Support for LSP completion requests

jvm/src/main/scala/kiama/util/Server.scala

@@ -411,6 +411,13 @@ trait LanguageService[N] {
   def getSymbols(source: Source): Option[Vector[DocumentSymbol]] =
     None
 
+  /**
+   * Return the corresponding completion items of the symbol at the
+   * given position (if any).
+   */
+  def getCompletion(position: Position): Option[Vector[CompletionItem]] =
+    None
+
   /**
    * The parameters are passed as an array, potentially containing gson.Json objects or primitives.
    * The first argument is required to be { uri: String } and used to obtain the source.
@@ -454,6 +461,7 @@ class Services[N, C <: Config, M <: Message](
       serverCapabilities.setDocumentSymbolProvider(true)
       serverCapabilities.setHoverProvider(true)
       serverCapabilities.setReferencesProvider(true)
+      serverCapabilities.setCompletionProvider(new CompletionOptions)
       serverCapabilities.setTextDocumentSync(TextDocumentSyncKind.Full)
       new InitializeResult(serverCapabilities)
     }
@@ -608,6 +616,18 @@ class Services[N, C <: Config, M <: Message](
           ) yield locations.toArray
         ).getOrElse(null)
     )
+
+  @JsonNotification("textDocument/completion")
+  def completion(params: CompletionParams): CompletableFuture[Array[CompletionItem]] =
+    CompletableFutures.computeAsync(
+      (_: CancelChecker) =>
+        (
+          for (
+            position <- positionOfNotification(params.getTextDocument, params.getPosition);
+            completion <- server.getCompletion(position)
+          ) yield completion.toArray
+        ).getOrElse(null)
+    )
 
   @JsonNotification("workspace/executeCommand")
   def commands(params: ExecuteCommandParams): CompletableFuture[Any] =