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 ast_matchers::internal::Matcher<NamedDecl>
25 hasAnyNameStdString(std::vector<std::string> Names) {
26   return ast_matchers::internal::Matcher<NamedDecl>(
27       new ast_matchers::internal::HasNameMatcher(std::move(Names)));
28 }
29 
30 static std::vector<std::string>
31 removeNamespaces(const std::vector<std::string> &Names) {
32   std::vector<std::string> Result;
33   Result.reserve(Names.size());
34   for (const std::string &Name : Names) {
35     std::string::size_type ColonPos = Name.rfind(':');
36     Result.push_back(
37         Name.substr(ColonPos == std::string::npos ? 0 : ColonPos + 1));
38   }
39   return Result;
40 }
41 
42 static const CXXConstructExpr *
43 getConstructExpr(const CXXCtorInitializer &CtorInit) {
44   const Expr *InitExpr = CtorInit.getInit();
45   if (const auto *CleanUpExpr = dyn_cast<ExprWithCleanups>(InitExpr))
46     InitExpr = CleanUpExpr->getSubExpr();
47   return dyn_cast<CXXConstructExpr>(InitExpr);
48 }
49 
50 static llvm::Optional<SourceRange>
51 getConstructExprArgRange(const CXXConstructExpr &Construct) {
52   SourceLocation B, E;
53   for (const Expr *Arg : Construct.arguments()) {
54     if (B.isInvalid())
55       B = Arg->getBeginLoc();
56     if (Arg->getEndLoc().isValid())
57       E = Arg->getEndLoc();
58   }
59   if (B.isInvalid() || E.isInvalid())
60     return llvm::None;
61   return SourceRange(B, E);
62 }
63 
64 RedundantStringInitCheck::RedundantStringInitCheck(StringRef Name,
65                                                    ClangTidyContext *Context)
66     : ClangTidyCheck(Name, Context),
67       StringNames(utils::options::parseStringList(
68           Options.get("StringNames", DefaultStringNames))) {}
69 
70 void RedundantStringInitCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
71   Options.store(Opts, "StringNames", DefaultStringNames);
72 }
73 
74 void RedundantStringInitCheck::registerMatchers(MatchFinder *Finder) {
75   const auto HasStringTypeName = hasAnyNameStdString(StringNames);
76   const auto HasStringCtorName =
77       hasAnyNameStdString(removeNamespaces(StringNames));
78 
79   // Match string constructor.
80   const auto StringConstructorExpr = expr(
81       anyOf(cxxConstructExpr(argumentCountIs(1),
82                              hasDeclaration(cxxMethodDecl(HasStringCtorName))),
83             // If present, the second argument is the alloc object which must
84             // not be present explicitly.
85             cxxConstructExpr(argumentCountIs(2),
86                              hasDeclaration(cxxMethodDecl(HasStringCtorName)),
87                              hasArgument(1, cxxDefaultArgExpr()))));
88 
89   // Match a string constructor expression with an empty string literal.
90   const auto EmptyStringCtorExpr = cxxConstructExpr(
91       StringConstructorExpr,
92       hasArgument(0, ignoringParenImpCasts(stringLiteral(hasSize(0)))));
93 
94   const auto EmptyStringCtorExprWithTemporaries =
95       cxxConstructExpr(StringConstructorExpr,
96                        hasArgument(0, ignoringImplicit(EmptyStringCtorExpr)));
97 
98   const auto StringType = hasType(hasUnqualifiedDesugaredType(
99       recordType(hasDeclaration(cxxRecordDecl(HasStringTypeName)))));
100   const auto EmptyStringInit = traverse(
101       TK_AsIs, expr(ignoringImplicit(anyOf(
102                    EmptyStringCtorExpr, EmptyStringCtorExprWithTemporaries))));
103 
104   // Match a variable declaration with an empty string literal as initializer.
105   // Examples:
106   //     string foo = "";
107   //     string bar("");
108   Finder->addMatcher(
109       traverse(TK_AsIs,
110                namedDecl(varDecl(StringType, hasInitializer(EmptyStringInit))
111                              .bind("vardecl"),
112                          unless(parmVarDecl()))),
113       this);
114   // Match a field declaration with an empty string literal as initializer.
115   Finder->addMatcher(
116       namedDecl(fieldDecl(StringType, hasInClassInitializer(EmptyStringInit))
117                     .bind("fieldDecl")),
118       this);
119   // Matches Constructor Initializers with an empty string literal as
120   // initializer.
121   // Examples:
122   //     Foo() : SomeString("") {}
123   Finder->addMatcher(
124       cxxCtorInitializer(
125           isWritten(),
126           forField(allOf(StringType, optionally(hasInClassInitializer(
127                                          EmptyStringInit.bind("empty_init"))))),
128           withInitializer(EmptyStringInit))
129           .bind("ctorInit"),
130       this);
131 }
132 
133 void RedundantStringInitCheck::check(const MatchFinder::MatchResult &Result) {
134   if (const auto *VDecl = Result.Nodes.getNodeAs<VarDecl>("vardecl")) {
135     // VarDecl's getSourceRange() spans 'string foo = ""' or 'string bar("")'.
136     // So start at getLocation() to span just 'foo = ""' or 'bar("")'.
137     SourceRange ReplaceRange(VDecl->getLocation(), VDecl->getEndLoc());
138     diag(VDecl->getLocation(), "redundant string initialization")
139         << FixItHint::CreateReplacement(ReplaceRange, VDecl->getName());
140   }
141   if (const auto *FDecl = Result.Nodes.getNodeAs<FieldDecl>("fieldDecl")) {
142     // FieldDecl's getSourceRange() spans 'string foo = ""'.
143     // So start at getLocation() to span just 'foo = ""'.
144     SourceRange ReplaceRange(FDecl->getLocation(), FDecl->getEndLoc());
145     diag(FDecl->getLocation(), "redundant string initialization")
146         << FixItHint::CreateReplacement(ReplaceRange, FDecl->getName());
147   }
148   if (const auto *CtorInit =
149           Result.Nodes.getNodeAs<CXXCtorInitializer>("ctorInit")) {
150     if (const FieldDecl *Member = CtorInit->getMember()) {
151       if (!Member->hasInClassInitializer() ||
152           Result.Nodes.getNodeAs<Expr>("empty_init")) {
153         // The String isn't declared in the class with an initializer or its
154         // declared with a redundant initializer, which will be removed. Either
155         // way the string will be default initialized, therefore we can remove
156         // the constructor initializer entirely.
157         diag(CtorInit->getMemberLocation(), "redundant string initialization")
158             << FixItHint::CreateRemoval(CtorInit->getSourceRange());
159         return;
160       }
161     }
162     const CXXConstructExpr *Construct = getConstructExpr(*CtorInit);
163     if (!Construct)
164       return;
165     if (llvm::Optional<SourceRange> RemovalRange =
166             getConstructExprArgRange(*Construct))
167       diag(CtorInit->getMemberLocation(), "redundant string initialization")
168           << FixItHint::CreateRemoval(*RemovalRange);
169   }
170 }
171 
172 } // namespace readability
173 } // namespace tidy
174 } // namespace clang
175