Improve completion triggering + add parameter hints (signature help)

Public/js/app.js

@@ -118,6 +118,38 @@ export class App {
           } else {
             promise.fulfill();
           }
+          break;
+        case "signatureHelp": {
+          if (!promise) {
+            return;
+          }
+          if (response.value && response.value.signatures) {
+            const signatures = response.value.signatures.map((sig) => ({
+              label: sig.label,
+              documentation: sig.documentation
+                ? sig.documentation.value ?? sig.documentation
+                : undefined,
+              parameters: (sig.parameters || []).map((parameter) => ({
+                label: parameter.label,
+                documentation: parameter.documentation
+                  ? parameter.documentation.value ?? parameter.documentation
+                  : undefined,
+              })),
+              activeParameter: sig.activeParameter,
+            }));
+            promise.fulfill({
+              value: {
+                signatures: signatures,
+                activeSignature: response.value.activeSignature ?? 0,
+                activeParameter: response.value.activeParameter ?? 0,
+              },
+              dispose: () => {},
+            });
+          } else {
+            promise.fulfill();
+          }
+          break;
+        }
         case "diagnostics":
           this.updateLanguageServerStatus(true);
           this.editor.clearMarkers();
@@ -229,6 +261,21 @@ export class App {
       return promise;
     };
 
+    this.editor.onsignaturehelp = (position) => {
+      if (!languageServer.isReady) {
+        return;
+      }
+
+      sequence++;
+      const row = position.lineNumber - 1;
+      const column = position.column - 1;
+      languageServer.requestSignatureHelp(sequence, row, column);
+
+      return new Promise((fulfill, reject) => {
+        promises[sequence] = { fulfill: fulfill, reject: reject };
+      });
+    };
+
     this.editor.focus();
     this.editor.scrollToBottm();
 

Public/js/editor.js

@@ -33,16 +33,40 @@ export class Editor {
       },
     });
 
+    // Trigger completion after "." as well as after these characters, which
+    // commonly start a new identifier/argument in Swift.
     monaco.languages.registerCompletionItemProvider("swift", {
-      triggerCharacters: ["."],
+      triggerCharacters: [".", "(", ":", "<", " ", ","],
       provideCompletionItems: (model, position) => {
         return this.oncompletion(position);
       },
     });
 
+    // Parameter hints (Xcode-style): pops up the function signature with the
+    // active argument highlighted when typing "(" or ",".
+    monaco.languages.registerSignatureHelpProvider("swift", {
+      signatureHelpTriggerCharacters: ["(", ","],
+      signatureHelpRetriggerCharacters: [",", ")"],
+      provideSignatureHelp: (model, position) => {
+        return this.onsignaturehelp(position);
+      },
+    });
+
+    // Explicit Ctrl+Space to trigger completion, like Xcode. (Cmd+Space is
+    // taken by Spotlight on macOS, so bind WinCtrl = the Control key.)
+    this.editor.addAction({
+      id: "trigger-suggest",
+      label: "Trigger Suggest",
+      keybindings: [monaco.KeyMod.WinCtrl | monaco.KeyCode.Space],
+      run: (ed) => {
+        ed.trigger("keyboard", "editor.action.triggerSuggest", {});
+      },
+    });
+
     this.onchange = () => {};
     this.onhover = () => {};
     this.oncompletion = () => {};
+    this.onsignaturehelp = () => {};
     this.onaction = () => {};
   }
 

Public/js/language_server.js

@@ -58,6 +58,17 @@ export class LanguageServer {
     this.connection.send(JSON.stringify(params));
   }
 
+  requestSignatureHelp(sequence, row, column) {
+    const params = {
+      method: "signatureHelp",
+      id: sequence,
+      row: row,
+      column: column,
+      sessionId: this.sessionId,
+    };
+    this.connection.send(JSON.stringify(params));
+  }
+
   requestFormat(code) {
     const params = {
       method: "format",

Public/js/main_view.js

@@ -28,6 +28,12 @@ export class MainView {
       wordWrap: "on",
       wrappingIndent: "indent",
       tabSize: 2,
+      // Make completion pop up while typing (not only after "."), with no
+      // delay, and allow Tab to accept. Ctrl+Space still triggers it manually.
+      quickSuggestions: { other: true, comments: false, strings: false },
+      quickSuggestionsDelay: 0,
+      suggestOnTriggerCharacters: true,
+      tabCompletion: "on",
       lightbulb: {
         enabled: true,
       },