feat(treesitter): add support for wasm parsers

Problem: Installing treesitter parser is hard (harder than
climbing to heaven).

Solution: Add optional support for wasm parsers with `wasmtime`.

Notes:

* Needs to be enabled by setting `ENABLE_WASMTIME` for tree-sitter and
  Neovim. Build with
  `make CMAKE_EXTRA_FLAGS=-DENABLE_WASMTIME=ON
  DEPS_CMAKE_FLAGS=-DENABLE_WASMTIME=ON`
* Adds optional Rust (obviously) and C11 dependencies.
* Wasmtime comes with a lot of features that can negatively affect
  Neovim performance due to library and symbol table size. Make sure to
  build with minimal features and full LTO.
* To reduce re-compilation times, install `sccache` and build with
  `RUSTC_WRAPPER=<path/to/sccache> make ...`

runtime/doc/treesitter.txt

@@ -51,6 +51,13 @@ treesitter parser for buffers with filetype `svg` or `xslt`, use: >lua
 
     vim.treesitter.language.register('xml', { 'svg', 'xslt' })
 <
+                                                    *treesitter-parsers-wasm*
+
+If Nvim is built with `ENABLE_WASMTIME`, then wasm parsers can also be
+loaded: >lua
+
+    vim.treesitter.language.add('python', { path = "/path/to/python.wasm" })
+<
 
 ==============================================================================
 TREESITTER TREES                                             *treesitter-tree*

runtime/lua/vim/treesitter/_meta.lua

@@ -72,7 +72,11 @@ vim._ts_get_language_version = function() end
 --- @param path string
 --- @param lang string
 --- @param symbol_name? string
-vim._ts_add_language = function(path, lang, symbol_name) end
+vim._ts_add_language_from_object = function(path, lang, symbol_name) end
+
+--- @param path string
+--- @param lang string
+vim._ts_add_language_from_wasm = function(path, lang) end
 
 ---@return integer
 vim._ts_get_minimum_language_version = function() end

runtime/lua/vim/treesitter/health.lua

@@ -28,6 +28,9 @@ function M.check()
       )
     end
   end
+
+  local can_wasm = vim._ts_add_language_from_wasm ~= nil
+  health.info(string.format('Can load WASM parsers: %s', tostring(can_wasm)))
 end
 
 return M

runtime/lua/vim/treesitter/language.lua

@@ -109,7 +109,14 @@ function M.add(lang, opts)
     path = paths[1]
   end
 
-  vim._ts_add_language(path, lang, symbol_name)
+  if vim.endswith(path, '.wasm') then
+    if not vim._ts_add_language_from_wasm then
+      error(string.format("Unable to load wasm parser '%s': not built with ENABLE_WASMTIME ", path))
+    end
+    vim._ts_add_language_from_wasm(path, lang)
+  else
+    vim._ts_add_language_from_object(path, lang, symbol_name)
+  end
   M.register(lang, filetype)
 end