition is the most general.
// 'unless()' must be the last match here and must be bound,
// otherwise the matcher does not work correctly, because it
// will not explicitly ignore enum conditions.
// This option is noisy, therefore matching is configurable.
if (WarnOnMissingElse) {
Finder->addMatcher(ifStmt(hasParent(ifStmt()), unless(hasElse(anything())))
static std::pair<std::size_t, bool> countCaseLabels(const SwitchStmt *Switch) {
std::size_t CaseCount = 0;
bool HasDefault = false;
const SwitchCase *CurrentCase = Switch->getSwitchCaseList();
while (CurrentCase) {
if (isa<DefaultStmt>(CurrentCase))
HasDefault = true;
CurrentCase = CurrentCase->getNextSwitchCase();
return std::make_pair(CaseCount, HasDefault);
/// This function calculate 2 ** Bits and returns
/// numeric_limits<std::size_t>::max() if an overflow occurred.
static std::size_t twoPow(std::size_t Bits) {
return Bits >= std::numeric_limits<std::size_t>::digits
? std::numeric_limits<std::size_t>::max()
: static_cast<size_t>(1) << Bits;
/// Get the number of possible values that can be switched on for the type T.
/// \return - 0 if bitcount could not be determined
/// - numeric_limits<std::size_t>::max() when overflow appeared due to
/// more than 64 bits type size.
static std::size_t getNumberOfPossibleValues(QualType T,
const ASTContext &Context) {
// `isBooleanType` must come first because `bool` is an integral type as well
// and would not return 2 as result.
if (T->isBooleanType())
return 2;
if (T->isIntegralType(Context))
return twoPow(Context.getTypeSize(T));
return 1;
void MultiwayPathsCoveredCheck::check(const MatchFinder::MatchResult &Result) {
if (const auto *ElseIfWithoutElse =
Result.Nodes.getNodeAs<IfStmt>("else-if")) {
"potentially uncovered codepath; add an ending else statement");
const auto *Switch = Result.Nodes.getNodeAs<SwitchStmt>("switch");
std::size_t SwitchCaseCount;
bool SwitchHasDefault;
std::tie(SwitchCaseCount, SwitchHasDefault) = countCaseLabels(Switch);
// Checks the sanity of 'switch' statements that actually do define
// a default branch but might be degenerated by having no or only one case.
if (SwitchHasDefault) {
handleSwitchWithDefault(Switch, SwitchCaseCount);
// Checks all 'switch' statements that do not define a default label.
// Here the heavy lifting happens.
if (!SwitchHasDefault && SwitchCaseCount > 0) {
handleSwitchWithoutDefault(Switch, SwitchCaseCount, Result);
// Warns for degenerated 'switch' statements that neither define a case nor
// a default label.
// FIXME: Evaluate, if emitting a fix-it to simplify that statement is
// reasonable.
if (!SwitchHasDefault && SwitchCaseCount == 0) {
"switch statement without labels has no effect");
llvm_unreachable("matched a case, that was not explicitly handled");
void MultiwayPathsCoveredCheck::handleSwitchWithDefault(
const SwitchStmt *Switch, std::size_t CaseCount) {
assert(CaseCount > 0 && "Switch statement with supposedly one default "
"branch did not contain any case labels");
if (CaseCount == 1 || CaseCount == 2)
CaseCount == 1
? "degenerated switch with default label only"
: "switch could be better written as an if/else statement");
void MultiwayPathsCoveredCheck::handleSwitchWithoutDefault(
const SwitchStmt *Switch, std::size_t CaseCount,
const MatchFinder::MatchResult &Result) {
// The matcher only works because some nodes are explicitly matched and
// bound but ignored. This is necessary to build the excluding logic for
// enums and 'switch' statements without a 'default' branch.
assert(!Result.Nodes.getNodeAs<DeclRefExpr>("enum-condition") &&
"switch over enum is handled by warnings already, explicitly ignoring "
// Determine the number of case labels. Because 'default' is not present
// and duplicating case labels is not allowed this number represents
// the number of codepaths. It can be directly compared to 'MaxPathsPossible'
// to see if some cases are missing.
// CaseCount == 0 is caught in DegenerateSwitch. Necessary because the
// matcher used for here does not match on degenerate 'switch'.
assert(CaseCount > 0 && "Switch statement without any case found. This case "
"should be excluded by the matcher and is handled "
std::size_t MaxPathsPossible = [&]() {
if (const auto *GeneralCondition =
Result.Nodes.getNodeAs<DeclRefExpr>("non-enum-condition")) {
return getNumberOfPossibleValues(GeneralCondition->getType(),
if (const auto *BitfieldDecl =
Result.Nodes.getNodeAs<FieldDecl>("bitfield")) {
return twoPow(BitfieldDecl->getBitWidthValue(*Result.Context));
return static_cast<std::size_t>(0);
// FIXME: Transform the 'switch' into an 'if' for CaseCount == 1.
if (CaseCount < MaxPathsPossible)
CaseCount == 1 ? "switch with only one case; use an if statement"
: "potential uncovered code path; add a default label");
} // namespace hicpp
} // namespace tidy
} // namespace clang