[clang] [llvm] [Support] Add VirtualOutputBackends to virtualize the output from tools (PR #68447)

[via cfe-commits]

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+//===- raw_ostream_proxy_test.cpp - Tests for raw ostream proxies ---------===//
+//
+// 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 "llvm/ADT/SmallString.h"
+#include "llvm/Support/WithColor.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/raw_ostream_proxy.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+/// Naive version of raw_svector_ostream that is buffered (by default) and
+/// doesn't support pwrite.
+class BufferedNoPwriteSmallVectorStream : public raw_ostream {
+public:
+  // Choose a strange buffer size to ensure it doesn't collide with the default
+  // on \a raw_ostream.
+  constexpr static const size_t PreferredBufferSize = 63;
+
+  size_t preferred_buffer_size() const override { return PreferredBufferSize; }
+  uint64_t current_pos() const override { return Vector.size(); }
+  void write_impl(const char *Ptr, size_t Size) override {
+    Vector.append(Ptr, Ptr + Size);
+  }
+
+  bool is_displayed() const override { return IsDisplayed; }
+
+  explicit BufferedNoPwriteSmallVectorStream(SmallVectorImpl<char> &Vector)
+      : Vector(Vector) {}
+  ~BufferedNoPwriteSmallVectorStream() override { flush(); }
+
+  SmallVectorImpl<char> &Vector;
+  bool IsDisplayed = false;
+};
+
+constexpr const size_t BufferedNoPwriteSmallVectorStream::PreferredBufferSize;
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zmodem wrote:

redundant `const`

https://github.com/llvm/llvm-project/pull/68447