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