Concise Magic File Names

[anandabits (Matthew Johnson)]

@beccadax

We propose that #file should evaluate to a human-readable string which uniquely identifies a source file in the process, but which does not contain the full path. Specifically, it will contain the file name and module name.[1]

This seems generally sufficient, although I would like the format to be fully specified. This is necessary in order to support use cases that need to parse the string in order to tie file and line information back to a specific line of source code (for example, this might be useful in logs).

@beccadax

[1] This is sufficient to uniquely identify a file because the Swift compiler will not build a module which contains two identically-named source files, even if they're in different directories. This limitation ensures that identically-named private and fileprivate declarations in different files will have unique mangled names.

Thanks for including this detail. I wasn’t aware of it and believe the guarantee of uniqueness is important.