[clang] [clang-tools-extra] [Clang] Implement CWG2813: Class member access with prvalues (PR #120223)

[Erich Keane via cfe-commits]

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@@ -1128,26 +1119,68 @@ Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
     BaseExpr = BuildCXXThisExpr(Loc, BaseExprType, /*IsImplicit=*/true);
   }
 
+  // C++17 [expr.ref]p2, per CWG2813:
+  //   For the first option (dot), if the id-expression names a static member or
+  //   an enumerator, the first expression is a discarded-value expression; if
+  //   the id-expression names a non-static data member, the first expression
+  //   shall be a glvalue.
+  auto MakeDiscardedValue = [&] {
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erichkeane wrote:

I would prefer some more descriptive names here?  Perhaps `ConvertBaseExprToDiscardedValue` and `ConvertBaseExprToGLValue` ?  

https://github.com/llvm/llvm-project/pull/120223