[clang-tools-extra] [clang-doc] Add standalone Markdown parsing library (PR #200302)

[Paul Kirth via cfe-commits]

================
@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "support/Markdown.h"
+#include "llvm/Support/Allocator.h"
+#include "gtest/gtest.h"
+
+using namespace clang::doc::markdown;
+
+namespace {
+
+TEST(MarkdownParserTest, EmptyInput) {
+  llvm::BumpPtrAllocator Arena;
----------------
ilovepi wrote:

I don't think we're particularly good about this in the current tests, but this can probably be something that gets set in setup and teardown instead of having a local variable for the arena everywhere.

https://github.com/llvm/llvm-project/pull/200302