feat: provide in-process lsp completion source

## Details

Rather than requiring a source to be added to completion engine by user
create an in-process LSP that provides completion capabilities to
whatever engine the user happens to be running.

That way the setup is the same for both `nvim-cmp` & `blink.cmp` and
more minimal since LSPs are enabled by default by completion engines.

Idea for this and the implementation came from [saecki/crates.nvim](https://github.com/saecki/crates.nvim)
and seems to have no downside. Can add more capabilities in the future
though I don't think there's a strong use case for this yet.

To avoid breaking existing `nvim-cmp` users we add opt-in configurations
for `lsp` & `coq`, and if neither of these are set we continue to
register the `nvim-cmp` source, keeping default behavior effectively unchanged.

To enable this feature set:

```lua
require('render-markdown').setup({
    completions = { lsp = { enabled = true } },
})
```

Since having multiple of these sources running at once would result in
duplicate suggestions we only setup the first one that is enabled in the
order `lsp` -> `coq` -> `cmp`.

Author: MeanderingProgrammer

Diff for: README.md

@@ -123,6 +123,17 @@ use({
 This plugin provides completions for both checkboxes and callouts provided you follow
 the relevant setup.
 
+## in-process lsp
+
+The recommended way of getting completions from this plugin. Only requires being
+enabled with no additional configuration, assuming you have general LSP completions.
+
+```lua
+require('render-markdown').setup({
+    completions = { lsp = { enabled = true } },
+})
+```
+
 ## nvim-cmp
 
 ```lua
@@ -154,7 +165,9 @@ require('blink.cmp').setup({
 ## coq_nvim
 
 ```lua
-require('render-markdown.integ.coq').setup()
+require('render-markdown').setup({
+    completions = { coq = { enabled = true } },
+})
 ```
 
 # Setup
@@ -263,6 +276,12 @@ require('render-markdown').setup({
         -- Called after plugin clears a buffer.
         clear = function() end,
     },
+    completions = {
+        -- Settings for coq_nvim completions source
+        coq = { enabled = false },
+        -- Settings for in-process language server completions
+        lsp = { enabled = false },
+    },
     -- Useful context to have when evaluating values.
     -- | level    | the number of '#' in the heading marker         |
     -- | sections | for each level how deeply nested the heading is |
@@ -1489,6 +1508,14 @@ The table below shows all the highlight groups with their default link
 - [Markdown Ecosystem](doc/markdown-ecosystem.md): Information about other `markdown`
   related plugins and how they co-exist
 
+# Acknowledgments
+
+- [headlines.nvim](https://github.com/lukas-reineke/headlines.nvim): The plugin that
+  inspired me to create this one and whose implementation I used as a reference for
+  the original version
+- [crates.nvim](https://github.com/Saecki/crates.nvim): Used the in-process lsp implementation
+  as an awesome reference [lsp.lua](https://github.com/saecki/crates.nvim/blob/main/lua/crates/lsp.lua)
+
 <!-- panvimdoc-ignore-start -->
 
 # Donate

Diff for: doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*           For 0.10.0          Last change: 2025 March 03
+*render-markdown.txt*           For 0.10.0          Last change: 2025 March 04
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*
@@ -12,6 +12,7 @@ Table of Contents                          *render-markdown-table-of-contents*
   - packer.nvim                          |render-markdown-install-packer.nvim|
 5. Commands                                         |render-markdown-commands|
 6. Completions                                   |render-markdown-completions|
+  - in-process lsp                |render-markdown-completions-in-process-lsp|
   - nvim-cmp                            |render-markdown-completions-nvim-cmp|
   - blink.cmp                          |render-markdown-completions-blink.cmp|
   - coq_nvim                            |render-markdown-completions-coq_nvim|
@@ -34,6 +35,7 @@ Table of Contents                          *render-markdown-table-of-contents*
   - obsidian.nvim                         |render-markdown-info-obsidian.nvim|
   - Images                                       |render-markdown-info-images|
   - Additional                               |render-markdown-info-additional|
+10. Acknowledgments                          |render-markdown-acknowledgments|
 
 ==============================================================================
 1. render-markdown.nvim                 *render-markdown-render-markdown.nvim*
@@ -180,6 +182,19 @@ This plugin provides completions for both checkboxes and callouts provided you
 follow the relevant setup.
 
 
+IN-PROCESS LSP                    *render-markdown-completions-in-process-lsp*
+
+The recommended way of getting completions from this plugin. Only requires
+being enabled with no additional configuration, assuming you have general LSP
+completions.
+
+>lua
+    require('render-markdown').setup({
+        completions = { lsp = { enabled = true } },
+    })
+<
+
+
 NVIM-CMP                                *render-markdown-completions-nvim-cmp*
 
 >lua
@@ -213,7 +228,9 @@ BLINK.CMP                              *render-markdown-completions-blink.cmp*
 COQ_NVIM                                *render-markdown-completions-coq_nvim*
 
 >lua
-    require('render-markdown.integ.coq').setup()
+    require('render-markdown').setup({
+        completions = { coq = { enabled = true } },
+    })
 <
 
 
@@ -324,6 +341,12 @@ Default Configuration ~
             -- Called after plugin clears a buffer.
             clear = function() end,
         },
+        completions = {
+            -- Settings for coq_nvim completions source
+            coq = { enabled = false },
+            -- Settings for in-process language server completions
+            lsp = { enabled = false },
+        },
         -- Useful context to have when evaluating values.
         -- | level    | the number of '#' in the heading marker         |
         -- | sections | for each level how deeply nested the heading is |
@@ -1573,6 +1596,16 @@ ADDITIONAL                                   *render-markdown-info-additional*
 - Markdown Ecosystem <doc/markdown-ecosystem.md>: Information about other `markdown`
     related plugins and how they co-exist
 
+
+==============================================================================
+10. Acknowledgments                          *render-markdown-acknowledgments*
+
+- headlines.nvim <https://github.com/lukas-reineke/headlines.nvim>: The plugin that
+    inspired me to create this one and whose implementation I used as a reference for
+    the original version
+- crates.nvim <https://github.com/Saecki/crates.nvim>: Used the in-process lsp implementation
+    as an awesome reference lsp.lua <https://github.com/saecki/crates.nvim/blob/main/lua/crates/lsp.lua>
+
 Generated by panvimdoc <https://github.com/kdheepak/panvimdoc>
 
 vim:tw=78:ts=8:noet:ft=help:norl:

Diff for: lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.0.19'
+M.version = '8.0.20'
 
 function M.check()
     M.start('version')

Diff for: lua/render-markdown/init.lua

@@ -19,6 +19,13 @@ local M = {}
 ---@field [1] string text
 ---@field [2] string|string[] highlights
 
+---@class (exact) render.md.UserCompletion
+---@field public enabled? boolean
+
+---@class (exact) render.md.UserCompletions
+---@field public coq? render.md.UserCompletion
+---@field public lsp? render.md.UserCompletion
+
 ---@class (exact) render.md.CallbackContext
 ---@field public buf integer
 
@@ -318,6 +325,7 @@ local M = {}
 ---@field public change_events? string[]
 ---@field public injections? table<string, render.md.UserInjection>
 ---@field public on? render.md.UserCallback
+---@field public completions? render.md.UserCompletions
 ---@field public overrides? render.md.UserConfigOverrides
 ---@field public custom_handlers? table<string, render.md.Handler>
 
@@ -412,6 +420,12 @@ M.default_config = {
         -- Called after plugin clears a buffer.
         clear = function() end,
     },
+    completions = {
+        -- Settings for coq_nvim completions source
+        coq = { enabled = false },
+        -- Settings for in-process language server completions
+        lsp = { enabled = false },
+    },
     -- Useful context to have when evaluating values.
     -- | level    | the number of '#' in the heading marker         |
     -- | sections | for each level how deeply nested the heading is |

Diff for: lua/render-markdown/integ/blink.lua

@@ -33,7 +33,6 @@ function Source:get_completions(context, callback)
         callback({
             is_incomplete_forward = false,
             is_incomplete_backward = false,
-            context = context,
             items = items,
         })
     end

Diff for: lua/render-markdown/integ/cmp.lua

@@ -30,10 +30,17 @@ function Source:complete(params, callback)
 end
 
 ---@class render.md.integ.Cmp
-local M = {}
+---@field private registered boolean
+local M = {
+    registered = false,
+}
 
----Should only be called from plugin directory
+---Should only be called from manager on initial buffer attach
 function M.setup()
+    if M.registered then
+        return
+    end
+    M.registered = true
     local has_cmp, cmp = pcall(require, 'cmp')
     if not has_cmp then
         return

Diff for: lua/render-markdown/integ/coq.lua

@@ -1,8 +1,34 @@
 local source = require('render-markdown.integ.source')
 
+---@class render.md.cmp.Coq
+---@field private registered boolean
+local M = {
+    registered = false,
+}
+
+---Should only be called from manager on initial buffer attach
+---or by a user to enable the integration
+function M.setup()
+    if M.registered then
+        return
+    end
+    M.registered = true
+    local has_coq = pcall(require, 'coq')
+    if not has_coq then
+        return
+    end
+    ---@type table<integer, table>
+    COQsources = COQsources or {}
+    COQsources[M.new_uid(COQsources)] = {
+        name = 'markdown',
+        fn = M.complete,
+    }
+end
+
+---@private
 ---@param map table<integer, table>
 ---@return integer
-local function new_uid(map)
+function M.new_uid(map)
     ---@type integer|nil
     local key = nil
     while true do
@@ -14,9 +40,10 @@ local function new_uid(map)
     end
 end
 
+---@private
 ---@param args { line: string, pos: { [1]: integer, [2]: integer } }
 ---@param callback fun(response?: lsp.CompletionItem[])
-local function complete(args, callback)
+function M.complete(args, callback)
     ---@return lsp.CompletionItem[]?
     local function get_items()
         if not source.enabled() then
@@ -31,21 +58,4 @@ local function complete(args, callback)
     callback(get_items())
 end
 
----@class render.md.cmp.Coq
-local M = {}
-
----Should only be called by a user to enable the integration
-function M.setup()
-    local has_coq = pcall(require, 'coq')
-    if not has_coq then
-        return
-    end
-    ---@type table<integer, table>
-    COQsources = COQsources or {}
-    COQsources[new_uid(COQsources)] = {
-        name = 'markdown',
-        fn = complete,
-    }
-end
-
 return M

Diff for: lua/render-markdown/integ/lsp.lua

@@ -0,0 +1,83 @@
+local source = require('render-markdown.integ.source')
+
+---@class render.md.integ.Lsp
+local M = {}
+
+---Should only be called from manager on initial buffer attach
+function M.setup()
+    local name = 'render-markdown'
+    ---@type vim.lsp.ClientConfig
+    local config = {
+        name = name,
+        cmd = M.server,
+    }
+    ---@type vim.lsp.start.Opts
+    local opts = {
+        bufnr = 0,
+        reuse_client = function(lsp_client, lsp_config)
+            return lsp_client.name == lsp_config.name
+        end,
+    }
+    vim.lsp.start(config, opts)
+end
+
+---@private
+---@param dispatchers vim.lsp.rpc.Dispatchers
+---@return vim.lsp.rpc.PublicClient
+function M.server(dispatchers)
+    local id = 0
+    local closing = false
+
+    ---@type vim.lsp.rpc.PublicClient
+    return {
+        request = function(method, params, callback)
+            if method == 'initialize' then
+                callback(nil, {
+                    capabilities = {
+                        completionProvider = {
+                            triggerCharacters = source.trigger_characters(),
+                        },
+                    },
+                })
+            elseif method == 'textDocument/completion' then
+                callback(nil, M.completions(params))
+            elseif method == 'shutdown' then
+                callback(nil, nil)
+            end
+            id = id + 1
+            return true, id
+        end,
+        notify = function(method)
+            if method == 'exit' then
+                -- code 0 (success), signal 15 (SIGTERM)
+                dispatchers.on_exit(0, 15)
+            end
+            return true
+        end,
+        is_closing = function()
+            return closing
+        end,
+        terminate = function()
+            closing = true
+        end,
+    }
+end
+
+---@private
+---@param params lsp.CompletionParams
+---@return lsp.CompletionList?
+function M.completions(params)
+    -- lsp position: (0,0)-indexed
+    local cursor = params.position
+    local items = source.items(0, cursor.line, cursor.character)
+    if items == nil then
+        return nil
+    end
+    ---@type lsp.CompletionList
+    return {
+        isIncomplete = false,
+        items = items,
+    }
+end
+
+return M

Diff for: lua/render-markdown/integ/source.lua

@@ -22,11 +22,15 @@ function M.trigger_characters()
     return { '-', '*', '+', '>', ' ' }
 end
 
----@param buf integer
+---@param buf integer 0 for current buffer
 ---@param row integer 0-indexed
 ---@param col integer 0-indexed
 ---@return lsp.CompletionItem[]?
 function M.items(buf, row, col)
+    if buf == 0 then
+        buf = util.current('buf')
+    end
+
     local has_parser, parser = pcall(vim.treesitter.get_parser, buf)
     if not has_parser or parser == nil then
         return nil

Diff for: lua/render-markdown/manager.lua

@@ -87,6 +87,13 @@ function M.attach(buf)
 
     local config = state.get(buf)
     state.on.attach({ buf = buf })
+    if state.completions.lsp.enabled then
+        require('render-markdown.integ.lsp').setup()
+    elseif state.completions.coq.enabled then
+        require('render-markdown.integ.coq').setup()
+    else
+        require('render-markdown.integ.cmp').setup()
+    end
 
     local events = { 'BufWinEnter', 'BufLeave', 'CmdlineChanged', 'CursorHold', 'CursorMoved', 'WinScrolled' }
     local change_events = { 'DiffUpdated', 'ModeChanged', 'TextChanged' }