Add spec tests for EXISTS (for SPARQL 1.2)

[rubensworks]

Now that the issues around EXISTS were fixed in SPARQL 1.2 (w3c/sparql-query#302), we should make sure we have good tests to capture this.

Luckily, @afs collected many tests already in https://github.com/afs/SPARQL-exists
So I would propose incorporating those tests into this repo.

@afs do you agree?
If so, do you want to make a PR?
I can also do it if this is lower on your priority list.

---

I manually went through the tests to validate them based on my understanding of what the spec says now.
This is my analysis:

• exists-1-empty-bgp: ok
• exists-2-def-var: Do we really want these to be negative syntax tests, or just evaluation errors? A negative syntax tests may require a lot of effort on the parser's side.
• exists-3-bgp: I think both of the tests there should produce a valid solution mapping (instead of only the second test).
• exists-4-minus: ok
• exists-5-scope/exists-subselect-projection: Should be valid I think
• exists-6-places: ok
• exists-bnodes: ok
• exists-filter/scope-filter-01: I would expect a single result here (as this follows the without-projection approach; values projected out in sub-SELECTs are affected)
• other: Not checked yet

[afs]

Now that the issues around EXISTS were fixed in SPARQL 1.2

Yes, we can get started.

We still have two things to follow-through on - remapping variables not projected (there is some descriptive text in the spec but renaming protects passing in the current row deep inside a nested select); and scoping.

These don't stop work on tests.

If so, do you want to make a PR?
I can also do it if this is lower on your priority list.

They need some clearing up and organisation - there's overlap/redundancy IIRC.

If you want to get something started, we could create a working branch here. I can target a PR for that.

As this is a significant area of 1.2, I think it should have it's own directory.

[rubensworks]

If you want to get something started, we could create a working branch here. I can target a PR for that.

Ok, I've initialized a branch here feature/exists-1-2 with an empty manifest for new exists tests under sparql/sparql12/exists/manifest.ttl.
Once your PR has been created, I will take a look.

[afs]

If so, do you want to make a PR?

PR #276

No changes made. No claim they are right!

This is my analysis:

Good starting point.

other: Not checked yet

I didn't include these.

They are collected examples from several sources used to illustrate various points. They aren't the desired outcome.

We can use them to check we have coverage as the exists tests settle down.

Available at : https://github.com/afs/SPARQL-exists/tree/main/tests/other