Validate CodeMirror modes

.gitmodules

@@ -791,3 +791,6 @@
 [submodule "vendor/grammars/language-babel"]
 	path = vendor/grammars/language-babel
 	url = https://github.com/github-linguist/language-babel
+[submodule "vendor/CodeMirror"]
+	path = vendor/CodeMirror
+	url = https://github.com/codemirror/CodeMirror

lib/linguist/language.rb

@@ -402,6 +402,9 @@ module Linguist
 
     # Public: Get CodeMirror mode
     #
+    # Maps to a directory in the `mode/` source code.
+    #   https://github.com/codemirror/CodeMirror/tree/master/mode
+    #
     # Examples
     #
     #  # => "nil"

lib/linguist/languages.yml

@@ -1083,7 +1083,7 @@ Ecere Projects:
   - ".epj"
   tm_scope: source.json
   ace_mode: json
-  codemirror_mode: json
+  codemirror_mode: javascript
   codemirror_mime_mode: application/json
   language_id: 98
 Eiffel:
@@ -1632,7 +1632,7 @@ HTML:
   type: markup
   tm_scope: text.html.basic
   ace_mode: html
-  codemirror_mode: html
+  codemirror_mode: htmlembedded
   codemirror_mime_mode: text/html
   color: "#e44b23"
   aliases:
@@ -2118,7 +2118,7 @@ KiCad:
 Kit:
   type: markup
   ace_mode: html
-  codemirror_mode: html
+  codemirror_mode: htmlembedded
   codemirror_mime_mode: text/html
   extensions:
   - ".kit"
@@ -2133,7 +2133,7 @@ Kotlin:
   - ".kts"
   tm_scope: source.Kotlin
   ace_mode: text
-  codemirror_mode: kotlin
+  codemirror_mode: clike
   codemirror_mime_mode: text/x-kotlin
   language_id: 189
 LFE:
@@ -2419,7 +2419,7 @@ MTML:
   - ".mtml"
   tm_scope: text.html.basic
   ace_mode: html
-  codemirror_mode: html
+  codemirror_mode: htmlembedded
   codemirror_mime_mode: text/html
   language_id: 218
 MUF:
@@ -4262,7 +4262,7 @@ TypeScript:
   - ".tsx"
   tm_scope: source.ts
   ace_mode: typescript
-  codemirror_mode: typescript
+  codemirror_mode: javascript
   codemirror_mime_mode: text/x-typescript
   language_id: 378
 Unified Parallel C:

test/test_language.rb

@@ -452,6 +452,14 @@ class TestLanguage < Minitest::Test
     assert missing.empty?, message
   end
 
+  def test_valid_codemirror_mode
+    Language.all.each do |language|
+      if mode = language.codemirror_mode
+        assert File.exist?(File.expand_path("../../vendor/CodeMirror/mode/#{mode}", __FILE__)), "#{mode} isn't a valid CodeMirror mode"
+      end
+    end
+  end
+
   def test_all_popular_languages_exist
     popular = YAML.load(File.read(File.expand_path("../../lib/linguist/popular.yml", __FILE__)))