clang-tools  10.0.0
UseNodiscardCheck.cpp
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1 //===--- UseNodiscardCheck.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 "UseNodiscardCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/AST/Decl.h"
12 #include "clang/AST/Type.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 
15 using namespace clang::ast_matchers;
16 
17 namespace clang {
18 namespace tidy {
19 namespace modernize {
20 
21 static bool doesNoDiscardMacroExist(ASTContext &Context,
22  const llvm::StringRef &MacroId) {
23  // Don't check for the Macro existence if we are using an attribute
24  // either a C++17 standard attribute or pre C++17 syntax
25  if (MacroId.startswith("[[") || MacroId.startswith("__attribute__"))
26  return true;
27 
28  // Otherwise look up the macro name in the context to see if its defined.
29  return Context.Idents.get(MacroId).hasMacroDefinition();
30 }
31 
32 namespace {
33 AST_MATCHER(CXXMethodDecl, isOverloadedOperator) {
34  // Don't put ``[[nodiscard]]`` in front of operators.
35  return Node.isOverloadedOperator();
36 }
37 AST_MATCHER(CXXMethodDecl, isConversionOperator) {
38  // Don't put ``[[nodiscard]]`` in front of a conversion decl
39  // like operator bool().
40  return isa<CXXConversionDecl>(Node);
41 }
42 AST_MATCHER(CXXMethodDecl, hasClassMutableFields) {
43  // Don't put ``[[nodiscard]]`` on functions on classes with
44  // mutable member variables.
45  return Node.getParent()->hasMutableFields();
46 }
47 AST_MATCHER(ParmVarDecl, hasParameterPack) {
48  // Don't put ``[[nodiscard]]`` on functions with parameter pack arguments.
49  return Node.isParameterPack();
50 }
51 AST_MATCHER(CXXMethodDecl, hasTemplateReturnType) {
52  // Don't put ``[[nodiscard]]`` in front of functions returning a template
53  // type.
54  return Node.getReturnType()->isTemplateTypeParmType() ||
55  Node.getReturnType()->isInstantiationDependentType();
56 }
57 AST_MATCHER(CXXMethodDecl, isDefinitionOrInline) {
58  // A function definition, with optional inline but not the declaration.
59  return !(Node.isThisDeclarationADefinition() && Node.isOutOfLine());
60 }
61 AST_MATCHER(QualType, isInstantiationDependentType) {
62  return Node->isInstantiationDependentType();
63 }
64 AST_MATCHER(QualType, isNonConstReferenceOrPointer) {
65  // If the function has any non-const-reference arguments
66  // bool foo(A &a)
67  // or pointer arguments
68  // bool foo(A*)
69  // then they may not care about the return value because of passing data
70  // via the arguments.
71  return (Node->isTemplateTypeParmType() || Node->isPointerType() ||
72  (Node->isReferenceType() &&
73  !Node.getNonReferenceType().isConstQualified()) ||
74  Node->isInstantiationDependentType());
75 }
76 } // namespace
77 
78 UseNodiscardCheck::UseNodiscardCheck(StringRef Name, ClangTidyContext *Context)
79  : ClangTidyCheck(Name, Context),
80  NoDiscardMacro(Options.get("ReplacementString", "[[nodiscard]]")) {}
81 
83  Options.store(Opts, "ReplacementString", NoDiscardMacro);
84 }
85 
86 void UseNodiscardCheck::registerMatchers(MatchFinder *Finder) {
87  // If we use ``[[nodiscard]]`` attribute, we require at least C++17. Use a
88  // macro or ``__attribute__`` with pre c++17 compilers by using
89  // ReplacementString option.
90  if ((NoDiscardMacro == "[[nodiscard]]" && !getLangOpts().CPlusPlus17) ||
91  !getLangOpts().CPlusPlus)
92  return;
93 
94  auto FunctionObj =
95  cxxRecordDecl(hasAnyName("::std::function", "::boost::function"));
96 
97  // Find all non-void const methods which have not already been marked to
98  // warn on unused result.
99  Finder->addMatcher(
100  cxxMethodDecl(
101  allOf(isConst(), isDefinitionOrInline(),
102  unless(anyOf(
103  returns(voidType()),
104  returns(hasDeclaration(decl(hasAttr(clang::attr::WarnUnusedResult)))),
105  isNoReturn(), isOverloadedOperator(),
106  isVariadic(), hasTemplateReturnType(),
107  hasClassMutableFields(), isConversionOperator(),
108  hasAttr(clang::attr::WarnUnusedResult),
109  hasType(isInstantiationDependentType()),
110  hasAnyParameter(anyOf(
111  parmVarDecl(anyOf(hasType(FunctionObj),
112  hasType(references(FunctionObj)))),
113  hasType(isNonConstReferenceOrPointer()),
114  hasParameterPack()))))))
115  .bind("no_discard"),
116  this);
117 }
118 
119 void UseNodiscardCheck::check(const MatchFinder::MatchResult &Result) {
120  const auto *MatchedDecl = Result.Nodes.getNodeAs<CXXMethodDecl>("no_discard");
121  // Don't make replacements if the location is invalid or in a macro.
122  SourceLocation Loc = MatchedDecl->getLocation();
123  if (Loc.isInvalid() || Loc.isMacroID())
124  return;
125 
126  SourceLocation RetLoc = MatchedDecl->getInnerLocStart();
127 
128  ASTContext &Context = *Result.Context;
129 
130  auto Diag = diag(RetLoc, "function %0 should be marked " + NoDiscardMacro)
131  << MatchedDecl;
132 
133  // Check for the existence of the keyword being used as the ``[[nodiscard]]``.
134  if (!doesNoDiscardMacroExist(Context, NoDiscardMacro))
135  return;
136 
137  // Possible false positives include:
138  // 1. A const member function which returns a variable which is ignored
139  // but performs some external I/O operation and the return value could be
140  // ignored.
141  Diag << FixItHint::CreateInsertion(RetLoc, NoDiscardMacro + " ");
142 }
143 
144 } // namespace modernize
145 } // namespace tidy
146 } // namespace clang
SourceLocation Loc
&#39;#&#39; location in the include directive
static bool doesNoDiscardMacroExist(ASTContext &Context, const llvm::StringRef &MacroId)
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
Base class for all clang-tidy checks.
const LangOptions & getLangOpts() const
Returns the language options from the context.
void store(ClangTidyOptions::OptionMap &Options, StringRef LocalName, StringRef Value) const
Stores an option with the check-local name LocalName with string value Value to Options.
static constexpr llvm::StringLiteral Name
std::map< std::string, std::string > OptionMap
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
DiagnosticBuilder diag(SourceLocation Loc, StringRef Description, DiagnosticIDs::Level Level=DiagnosticIDs::Warning)
Add a diagnostic with the check&#39;s name.