feat(extmark): window scoped namespace

[altermo]

By @bfredl suggestion #27361 (comment):
Make namespaces have the possibility of being window-local (only show the namespaces's extmarks in specific windows).
Currently, one needs to set a flag on the extmark (called scoped) to make this take effect (may be changed).

Closes #19654

[bfredl]

Alternative representation: for each decoration, just store a single bit (in the flags field for the extmark) whether this is a "scoped" extmark. then for each window, store a set of all the active namespaces from which scoped extmarks are considered.

It is less granular in one way (either all or nothing of scoped marks in a namespace is visible) but a lot more flexible in another (a given extmark category can be displayed in a subset of windows, not just one).

[altermo]

I thought about instead of having a scoped option for the extmark; have a scoped option for the namespace, as I don't see many people creating a namespace with a combination of scoped and unscoped extmarks.
But as namespaces don't have any struct and are just numbers, I don't know where to store this information.

[bfredl]

That might be an option as well.

But as namespaces don't have any struct and are just numbers, I don't know where to store this information.

That's mostly a consequence of just a single item of info being used currently. changing that to a struct would be fine if we go that path.

[bfredl]

otherwise LGTM. thanks for looking into this.

[altermo]

I don't really favor the current PR so I thought a bit more about whether it would be better to have the namespaces themselves be scoped and this is what I came up with (only a proposal):

Each namespace would have some scopes. By default(if there are no scopes set) the namespace would fallback to the default behavior (which is that namespace-highlight won't be displayed anywhere and extmarks would be displayed everywhere).

If multiple scopes are set then they are a union instead of an intersection.

These are the scopes:

• Window-scoped: Only display in specific window.
• Buffer-scoped: Only display in specific buffer.
• Tab-scoped: Only display in specific tabpage.
• UI-scoped: Only display in specific UI.
• Global-scoped: Display everywhere.

The affected namespace elements would be: buffer-local-extmark(and any other future extmark) and namespace-highlight.

Some api for this (not final design):

• nvim_ns_add_{win,buf,tab,global}_scope: Adds the scope to namespace. Takes one (or zero for global) argument of bufnr/winid/tabpage.
• nvim_ns_get_scopes: Get the scopes.
• nvim_ns_del_{win,buf,tab,global}_scope: Deletes a scope of namespace. Takes one (or zero for global) argument of bufnr/winid/tabpage.
• nvim_get_ns_scoped: Gets all namespaces with specific scope. Takes some arguments.

Depreciated api functions and their replacements:

• nvim_get_hl_ns: Use nvim_get_ns_scoped to get global scoped namespaces and check if the namespace has higlight with nvim_get_hl.
• nvim_set_hl_ns: Use nvim_ns_add_global_scope.
• nvim_set_hl_ns_fast: I don't know a good replacement.
• nvim_win_set_hl_ns: Use nvim_ns_add_win_scope.

---

NOTE: I won't implement namespace-highlight in this PR (if the proposal is good to go).

If you're okay with this proposal then signal so that I can start working on it.

[bfredl]

Hmm, I'd still like to just get window-scoped extmarks merged first and then extend upon it as needed.

As far as I can tell this PR by itself is mostly forward-compatible with this extended proposal. The only difference I think is if we want to "mark" each individual extmark as scoped, or as you say, mark the entire namespace as scoped and then need to opt-in to it in specific windows.

nvim_ns_add_tabpage_scope would be a convenient short-hand for marking each individual window in that tab. convenient, but can be done as an addon. buffer-scoped would be mostly relevant for highlight namespaces, which we can consider but is separate work from this (and needs design discussion on its own. I have some other ideas how to rework those)

IMO I would first merge this pr pretty much as-is so that plugin authors can play with it. From there one we can gather feedback of what add-on features are mostly desired.

[altermo]

Then this PR is ready to merge.

[justinmk]

This extra flag seems kind of random. It allows opt-ing out ("ignore the scopes for the given namespace"). If you don't want an extmark to obey the properties of its namespace, why not create a separate namespace ?

Edit: #28469

[zeertzjq]

If opting out is not allowed, that means an extmark will be invisible until its namespace is added to a window, which is undesirable.

[justinmk]

an extmark will be invisible until its namespace is added to a window

Why must it be like that? If a namespace has no "window scopes", can't we assume it has "all windows" scope?

[justinmk]

But as namespaces don't have any struct and are just numbers, I don't know where to store this information.

That's mostly a consequence of just a single item of info being used currently. changing that to a struct would be fine if we go that path.

💯

Alternatively, we could use options/variables (b:/w:/t:) to manage scopes. For example, window-scoped namespaces could be controlled by w:nvim.ns.