Use the correct file/line for doctests on both inner and outer attributes

[Swatinem]

When adding two separate doc comments to a mod, one item-level doc
for the mod statement, and one file-level doc for the module file,
doctests that are defined in the module file get the wrong filename/line
assigned to them.

does not yet fix issue #79764, as I still have to figure out how all of this fits together ;-) So far, I just created a testcase for this.

[rust-highfive]

r? @Mark-Simulacrum

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[camelid]

(I added the word 'issue' between 'fix' and the issue number in the PR description so the issue won't be closed.)

[jyn514]

@Swatinem I expect the fix will look something like #78611. But it seemed like a lot of complexity for not much benefit :/

#79764 is confusing me - can you explain why it should say mod_with_file_doctest.rs instead of lib.rs? It's hard for me to keep track of which code belongs to which example, it sounds like there are 5 or so examples and only one is buggy?

[Swatinem]

@jyn514 thanks for the quick reply. Yes, it seems very much like the root cause is similar to #78611, essentially when you have both outer- and inner doctests, the inner doctest takes the file/line information from the outer doc, which is then wrong.

And yes, from #79764, only one of the examples is wrong, the inner-doctest for the mod that also has an outer-doctest. The doctest points to a line number that doesn’t even exist in the file.

I’m not sure how widely this is used (mixing outer- and inner- doctests), but it is a bug nonetheless.

[jyn514]

@Swatinem sounds good to me - I'm not planning to follow up on #78611 so feel free to copy as much of that code as you need to make this work.

[jyn514]

@Swatinem let me know if you need help figuring out how #78611 works.

[jyn514]

I'm going to close this for now since it hasn't seen activity in a while. Feel free to re-open if you have time to work on this :)