[ty] print function names for bare Signatures opportunistically

[Gankra]

This is a followup to #21417 that improves some places where we pretty-display types (hence being restricted to multiline printing). Even in cases where we can't get the name it behooves us to add a def _ to fix python syntax highlighting in e.g. hovers.

[astral-sh-bot]

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

[astral-sh-bot]

mypy_primer results

No ecosystem changes detected ✅

No memory usage changes detected ✅

[Gankra]

With the two PRs combined, stdlib calls become readable on hover, if a bit innaccurate about methods:

[codspeed-hq]

CodSpeed Performance Report

Merging #21438 will improve performances by 5.08%

_{Comparing gankra/signature-print (cfd7591) with gankra/overloads (dcc451d)}

Summary

⚡ 2 improvements
✅ 20 untouched
⏩ 30 skipped¹

Benchmarks breakdown

	Mode	Benchmark	BASE	HEAD	Change
⚡	Simulation	ty_micro[complex_constrained_attributes_1]	70.1 ms	67 ms	+4.59%
⚡	Simulation	ty_micro[complex_constrained_attributes_2]	70.3 ms	66.9 ms	+5.08%

Footnotes

1. 30 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[carljm]

Signatures don't necessarily come from def statements (or functions), so I feel like it's kind of misleading to prepend def _ arbitrarily to signature rendering. I understand that this gives us syntax highlighting for free :/ Probably worth it, but unfortunate.

[MichaReiser]

What's an example where we don't have a name? Is it for Callable types?

Pylance uses a different rendering for callable types:

Which I think I prefer, as it emphasizes the fact that one is a callable rather than a specific function instance

[dhruvmanila]

Yes, it's for Callable and lambda expressions and we do use the same display approach.

[dhruvmanila]

I'll put this in draft for now as this might not be necessary, refer to my comment here: #21417 (comment).

[Gankra]

Yeah I'm gonna send this to hell for now