[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]

================
@@ -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;
----------------
localspook wrote:

```suggestion
           "local copy %0 of the subobject '%1' of type %2 is never "
           "modified%select{"
           "| and never used}3; consider %select{avoiding the copy|removing "
           "the statement}3")
      << &Ctx.Var << MEStr << Ctx.Var.getType() << Ctx.IsVarUnused;
```
Then, the `OldVar` parameter can be removed.

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