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