[clang] [clang-tools-extra] [Clang] Implement CWG2813: Class member access with prvalues (PR #95112)

[via cfe-commits]

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@@ -387,9 +388,16 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S, unsigned DiagID) {
   // Do not diagnose use of a comma operator in a SFINAE context because the
   // type of the left operand could be used for SFINAE, so technically it is
   // *used*.
-  if (DiagID != diag::warn_unused_comma_left_operand || !isSFINAEContext())
-    DiagIfReachable(Loc, S ? llvm::ArrayRef(S) : std::nullopt,
-                    PDiag(DiagID) << R1 << R2);
+  if (DiagID == diag::warn_unused_comma_left_operand && isSFINAEContext())
+    return;
+
+  // Don't diagnose discarded left of dot in static class member access
+  // because its type is "used" to determine the class to access
+  if (OrigDiagID == diag::warn_discarded_class_member_access)
+    return;
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Sirraide wrote:

Er, doesn’t this prevent all diagnostics that this pr is supposed to introduce, or am I missing something? I don’t think we should be suppressing the diagnostic here. If you want to access a *static* member of a specific class, we already have a syntax for that that doesn’t involve constructing a temporary, after all: `S::x`.

https://github.com/llvm/llvm-project/pull/95112