clang-tools-extra/clang-tidy/abseil/RedundantStrcatCallsCheck.cpp

   1 //===--- RedundantStrcatCallsCheck.cpp - clang-tidy------------------------===//
   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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "RedundantStrcatCallsCheck.h"
  10 #include "clang/AST/ASTContext.h"
  11 #include "clang/ASTMatchers/ASTMatchFinder.h"
  12
  13 using namespace clang::ast_matchers;
  14
  15 namespace clang::tidy::abseil {
  16
  17 // TODO: Features to add to the check:
  18 //  - Make it work if num_args > 26.
  19 //  - Remove empty literal string arguments.
  20 //  - Collapse consecutive literal string arguments into one (remove the ,).
  21 //  - Replace StrCat(a + b)  ->  StrCat(a, b)  if a or b are strings.
  22 //  - Make it work in macros if the outer and inner StrCats are both in the
  23 //    argument.
  24
  25 void RedundantStrcatCallsCheck::registerMatchers(MatchFinder* Finder) {
  26   const auto CallToStrcat =
  27       callExpr(callee(functionDecl(hasName("::absl::StrCat"))));
  28   const auto CallToStrappend =
  29       callExpr(callee(functionDecl(hasName("::absl::StrAppend"))));
  30   // Do not match StrCat() calls that are descendants of other StrCat calls.
  31   // Those are handled on the ancestor call.
  32   const auto CallToEither = callExpr(
  33       callee(functionDecl(hasAnyName("::absl::StrCat", "::absl::StrAppend"))));
  34   Finder->addMatcher(
  35       callExpr(CallToStrcat, unless(hasAncestor(CallToEither))).bind("StrCat"),
  36       this);
  37   Finder->addMatcher(CallToStrappend.bind("StrAppend"), this);
  38 }
  39
  40 namespace {
  41
  42 struct StrCatCheckResult {
  43   int NumCalls = 0;
  44   std::vector<FixItHint> Hints;
  45 };
  46
  47 void removeCallLeaveArgs(const CallExpr *Call, StrCatCheckResult *CheckResult) {
  48   if (Call->getNumArgs() == 0)
  49     return;
  50   // Remove 'Foo('
  51   CheckResult->Hints.push_back(
  52       FixItHint::CreateRemoval(CharSourceRange::getCharRange(
  53           Call->getBeginLoc(), Call->getArg(0)->getBeginLoc())));
  54   // Remove the ')'
  55   CheckResult->Hints.push_back(
  56       FixItHint::CreateRemoval(CharSourceRange::getCharRange(
  57           Call->getRParenLoc(), Call->getEndLoc().getLocWithOffset(1))));
  58 }
  59
  60 const clang::CallExpr *processArgument(const Expr *Arg,
  61                                        const MatchFinder::MatchResult &Result,
  62                                        StrCatCheckResult *CheckResult) {
  63   const auto IsAlphanum = hasDeclaration(cxxMethodDecl(hasName("AlphaNum")));
  64   static const auto* const Strcat = new auto(hasName("::absl::StrCat"));
  65   const auto IsStrcat = cxxBindTemporaryExpr(
  66       has(callExpr(callee(functionDecl(*Strcat))).bind("StrCat")));
  67   if (const auto *SubStrcatCall = selectFirst<const CallExpr>(
  68           "StrCat",
  69           match(stmt(traverse(TK_AsIs,
  70                               anyOf(cxxConstructExpr(IsAlphanum,
  71                                                      hasArgument(0, IsStrcat)),
  72                                     IsStrcat))),
  73                 *Arg->IgnoreParenImpCasts(), *Result.Context))) {
  74     removeCallLeaveArgs(SubStrcatCall, CheckResult);
  75     return SubStrcatCall;
  76   }
  77   return nullptr;
  78 }
  79
  80 StrCatCheckResult processCall(const CallExpr *RootCall, bool IsAppend,
  81                               const MatchFinder::MatchResult &Result) {
  82   StrCatCheckResult CheckResult;
  83   std::deque<const CallExpr*> CallsToProcess = {RootCall};
  84
  85   while (!CallsToProcess.empty()) {
  86     ++CheckResult.NumCalls;
  87
  88     const CallExpr* CallExpr = CallsToProcess.front();
  89     CallsToProcess.pop_front();
  90
  91     int StartArg = CallExpr == RootCall && IsAppend;
  92     for (const auto *Arg : CallExpr->arguments()) {
  93       if (StartArg-- > 0)
  94         continue;
  95       if (const clang::CallExpr *Sub =
  96               processArgument(Arg, Result, &CheckResult)) {
  97         CallsToProcess.push_back(Sub);
  98       }
  99     }
 100   }
 101   return CheckResult;
 102 }
 103 }  // namespace
 104
 105 void RedundantStrcatCallsCheck::check(const MatchFinder::MatchResult& Result) {
 106   bool IsAppend = false;
 107
 108   const CallExpr *RootCall = nullptr;
 109   if ((RootCall = Result.Nodes.getNodeAs<CallExpr>("StrCat")))
 110         IsAppend = false;
 111   else if ((RootCall = Result.Nodes.getNodeAs<CallExpr>("StrAppend")))
 112         IsAppend = true;
 113   else
 114         return;
 115
 116   if (RootCall->getBeginLoc().isMacroID()) {
 117     // Ignore calls within macros.
 118     // In many cases the outer StrCat part of the macro and the inner StrCat is
 119     // a macro argument. Removing the inner StrCat() converts one macro
 120     // argument into many.
 121     return;
 122   }
 123
 124   const StrCatCheckResult CheckResult = processCall(RootCall, IsAppend, Result);
 125   if (CheckResult.NumCalls == 1) {
 126     // Just one call, so nothing to fix.
 127     return;
 128   }
 129
 130   diag(RootCall->getBeginLoc(),
 131            "multiple calls to 'absl::StrCat' can be flattened into a single call")
 132       << CheckResult.Hints;
 133 }
 134
 135 } // namespace clang::tidy::abseil