[clang] [Clang] [P2996] Support reflecting arbitrary types and aliases (PR #232074)

[Oliver Hunt via cfe-commits]

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@@ -18563,6 +18556,58 @@ ExprResult Sema::ActOnCXXReflectExpr(SourceLocation CaretCaretLoc,
 
 ExprResult Sema::BuildCXXReflectExpr(SourceLocation CaretCaretLoc,
                                      TypeSourceInfo *TSI) {
+  QualType QT = TSI->getType();
+  SourceLocation TypeLoc = TSI->getTypeLoc().getBeginLoc();
+
+  // Don't bother supporting VLAs here.
+  if (QT->isVariablyModifiedType()) {
+    Diag(TypeLoc, diag::err_reflect_variably_modified_type) << QT;
+    return ExprError();
+  }
+
+  // Canonicalize template arguments of alias template specializations.
+  //
+  // A parsed TST retains template arguments as written. Rebuild it with the
+  // canonical template declaration and normalized arguments so equivalent
+  // alias specializations have the same reflection identity.
+  //
+  // FIXME: This does mean that e.g. ^^A<1+2> becomes ^^A<3>; we might
+  // want to retain the original arguments somehow, but we need to make sure
+  // that doing so doesn't change the fact that ^^A<1+2> == ^^A<3>.
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ojhunt wrote:

We could have a side table from the ReflectExpr to the TSI if the canonical type is not the original? Not something needed now of course.

https://github.com/llvm/llvm-project/pull/232074