[clang] [clang-tools-extra] [llvm] [clang]: reflection operator parsing for global namespace and primitive types (PR #164692)

[Daniel M. Katz via llvm-commits]

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@@ -0,0 +1,61 @@
+//===--- ParseReflect.cpp - C++26 Reflection Parsing ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements parsing for reflection facilities.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/AST/LocInfoType.h"
+#include "clang/Basic/DiagnosticParse.h"
+#include "clang/Parse/Parser.h"
+#include "clang/Sema/EnterExpressionEvaluationContext.h"
+using namespace clang;
+
+ExprResult Parser::ParseCXXReflectExpression(SourceLocation OpLoc) {
+  // TODO(reflection) : support parsing for more reflect-expressions.
+  EnterExpressionEvaluationContext Unevaluated(
+      Actions, Sema::ExpressionEvaluationContext::Unevaluated);
+
+  SourceLocation OperandLoc = Tok.getLocation();
+
+  {
+    TentativeParsingAction TPA(*this);
+    // global namespace ::
+    if (Tok.is(tok::coloncolon)) {
+      ConsumeToken();
+      TPA.Commit();
----------------
katzdm wrote:

I think this is wrong; it will parse `^^::std::vector` as `^^::` and then fail with an unrelated diagnostic when it reaches `std::vector`.

I implemented this [here](https://github.com/bloomberg/clang-p2996/blob/p2996/clang/lib/Parse/ParseReflect.cpp#L29-L76); note that I start by first trying to parse a `CXXScopeSpec` (i.e., _nested-name-specifier_), then determine whether it's `^^::` based on
1. the tokens that follow and
2. the "kind" of the `CXXScopeSpec`.

https://github.com/llvm/llvm-project/pull/164692