Use the VFS from the CompilerInvocation by default

Summary:
The CompilerInstance should create its default VFS from its CompilerInvocation. Right now the
user has to manually create the VFS before creating the FileManager even though
`-ivfsoverlay file.yaml` was passed via the CompilerInvocation (which is exactly how we worked
around this issue in `FrontendAction.cpp` so far).

This patch uses the invocation's VFS by default and also tests this behavior now from the
point of view of a program that uses the clang API.

Reviewers: benlangmuir, v.g.vassilev

Reviewed By: v.g.vassilev

Subscribers: mgorny, cfe-commits, v.g.vassilev

Differential Revision: https://reviews.llvm.org/D37416

llvm-svn: 313049

1 files changed, 7 insertions, 3 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 5c1678262c1..d97ebb0a0e4 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -300,12 +300,16 @@ CompilerInstance::createDiagnostics(DiagnosticOptions *Opts,
 
 // File Manager
 
-void CompilerInstance::createFileManager() {
+FileManager *CompilerInstance::createFileManager() {
   if (!hasVirtualFileSystem()) {
-    // TODO: choose the virtual file system based on the CompilerInvocation.
-    setVirtualFileSystem(vfs::getRealFileSystem());
+    if (IntrusiveRefCntPtr<vfs::FileSystem> VFS =
+            createVFSFromCompilerInvocation(getInvocation(), getDiagnostics()))
+      setVirtualFileSystem(VFS);
+    else
+      return nullptr;
   }
   FileMgr = new FileManager(getFileSystemOpts(), VirtualFileSystem);
+  return FileMgr.get();
 }
 
 // Source Manager