feat: integrate tree-sitter injections for known filetypes

## Details

Discussed here: #141

When using this plugin with multiple filetypes it would be nice if the
tree-sitter injection logic could be offloaded from the user and be
handled by the plugin. Especially when the way markdown would be
injected is likely to be the same for anyone that wants the plugin to
work within the filetype.

Turns out this is fairly straightforward using the
vim.treesitter.query.set API, and specifying the injections query name.
The only slight complication is that in order to be able to extend the
existing injections (instead of overwriting them) we need a way to get
the current injection query as a string. The only way I found to do that
is to pull the files associated with injections then read and append
them together. All other ways to get the query return different kinds of
objects that would need to be serialized back into a string.

I have made this part of the configuration users can modify with the top
level `injections` field. Currently a value is only specified for the
gitcommit filetype. Injections are only processed if this plugin is
meant to run on that filetype, meaning additional configurations can be
added without impacting users who do not use this plugin on multiple
file types.

Users are free to:

- modify the queries used
- disable the injection, by setting enabled to false
- add entirely new queries that are coupled to this plugin rather than needing to
  live in their global queries configuration

Author: MeanderingProgrammer

README.md

@@ -208,6 +208,20 @@ require('render-markdown').setup({
     log_level = 'error',
     -- Filetypes this plugin will run on
     file_types = { 'markdown' },
+    -- Out of the box language injections for known filetypes that allow markdown to be
+    -- interpreted in specified locations, see :h treesitter-language-injections
+    -- Set enabled to false in order to disable
+    injections = {
+        gitcommit = {
+            enabled = true,
+            query = [[
+                ((message) @injection.content
+                    (#set! injection.combined)
+                    (#set! injection.include-children)
+                    (#set! injection.language "markdown"))
+            ]],
+        },
+    },
     -- Vim modes that will show a rendered view of the markdown file
     -- All other modes will be uneffected by this plugin
     render_modes = { 'n', 'c' },

doc/render-markdown.txt

@@ -237,6 +237,20 @@ Full Default Configuration ~
         log_level = 'error',
         -- Filetypes this plugin will run on
         file_types = { 'markdown' },
+        -- Out of the box language injections for known filetypes that allow markdown to be
+        -- interpreted in specified locations, see :h treesitter-language-injections
+        -- Set enabled to false in order to disable
+        injections = {
+            gitcommit = {
+                enabled = true,
+                query = [[
+                    ((message) @injection.content
+                        (#set! injection.combined)
+                        (#set! injection.include-children)
+                        (#set! injection.language "markdown"))
+                ]],
+            },
+        },
         -- Vim modes that will show a rendered view of the markdown file
         -- All other modes will be uneffected by this plugin
         render_modes = { 'n', 'c' },

lua/render-markdown/core/treesitter.lua

@@ -0,0 +1,24 @@
+---@class render.md.TreeSitter
+local M = {}
+
+---@param language string
+---@param injection render.md.Injection?
+function M.inject(language, injection)
+    if injection == nil or not injection.enabled then
+        return
+    end
+
+    local query = ''
+    local files = vim.treesitter.query.get_files(language, 'injections')
+    for _, file in ipairs(files) do
+        local f = io.open(file, 'r')
+        if f ~= nil then
+            query = query .. f:read('*all') .. '\n'
+            f:close()
+        end
+    end
+    query = query .. injection.query
+    pcall(vim.treesitter.query.set, language, 'injections', query)
+end
+
+return M

lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local M = {}
 
 ---@private
 ---@type string
-M.version = '6.2.8'
+M.version = '6.2.9'
 
 function M.check()
     vim.health.start('render-markdown.nvim [version]')

lua/render-markdown/init.lua

@@ -18,6 +18,10 @@ local M = {}
 ---@field public top_pad? integer
 ---@field public bottom_pad? integer
 
+---@class (exact) render.md.UserInjection
+---@field public enabled? boolean
+---@field public query? string
+
 ---@class (exact) render.md.UserWindowOption
 ---@field public default? number|string|boolean
 ---@field public rendered? number|string|boolean
@@ -175,6 +179,7 @@ local M = {}
 ---@field public inline_query? string
 ---@field public log_level? render.md.config.LogLevel
 ---@field public file_types? string[]
+---@field public injections? table<string, render.md.UserInjection>
 ---@field public acknowledge_conflicts? boolean
 ---@field public latex? render.md.UserLatex
 ---@field public overrides? render.md.UserConfigOverrides
@@ -252,6 +257,20 @@ M.default_config = {
     log_level = 'error',
     -- Filetypes this plugin will run on
     file_types = { 'markdown' },
+    -- Out of the box language injections for known filetypes that allow markdown to be
+    -- interpreted in specified locations, see :h treesitter-language-injections
+    -- Set enabled to false in order to disable
+    injections = {
+        gitcommit = {
+            enabled = true,
+            query = [[
+                ((message) @injection.content
+                    (#set! injection.combined)
+                    (#set! injection.include-children)
+                    (#set! injection.language "markdown"))
+            ]],
+        },
+    },
     -- Vim modes that will show a rendered view of the markdown file
     -- All other modes will be uneffected by this plugin
     render_modes = { 'n', 'c' },

lua/render-markdown/state.lua

@@ -1,4 +1,5 @@
 local presets = require('render-markdown.presets')
+local treesitter = require('render-markdown.core.treesitter')
 local util = require('render-markdown.core.util')
 
 ---@type table<integer, render.md.BufferConfig>
@@ -44,6 +45,9 @@ function M.setup(default_config, user_config)
         M.markdown_quote_query = vim.treesitter.query.parse('markdown', config.markdown_quote_query)
         M.inline_query = vim.treesitter.query.parse('markdown_inline', config.inline_query)
     end)
+    for _, language in ipairs(M.file_types) do
+        treesitter.inject(language, config.injections[language])
+    end
 end
 
 function M.invalidate_cache()
@@ -420,6 +424,7 @@ function M.validate()
         inline_query = { config.inline_query, 'string' },
         log_level = one_of(config.log_level, { 'debug', 'error' }, {}, false),
         file_types = string_array(config.file_types, false),
+        injections = { config.injections, 'table' },
         acknowledge_conflicts = { config.acknowledge_conflicts, 'boolean' },
         latex = { config.latex, 'table' },
         overrides = { config.overrides, 'table' },
@@ -428,6 +433,14 @@ function M.validate()
 
     validate_buffer_config('render-markdown', config, false)
 
+    local injections = config.injections
+    for name, injection in pairs(injections) do
+        append_errors('render-markdown.injections.' .. name, injection, {
+            enabled = { injection.enabled, 'boolean' },
+            query = { injection.query, 'string' },
+        })
+    end
+
     local latex = config.latex
     append_errors('render-markdown.latex', latex, {
         enabled = { latex.enabled, 'boolean' },

lua/render-markdown/types.lua

@@ -7,6 +7,10 @@
 ---@field public top_pad integer
 ---@field public bottom_pad integer
 
+---@class (exact) render.md.Injection
+---@field public enabled boolean
+---@field public query string
+
 ---@class (exact) render.md.WindowOption
 ---@field public default number|string|boolean
 ---@field public rendered number|string|boolean
@@ -147,6 +151,7 @@
 ---@field public inline_query string
 ---@field public log_level render.md.config.LogLevel
 ---@field public file_types string[]
+---@field public injections table<string, render.md.Injection>
 ---@field public acknowledge_conflicts boolean
 ---@field public latex render.md.Latex
 ---@field public overrides render.md.ConfigOverrides