Hyperlinked sources as generated by the Nix toolchain prepend `../` in absolute paths

[lf-]

Sample bit of bad source from the Persistent Database.Persist.TH hyperlinked docs generated by haddock 2.25.1:

<span class="annot"><span class="annottext">Exp -&gt; Stmt
</span><a href="../file:///nix/store/3bwbsy0llxxn1pixx3ll02alln56ivxy-ghc-9.0.2-doc/share/doc/ghc/html/libraries/template-haskell-2.17.0.0/src" class=""><span class="hs-identifier hs-var">NoBindS</span></a></span>

It's also the case in other packages such as aeson linking to functions in packages included with ghc. I don't know/remember if it affects links to packages sourced from hackage.

I am guessing that the following code, or code near it, is the cause of the leading ../:

haddock/haddock-api/src/Haddock/Backends/Hyperlinker/Renderer.hs

Lines 265 to 270 in bc0f2d6

	Just SrcLocal -> Html.anchor content !
	[ Html.href $ hypSrcModuleUrl' moduleName ]
	Just (SrcExternal path) -> Html.anchor content !
	[ Html.href $ spliceURL' Nothing (Just moduleName) Nothing Nothing (".." </> path) ]
	Nothing -> content

However, setting up a development environment such that I can test it with the Nix builder is running into some bugs in nixpkgs, so I can't proceed any further on figuring this out myself.

[lf-]

Exact repro with aeson:

$ nix-build '<nixpkgs>' -A haskell.packages.ghc922.aeson.doc
/nix/store/nwk37d36j9zjkalxs58qfli9cfa9jvd5-aeson-2.0.3.0-doc

then go to file:///nix/store/nwk37d36j9zjkalxs58qfli9cfa9jvd5-aeson-2.0.3.0-doc/share/doc/aeson-2.0.3.0/html/src/Data.Aeson.Text.html in a browser and TB.singleton is an example of a bad link.

[Kleidukos]

@lf- Hi! I don't personally use Nix so I'm not really sure how to approach this.
We could probably have a heuristic that determines whether or not to insert the ../ if the path starts with file://.
What do you think of that?

[lf-]

That was what I was thinking as well. Detect if it's absolute and go from there. I'm not sure who gives us the file:// URLs (or indeed if we are given them at all; might be some Nix hack), but it's easy enough to detect them and not do the prepend. I have now figured out the setup to test a proposed patch so I might write one.

[Kleidukos]

@lf- Very well. Ping me if you can't find the time, I'll handle it. :)