feat(#2948): add custom decorators, :help nvim-tree-decorators (#2996)

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator

* feat(#2948): add UserDecorator

* feat(#2948): add UserDecorator

* feat(#2948): add Decorator node icon override

* feat(#2948): add nvim_tree.api.* node classes

* feat(#2948): extract _meta following nvim pattern

* feat(#2948): extract _meta following nvim pattern

* feat(#2948): add decorator registry and order

* feat(#2948): add decorator registry and order

* feat(#2948): tidy

* feat(#2948): document API

* feat(#2948): document API

* feat(#2948): document API

* feat(#2948): pass api nodes to user decorators

* feat(#2948): document API

* feat(#2948): use renderer.decorators to define order and register

* feat(#2948): tidy decorator args and complete documentation

* feat(#2948): decorator classes specified by prefix rather than suffix

* feat(#2948): improve doc

* feat(#2948): improve doc

* feat(#2948): improve doc

* feat(#2948): additional user decorator safety

* feat(#2948): create nvim_tree.api.decorator.UserDecorator class in API, add :extend

* feat(#2948): improve doc

lua/nvim-tree/_meta/api.lua

@@ -0,0 +1,51 @@
+---@meta
+error("Cannot require a meta file")
+
+--
+-- Nodes
+--
+
+---Base Node, Abstract
+---@class (exact) nvim_tree.api.Node
+---@field type "file" | "directory" | "link" uv.fs_stat.result.type
+---@field absolute_path string
+---@field executable boolean
+---@field fs_stat uv.fs_stat.result?
+---@field git_status GitNodeStatus?
+---@field hidden boolean
+---@field name string
+---@field parent nvim_tree.api.DirectoryNode?
+---@field diag_severity lsp.DiagnosticSeverity?
+
+---File
+---@class (exact) nvim_tree.api.FileNode: nvim_tree.api.Node
+---@field extension string
+
+---Directory
+---@class (exact) nvim_tree.api.DirectoryNode: nvim_tree.api.Node
+---@field has_children boolean
+---@field nodes nvim_tree.api.Node[]
+---@field open boolean
+
+---Root Directory
+---@class (exact) nvim_tree.api.RootNode: nvim_tree.api.DirectoryNode
+
+---Link mixin
+---@class (exact) nvim_tree.api.LinkNode
+---@field link_to string
+---@field fs_stat_target uv.fs_stat.result
+
+---File Link
+---@class (exact) nvim_tree.api.FileLinkNode: nvim_tree.api.FileNode, nvim_tree.api.LinkNode
+
+---DirectoryLink
+---@class (exact) nvim_tree.api.DirectoryLinkNode: nvim_tree.api.DirectoryNode, nvim_tree.api.LinkNode
+
+--
+-- Various Types
+--
+
+---A string for rendering, with optional highlight groups to apply to it
+---@class (exact) nvim_tree.api.HighlightedString
+---@field str string
+---@field hl string[]

lua/nvim-tree/_meta/api_decorator.lua

@@ -0,0 +1,54 @@
+---@meta
+error("Cannot require a meta file")
+
+local nvim_tree = { api = { decorator = {} } }
+
+---Highlight group range as per nvim-tree.renderer.highlight_*
+---@alias nvim_tree.api.decorator.HighlightRange "none" | "icon" | "name" | "all"
+
+---Icon position as per renderer.icons.*_placement
+---@alias nvim_tree.api.decorator.IconPlacement "none" | "before" | "after" | "signcolumn" | "right_align"
+
+---Names of builtin decorators or your decorator classes. Builtins are ordered lowest to highest priority.
+---@alias nvim_tree.api.decorator.Name "Git" | "Opened" | "Hidden" | "Modified" | "Bookmarks" | "Diagnostics" | "Copied" | "Cut" | nvim_tree.api.decorator.UserDecorator
+
+---Custom decorator, see :help nvim-tree-decorators
+---
+---@class (exact) nvim_tree.api.decorator.UserDecorator
+---@field protected enabled boolean
+---@field protected highlight_range nvim_tree.api.decorator.HighlightRange
+---@field protected icon_placement nvim_tree.api.decorator.IconPlacement
+nvim_tree.api.decorator.UserDecorator = {}
+
+---Create your decorator class
+---
+function nvim_tree.api.decorator.UserDecorator:extend() end
+
+---Abstract: no-args constructor must be implemented and will be called once per tree render.
+---Must set all fields.
+---
+function nvim_tree.api.decorator.UserDecorator:new() end
+
+---Abstract: optionally implement to set the node's icon
+---
+---@param node nvim_tree.api.Node
+---@return nvim_tree.api.HighlightedString? icon_node
+function nvim_tree.api.decorator.UserDecorator:icon_node(node) end
+
+---Abstract: optionally implement to provide icons and the highlight groups for your icon_placement.
+---
+---@param node nvim_tree.api.Node
+---@return nvim_tree.api.HighlightedString[]? icons
+function nvim_tree.api.decorator.UserDecorator:icons(node) end
+
+---Abstract: optionally implement to provide one highlight group to apply to your highlight_range.
+---
+---@param node nvim_tree.api.Node
+---@return string? highlight_group
+function nvim_tree.api.decorator.UserDecorator:highlight_group(node) end
+
+---Define a sign. This should be called in the constructor.
+---
+---@protected
+---@param icon nvim_tree.api.HighlightedString?
+function nvim_tree.api.decorator.UserDecorator:define_sign(icon) end