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1 //===--- StrCatAppendCheck.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 "StrCatAppendCheck.h"
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10 #include "clang/AST/ASTContext.h"
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11 #include "clang/ASTMatchers/ASTMatchFinder.h"
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12
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13 using namespace clang::ast_matchers;
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14
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15 namespace clang {
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16 namespace tidy {
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17 namespace abseil {
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18
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19 namespace {
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20 // Skips any combination of temporary materialization, temporary binding and
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21 // implicit casting.
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22 AST_MATCHER_P(Stmt, IgnoringTemporaries, ast_matchers::internal::Matcher<Stmt>,
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23 InnerMatcher) {
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24 const Stmt *E = &Node;
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25 while (true) {
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26 if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(E))
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27 E = MTE->getSubExpr();
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28 if (const auto *BTE = dyn_cast<CXXBindTemporaryExpr>(E))
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29 E = BTE->getSubExpr();
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30 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E))
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31 E = ICE->getSubExpr();
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32 else
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33 break;
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34 }
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35
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36 return InnerMatcher.matches(*E, Finder, Builder);
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37 }
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38
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39 } // namespace
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40
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41 // TODO: str += StrCat(...)
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42 // str.append(StrCat(...))
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43
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44 void StrCatAppendCheck::registerMatchers(MatchFinder *Finder) {
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45 const auto StrCat = functionDecl(hasName("::absl::StrCat"));
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46 // The arguments of absl::StrCat are implicitly converted to AlphaNum. This
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47 // matches to the arguments because of that behavior.
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48 const auto AlphaNum = IgnoringTemporaries(cxxConstructExpr(
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49 argumentCountIs(1), hasType(cxxRecordDecl(hasName("::absl::AlphaNum"))),
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50 hasArgument(0, ignoringImpCasts(declRefExpr(to(equalsBoundNode("LHS")),
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51 expr().bind("Arg0"))))));
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52
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53 const auto HasAnotherReferenceToLhs =
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54 callExpr(hasAnyArgument(expr(hasDescendant(declRefExpr(
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55 to(equalsBoundNode("LHS")), unless(equalsBoundNode("Arg0")))))));
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56
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57 // Now look for calls to operator= with an object on the LHS and a call to
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58 // StrCat on the RHS. The first argument of the StrCat call should be the same
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59 // as the LHS. Ignore calls from template instantiations.
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60 Finder->addMatcher(
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173
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61 traverse(ast_type_traits::TK_AsIs,
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62 cxxOperatorCallExpr(
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63 unless(isInTemplateInstantiation()),
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64 hasOverloadedOperatorName("="),
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65 hasArgument(0, declRefExpr(to(decl().bind("LHS")))),
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66 hasArgument(
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67 1, IgnoringTemporaries(
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68 callExpr(callee(StrCat), hasArgument(0, AlphaNum),
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69 unless(HasAnotherReferenceToLhs))
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70 .bind("Call"))))
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71 .bind("Op")),
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150
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72 this);
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73 }
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74
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75 void StrCatAppendCheck::check(const MatchFinder::MatchResult &Result) {
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76 const auto *Op = Result.Nodes.getNodeAs<CXXOperatorCallExpr>("Op");
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77 const auto *Call = Result.Nodes.getNodeAs<CallExpr>("Call");
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78 assert(Op != nullptr && Call != nullptr && "Matcher does not work as expected");
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79
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80 // Handles the case 'x = absl::StrCat(x)', which has no effect.
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81 if (Call->getNumArgs() == 1) {
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82 diag(Op->getBeginLoc(), "call to 'absl::StrCat' has no effect");
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83 return;
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84 }
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85
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86 // Emit a warning and emit fixits to go from
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87 // x = absl::StrCat(x, ...)
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88 // to
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89 // absl::StrAppend(&x, ...)
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90 diag(Op->getBeginLoc(),
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91 "call 'absl::StrAppend' instead of 'absl::StrCat' when appending to a "
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92 "string to avoid a performance penalty")
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93 << FixItHint::CreateReplacement(
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94 CharSourceRange::getTokenRange(Op->getBeginLoc(),
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95 Call->getCallee()->getEndLoc()),
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96 "absl::StrAppend")
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97 << FixItHint::CreateInsertion(Call->getArg(0)->getBeginLoc(), "&");
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98 }
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99
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100 } // namespace abseil
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101 } // namespace tidy
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102 } // namespace clang
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