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1 //===--- MultiwayPathsCoveredCheck.cpp - clang-tidy------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #include "MultiwayPathsCoveredCheck.h"
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10 #include "clang/AST/ASTContext.h"
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11
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12 #include <limits>
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13
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14 using namespace clang::ast_matchers;
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15
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252
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16 namespace clang::tidy::hicpp {
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150
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17
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18 void MultiwayPathsCoveredCheck::storeOptions(
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19 ClangTidyOptions::OptionMap &Opts) {
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20 Options.store(Opts, "WarnOnMissingElse", WarnOnMissingElse);
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21 }
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22
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23 void MultiwayPathsCoveredCheck::registerMatchers(MatchFinder *Finder) {
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24 Finder->addMatcher(
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25 switchStmt(
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26 hasCondition(expr(
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27 // Match on switch statements that have either a bit-field or
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28 // an integer condition. The ordering in 'anyOf()' is
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29 // important because the last condition is the most general.
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30 anyOf(ignoringImpCasts(memberExpr(hasDeclaration(
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31 fieldDecl(isBitField()).bind("bitfield")))),
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32 ignoringImpCasts(declRefExpr().bind("non-enum-condition"))),
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33 // 'unless()' must be the last match here and must be bound,
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34 // otherwise the matcher does not work correctly, because it
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35 // will not explicitly ignore enum conditions.
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36 unless(ignoringImpCasts(
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236
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37 declRefExpr(hasType(hasCanonicalType(enumType())))
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38 .bind("enum-condition"))))))
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150
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39 .bind("switch"),
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40 this);
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41
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42 // This option is noisy, therefore matching is configurable.
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43 if (WarnOnMissingElse) {
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44 Finder->addMatcher(ifStmt(hasParent(ifStmt()), unless(hasElse(anything())))
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45 .bind("else-if"),
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46 this);
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47 }
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48 }
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49
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50 static std::pair<std::size_t, bool> countCaseLabels(const SwitchStmt *Switch) {
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51 std::size_t CaseCount = 0;
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52 bool HasDefault = false;
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53
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54 const SwitchCase *CurrentCase = Switch->getSwitchCaseList();
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55 while (CurrentCase) {
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56 ++CaseCount;
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57 if (isa<DefaultStmt>(CurrentCase))
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58 HasDefault = true;
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59
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60 CurrentCase = CurrentCase->getNextSwitchCase();
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61 }
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62
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63 return std::make_pair(CaseCount, HasDefault);
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64 }
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65
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66 /// This function calculate 2 ** Bits and returns
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173
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67 /// numeric_limits<std::size_t>::max() if an overflow occurred.
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150
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68 static std::size_t twoPow(std::size_t Bits) {
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69 return Bits >= std::numeric_limits<std::size_t>::digits
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70 ? std::numeric_limits<std::size_t>::max()
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71 : static_cast<size_t>(1) << Bits;
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72 }
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73
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74 /// Get the number of possible values that can be switched on for the type T.
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75 ///
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76 /// \return - 0 if bitcount could not be determined
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77 /// - numeric_limits<std::size_t>::max() when overflow appeared due to
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78 /// more than 64 bits type size.
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79 static std::size_t getNumberOfPossibleValues(QualType T,
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80 const ASTContext &Context) {
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81 // `isBooleanType` must come first because `bool` is an integral type as well
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82 // and would not return 2 as result.
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83 if (T->isBooleanType())
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84 return 2;
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221
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85 if (T->isIntegralType(Context))
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150
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86 return twoPow(Context.getTypeSize(T));
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221
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87 return 1;
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150
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88 }
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89
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90 void MultiwayPathsCoveredCheck::check(const MatchFinder::MatchResult &Result) {
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91 if (const auto *ElseIfWithoutElse =
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92 Result.Nodes.getNodeAs<IfStmt>("else-if")) {
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93 diag(ElseIfWithoutElse->getBeginLoc(),
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94 "potentially uncovered codepath; add an ending else statement");
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95 return;
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96 }
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97 const auto *Switch = Result.Nodes.getNodeAs<SwitchStmt>("switch");
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98 std::size_t SwitchCaseCount;
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99 bool SwitchHasDefault;
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100 std::tie(SwitchCaseCount, SwitchHasDefault) = countCaseLabels(Switch);
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101
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102 // Checks the sanity of 'switch' statements that actually do define
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103 // a default branch but might be degenerated by having no or only one case.
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104 if (SwitchHasDefault) {
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105 handleSwitchWithDefault(Switch, SwitchCaseCount);
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106 return;
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107 }
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108 // Checks all 'switch' statements that do not define a default label.
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109 // Here the heavy lifting happens.
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110 if (!SwitchHasDefault && SwitchCaseCount > 0) {
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111 handleSwitchWithoutDefault(Switch, SwitchCaseCount, Result);
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112 return;
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113 }
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114 // Warns for degenerated 'switch' statements that neither define a case nor
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115 // a default label.
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116 // FIXME: Evaluate, if emitting a fix-it to simplify that statement is
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117 // reasonable.
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118 if (!SwitchHasDefault && SwitchCaseCount == 0) {
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119 diag(Switch->getBeginLoc(),
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120 "switch statement without labels has no effect");
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121 return;
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122 }
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123 llvm_unreachable("matched a case, that was not explicitly handled");
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124 }
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125
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126 void MultiwayPathsCoveredCheck::handleSwitchWithDefault(
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127 const SwitchStmt *Switch, std::size_t CaseCount) {
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128 assert(CaseCount > 0 && "Switch statement with supposedly one default "
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129 "branch did not contain any case labels");
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130 if (CaseCount == 1 || CaseCount == 2)
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131 diag(Switch->getBeginLoc(),
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132 CaseCount == 1
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133 ? "degenerated switch with default label only"
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134 : "switch could be better written as an if/else statement");
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135 }
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136
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137 void MultiwayPathsCoveredCheck::handleSwitchWithoutDefault(
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138 const SwitchStmt *Switch, std::size_t CaseCount,
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139 const MatchFinder::MatchResult &Result) {
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140 // The matcher only works because some nodes are explicitly matched and
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141 // bound but ignored. This is necessary to build the excluding logic for
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142 // enums and 'switch' statements without a 'default' branch.
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143 assert(!Result.Nodes.getNodeAs<DeclRefExpr>("enum-condition") &&
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144 "switch over enum is handled by warnings already, explicitly ignoring "
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145 "them");
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146 // Determine the number of case labels. Because 'default' is not present
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147 // and duplicating case labels is not allowed this number represents
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148 // the number of codepaths. It can be directly compared to 'MaxPathsPossible'
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149 // to see if some cases are missing.
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150 // CaseCount == 0 is caught in DegenerateSwitch. Necessary because the
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151 // matcher used for here does not match on degenerate 'switch'.
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152 assert(CaseCount > 0 && "Switch statement without any case found. This case "
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153 "should be excluded by the matcher and is handled "
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173
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154 "separately.");
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150
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155 std::size_t MaxPathsPossible = [&]() {
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156 if (const auto *GeneralCondition =
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157 Result.Nodes.getNodeAs<DeclRefExpr>("non-enum-condition")) {
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158 return getNumberOfPossibleValues(GeneralCondition->getType(),
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159 *Result.Context);
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160 }
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161 if (const auto *BitfieldDecl =
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162 Result.Nodes.getNodeAs<FieldDecl>("bitfield")) {
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163 return twoPow(BitfieldDecl->getBitWidthValue(*Result.Context));
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164 }
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165
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166 return static_cast<std::size_t>(0);
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167 }();
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168
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169 // FIXME: Transform the 'switch' into an 'if' for CaseCount == 1.
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170 if (CaseCount < MaxPathsPossible)
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171 diag(Switch->getBeginLoc(),
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172 CaseCount == 1 ? "switch with only one case; use an if statement"
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173 : "potential uncovered code path; add a default label");
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174 }
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252
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175 } // namespace clang::tidy::hicpp
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