:term: referenced via intersphinx is case sensitive

[tomoinn]

Describe the bug

When a doc website A contains a term in a glossary, that term can be referenced without case sensitivity applied. If, however, that term is referenced from a second doc build B, by adding an intersphinx reference to A, only exact cases match.

To Reproduce
Steps to reproduce the behavior:

Add the following intersphinx reference:

'oe': ('https://icebreakerone.github.io/open-energy-technical-docs/main/', None)

Then attempt to reference a term within the glossary from a second project, i.e.

:term:`data provider` - this fails
:term:`Data Provider` - this correctly references back into the external glossary

Expected behavior

References to terms in external projects linked through intersphinx resolve in the same way as those defined locally.

Your project

https://github.com/icebreakerone/open-energy-technical-docs contains source, https://icebreakerone.github.io/open-energy-technical-docs/main/index.html is the site containing the manifest from which I'm trying to import terms.

Environment info

Sphinx build run from linux, python 3.8.6, sphinx 4.0.2

[jhuitema]

I've also just run into this. From my (non-exhaustive) testing, it looks like the case-insensitive intersphinx term linking stopped working with Sphinx v3. The term links work correctly in Sphinx 2.4.4 and under.

[AWhetter]

A git bisect indicates that this was an intentional change made in a5dadeb to address #7418.
It's documented that terms are now case sensitive, and this was a breaking change introduced for Sphinx v3.
There was a change made in 61f00bf (v3.0.2) to fall back to case insensitive matching and to raise a warning when this happens, but from testing it seems like this doesn't happen for matches against an intersphinx mapping.

[tomoinn]

Yup, it looks like the resolver for :term: isn't used when loading references from intersphinx? If anyone has better knowledge of how things are structured they'd probably have a better idea, but as far as I can tell the resolution in intersphinx is happening in

sphinx/sphinx/ext/intersphinx.py

Line 261 in 4d90277

def missing_reference(app: Sphinx, env: BuildEnvironment, node: pending_xref,

and just doing a straight 'is X in Y' check

[tomoinn]

I've had a play patching intersphinx.py, adding the following within missing_reference(...) and it does what I need, in that it allows for case insensitive match of terms from intersphinx:

This is inside the loop on line 319 of the current version

            if objtype == 'std:term' and objtype in inventory:
                cased_keys = {k.lower(): k for k in inventory[objtype].keys()}
                if target.lower() in cased_keys:
                    corrected_target = cased_keys[target.lower()]
                    proj, version, uri, dispname = inventory[objtype][corrected_target]
                else:
                    continue
            else:
                if objtype not in inventory or target not in inventory[objtype]:
                    continue
                proj, version, uri, dispname = inventory[objtype][target]