[clang-tools-extra] [clang-doc] Add standalone Markdown parsing library (PR #202991)

[Neil Nair via cfe-commits]

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@@ -0,0 +1,299 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "Markdown.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/DebugLog.h"
+#include <cassert>
+
+#define DEBUG_TYPE "clang-doc"
+
+using namespace llvm;
+
+namespace clang::doc::markdown {
+
+// Allocates a contiguous array of T in the arena and returns an ArrayRef.
+template <typename T>
+static ArrayRef<T> allocateArray(SmallVectorImpl<T> &Vec,
+                                 BumpPtrAllocator &Arena) {
+  if (Vec.empty())
+    return {};
+  T *Allocated = Arena.Allocate<T>(Vec.size());
+  std::uninitialized_copy(Vec.begin(), Vec.end(), Allocated);
+  return ArrayRef<T>(Allocated, Vec.size());
+}
+
+// Interns a StringRef into the arena so it outlives the parse loop.
+static StringRef internString(StringRef S, BumpPtrAllocator &Arena) {
+  if (S.empty())
+    return {};
+  char *Buf = Arena.Allocate<char>(S.size());
+  std::copy(S.begin(), S.end(), Buf);
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Neil-N4 wrote:

Hadn't seen that, will look into it

https://github.com/llvm/llvm-project/pull/202991