[clang-tools-extra] [clang-tidy] performance-unnecessary-copy-initialization: Enhance the check for the scenario with MemberExpr initialization. (PR #151936)

[Victor Chernyakin via cfe-commits]

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@@ -371,6 +392,21 @@ void UnnecessaryCopyInitialization::diagnoseCopyFromLocalVar(
   maybeIssueFixes(Ctx, Diagnostic);
 }
 
+void UnnecessaryCopyInitialization::diagnoseCopyFromConstVarMember(
+    const CheckContext &Ctx, const VarDecl &OldVar, const MemberExpr &ME) {
+  std::string MEStr(Lexer::getSourceText(
+      CharSourceRange::getTokenRange(ME.getSourceRange()),
+      Ctx.ASTCtx.getSourceManager(), Ctx.ASTCtx.getLangOpts()));
+  auto Diagnostic =
+      diag(Ctx.Var.getLocation(),
+           "local copy %0 of the subobject '%1' of type %2 is never "
+           "modified%select{"
+           "| and never used}4; consider %select{avoiding the copy|removing "
+           "the statement}4")
+      << &Ctx.Var << MEStr << Ctx.Var.getType() << &OldVar << Ctx.IsVarUnused;
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localspook wrote:

I think the check is correct to not warn in that case (and it would be good to add a test to check that it doesn't). For the same reason that it doesn't warn here:
https://github.com/llvm/llvm-project/blob/1c499351d682aa46c2f087a6f757d22b01d18aa7/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-copy-initialization.cpp#L852-L859

https://github.com/llvm/llvm-project/pull/151936