Fix Issue 21570 - Deprecate __traits(isStaticArray, ...) accepts enums...

[MoonlightSentinel]

...with static array as base type.

The spec[1] states that a named enum creates a distinct type which is
implicitly convertible to it's base type. Hence __traits(isStaticArray, <enum>)
should yield false as done for an equivalent is(...) expression.

[1] https://dlang.org/spec/enum.html#named_enums

[RazvanN7]

This requires a changelog entry and a deprecation as it is silently changing behavior. Looks good otherwise.

[RazvanN7]

Also, it looks like there are some public examples that need to be updated.

Later edit: Hm... it seems that this might not be a bug? Look at this documentation example [1].

From the is expression perspective those are different types, however, it seems that traits(isStaticArray)
considers the enum just a shell. This might be the intended behavior.

[1] https://dlang.org/spec/traits.html#isStaticArray

[MoonlightSentinel]

This requires a changelog entry and a deprecation as it is silently changing behavior. Looks good otherwise.

How should that deprecation work? Retain the current behaviour and issue a deprecation message for enums?

Later edit: Hm... it seems that this might not be a bug? Look at this documentation example [1].

Those examples were added long after the introduction of isStaticArray to document the current behaviour (see dlang/dlang.org#2507). But if this is intended behaviour it should be documented more obviously, especially because of the missmatch to is(...).

[RazvanN7]

How should that deprecation work? Retain the current behaviour and issue a deprecation message for enums?

Yes.

Those examples were added long after the introduction of isStaticArray to document the current behaviour (see dlang/dlang.org#2507). But if this is intended behaviour it should be documented more obviously, especially because of the missmatch to is(...).

cc @WalterBright @ibuclaw @Geod24

[dlang-bot]

Thanks for your pull request and interest in making D better, @MoonlightSentinel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21570	normal	__traits(isStaticArray, ...) accepts enums with static array as base type

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#12142"

[RazvanN7]

Why did you delete Fix keyword? This does bring a solution to the issue.

[MoonlightSentinel]

Because this PR just adds a warning for the user, the current behaviour remains unchanged, But I can re-add the fix if preferred.

[RazvanN7]

My point was that the deprecation should close the issue. An action was taken (i.e. the behavior is deprecated and will be changed) and the bug report no longer has any usefulness. So please re-add the "Fix" keyword.

[MoonlightSentinel]

Fair enough

[RazvanN7]

Can you also, please, add a changelog entry?

[MoonlightSentinel]

Sorry, see static_array_enum.md

[RazvanN7]

This would also require a spec change . Specifically, this: https://dlang.org/spec/traits.html#isStaticArray

[RazvanN7]

After discussing with Walter, it seems that this is not actually a bug. __traits(isStaticArray) is designed to see through to the base type. Other traits such as isArithmetic, isFloating etc. work similarly (e.g. in the case of enums they use the basetype), therefore what should be done is to update the spec to clarify this.