[clang-tidy] performance-unnecessary-copy-init: Add a hook... (#73921)

... so that derived checks can can observe for which
variables a warning has been emitted. Does nothing by default, which
makes this an NFC.

Author: legrosbuffle

clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.cpp

@@ -15,6 +15,7 @@
 #include "clang/AST/Decl.h"
 #include "clang/Basic/Diagnostic.h"
 #include <optional>
+#include <utility>
 
 namespace clang::tidy::performance {
 namespace {
@@ -263,19 +264,25 @@ void UnnecessaryCopyInitialization::registerMatchers(MatchFinder *Finder) {
 
 void UnnecessaryCopyInitialization::check(
     const MatchFinder::MatchResult &Result) {
-  const auto *NewVar = Result.Nodes.getNodeAs<VarDecl>("newVarDecl");
+  const auto &NewVar = *Result.Nodes.getNodeAs<VarDecl>("newVarDecl");
+  const auto &BlockStmt = *Result.Nodes.getNodeAs<Stmt>("blockStmt");
+  const auto &VarDeclStmt = *Result.Nodes.getNodeAs<DeclStmt>("declStmt");
+  // Do not propose fixes if the DeclStmt has multiple VarDecls or in
+  // macros since we cannot place them correctly.
+  const bool IssueFix =
+      VarDeclStmt.isSingleDecl() && !NewVar.getLocation().isMacroID();
+  const bool IsVarUnused = isVariableUnused(NewVar, BlockStmt, *Result.Context);
+  const bool IsVarOnlyUsedAsConst =
+      isOnlyUsedAsConst(NewVar, BlockStmt, *Result.Context);
+  const CheckContext Context{
+      NewVar,   BlockStmt,   VarDeclStmt,         *Result.Context,
+      IssueFix, IsVarUnused, IsVarOnlyUsedAsConst};
   const auto *OldVar = Result.Nodes.getNodeAs<VarDecl>(OldVarDeclId);
   const auto *ObjectArg = Result.Nodes.getNodeAs<VarDecl>(ObjectArgId);
-  const auto *BlockStmt = Result.Nodes.getNodeAs<Stmt>("blockStmt");
   const auto *CtorCall = Result.Nodes.getNodeAs<CXXConstructExpr>("ctorCall");
-  const auto *Stmt = Result.Nodes.getNodeAs<DeclStmt>("declStmt");
 
   TraversalKindScope RAII(*Result.Context, TK_AsIs);
 
-  // Do not propose fixes if the DeclStmt has multiple VarDecls or in macros
-  // since we cannot place them correctly.
-  bool IssueFix = Stmt->isSingleDecl() && !NewVar->getLocation().isMacroID();
-
   // A constructor that looks like T(const T& t, bool arg = false) counts as a
   // copy only when it is called with default arguments for the arguments after
   // the first.
@@ -289,74 +296,71 @@ void UnnecessaryCopyInitialization::check(
   // instantiations where the types differ and rely on implicit conversion would
   // no longer compile if we switched to a reference.
   if (differentReplacedTemplateParams(
-          NewVar->getType(), constructorArgumentType(OldVar, Result.Nodes),
+          Context.Var.getType(), constructorArgumentType(OldVar, Result.Nodes),
           *Result.Context))
     return;
 
   if (OldVar == nullptr) {
-    handleCopyFromMethodReturn(*NewVar, *BlockStmt, *Stmt, IssueFix, ObjectArg,
-                               *Result.Context);
+    // `auto NewVar = functionCall();`
+    handleCopyFromMethodReturn(Context, ObjectArg);
   } else {
-    handleCopyFromLocalVar(*NewVar, *OldVar, *BlockStmt, *Stmt, IssueFix,
-                           *Result.Context);
+    // `auto NewVar = OldVar;`
+    handleCopyFromLocalVar(Context, *OldVar);
   }
 }
 
 void UnnecessaryCopyInitialization::handleCopyFromMethodReturn(
-    const VarDecl &Var, const Stmt &BlockStmt, const DeclStmt &Stmt,
-    bool IssueFix, const VarDecl *ObjectArg, ASTContext &Context) {
-  bool IsConstQualified = Var.getType().isConstQualified();
-  if (!IsConstQualified && !isOnlyUsedAsConst(Var, BlockStmt, Context))
+    const CheckContext &Ctx, const VarDecl *ObjectArg) {
+  bool IsConstQualified = Ctx.Var.getType().isConstQualified();
+  if (!IsConstQualified && !Ctx.IsVarOnlyUsedAsConst)
     return;
   if (ObjectArg != nullptr &&
-      !isInitializingVariableImmutable(*ObjectArg, BlockStmt, Context,
+      !isInitializingVariableImmutable(*ObjectArg, Ctx.BlockStmt, Ctx.ASTCtx,
                                        ExcludedContainerTypes))
     return;
-  if (isVariableUnused(Var, BlockStmt, Context)) {
-    auto Diagnostic =
-        diag(Var.getLocation(),
-             "the %select{|const qualified }0variable %1 is copy-constructed "
-             "from a const reference but is never used; consider "
-             "removing the statement")
-        << IsConstQualified << &Var;
-    if (IssueFix)
-      recordRemoval(Stmt, Context, Diagnostic);
-  } else {
-    auto Diagnostic =
-        diag(Var.getLocation(),
-             "the %select{|const qualified }0variable %1 is copy-constructed "
-             "from a const reference%select{ but is only used as const "
-             "reference|}0; consider making it a const reference")
-        << IsConstQualified << &Var;
-    if (IssueFix)
-      recordFixes(Var, Context, Diagnostic);
-  }
+  diagnoseCopyFromMethodReturn(Ctx);
 }
 
 void UnnecessaryCopyInitialization::handleCopyFromLocalVar(
-    const VarDecl &NewVar, const VarDecl &OldVar, const Stmt &BlockStmt,
-    const DeclStmt &Stmt, bool IssueFix, ASTContext &Context) {
-  if (!isOnlyUsedAsConst(NewVar, BlockStmt, Context) ||
-      !isInitializingVariableImmutable(OldVar, BlockStmt, Context,
+    const CheckContext &Ctx, const VarDecl &OldVar) {
+  if (!Ctx.IsVarOnlyUsedAsConst ||
+      !isInitializingVariableImmutable(OldVar, Ctx.BlockStmt, Ctx.ASTCtx,
                                        ExcludedContainerTypes))
     return;
+  diagnoseCopyFromLocalVar(Ctx, OldVar);
+}
 
-  if (isVariableUnused(NewVar, BlockStmt, Context)) {
-    auto Diagnostic = diag(NewVar.getLocation(),
-                           "local copy %0 of the variable %1 is never modified "
-                           "and never used; "
-                           "consider removing the statement")
-                      << &NewVar << &OldVar;
-    if (IssueFix)
-      recordRemoval(Stmt, Context, Diagnostic);
-  } else {
-    auto Diagnostic =
-        diag(NewVar.getLocation(),
-             "local copy %0 of the variable %1 is never modified; "
-             "consider avoiding the copy")
-        << &NewVar << &OldVar;
-    if (IssueFix)
-      recordFixes(NewVar, Context, Diagnostic);
+void UnnecessaryCopyInitialization::diagnoseCopyFromMethodReturn(
+    const CheckContext &Ctx) {
+  auto Diagnostic =
+      diag(Ctx.Var.getLocation(),
+           "the %select{|const qualified }0variable %1 is "
+           "copy-constructed "
+           "from a const reference%select{%select{ but is only used as const "
+           "reference|}0| but is never used}2; consider "
+           "%select{making it a const reference|removing the statement}2")
+      << Ctx.Var.getType().isConstQualified() << &Ctx.Var << Ctx.IsVarUnused;
+  maybeIssueFixes(Ctx, Diagnostic);
+}
+
+void UnnecessaryCopyInitialization::diagnoseCopyFromLocalVar(
+    const CheckContext &Ctx, const VarDecl &OldVar) {
+  auto Diagnostic =
+      diag(Ctx.Var.getLocation(),
+           "local copy %1 of the variable %0 is never modified%select{"
+           "| and never used}2; consider %select{avoiding the copy|removing "
+           "the statement}2")
+      << &OldVar << &Ctx.Var << Ctx.IsVarUnused;
+  maybeIssueFixes(Ctx, Diagnostic);
+}
+
+void UnnecessaryCopyInitialization::maybeIssueFixes(
+    const CheckContext &Ctx, DiagnosticBuilder &Diagnostic) {
+  if (Ctx.IssueFix) {
+    if (Ctx.IsVarUnused)
+      recordRemoval(Ctx.VarDeclStmt, Ctx.ASTCtx, Diagnostic);
+    else
+      recordFixes(Ctx.Var, Ctx.ASTCtx, Diagnostic);
   }
 }
 

clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitialization.h

@@ -32,14 +32,32 @@ class UnnecessaryCopyInitialization : public ClangTidyCheck {
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
   void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
 
+protected:
+  // A helper to manipulate the state common to
+  // `CopyFromMethodReturn` and `CopyFromLocalVar`.
+  struct CheckContext {
+    const VarDecl &Var;
+    const Stmt &BlockStmt;
+    const DeclStmt &VarDeclStmt;
+    clang::ASTContext &ASTCtx;
+    const bool IssueFix;
+    const bool IsVarUnused;
+    const bool IsVarOnlyUsedAsConst;
+  };
+
+  // Create diagnostics. These are virtual so that derived classes can change
+  // behaviour.
+  virtual void diagnoseCopyFromMethodReturn(const CheckContext &Ctx);
+  virtual void diagnoseCopyFromLocalVar(const CheckContext &Ctx,
+                                        const VarDecl &OldVar);
+
 private:
-  void handleCopyFromMethodReturn(const VarDecl &Var, const Stmt &BlockStmt,
-                                  const DeclStmt &Stmt, bool IssueFix,
-                                  const VarDecl *ObjectArg,
-                                  ASTContext &Context);
-  void handleCopyFromLocalVar(const VarDecl &NewVar, const VarDecl &OldVar,
-                              const Stmt &BlockStmt, const DeclStmt &Stmt,
-                              bool IssueFix, ASTContext &Context);
+  void handleCopyFromMethodReturn(const CheckContext &Ctx,
+                                  const VarDecl *ObjectArg);
+  void handleCopyFromLocalVar(const CheckContext &Ctx, const VarDecl &OldVar);
+
+  void maybeIssueFixes(const CheckContext &Ctx, DiagnosticBuilder &Diagnostic);
+
   const std::vector<StringRef> AllowedTypes;
   const std::vector<StringRef> ExcludedContainerTypes;
 };