is duplicated by:

• SR-513 Add file name for dumped files in AST

Issue Description:

The Swift compiler's -dump-ast functionality prints an output that doesn't include the file names, which can make it impossible to distinguish between different files.

For instance, when compiling two files a.swift and b.swift, both containing the code "private func foo() { }", with the command "$ swiftc b.swift a.swift -dump-ast", we get this output:

(source_file
  (func_decl "foo()" interface type='() -> ()' access=private
    (parameter_list)
    (brace_stmt)))
(source_file
  (func_decl "foo()" interface type='() -> ()' access=private
    (parameter_list)
    (brace_stmt)))

It would be very useful if this information included the file name (or, even better, the file path). Something like this:

(source_file "/path/to/a.swift"
  (func_decl "foo()" interface type='() -> ()' access=private
    (parameter_list)
    (brace_stmt)))
(source_file "/path/to/b.swift"
  (func_decl "foo()" interface type='() -> ()' access=private
    (parameter_list)
    (brace_stmt)))