Fix workspace initialization

Closes GH-27.

Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>
Reviewed-by: Titus Wormer <tituswormer@gmail.com>

lib/index.js

@@ -162,6 +162,7 @@ export function configureUnifiedLanguageServer(
 ) {
   /** @type {Set<string>} */
   const workspaces = new Set()
+  let hasWorkspaceFolderCapability = false
 
   /**
    * Process various LSP text documents using unified and send back the
@@ -325,22 +326,10 @@ export function configureUnifiedLanguageServer(
       workspaces.add(event.rootUri)
     }
 
-    if (
+    hasWorkspaceFolderCapability = Boolean(
       event.capabilities.workspace &&
-      event.capabilities.workspace.workspaceFolders
-    ) {
-      connection.workspace.onDidChangeWorkspaceFolders(function (event) {
-        for (const workspace of event.removed) {
-          workspaces.delete(workspace.uri)
-        }
-
-        for (const workspace of event.added) {
-          workspaces.add(workspace.uri)
-        }
-
-        checkDocuments(...documents.all())
-      })
-    }
+        event.capabilities.workspace.workspaceFolders
+    )
 
     return {
       capabilities: {
@@ -350,13 +339,29 @@ export function configureUnifiedLanguageServer(
           codeActionKinds: [CodeActionKind.QuickFix],
           resolveProvider: true
         },
-        workspace: {
-          workspaceFolders: {supported: true, changeNotifications: true}
-        }
+        workspace: hasWorkspaceFolderCapability
+          ? {workspaceFolders: {supported: true, changeNotifications: true}}
+          : undefined
       }
     }
   })
 
+  connection.onInitialized(() => {
+    if (hasWorkspaceFolderCapability) {
+      connection.workspace.onDidChangeWorkspaceFolders((event) => {
+        for (const workspace of event.removed) {
+          workspaces.delete(workspace.uri)
+        }
+
+        for (const workspace of event.added) {
+          workspaces.add(workspace.uri)
+        }
+
+        checkDocuments(...documents.all())
+      })
+    }
+  })
+
   connection.onDocumentFormatting(async (event) => {
     const document = documents.get(event.textDocument.uri)
 

test/index.js

@@ -15,7 +15,7 @@ import * as exports from 'unified-language-server'
 
 const sleep = promisify(setTimeout)
 
-const delay = process.platform === 'win32' ? 600 : 300
+const delay = process.platform === 'win32' ? 800 : 400
 const timeout = 10_000
 
 test('exports', (t) => {
@@ -51,6 +51,61 @@ test('`initialize`', async (t) => {
   assert(promise.stdout)
   promise.stdout.on('data', () => setImmediate(() => stdin.end()))
 
+  try {
+    await promise
+    t.fail('should reject')
+  } catch (error) {
+    const exception = /** @type {ExecError} */ (error)
+    const messages = fromMessages(exception.stdout)
+    t.equal(messages.length, 1, 'should emit messages')
+    const parameters = messages[0].result
+
+    t.deepEqual(
+      parameters,
+      {
+        capabilities: {
+          textDocumentSync: 1,
+          documentFormattingProvider: true,
+          codeActionProvider: {
+            codeActionKinds: ['quickfix'],
+            resolveProvider: true
+          }
+        }
+      },
+      'should emit an introduction on `initialize`'
+    )
+  }
+
+  t.end()
+})
+
+test('`initialize` workspace capabilities', async (t) => {
+  const stdin = new PassThrough()
+  const promise = execa('node', ['remark.js', '--stdio'], {
+    cwd: fileURLToPath(new URL('.', import.meta.url)),
+    input: stdin,
+    timeout
+  })
+
+  stdin.write(
+    toMessage({
+      method: 'initialize',
+      id: 0,
+      /** @type {import('vscode-languageserver').InitializeParams} */
+      params: {
+        processId: null,
+        rootUri: null,
+        capabilities: {workspace: {workspaceFolders: true}},
+        workspaceFolders: null
+      }
+    })
+  )
+
+  await sleep(delay)
+
+  assert(promise.stdout)
+  promise.stdout.on('data', () => setImmediate(() => stdin.end()))
+
   try {
     await promise
     t.fail('should reject')
@@ -754,9 +809,6 @@ test('`textDocument/codeAction` (and diagnostics)', async (t) => {
               codeActionProvider: {
                 codeActionKinds: ['quickfix'],
                 resolveProvider: true
-              },
-              workspace: {
-                workspaceFolders: {supported: true, changeNotifications: true}
               }
             }
           }
@@ -1066,6 +1118,16 @@ test('`workspace/didChangeWorkspaceFolders`', async (t) => {
 
   await sleep(delay)
 
+  stdin.write(
+    toMessage({
+      method: 'initialized',
+      /** @type {import('vscode-languageserver').InitializedParams} */
+      params: {}
+    })
+  )
+
+  await sleep(delay)
+
   const otherCwd = new URL('./folder/', processCwd)
 
   stdin.write(