Change Details

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.

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.

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. 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 the `InMemoryOutputFileSystem` instead of the real file system.