[support] Use VFS in SourceMgr for loading includes

Most `SourceMgr` clients don't make use of include files, but those that do might want to specify the file system to use. This patch enables that by making it possible to pass a `vfs::FileSystem` instance into `SourceMgr`.

Author: jansvoboda11

llvm/include/llvm/Support/SourceMgr.h

@@ -15,6 +15,7 @@
 #ifndef LLVM_SUPPORT_SOURCEMGR_H
 #define LLVM_SUPPORT_SOURCEMGR_H
 
+#include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -23,6 +24,10 @@
 
 namespace llvm {
 
+namespace vfs {
+class FileSystem;
+} // end namespace vfs
+
 class raw_ostream;
 class SMDiagnostic;
 class SMFixIt;
@@ -91,15 +96,25 @@ class SourceMgr {
   DiagHandlerTy DiagHandler = nullptr;
   void *DiagContext = nullptr;
 
+  // Optional file system for finding include files.
+  IntrusiveRefCntPtr<vfs::FileSystem> FS;
+
   bool isValidBufferID(unsigned i) const { return i && i <= Buffers.size(); }
 
 public:
-  SourceMgr() = default;
+  /// Create new source manager without support for include files.
+  SourceMgr();
+  /// Create new source manager with the capability of finding include files
+  /// via the provided file system.
+  explicit SourceMgr(IntrusiveRefCntPtr<vfs::FileSystem> FS);
   SourceMgr(const SourceMgr &) = delete;
   SourceMgr &operator=(const SourceMgr &) = delete;
-  SourceMgr(SourceMgr &&) = default;
-  SourceMgr &operator=(SourceMgr &&) = default;
-  ~SourceMgr() = default;
+  SourceMgr(SourceMgr &&);
+  SourceMgr &operator=(SourceMgr &&);
+  ~SourceMgr();
+
+  IntrusiveRefCntPtr<vfs::FileSystem> getVirtualFileSystem() const;
+  void setVirtualFileSystem(IntrusiveRefCntPtr<vfs::FileSystem> FS);
 
   /// Return the include directories of this source manager.
   ArrayRef<std::string> getIncludeDirs() const { return IncludeDirectories; }

llvm/lib/Support/SourceMgr.cpp

@@ -24,6 +24,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/SMLoc.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
@@ -38,6 +39,22 @@ using namespace llvm;
 
 static const size_t TabStop = 8;
 
+// Out of line to avoid needing definition of vfs::FileSystem in header.
+SourceMgr::SourceMgr() = default;
+SourceMgr::SourceMgr(IntrusiveRefCntPtr<vfs::FileSystem> FS)
+    : FS(std::move(FS)) {}
+SourceMgr::SourceMgr(SourceMgr &&) = default;
+SourceMgr &SourceMgr::operator=(SourceMgr &&) = default;
+SourceMgr::~SourceMgr() = default;
+
+IntrusiveRefCntPtr<vfs::FileSystem> SourceMgr::getVirtualFileSystem() const {
+  return FS;
+}
+
+void SourceMgr::setVirtualFileSystem(IntrusiveRefCntPtr<vfs::FileSystem> FS) {
+  this->FS = std::move(FS);
+}
+
 unsigned SourceMgr::AddIncludeFile(const std::string &Filename,
                                    SMLoc IncludeLoc,
                                    std::string &IncludedFile) {
@@ -52,16 +69,19 @@ unsigned SourceMgr::AddIncludeFile(const std::string &Filename,
 ErrorOr<std::unique_ptr<MemoryBuffer>>
 SourceMgr::OpenIncludeFile(const std::string &Filename,
                            std::string &IncludedFile) {
+  if (!FS)
+    reportFatalInternalError("Opening include file from SourceMgr without VFS");
+
   ErrorOr<std::unique_ptr<MemoryBuffer>> NewBufOrErr =
-      MemoryBuffer::getFile(Filename);
+      FS->getBufferForFile(Filename);
 
   SmallString<64> Buffer(Filename);
   // If the file didn't exist directly, see if it's in an include path.
   for (unsigned i = 0, e = IncludeDirectories.size(); i != e && !NewBufOrErr;
        ++i) {
     Buffer = IncludeDirectories[i];
     sys::path::append(Buffer, Filename);
-    NewBufOrErr = MemoryBuffer::getFile(Buffer);
+    NewBufOrErr = FS->getBufferForFile(Buffer);
   }
 
   if (NewBufOrErr)

llvm/lib/TableGen/Main.cpp

@@ -26,6 +26,7 @@
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/ToolOutputFile.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
@@ -129,6 +130,8 @@ int llvm::TableGenMain(const char *argv0,
   // it later.
   SrcMgr.setIncludeDirs(IncludeDirs);
 
+  SrcMgr.setVirtualFileSystem(vfs::getRealFileSystem());
+
   TGParser Parser(SrcMgr, MacroNames, Records, NoWarnOnUnusedTemplateArgs);
 
   if (Parser.ParseFile())

llvm/lib/TableGen/Parser.cpp

@@ -9,6 +9,7 @@
 #include "llvm/TableGen/Parser.h"
 #include "TGParser.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/TableGen/Record.h"
 
 using namespace llvm;
@@ -20,6 +21,7 @@ bool llvm::TableGenParseFile(SourceMgr &InputSrcMgr, RecordKeeper &Records) {
   // this reliance, we could drop all of this.
   SrcMgr = SourceMgr();
   SrcMgr.takeSourceBuffersFrom(InputSrcMgr);
+  SrcMgr.setVirtualFileSystem(InputSrcMgr.getVirtualFileSystem());
   SrcMgr.setIncludeDirs(InputSrcMgr.getIncludeDirs());
   SrcMgr.setDiagHandler(InputSrcMgr.getDiagHandler(),
                         InputSrcMgr.getDiagContext());