176 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "MultiwayPathsCoveredCheck.h"10#include "clang/AST/ASTContext.h"11 12#include <limits>13 14using namespace clang::ast_matchers;15 16namespace clang::tidy::hicpp {17 18void MultiwayPathsCoveredCheck::storeOptions(19 ClangTidyOptions::OptionMap &Opts) {20 Options.store(Opts, "WarnOnMissingElse", WarnOnMissingElse);21}22 23void MultiwayPathsCoveredCheck::registerMatchers(MatchFinder *Finder) {24 Finder->addMatcher(25 switchStmt(26 hasCondition(expr(27 // Match on switch statements that have either a bit-field or28 // an integer condition. The ordering in 'anyOf()' is29 // important because the last condition is the most general.30 anyOf(ignoringImpCasts(memberExpr(hasDeclaration(31 fieldDecl(isBitField()).bind("bitfield")))),32 ignoringImpCasts(declRefExpr().bind("non-enum-condition"))),33 // 'unless()' must be the last match here and must be bound,34 // otherwise the matcher does not work correctly, because it35 // will not explicitly ignore enum conditions.36 unless(ignoringImpCasts(37 declRefExpr(hasType(hasCanonicalType(enumType())))38 .bind("enum-condition"))))))39 .bind("switch"),40 this);41 42 // This option is noisy, therefore matching is configurable.43 if (WarnOnMissingElse) {44 Finder->addMatcher(ifStmt(hasParent(ifStmt()), unless(hasElse(anything())))45 .bind("else-if"),46 this);47 }48}49 50static std::pair<std::size_t, bool> countCaseLabels(const SwitchStmt *Switch) {51 std::size_t CaseCount = 0;52 bool HasDefault = false;53 54 const SwitchCase *CurrentCase = Switch->getSwitchCaseList();55 while (CurrentCase) {56 ++CaseCount;57 if (isa<DefaultStmt>(CurrentCase))58 HasDefault = true;59 60 CurrentCase = CurrentCase->getNextSwitchCase();61 }62 63 return std::make_pair(CaseCount, HasDefault);64}65 66/// This function calculate 2 ** Bits and returns67/// numeric_limits<std::size_t>::max() if an overflow occurred.68static std::size_t twoPow(std::size_t Bits) {69 return Bits >= std::numeric_limits<std::size_t>::digits70 ? std::numeric_limits<std::size_t>::max()71 : static_cast<size_t>(1) << Bits;72}73 74/// Get the number of possible values that can be switched on for the type T.75///76/// \return - 0 if bitcount could not be determined77/// - numeric_limits<std::size_t>::max() when overflow appeared due to78/// more than 64 bits type size.79static std::size_t getNumberOfPossibleValues(QualType T,80 const ASTContext &Context) {81 // `isBooleanType` must come first because `bool` is an integral type as well82 // and would not return 2 as result.83 if (T->isBooleanType())84 return 2;85 if (T->isIntegralType(Context))86 return twoPow(Context.getTypeSize(T));87 return 1;88}89 90void MultiwayPathsCoveredCheck::check(const MatchFinder::MatchResult &Result) {91 if (const auto *ElseIfWithoutElse =92 Result.Nodes.getNodeAs<IfStmt>("else-if")) {93 diag(ElseIfWithoutElse->getBeginLoc(),94 "potentially uncovered codepath; add an ending else statement");95 return;96 }97 const auto *Switch = Result.Nodes.getNodeAs<SwitchStmt>("switch");98 std::size_t SwitchCaseCount = 0;99 bool SwitchHasDefault = false;100 std::tie(SwitchCaseCount, SwitchHasDefault) = countCaseLabels(Switch);101 102 // Checks the sanity of 'switch' statements that actually do define103 // a default branch but might be degenerated by having no or only one case.104 if (SwitchHasDefault) {105 handleSwitchWithDefault(Switch, SwitchCaseCount);106 return;107 }108 // Checks all 'switch' statements that do not define a default label.109 // Here the heavy lifting happens.110 if (!SwitchHasDefault && SwitchCaseCount > 0) {111 handleSwitchWithoutDefault(Switch, SwitchCaseCount, Result);112 return;113 }114 // Warns for degenerated 'switch' statements that neither define a case nor115 // a default label.116 // FIXME: Evaluate, if emitting a fix-it to simplify that statement is117 // reasonable.118 if (!SwitchHasDefault && SwitchCaseCount == 0) {119 diag(Switch->getBeginLoc(),120 "switch statement without labels has no effect");121 return;122 }123 llvm_unreachable("matched a case, that was not explicitly handled");124}125 126void MultiwayPathsCoveredCheck::handleSwitchWithDefault(127 const SwitchStmt *Switch, std::size_t CaseCount) {128 assert(CaseCount > 0 && "Switch statement with supposedly one default "129 "branch did not contain any case labels");130 if (CaseCount == 1 || CaseCount == 2)131 diag(Switch->getBeginLoc(),132 CaseCount == 1133 ? "degenerated switch with default label only"134 : "switch could be better written as an if/else statement");135}136 137void MultiwayPathsCoveredCheck::handleSwitchWithoutDefault(138 const SwitchStmt *Switch, std::size_t CaseCount,139 const MatchFinder::MatchResult &Result) {140 // The matcher only works because some nodes are explicitly matched and141 // bound but ignored. This is necessary to build the excluding logic for142 // enums and 'switch' statements without a 'default' branch.143 assert(!Result.Nodes.getNodeAs<DeclRefExpr>("enum-condition") &&144 "switch over enum is handled by warnings already, explicitly ignoring "145 "them");146 // Determine the number of case labels. Because 'default' is not present147 // and duplicating case labels is not allowed this number represents148 // the number of codepaths. It can be directly compared to 'MaxPathsPossible'149 // to see if some cases are missing.150 // CaseCount == 0 is caught in DegenerateSwitch. Necessary because the151 // matcher used for here does not match on degenerate 'switch'.152 assert(CaseCount > 0 && "Switch statement without any case found. This case "153 "should be excluded by the matcher and is handled "154 "separately.");155 const std::size_t MaxPathsPossible = [&]() {156 if (const auto *GeneralCondition =157 Result.Nodes.getNodeAs<DeclRefExpr>("non-enum-condition")) {158 return getNumberOfPossibleValues(GeneralCondition->getType(),159 *Result.Context);160 }161 if (const auto *BitfieldDecl =162 Result.Nodes.getNodeAs<FieldDecl>("bitfield")) {163 return twoPow(BitfieldDecl->getBitWidthValue());164 }165 166 return static_cast<std::size_t>(0);167 }();168 169 // FIXME: Transform the 'switch' into an 'if' for CaseCount == 1.170 if (CaseCount < MaxPathsPossible)171 diag(Switch->getBeginLoc(),172 CaseCount == 1 ? "switch with only one case; use an if statement"173 : "potential uncovered code path; add a default label");174}175} // namespace clang::tidy::hicpp176