1 //===--- StrCatAppendCheck.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 "StrCatAppendCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12
13 using namespace clang::ast_matchers;
14
15 namespace clang {
16 namespace tidy {
17 namespace abseil {
18
19 namespace {
20 // Skips any combination of temporary materialization, temporary binding and
21 // implicit casting.
AST_MATCHER_P(Stmt,IgnoringTemporaries,ast_matchers::internal::Matcher<Stmt>,InnerMatcher)22 AST_MATCHER_P(Stmt, IgnoringTemporaries, ast_matchers::internal::Matcher<Stmt>,
23 InnerMatcher) {
24 const Stmt *E = &Node;
25 while (true) {
26 if (const auto *MTE = dyn_cast<MaterializeTemporaryExpr>(E))
27 E = MTE->getSubExpr();
28 if (const auto *BTE = dyn_cast<CXXBindTemporaryExpr>(E))
29 E = BTE->getSubExpr();
30 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(E))
31 E = ICE->getSubExpr();
32 else
33 break;
34 }
35
36 return InnerMatcher.matches(*E, Finder, Builder);
37 }
38
39 } // namespace
40
41 // TODO: str += StrCat(...)
42 // str.append(StrCat(...))
43
registerMatchers(MatchFinder * Finder)44 void StrCatAppendCheck::registerMatchers(MatchFinder *Finder) {
45 const auto StrCat = functionDecl(hasName("::absl::StrCat"));
46 // The arguments of absl::StrCat are implicitly converted to AlphaNum. This
47 // matches to the arguments because of that behavior.
48 const auto AlphaNum = IgnoringTemporaries(cxxConstructExpr(
49 argumentCountIs(1), hasType(cxxRecordDecl(hasName("::absl::AlphaNum"))),
50 hasArgument(0, ignoringImpCasts(declRefExpr(to(equalsBoundNode("LHS")),
51 expr().bind("Arg0"))))));
52
53 const auto HasAnotherReferenceToLhs =
54 callExpr(hasAnyArgument(expr(hasDescendant(declRefExpr(
55 to(equalsBoundNode("LHS")), unless(equalsBoundNode("Arg0")))))));
56
57 // Now look for calls to operator= with an object on the LHS and a call to
58 // StrCat on the RHS. The first argument of the StrCat call should be the same
59 // as the LHS. Ignore calls from template instantiations.
60 Finder->addMatcher(
61 traverse(ast_type_traits::TK_AsIs,
62 cxxOperatorCallExpr(
63 unless(isInTemplateInstantiation()),
64 hasOverloadedOperatorName("="),
65 hasArgument(0, declRefExpr(to(decl().bind("LHS")))),
66 hasArgument(
67 1, IgnoringTemporaries(
68 callExpr(callee(StrCat), hasArgument(0, AlphaNum),
69 unless(HasAnotherReferenceToLhs))
70 .bind("Call"))))
71 .bind("Op")),
72 this);
73 }
74
check(const MatchFinder::MatchResult & Result)75 void StrCatAppendCheck::check(const MatchFinder::MatchResult &Result) {
76 const auto *Op = Result.Nodes.getNodeAs<CXXOperatorCallExpr>("Op");
77 const auto *Call = Result.Nodes.getNodeAs<CallExpr>("Call");
78 assert(Op != nullptr && Call != nullptr && "Matcher does not work as expected");
79
80 // Handles the case 'x = absl::StrCat(x)', which has no effect.
81 if (Call->getNumArgs() == 1) {
82 diag(Op->getBeginLoc(), "call to 'absl::StrCat' has no effect");
83 return;
84 }
85
86 // Emit a warning and emit fixits to go from
87 // x = absl::StrCat(x, ...)
88 // to
89 // absl::StrAppend(&x, ...)
90 diag(Op->getBeginLoc(),
91 "call 'absl::StrAppend' instead of 'absl::StrCat' when appending to a "
92 "string to avoid a performance penalty")
93 << FixItHint::CreateReplacement(
94 CharSourceRange::getTokenRange(Op->getBeginLoc(),
95 Call->getCallee()->getEndLoc()),
96 "absl::StrAppend")
97 << FixItHint::CreateInsertion(Call->getArg(0)->getBeginLoc(), "&");
98 }
99
100 } // namespace abseil
101 } // namespace tidy
102 } // namespace clang
103