Implement textDocument/inlayHint

[Techatrix]

The LSP Specification introduced inlay hints in version 3.17 Reference

This PR adds supports for parameter inlay hints for function calls including builtins.

This feature is disabled by default and must be enabled by settings enable_inlay_hints in zls.json or through zls config

If a function call can display hover information but can't show inlay hints its probably a bug, feel free to inform me.

Options

The following options are currently implemented:

Option	Type	Default value	What it Does
inlay_hints_show_builtin	bool	true	Enable inlay hints for builtin functions
inlay_hints_exclude_builtins	[][]const u8	[]	Don't show inlay hints for the given builtin functions. Builtins with one parameter are skipped automatically
inlay_hints_exclude_single_argument	bool	true	Don't show inlay hints for single argument calls

Note that these options are located in src/inlay_hints.zig and are currently not part of zls config or zls.json.

I am open to suggestions for more options and better defaults.

Examples taken from VS Code

Hovering over a hint will show its type

Tested on

• Platforms: Linux, Windows
• Code Editors: VS Code
• VS Code extensions: augusterame.zls-vscode and tiehuis.zig
• Code bases: zig std lib, zls itself, gyro, zig-gamedev
• zig compiler: 0.10.0-dev.3258+9734e643f

[SuperAuguste]

Ok so this is absolutely awesome!! Heading to bed now but I'll look at this ASAP tomorrow! Thank you so much!

[SuperAuguste]

I'll take care of the TODO expose options right now! :)

[SuperAuguste]

Gotta figure out what's up with the CI, I'll try to unbrick it really quickly and then merge this!

[Techatrix]

Aren't the config options meant for the end user?
Because i don't think inlay_hints_max_inline_children should be put among them. It is meant to reduce run times and doesn't affect the (visible) output.

[SuperAuguste]

Aren't the config options meant for the end user? Because i don't think inlay_hints_max_inline_children should be put among them. It is meant to reduce run times and doesn't affect the (visible) output.

I couldn't quite figure out what it was doing so I added it to the config anyways, thanks for letting me know that this isn't meant to be configurable for end-users! I'll fix it up once I get tests passing.

[SuperAuguste]

I couldn't salvage tests, I'll finalize the config and then work on fixing them in a separate PR; sorry for the trouble!

[smokku]

@Techatrix Thank you so much for this! :-)

Do you have plans for adding inlay hints for local const/var variables?

[Techatrix]

I didn't implement them because right now they wouldn't work in many cases. You can check that by hovering over many symbols, if you see 'unknown' as the type then inlay hints wouldn't show a type as well. Once type resolution is improved we can work on inlay hints for types.