Re-provided identifiers are not tracked across submodules

When a library requires and re-provides an identifier without modification, it is normally linked back to the original in documentation for files that require the library for-label. This behaviour is however broken when the chain of require and re-provide is going through a submodule. To test this, install the following package (I guessed the issue number wrong when naming the github repo…):

raco pkg install https://github.com/jsmaniac/example-bug-track-submodule-issue43.git#40c26708c8bec0041a1df444775d6f55161b9e5a

The package consists of three files:

other.rkt:

#lang racket/base
(module m racket/base
  (require syntax/stx)
  (provide (all-from-out syntax/stx)))

main.rkt:

#lang racket/base
(require (submod "other.rkt" m))
(provide (all-from-out (submod "other.rkt" m)))

scribblings/example-bug-track-submodule.scrbl:

#lang scribble/manual
@(require (for-label example-bug-track-submodule
                     racket/base))
@title{example-bug-track-submodule}
@author{georges}
@defmodule[example-bug-track-submodule]

The @racket[stx-map] function is re-provided from @racketmodname[syntax/stx].

On the last line of the scribble file, the @racket[stx-map] is not linked to the syntax/stx library's documentation, and causes the following warning:

raco: --- building documentation ---
raco: 1 running: <pkgs>/example-bug-track-submodule/scribblings/example-bug-track-submodule.scrbl
raco: WARNING: undefined tag in <pkgs>/example-bug-track-submodule/scribblings/example-bug-track-submodule.scrbl:
raco:  ((lib "example-bug-track-submodule/main.rkt") stx-map)

If the code in other.rkt is moved out of the submodule, and main.rkt is adjusted accordingly, then the warning disappears and the @racket[stx-map] becomes a link to the syntax/stx library's documentation. This can be tested using the without-submod branch of that package:

raco pkg remove example-bug-track-submodule-issue43
raco pkg install https://github.com/jsmaniac/example-bug-track-submodule-issue43.git#9747adce0f66bf2a60b58f86b51a0d39c24c0d4b

Install the example-bug-track-submodule package at the supplied commit and run the documented raco documentation build to reproduce the undefined-tag warning. Start by tracing how the require/provide chain through other.rkt's submodule and main.rkt is handled for documentation links. Done means stx-map links to syntax/stx without the warning, while the without-submod comparison remains working.