Add __traits isDynamicArray

[nordlow]

Partially resolves #23784.

I can split the PR up into two if requested.

Changelog will be updated if this gets approved.

Looking into failing tests.

[github-actions]

DMD perf check

Metric	Base	PR	Δ
dmd binary size (stripped)	6.86 MB	6.88 MB	+0.28%

All measurements

Metric	Base	PR	Δ
compile hello.d (instr)	215.1 M	215.1 M	-0.001%
compile hello.d -O -release (instr)	233.4 M	233.4 M	+0.002%
compile Phobos (instr)	5,120.9 M	5,120.8 M	-0.002%
compile Phobos codegen (instr)	1,472.4 M	1,472.4 M	-0.004%
compile vibe.d (instr)	15,113.8 M	15,112.9 M	-0.006%
dmd binary size (stripped)	6.86 MB	6.88 MB	+0.28%
hello binary size (stripped)	0.72 MB	0.72 MB	0.00%
peak RSS (compile hello.d)	43.48 MB	43.51 MB	+0.07%
peak RSS (compile Phobos)	617.2 MB	620.0 MB	+0.45%
peak RSS (compile vibe.d)	1916 MB	1918 MB	+0.09%
compile dmd itself (wall)	12.1 s	12.1 s	+0.33%
compile hello.d (wall)	64.1 ms	63.7 ms	-0.62%
compile Phobos (wall)	1,545 ms	1,549 ms	+0.26%

_{4c2c3be vs merge-base 86b74e2 · about these metrics}

[ntrel]

runnable/traits.d TEST_OUTPUT needs updating.

[dkorpel]

What's the rationale for isArray and why is an Associative Array not one?

[dkorpel]

From the issue

Please do not allow this trait to accept enums!

This PR's implementation accepts enums

[nordlow]

What's the rationale for isArray and why is an Associative Array not one?

Good point. I agree that isArray should be true for AAs.

Update: I removed isArray from this PR.

[nordlow]

From the issue

Please do not allow this trait to accept enums!

This PR's implementation accepts enums

Shouldn't we mimic the behavior __traits(isStaticArray, ...) in this case? Despite it accepting enums is a bad design.

And then later disallow all traits of this kind to not accept enums?

For the sake of consistency.

I'm ok with both alternatives.

[dkorpel]

Good point. I agree that isArray should be true for AAs.

That's not what I meant, I don't see why it needs to exist in the first place. What's the real world use case?

[nordlow]

Good point. I agree that isArray should be true for AAs.

That's not what I meant, I don't see why it needs to exist in the first place. What's the real world use case?

I don't know.

[nordlow]

compiler/test/run.d runnable/traits.d now passes locally for me.

[nordlow]

What's the rationale for isArray and why is an Associative Array not one?

Removed isArray changes from this PR.