feat(comment): allow commentstring to be determined from node metadata

**Problem:** Some weird languages have different comment syntax
depending on the location in the code, and we do not have a way to
determine the correct `commentstring` for these special cases.

**Solution:** Allow queries to specify `commentstring` values in
metadata, allowing users/`nvim-treesitter` to provide a better
commenting experience without hugely increasing the scope of the code in
core.

2 files changed, 13 insertions, 0 deletions

diff --git a/runtime/lua/vim/_comment.lua b/runtime/lua/vim/_comment.lua
index de7f62632c..57fd3d73d6 100644
--- a/runtime/lua/vim/_comment.lua
+++ b/runtime/lua/vim/_comment.lua
@@ -19,6 +19,18 @@ local function get_commentstring(ref_position)
   local row, col = ref_position[1] - 1, ref_position[2]
   local ref_range = { row, col, row, col + 1 }
 
+  -- Get 'commentstring' from tree-sitter captures' metadata.
+  -- Traverse backwards to prefer narrower captures.
+  local caps = vim.treesitter.get_captures_at_pos(0, row, col)
+  for i = #caps, 1, -1 do
+    local id, metadata = caps[i].id, caps[i].metadata
+    local md_cms = metadata['bo.commentstring'] or metadata[id] and metadata[id]['bo.commentstring']
+
+    if md_cms then
+      return md_cms
+    end
+  end
+
   -- - Get 'commentstring' from the deepest LanguageTree which both contains
   --   reference range and has valid 'commentstring' (meaning it has at least
   --   one associated 'filetype' with valid 'commentstring').
diff --git a/runtime/lua/vim/treesitter/query.lua b/runtime/lua/vim/treesitter/query.lua
index 1b72151aac..17088ac0eb 100644
--- a/runtime/lua/vim/treesitter/query.lua
+++ b/runtime/lua/vim/treesitter/query.lua
@@ -608,6 +608,7 @@ predicate_handlers['any-vim-match?'] = predicate_handlers['any-match?']
 ---@class vim.treesitter.query.TSMetadata
 ---@field range? Range
 ---@field conceal? string
+---@field bo.commentstring? string
 ---@field [integer]? vim.treesitter.query.TSMetadata
 ---@field [string]? integer|string