[llvm] Support: Add vfs::OutputBackend and OutputFile to virtualize compiler outputs (PR #113363)

[Alexandre Ganea via llvm-commits]

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@@ -0,0 +1,116 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declarations of the VirtualOutputBackend classes,
+/// which can be used to virtual outputs from LLVM tools.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_VIRTUALOUTPUTBACKENDS_H
+#define LLVM_SUPPORT_VIRTUALOUTPUTBACKENDS_H
+
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/Support/VirtualOutputBackend.h"
+#include "llvm/Support/VirtualOutputConfig.h"
+
+namespace llvm::vfs {
+
+/// Create a backend that ignores all output.
+IntrusiveRefCntPtr<OutputBackend> makeNullOutputBackend();
+
+/// Make a backend where \a OutputBackend::createFile() forwards to
+/// \p UnderlyingBackend when \p Filter is true, and otherwise returns a
+/// \a NullOutput.
+IntrusiveRefCntPtr<OutputBackend> makeFilteringOutputBackend(
+    IntrusiveRefCntPtr<OutputBackend> UnderlyingBackend,
+    std::function<bool(StringRef, std::optional<OutputConfig>)> Filter);
+
+/// Create a backend that forwards \a OutputBackend::createFile() to both \p
+/// Backend1 and \p Backend2 and sends content to both places.
+IntrusiveRefCntPtr<OutputBackend>
+makeMirroringOutputBackend(IntrusiveRefCntPtr<OutputBackend> Backend1,
+                           IntrusiveRefCntPtr<OutputBackend> Backend2);
+
+/// A helper class for proxying another backend, with the default
+/// implementation to forward to the underlying backend.
+class ProxyOutputBackend : public OutputBackend {
+  void anchor() override;
+
+protected:
+  // Require subclass to implement cloneImpl().
+  //
+  // IntrusiveRefCntPtr<OutputBackend> cloneImpl() const override;
+
+  Expected<std::unique_ptr<OutputFileImpl>>
+  createFileImpl(StringRef Path, std::optional<OutputConfig> Config) override {
+    OutputFile File;
+    if (Error E = UnderlyingBackend->createFile(Path, Config).moveInto(File))
+      return std::move(E);
+    return File.takeImpl();
+  }
+
+  OutputBackend &getUnderlyingBackend() const { return *UnderlyingBackend; }
+
+public:
+  ProxyOutputBackend(IntrusiveRefCntPtr<OutputBackend> UnderlyingBackend)
+      : UnderlyingBackend(std::move(UnderlyingBackend)) {
+    assert(this->UnderlyingBackend && "Expected non-null backend");
+  }
+
+private:
+  IntrusiveRefCntPtr<OutputBackend> UnderlyingBackend;
+};
+
+/// An output backend that creates files on disk, wrapping APIs in sys::fs.
+class OnDiskOutputBackend : public OutputBackend {
+  void anchor() override;
+
+protected:
+  IntrusiveRefCntPtr<OutputBackend> cloneImpl() const override {
+    return clone();
+  }
+
+  Expected<std::unique_ptr<OutputFileImpl>>
+  createFileImpl(StringRef Path, std::optional<OutputConfig> Config) override;
+
+public:
+  /// Resolve an absolute path.
+  Error makeAbsolute(SmallVectorImpl<char> &Path) const;
+
+  /// On disk output settings.
+  struct OutputSettings {
+    /// Register output files to be deleted if a signal is received. Also
+    /// disabled for outputs with \a OutputConfig::getNoDiscardOnSignal().
+    bool DisableRemoveOnSignal = false;
----------------
aganea wrote:

Where possible, I usually prefer active/positive variable names, rather that negative, which are harder to reason about. https://medium.com/dfind-consulting/about-writing-positive-and-negative-variable-names-b42328d51e9c

So that would be `RemoveOnSignal = true;` here. Ditto below.

https://github.com/llvm/llvm-project/pull/113363