Add ShowDeclarationsOfOperation helper

[fingolfin]

When debugging issues with method installations for operations (including
attributes and properties), it can be helpful to find out what all
declarations of a given operation are. This helper function does just that.

The placement of this function in the manual could perhaps be better, I am open to suggestions, but generally feel that this could and should be improved in that whole chapter

This is a new feature and hence should be listed in the release notes.

[coveralls]

Coverage decreased (-0.002%) to 85.167% when pulling 402644d on fingolfin:mh/ShowDeclarationsOfOperation into 87794e8 on gap-system:master.

[DominikBernhardt]

Thanks, this is indeed a very helpful function!
I don't have anything against the placement in the manual, although one could also think about putting it closer to the explanation of operations, i.e. 5.5-2 after IsOperation? It's not ideal either, but maybe a user would rather search there?

[markusbaumeister]

This looks very helpful for debugging purposes.

Concerning the manual placement: I believe the whole section "Global Variables in the Library" seems to be mislabeled - I would not have (and still don't) associate "global variables" with methods like "DeclareCategory" or "TypeOfOperation". While @DominikBernhardt has a slightly better suggestion, putting it under the header "Function Types" also feels weird.

If I were to search for this functionality, I would naturally look for a chapter that explains "Operations in GAP" (or "Categories in GAP" for the "IsCategory"), ideally in a chapter whose name makes it clear that these are internal data structures or methods usually only used by developers. Unfortunately, such a chapter does not currently exist. Lacking it, I would ask whether this method would fit into chapter 7 ("Debugging"), since that seems to be one of the primary use cases I can discern.

[DominikBernhardt]

I agree with @markusbaumeister that the header Function Types itself does not feel perfect. But we have already established that there is no perfect chapter name for this function, so I would rather put it near to IsOperation and imho 5.5-2 fits this. Ultimately, this is a matter of taste I guess.

[fingolfin]

Yeah, I also find the section title "Global Variables in the Library" super confusing and rather inappropriate. And there are indeed some key concepts related to these operations/filters/categories/ etc. which don't seem to be explained in that chapter (or anywhere in the reference manual that I could find now).

I'll think some more about it...

[PaulaHaehndel]

The code returns the following error for ShowDeclarationsOfOperation(IsOperation);

Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `Length' on 1 arguments
The 1st argument is 'fail' which might point to an earlier problem
 at /mnt/c/gap/lib/methsel2.g:249 called from
Length( locs ) at /mnt/c/gap/lib/methwhy.g:422 called from
<function "ShowDeclarationsOfOperation">( <arguments> )
 called from read-eval loop at *stdin*:2
type 'quit;' to quit to outer loop```

[PaulaHaehndel]

I also wouldn't expect it in the current place and more likely would search for it in 7 Debugging and Profiling Facilities.

[fingolfin]

@PaulaHaehndel yes, it breaks if you give it IsOperation. Just like it breaks when you give it a string, the integer 42, or anything else that's not an operation. So, what are you saying -- is that an implicit request for argument validation?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@87794e8). Click here to learn what that means.
The diff coverage is 58.82%.

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Impacted Files	Coverage Δ
lib/methwhy.g	79% <58.82%> (ø)

[fingolfin]

@PaulaHaehndel regarding the error with IsOperation as input: I stand corrected, IsOperation is an operation, I badly mixed this up with something else. My apologies! I've now added a check for that.

[fingolfin]

I'll merge this now, and then provide another PR to improve the arrangement of things a bit. Thank you all for your feedback!