Open Radar

 
Summary:
When using an ivfsoverlay to point swift to a modulemap file that describes an objective-c module, if the path to the ivfsoverlay is not absolute this breaks autocomplete in Xcode.

Steps to Reproduce:
- Create a swift app and a static library dependency with an objective-c class
- Create a modulemap file to describe the dependency, name it dep.modulemap
- Create an ivfsoverlay to expose the modulemap to swift
- Add HEADER_SEARCH_PATHS to the dep headers
- Add swiftc arguments `-Xcc -ivfsoverlay -Xcc dep/module.yaml` to the main swift target
- Add a target dependency in project settings.
- In the main swift target, add an import statement the dependency. 
- Start typing some symbol from the dependency. 
- Hit cmd + space or esc for autocomplete.
===========
- Autocomplete does not work
===========
- write correct code without autocomplete
- build the project successfully

See the attached Xcode project. You'll need to fix the absolute paths present in the module.yaml file before it will build.


Expected Results:
Xcode autocompletes.

Actual Results:
Autocomplete does not work.

Version/Build:
Xcode 9.2.0 (9C40b)

Configuration:
I found a workaround in changing using an absolute path for the ivfsoverlay:

OTHER_SWIFT_FLAGS = $(inherited) -Xcc -ivfsoverlay -Xcc dep/module.yaml

to 

OTHER_SWIFT_FLAGS = $(inherited) -Xcc -ivfsoverlay -Xcc $(PROJECT_DIR)/dep/module.yaml

This is odd as one of the arguments passed to swiftc is 
```
-Xcc
-working-directory/Users/robbertvanginkel/Desktop/IndexingError
```
It seems like swift/clang when indexing doesn't respect the `-working-directory` argument when looking for the ivfsoverlay. It does seem to do it for other arguments such as the header search paths.