[clang] [Clang] Diagnose unsatisfied `std::is_assignable`. (PR #144836)

[Ross Kirsling via cfe-commits]

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@@ -2285,6 +2286,31 @@ static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
   SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
 }
 
+static void DiagnoseNonAssignableReason(Sema &SemaRef, SourceLocation Loc,
+                                        QualType T, QualType U) {
+  const CXXRecordDecl *D = T->getAsCXXRecordDecl();
+
+  if (T->isObjectType() || T->isFunctionType())
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rkirsling wrote:

Sounds great! Updated.

https://github.com/llvm/llvm-project/pull/144836