1 //===- RedundantStringInitCheck.cpp - clang-tidy ----------------*- C++ -*-===//
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 "RedundantStringInitCheck.h"
10 #include "../utils/Matchers.h"
11 #include "../utils/OptionsUtils.h"
12 #include "clang/ASTMatchers/ASTMatchers.h"
13 
14 using namespace clang::ast_matchers;
15 using namespace clang::tidy::matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace readability {
20 
21 const char DefaultStringNames[] =
22     "::std::basic_string_view;::std::basic_string";
23 
24 static std::vector<StringRef> removeNamespaces(ArrayRef<StringRef> Names) {
25   std::vector<StringRef> Result;
26   Result.reserve(Names.size());
27   for (StringRef Name : Names) {
28     StringRef::size_type ColonPos = Name.rfind(':');
29     Result.push_back(
30         Name.drop_front(ColonPos == StringRef::npos ? 0 : ColonPos + 1));
31   }
32   return Result;
33 }
34 
35 static const CXXConstructExpr *
36 getConstructExpr(const CXXCtorInitializer &CtorInit) {
37   const Expr *InitExpr = CtorInit.getInit();
38   if (const auto *CleanUpExpr = dyn_cast<ExprWithCleanups>(InitExpr))
39     InitExpr = CleanUpExpr->getSubExpr();
40   return dyn_cast<CXXConstructExpr>(InitExpr);
41 }
42 
43 static llvm::Optional<SourceRange>
44 getConstructExprArgRange(const CXXConstructExpr &Construct) {
45   SourceLocation B, E;
46   for (const Expr *Arg : Construct.arguments()) {
47     if (B.isInvalid())
48       B = Arg->getBeginLoc();
49     if (Arg->getEndLoc().isValid())
50       E = Arg->getEndLoc();
51   }
52   if (B.isInvalid() || E.isInvalid())
53     return llvm::None;
54   return SourceRange(B, E);
55 }
56 
57 RedundantStringInitCheck::RedundantStringInitCheck(StringRef Name,
58                                                    ClangTidyContext *Context)
59     : ClangTidyCheck(Name, Context),
60       StringNames(utils::options::parseStringList(
61           Options.get("StringNames", DefaultStringNames))) {}
62 
63 void RedundantStringInitCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
64   Options.store(Opts, "StringNames", DefaultStringNames);
65 }
66 
67 void RedundantStringInitCheck::registerMatchers(MatchFinder *Finder) {
68   const auto HasStringTypeName = hasAnyName(StringNames);
69   const auto HasStringCtorName = hasAnyName(removeNamespaces(StringNames));
70 
71   // Match string constructor.
72   const auto StringConstructorExpr = expr(
73       anyOf(cxxConstructExpr(argumentCountIs(1),
74                              hasDeclaration(cxxMethodDecl(HasStringCtorName))),
75             // If present, the second argument is the alloc object which must
76             // not be present explicitly.
77             cxxConstructExpr(argumentCountIs(2),
78                              hasDeclaration(cxxMethodDecl(HasStringCtorName)),
79                              hasArgument(1, cxxDefaultArgExpr()))));
80 
81   // Match a string constructor expression with an empty string literal.
82   const auto EmptyStringCtorExpr = cxxConstructExpr(
83       StringConstructorExpr,
84       hasArgument(0, ignoringParenImpCasts(stringLiteral(hasSize(0)))));
85 
86   const auto EmptyStringCtorExprWithTemporaries =
87       cxxConstructExpr(StringConstructorExpr,
88                        hasArgument(0, ignoringImplicit(EmptyStringCtorExpr)));
89 
90   const auto StringType = hasType(hasUnqualifiedDesugaredType(
91       recordType(hasDeclaration(cxxRecordDecl(HasStringTypeName)))));
92   const auto EmptyStringInit = traverse(
93       TK_AsIs, expr(ignoringImplicit(anyOf(
94                    EmptyStringCtorExpr, EmptyStringCtorExprWithTemporaries))));
95 
96   // Match a variable declaration with an empty string literal as initializer.
97   // Examples:
98   //     string foo = "";
99   //     string bar("");
100   Finder->addMatcher(
101       traverse(TK_AsIs,
102                namedDecl(varDecl(StringType, hasInitializer(EmptyStringInit))
103                              .bind("vardecl"),
104                          unless(parmVarDecl()))),
105       this);
106   // Match a field declaration with an empty string literal as initializer.
107   Finder->addMatcher(
108       namedDecl(fieldDecl(StringType, hasInClassInitializer(EmptyStringInit))
109                     .bind("fieldDecl")),
110       this);
111   // Matches Constructor Initializers with an empty string literal as
112   // initializer.
113   // Examples:
114   //     Foo() : SomeString("") {}
115   Finder->addMatcher(
116       cxxCtorInitializer(
117           isWritten(),
118           forField(allOf(StringType, optionally(hasInClassInitializer(
119                                          EmptyStringInit.bind("empty_init"))))),
120           withInitializer(EmptyStringInit))
121           .bind("ctorInit"),
122       this);
123 }
124 
125 void RedundantStringInitCheck::check(const MatchFinder::MatchResult &Result) {
126   if (const auto *VDecl = Result.Nodes.getNodeAs<VarDecl>("vardecl")) {
127     // VarDecl's getSourceRange() spans 'string foo = ""' or 'string bar("")'.
128     // So start at getLocation() to span just 'foo = ""' or 'bar("")'.
129     SourceRange ReplaceRange(VDecl->getLocation(), VDecl->getEndLoc());
130     diag(VDecl->getLocation(), "redundant string initialization")
131         << FixItHint::CreateReplacement(ReplaceRange, VDecl->getName());
132   }
133   if (const auto *FDecl = Result.Nodes.getNodeAs<FieldDecl>("fieldDecl")) {
134     // FieldDecl's getSourceRange() spans 'string foo = ""'.
135     // So start at getLocation() to span just 'foo = ""'.
136     SourceRange ReplaceRange(FDecl->getLocation(), FDecl->getEndLoc());
137     diag(FDecl->getLocation(), "redundant string initialization")
138         << FixItHint::CreateReplacement(ReplaceRange, FDecl->getName());
139   }
140   if (const auto *CtorInit =
141           Result.Nodes.getNodeAs<CXXCtorInitializer>("ctorInit")) {
142     if (const FieldDecl *Member = CtorInit->getMember()) {
143       if (!Member->hasInClassInitializer() ||
144           Result.Nodes.getNodeAs<Expr>("empty_init")) {
145         // The String isn't declared in the class with an initializer or its
146         // declared with a redundant initializer, which will be removed. Either
147         // way the string will be default initialized, therefore we can remove
148         // the constructor initializer entirely.
149         diag(CtorInit->getMemberLocation(), "redundant string initialization")
150             << FixItHint::CreateRemoval(CtorInit->getSourceRange());
151         return;
152       }
153     }
154     const CXXConstructExpr *Construct = getConstructExpr(*CtorInit);
155     if (!Construct)
156       return;
157     if (llvm::Optional<SourceRange> RemovalRange =
158             getConstructExprArgRange(*Construct))
159       diag(CtorInit->getMemberLocation(), "redundant string initialization")
160           << FixItHint::CreateRemoval(*RemovalRange);
161   }
162 }
163 
164 } // namespace readability
165 } // namespace tidy
166 } // namespace clang
167