fix(treesitter): don't throw an error for missing injected langs

runtime/lua/vim/treesitter/language.lua

@@ -8,7 +8,8 @@ local M = {}
 --
 -- @param lang The language the parser should parse
 -- @param path Optionnal path the parser is located at
-function M.require_language(lang, path)
+-- @param silent Don't throw an error if language not found
+function M.require_language(lang, path, silent)
   if vim._ts_has_language(lang) then
     return true
   end
@@ -16,12 +17,23 @@ function M.require_language(lang, path)
     local fname = 'parser/' .. lang .. '.*'
     local paths = a.nvim_get_runtime_file(fname, false)
     if #paths == 0 then
+      if silent then
+        return false
+      end
+
       -- TODO(bfredl): help tag?
       error("no parser for '"..lang.."' language, see :help treesitter-parsers")
     end
     path = paths[1]
   end
-  vim._ts_add_language(path, lang)
+
+  if silent then
+    return pcall(function() vim._ts_add_language(path, lang) end)
+  else
+    vim._ts_add_language(path, lang)
+  end
+
+  return true
 end
 
 --- Inspects the provided language.

runtime/lua/vim/treesitter/languagetree.lua

@@ -121,23 +121,30 @@ function LanguageTree:parse()
   local seen_langs = {}
 
   for lang, injection_ranges in pairs(injections_by_lang) do
-    local child = self._children[lang]
+    local has_lang = language.require_language(lang, nil, true)
 
-    if not child then
-      child = self:add_child(lang)
+    -- Child language trees should just be ignored if not found, since
+    -- they can depend on the text of a node. Intermediate strings
+    -- would cause errors for unknown parsers.
+    if has_lang then
+      local child = self._children[lang]
+
+      if not child then
+        child = self:add_child(lang)
+      end
+
+      child:set_included_regions(injection_ranges)
+
+      local _, child_changes = child:parse()
+
+      -- Propagate any child changes so they are included in the
+      -- the change list for the callback.
+      if child_changes then
+        vim.list_extend(changes, child_changes)
+      end
+
+      seen_langs[lang] = true
     end
-
-    child:set_included_regions(injection_ranges)
-
-    local _, child_changes = child:parse()
-
-    -- Propagate any child changes so they are included in the
-    -- the change list for the callback.
-    if child_changes then
-      vim.list_extend(changes, child_changes)
-    end
-
-    seen_langs[lang] = true
   end
 
   for lang, _ in pairs(self._children) do

test/functional/lua/treesitter_spec.lua

@@ -22,6 +22,10 @@ describe('treesitter API', function()
     matches("Error executing lua: Failed to load parser: uv_dlopen: .+",
        pcall_err(exec_lua, "parser = vim.treesitter.require_language('borklang', 'borkbork.so')"))
 
+    -- Should not throw an error when silent
+    eq(false, exec_lua("return vim.treesitter.require_language('borklang', nil, true)"))
+    eq(false, exec_lua("return vim.treesitter.require_language('borklang', 'borkbork.so', true)"))
+
     eq("Error executing lua: .../language.lua:0: no parser for 'borklang' language, see :help treesitter-parsers",
        pcall_err(exec_lua, "parser = vim.treesitter.inspect_language('borklang')"))
   end)