From 4470bbbeb5594e9a7854b3427c0501a454a121dd Mon Sep 17 00:00:00 2001
From: Semih702 <semih702do@gmail.com>
Date: Thu, 20 Aug 2026 16:16:19 +0300
Subject: [PATCH] Use @codemirror/lang-go for the Go editor

Go was still on the legacy stream mode, which registers no `autocomplete`
language data, so the editor had no completion sources for Go at all.
`@codemirror/lang-go` adds local completion of parameters, variables and
same-file functions, plus a Lezer parser for highlighting and indentation.
---
 .../misc/CodeMirror/languageCompartment.ts    |  8 +--
 package.json                                  |  1 +
 .../CodeMirror/languageCompartment.test.ts    | 56 +++++++++++++++++++
 yarn.lock                                     | 20 +++++++
 4 files changed, 81 insertions(+), 4 deletions(-)
 create mode 100644 test/javascript/components/misc/CodeMirror/languageCompartment.test.ts

diff --git a/app/javascript/components/misc/CodeMirror/languageCompartment.ts b/app/javascript/components/misc/CodeMirror/languageCompartment.ts
index b3549cbf67..a5fb92eda4 100644
--- a/app/javascript/components/misc/CodeMirror/languageCompartment.ts
+++ b/app/javascript/components/misc/CodeMirror/languageCompartment.ts
@@ -27,6 +27,10 @@ export const loadLanguageCompartment = async (
       const { gleam } = await import('@exercism/codemirror-lang-gleam')
       return compartment.of(gleam())
     }
+    case 'go': {
+      const { go } = await import('@codemirror/lang-go')
+      return compartment.of(go())
+    }
     case 'javascript':
     case 'typescript': {
       const { javascript } = await import('@codemirror/lang-javascript')
@@ -158,10 +162,6 @@ export const loadLanguageCompartment = async (
       const { apl } = await import('@codemirror/legacy-modes/mode/apl')
       return compartment.of(StreamLanguage.define(apl))
     }
-    case 'go': {
-      const { go } = await import('@codemirror/legacy-modes/mode/go')
-      return compartment.of(StreamLanguage.define(go))
-    }
     case 'groovy': {
       const { groovy } = await import('@codemirror/legacy-modes/mode/groovy')
       return compartment.of(StreamLanguage.define(groovy))
diff --git a/package.json b/package.json
index 700a4f3cae..021f62ec94 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
     "@codemirror/commands": "^6.7.1",
     "@codemirror/lang-cpp": "^6.0.2",
     "@codemirror/lang-css": "^6.3.1",
+    "@codemirror/lang-go": "^6.0.1",
     "@codemirror/lang-java": "^6.0.1",
     "@codemirror/lang-javascript": "^6.2.1",
     "@codemirror/lang-php": "^6.0.1",
diff --git a/test/javascript/components/misc/CodeMirror/languageCompartment.test.ts b/test/javascript/components/misc/CodeMirror/languageCompartment.test.ts
new file mode 100644
index 0000000000..bfd31e0f99
--- /dev/null
+++ b/test/javascript/components/misc/CodeMirror/languageCompartment.test.ts
@@ -0,0 +1,56 @@
+import { EditorState } from '@codemirror/state'
+import type { CompletionSource } from '@codemirror/autocomplete'
+import { CompletionContext } from '@codemirror/autocomplete'
+import { syntaxTree } from '@codemirror/language'
+import { loadLanguageCompartment } from '@/components/misc/CodeMirror/languageCompartment'
+
+const GO_EXERCISE = [
+  'package main',
+  '',
+  'func Welcome(name string) string {',
+  '\treturn na',
+  '}',
+].join('\n')
+
+async function goState() {
+  return EditorState.create({
+    doc: GO_EXERCISE,
+    extensions: [await loadLanguageCompartment('go')],
+  })
+}
+
+// Candidates come from the sources a language registers as `autocomplete`
+// language data, which is what the legacy Go stream mode was missing.
+async function completionsAt(state: EditorState, pos: number) {
+  const sources = state.languageDataAt<CompletionSource>('autocomplete', pos)
+  const options = []
+
+  for (const source of sources) {
+    const result = await source(new CompletionContext(state, pos, false))
+
+    if (result) options.push(...result.options)
+  }
+
+  return options
+}
+
+test('go suggests names declared in the file', async () => {
+  const state = await goState()
+  const options = await completionsAt(state, GO_EXERCISE.indexOf('na\n') + 2)
+
+  expect(options).toContainEqual(
+    expect.objectContaining({ label: 'name', type: 'var' })
+  )
+})
+
+test('go parses without errors', async () => {
+  const errors: string[] = []
+
+  syntaxTree(await goState()).iterate({
+    enter: (node) => {
+      if (node.type.isError) errors.push(node.name)
+    },
+  })
+
+  expect(errors).toEqual([])
+})
diff --git a/yarn.lock b/yarn.lock
index 50a14353fe..bac92d84de 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1102,6 +1102,17 @@
     "@lezer/common" "^1.0.2"
     "@lezer/css" "^1.1.7"
 
+"@codemirror/lang-go@^6.0.1":
+  version "6.0.1"
+  resolved "https://registry.yarnpkg.com/@codemirror/lang-go/-/lang-go-6.0.1.tgz#598222c90f56eae28d11069c612ca64d0306b057"
+  integrity sha512-7fNvbyNylvqCphW9HD6WFnRpcDjr+KXX/FgqXy5H5ZS0eC5edDljukm/yNgYkwTsgp2busdod50AOTIy6Jikfg==
+  dependencies:
+    "@codemirror/autocomplete" "^6.0.0"
+    "@codemirror/language" "^6.6.0"
+    "@codemirror/state" "^6.0.0"
+    "@lezer/common" "^1.0.0"
+    "@lezer/go" "^1.0.0"
+
 "@codemirror/lang-html@^6.0.0":
   version "6.4.9"
   resolved "https://registry.yarnpkg.com/@codemirror/lang-html/-/lang-html-6.4.9.tgz#d586f2cc9c341391ae07d1d7c545990dfa069727"
@@ -1854,6 +1865,15 @@
     "@lezer/highlight" "^1.0.0"
     "@lezer/lr" "^1.0.0"
 
+"@lezer/go@^1.0.0":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/@lezer/go/-/go-1.0.1.tgz#3004b54f5e4c9719edcba98653f380baf8c0d1a2"
+  integrity sha512-xToRsYxwsgJNHTgNdStpcvmbVuKxTapV0dM0wey1geMMRc9aggoVyKgzYp41D2/vVOx+Ii4hmE206kvxIXBVXQ==
+  dependencies:
+    "@lezer/common" "^1.2.0"
+    "@lezer/highlight" "^1.0.0"
+    "@lezer/lr" "^1.3.0"
+
 "@lezer/highlight@^1.0.0", "@lezer/highlight@^1.1.3", "@lezer/highlight@^1.2.0":
   version "1.2.1"
   resolved "https://registry.yarnpkg.com/@lezer/highlight/-/highlight-1.2.1.tgz#596fa8f9aeb58a608be0a563e960c373cbf23f8b"