[VFS] Add 'overlay-relative' field to YAML files

The VFS overlay mapping between virtual paths and real paths is done through
the 'external-contents' entries in YAML files, which contains hardcoded paths
to the real files.

When a module compilation crashes, headers are dumped into <name>.cache/vfs
directory and are mapped via the <name>.cache/vfs/vfs.yaml. The script
generated for reproduction uses -ivfsoverlay pointing to file to gather the
mapping between virtual paths and files inside <name>.cache/vfs. Currently, we
are only capable of reproducing such crashes in the same machine as they
happen, because of the hardcoded paths in 'external-contents'.

To be able to reproduce a crash in another machine, this patch introduces a new
option in the VFS yaml file called 'overlay-relative'. When it's equal to
'true' it means that the provided path to the YAML file through the
-ivfsoverlay option should also be used to prefix the final path for every
'external-contents'.

Example, given the invocation snippet "... -ivfsoverlay
<name>.cache/vfs/vfs.yaml" and the following entry in the yaml file:

"overlay-relative": "true",
"roots": [
...
  "type": "directory",
  "name": "/usr/include",
  "contents": [
    {
      "type": "file",
      "name": "stdio.h",
      "external-contents": "/usr/include/stdio.h"
    },
...

Here, a file manager request for virtual "/usr/include/stdio.h", that will map
into real path "/<absolute_path_to>/<name>.cache/vfs/usr/include/stdio.h.

This is a useful feature for debugging module crashes in machines other than
the one where the error happened.

Differential Revision: http://reviews.llvm.org/D17457

rdar://problem/24499339

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@261552 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/Frontend/ModuleDependencyCollector.cpp b/lib/Frontend/ModuleDependencyCollector.cpp
index df5e19df91..7ba0464559 100644
--- a/lib/Frontend/ModuleDependencyCollector.cpp
+++ b/lib/Frontend/ModuleDependencyCollector.cpp
@@ -51,6 +51,10 @@ void ModuleDependencyCollector::writeFileMap() {
   SmallString<256> Dest = getDest();
   llvm::sys::path::append(Dest, "vfs.yaml");
 
+  // Default to use relative overlay directories in the VFS yaml file. This
+  // allows crash reproducer scripts to work across machines.
+  VFSWriter.setOverlayDir(getDest());
+
   std::error_code EC;
   llvm::raw_fd_ostream OS(Dest, EC, llvm::sys::fs::F_Text);
   if (EC) {