Add support for labeled module references

[garetxe]

Support a markdown-style way of annotating module references. For instance

-- | label

will create a link that points to the same place as the module
reference "Module.Name#anchor" but the text displayed on the link will
be "label".

(This is a rebase of #1181 for ghc-9.0, as requested in #1181 (comment))

[garetxe]

Just to clarify: this was already merged in the ghc-8.10 branch, but was not brought forward to ghc-9.0. I rebased so it is easier to merge in ghc-9.0, as @Kleidukos suggested.

[Kleidukos]

@garetxe Any idea why we're hitting https://github.com/haskell/haddock/pull/1315/checks?check_run_id=1845591424#step:7:65 ?

[garetxe]

Yes, this should be fixed by 0fd9131 : the DocModule constructor now takes a ModLink argument, and not a plain String. The error was due to OverloadedStrings trying to make sense out of this.

[Kleidukos]

Alright now we're hitting

2021-02-06T20:55:25.2278472Z hoogle-test: hoogle-test/out/Bug873: removeDirectoryRecursive:getSymbolicLinkStatus: does not exist (No such file or directory)
2021-02-06T20:55:25.2280079Z Failed to run Haddock on test package 'Bug873'

[garetxe]

There is still a failing test, but this is the same Bug873 as last time, due to the change on the interface version (see comments #1181 (comment) and #1296 (comment)). If I remove that test the tests pass locally for me.

Please let me know if you would like me to add a commit removing that test from my branch.

[Kleidukos]

@garetxe This is also the symptom of something deeper. I have a call with Alex tomorrow and we'll decide of a solution. Otherwise, it's all good. I'll merge the PR when it's all green. :)

[garetxe]

OK, great, thanks a lot :)

[Kleidukos]

@garetxe Alright, I've had the call with @alexbiehl and we decided to make some changes to the PR to ensure backward compatibility.
Either you can upstream those changes in your own PR, or another PR can be opened so that you're not bothered anymore. We shall put your name in the "Authored by" field in the commit.
Thanks a lot! ✨

[garetxe]

Great, thanks a lot! :)

[garetxe]

Oh, and I don't care about the authorship part, as long as the patch goes in in some form I am happy!
So feel free to directly commit your changes.