clang-tools-extra/clang-tidy/misc/UnusedParametersCheck.cpp

   1 //===--- UnusedParametersCheck.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 "UnusedParametersCheck.h"
  10 #include "clang/AST/ASTContext.h"
  11 #include "clang/AST/ASTLambda.h"
  12 #include "clang/AST/RecursiveASTVisitor.h"
  13 #include "clang/ASTMatchers/ASTMatchFinder.h"
  14 #include "clang/Lex/Lexer.h"
  15 #include "llvm/ADT/STLExtras.h"
  16 #include <unordered_map>
  17 #include <unordered_set>
  18
  19 using namespace clang::ast_matchers;
  20
  21 namespace clang::tidy::misc {
  22
  23 namespace {
  24 bool isOverrideMethod(const FunctionDecl *Function) {
  25   if (const auto *MD = dyn_cast<CXXMethodDecl>(Function))
  26     return MD->size_overridden_methods() > 0 || MD->hasAttr<OverrideAttr>();
  27   return false;
  28 }
  29 } // namespace
  30
  31 void UnusedParametersCheck::registerMatchers(MatchFinder *Finder) {
  32   Finder->addMatcher(functionDecl(isDefinition(), hasBody(stmt()),
  33                                   hasAnyParameter(decl()),
  34                                   unless(hasAttr(attr::Kind::Naked)))
  35                          .bind("function"),
  36                      this);
  37 }
  38
  39 template <typename T>
  40 static CharSourceRange removeNode(const MatchFinder::MatchResult &Result,
  41                                   const T *PrevNode, const T *Node,
  42                                   const T *NextNode) {
  43   if (NextNode)
  44     return CharSourceRange::getCharRange(Node->getBeginLoc(),
  45                                          NextNode->getBeginLoc());
  46
  47   if (PrevNode)
  48     return CharSourceRange::getTokenRange(
  49         Lexer::getLocForEndOfToken(PrevNode->getEndLoc(), 0,
  50                                    *Result.SourceManager,
  51                                    Result.Context->getLangOpts()),
  52         Node->getEndLoc());
  53
  54   return CharSourceRange::getTokenRange(Node->getSourceRange());
  55 }
  56
  57 static FixItHint removeParameter(const MatchFinder::MatchResult &Result,
  58                                  const FunctionDecl *Function, unsigned Index) {
  59   return FixItHint::CreateRemoval(removeNode(
  60       Result, Index > 0 ? Function->getParamDecl(Index - 1) : nullptr,
  61       Function->getParamDecl(Index),
  62       Index + 1 < Function->getNumParams() ? Function->getParamDecl(Index + 1)
  63                                            : nullptr));
  64 }
  65
  66 static FixItHint removeArgument(const MatchFinder::MatchResult &Result,
  67                                 const CallExpr *Call, unsigned Index) {
  68   return FixItHint::CreateRemoval(removeNode(
  69       Result, Index > 0 ? Call->getArg(Index - 1) : nullptr,
  70       Call->getArg(Index),
  71       Index + 1 < Call->getNumArgs() ? Call->getArg(Index + 1) : nullptr));
  72 }
  73
  74 class UnusedParametersCheck::IndexerVisitor
  75     : public RecursiveASTVisitor<IndexerVisitor> {
  76 public:
  77   IndexerVisitor(ASTContext &Ctx) { TraverseAST(Ctx); }
  78
  79   const std::unordered_set<const CallExpr *> &
  80   getFnCalls(const FunctionDecl *Fn) {
  81     return Index[Fn->getCanonicalDecl()].Calls;
  82   }
  83
  84   const std::unordered_set<const DeclRefExpr *> &
  85   getOtherRefs(const FunctionDecl *Fn) {
  86     return Index[Fn->getCanonicalDecl()].OtherRefs;
  87   }
  88
  89   bool shouldTraversePostOrder() const { return true; }
  90
  91   bool WalkUpFromDeclRefExpr(DeclRefExpr *DeclRef) {
  92     if (const auto *Fn = dyn_cast<FunctionDecl>(DeclRef->getDecl())) {
  93       Fn = Fn->getCanonicalDecl();
  94       Index[Fn].OtherRefs.insert(DeclRef);
  95     }
  96     return true;
  97   }
  98
  99   bool WalkUpFromCallExpr(CallExpr *Call) {
 100     if (const auto *Fn =
 101             dyn_cast_or_null<FunctionDecl>(Call->getCalleeDecl())) {
 102       Fn = Fn->getCanonicalDecl();
 103       if (const auto *Ref =
 104               dyn_cast<DeclRefExpr>(Call->getCallee()->IgnoreImplicit())) {
 105         Index[Fn].OtherRefs.erase(Ref);
 106       }
 107       Index[Fn].Calls.insert(Call);
 108     }
 109     return true;
 110   }
 111
 112 private:
 113   struct IndexEntry {
 114     std::unordered_set<const CallExpr *> Calls;
 115     std::unordered_set<const DeclRefExpr *> OtherRefs;
 116   };
 117
 118   std::unordered_map<const FunctionDecl *, IndexEntry> Index;
 119 };
 120
 121 UnusedParametersCheck::~UnusedParametersCheck() = default;
 122
 123 UnusedParametersCheck::UnusedParametersCheck(StringRef Name,
 124                                              ClangTidyContext *Context)
 125     : ClangTidyCheck(Name, Context),
 126       StrictMode(Options.getLocalOrGlobal("StrictMode", false)),
 127       IgnoreVirtual(Options.get("IgnoreVirtual", false)) {}
 128
 129 void UnusedParametersCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
 130   Options.store(Opts, "StrictMode", StrictMode);
 131   Options.store(Opts, "IgnoreVirtual", IgnoreVirtual);
 132 }
 133
 134 void UnusedParametersCheck::warnOnUnusedParameter(
 135     const MatchFinder::MatchResult &Result, const FunctionDecl *Function,
 136     unsigned ParamIndex) {
 137   const auto *Param = Function->getParamDecl(ParamIndex);
 138   // Don't bother to diagnose invalid parameters as being unused.
 139   if (Param->isInvalidDecl())
 140     return;
 141   auto MyDiag = diag(Param->getLocation(), "parameter %0 is unused") << Param;
 142
 143   if (!Indexer) {
 144     Indexer = std::make_unique<IndexerVisitor>(*Result.Context);
 145   }
 146
 147   // Cannot remove parameter for non-local functions.
 148   if (Function->isExternallyVisible() ||
 149       !Result.SourceManager->isInMainFile(Function->getLocation()) ||
 150       !Indexer->getOtherRefs(Function).empty() || isOverrideMethod(Function) ||
 151       isLambdaCallOperator(Function)) {
 152
 153     // It is illegal to omit parameter name here in C code, so early-out.
 154     if (!Result.Context->getLangOpts().CPlusPlus)
 155       return;
 156
 157     SourceRange RemovalRange(Param->getLocation());
 158     // Note: We always add a space before the '/*' to not accidentally create
 159     // a '*/*' for pointer types, which doesn't start a comment. clang-format
 160     // will clean this up afterwards.
 161     MyDiag << FixItHint::CreateReplacement(
 162         RemovalRange, (Twine(" /*") + Param->getName() + "*/").str());
 163     return;
 164   }
 165
 166   // Fix all redeclarations.
 167   for (const FunctionDecl *FD : Function->redecls())
 168     if (FD->param_size())
 169       MyDiag << removeParameter(Result, FD, ParamIndex);
 170
 171   // Fix all call sites.
 172   for (const CallExpr *Call : Indexer->getFnCalls(Function))
 173     if (ParamIndex < Call->getNumArgs()) // See PR38055 for example.
 174       MyDiag << removeArgument(Result, Call, ParamIndex);
 175 }
 176
 177 void UnusedParametersCheck::check(const MatchFinder::MatchResult &Result) {
 178   const auto *Function = Result.Nodes.getNodeAs<FunctionDecl>("function");
 179   if (!Function->hasWrittenPrototype() || Function->isTemplateInstantiation())
 180     return;
 181   if (const auto *Method = dyn_cast<CXXMethodDecl>(Function)) {
 182     if (IgnoreVirtual && Method->isVirtual())
 183       return;
 184     if (Method->isLambdaStaticInvoker())
 185       return;
 186   }
 187   for (unsigned I = 0, E = Function->getNumParams(); I != E; ++I) {
 188     const auto *Param = Function->getParamDecl(I);
 189     if (Param->isUsed() || Param->isReferenced() || !Param->getDeclName() ||
 190         Param->hasAttr<UnusedAttr>())
 191       continue;
 192
 193     // In non-strict mode ignore function definitions with empty bodies
 194     // (constructor initializer counts for non-empty body).
 195     if (StrictMode ||
 196         (Function->getBody()->child_begin() !=
 197          Function->getBody()->child_end()) ||
 198         (isa<CXXConstructorDecl>(Function) &&
 199          cast<CXXConstructorDecl>(Function)->getNumCtorInitializers() > 0))
 200       warnOnUnusedParameter(Result, Function, I);
 201   }
 202 }
 203
 204 } // namespace clang::tidy::misc