1 //===--- ExplicitConstructorCheck.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 "ExplicitConstructorCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/ASTMatchers/ASTMatchFinder.h"
12 #include "clang/ASTMatchers/ASTMatchers.h"
13 #include "clang/Lex/Lexer.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace google {
20 
21 void ExplicitConstructorCheck::registerMatchers(MatchFinder *Finder) {
22   // Only register the matchers for C++; the functionality currently does not
23   // provide any benefit to other languages, despite being benign.
24   if (!getLangOpts().CPlusPlus)
25     return;
26   Finder->addMatcher(
27       cxxConstructorDecl(unless(anyOf(isImplicit(), // Compiler-generated.
28                                       isDeleted(), isInstantiated())))
29           .bind("ctor"),
30       this);
31   Finder->addMatcher(
32       cxxConversionDecl(unless(anyOf(isExplicit(), // Already marked explicit.
33                                      isImplicit(), // Compiler-generated.
34                                      isDeleted(), isInstantiated())))
35 
36           .bind("conversion"),
37       this);
38 }
39 
40 // Looks for the token matching the predicate and returns the range of the found
41 // token including trailing whitespace.
42 static SourceRange FindToken(const SourceManager &Sources,
43                              const LangOptions &LangOpts,
44                              SourceLocation StartLoc, SourceLocation EndLoc,
45                              bool (*Pred)(const Token &)) {
46   if (StartLoc.isMacroID() || EndLoc.isMacroID())
47     return SourceRange();
48   FileID File = Sources.getFileID(Sources.getSpellingLoc(StartLoc));
49   StringRef Buf = Sources.getBufferData(File);
50   const char *StartChar = Sources.getCharacterData(StartLoc);
51   Lexer Lex(StartLoc, LangOpts, StartChar, StartChar, Buf.end());
52   Lex.SetCommentRetentionState(true);
53   Token Tok;
54   do {
55     Lex.LexFromRawLexer(Tok);
56     if (Pred(Tok)) {
57       Token NextTok;
58       Lex.LexFromRawLexer(NextTok);
59       return SourceRange(Tok.getLocation(), NextTok.getLocation());
60     }
61   } while (Tok.isNot(tok::eof) && Tok.getLocation() < EndLoc);
62 
63   return SourceRange();
64 }
65 
66 static bool declIsStdInitializerList(const NamedDecl *D) {
67   // First use the fast getName() method to avoid unnecessary calls to the
68   // slow getQualifiedNameAsString().
69   return D->getName() == "initializer_list" &&
70          D->getQualifiedNameAsString() == "std::initializer_list";
71 }
72 
73 static bool isStdInitializerList(QualType Type) {
74   Type = Type.getCanonicalType();
75   if (const auto *TS = Type->getAs<TemplateSpecializationType>()) {
76     if (const TemplateDecl *TD = TS->getTemplateName().getAsTemplateDecl())
77       return declIsStdInitializerList(TD);
78   }
79   if (const auto *RT = Type->getAs<RecordType>()) {
80     if (const auto *Specialization =
81             dyn_cast<ClassTemplateSpecializationDecl>(RT->getDecl()))
82       return declIsStdInitializerList(Specialization->getSpecializedTemplate());
83   }
84   return false;
85 }
86 
87 void ExplicitConstructorCheck::check(const MatchFinder::MatchResult &Result) {
88   constexpr char WarningMessage[] =
89       "%0 must be marked explicit to avoid unintentional implicit conversions";
90 
91   if (const auto *Conversion =
92       Result.Nodes.getNodeAs<CXXConversionDecl>("conversion")) {
93     if (Conversion->isOutOfLine())
94       return;
95     SourceLocation Loc = Conversion->getLocation();
96     // Ignore all macros until we learn to ignore specific ones (e.g. used in
97     // gmock to define matchers).
98     if (Loc.isMacroID())
99       return;
100     diag(Loc, WarningMessage)
101         << Conversion << FixItHint::CreateInsertion(Loc, "explicit ");
102     return;
103   }
104 
105   const auto *Ctor = Result.Nodes.getNodeAs<CXXConstructorDecl>("ctor");
106   if (Ctor->isOutOfLine() || Ctor->getNumParams() == 0 ||
107       Ctor->getMinRequiredArguments() > 1)
108     return;
109 
110   bool takesInitializerList = isStdInitializerList(
111       Ctor->getParamDecl(0)->getType().getNonReferenceType());
112   if (Ctor->isExplicit() &&
113       (Ctor->isCopyOrMoveConstructor() || takesInitializerList)) {
114     auto isKWExplicit = [](const Token &Tok) {
115       return Tok.is(tok::raw_identifier) &&
116              Tok.getRawIdentifier() == "explicit";
117     };
118     SourceRange ExplicitTokenRange =
119         FindToken(*Result.SourceManager, getLangOpts(),
120                   Ctor->getOuterLocStart(), Ctor->getEndLoc(), isKWExplicit);
121     StringRef ConstructorDescription;
122     if (Ctor->isMoveConstructor())
123       ConstructorDescription = "move";
124     else if (Ctor->isCopyConstructor())
125       ConstructorDescription = "copy";
126     else
127       ConstructorDescription = "initializer-list";
128 
129     auto Diag = diag(Ctor->getLocation(),
130                      "%0 constructor should not be declared explicit")
131                 << ConstructorDescription;
132     if (ExplicitTokenRange.isValid()) {
133       Diag << FixItHint::CreateRemoval(
134           CharSourceRange::getCharRange(ExplicitTokenRange));
135     }
136     return;
137   }
138 
139   if (Ctor->isExplicit() || Ctor->isCopyOrMoveConstructor() ||
140       takesInitializerList)
141     return;
142 
143   bool SingleArgument =
144       Ctor->getNumParams() == 1 && !Ctor->getParamDecl(0)->isParameterPack();
145   SourceLocation Loc = Ctor->getLocation();
146   diag(Loc, WarningMessage)
147       << (SingleArgument
148               ? "single-argument constructors"
149               : "constructors that are callable with a single argument")
150       << FixItHint::CreateInsertion(Loc, "explicit ");
151 }
152 
153 } // namespace google
154 } // namespace tidy
155 } // namespace clang
156