[PATCH] D78058: option to write files to memory instead of disk

[Marc Rasi via Phabricator via cfe-commits]

marcrasi created this revision.
Herald added subscribers: cfe-commits, jfb, mgorny.
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marcrasi edited the summary of this revision.

This allows clients to invoke clang without writing anything to disk.

I'm not sure if this is the right design, so I'm sending this patch to
start a discussion about the right way to do this. I'll be happy to make
changes and add tests after talking about the right way to do this!

Motivation:

At Google, we run some Swift source tooling on diskless servers. The
Swift source tooling calls Clang through the ClangImporter
(https://github.com/apple/swift/blob/master/lib/ClangImporter/ClangImporter.cpp).
Clang compiles module to an on-disk module cache, which does not work on
the diskless servers. This patch lets clients ask Clang to write the
module cache to memory.

Current design:

- Adds `class InMemoryOutputFileSystem : public llvm::vfs::FileSystem` that supports write operations backed by memory. After a file is written, its contents are accessible through the `llvm::vfs::FileSystem` interface.
- Adds an `InMemoryOutputFileSystem` field to `CompilerInstance`. When this field is set, the `CompilerInstance` writes to the `InMemoryOutputFileSystem` instead of the real file system.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78058

Files:
  clang/include/clang/Basic/InMemoryOutputFileSystem.h
  clang/include/clang/Frontend/CompilerInstance.h
  clang/lib/Basic/CMakeLists.txt
  clang/lib/Basic/InMemoryOutputFileSystem.cpp
  clang/lib/Frontend/CompilerInstance.cpp

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