ayazhafiz · Dec 26, 2019 · Dec 26, 2019 · Jan 18, 2020 · Jan 18, 2020 · Jan 23, 2020
diff --git a/packages/language-service/src/expression_diagnostics.ts b/packages/language-service/src/expression_diagnostics.ts
@@ -12,7 +12,7 @@ import * as ts from 'typescript';
 import {AstType, ExpressionDiagnosticsContext, TypeDiagnostic} from './expression_type';
 import {BuiltinType, Definition, Span, Symbol, SymbolDeclaration, SymbolQuery, SymbolTable} from './symbols';
 import {Diagnostic} from './types';
-import {getPathToNodeAtPosition} from './utils';
+import {findOutputBinding, getPathToNodeAtPosition} from './utils';
 
 export interface DiagnosticTemplateInfo {
   fileName?: string;
@@ -193,26 +193,51 @@ function refinedVariableType(
   return query.getBuiltinType(BuiltinType.Any);
 }
 
-function getEventDeclaration(info: DiagnosticTemplateInfo, path: TemplateAstPath) {
-  let result: SymbolDeclaration[] = [];
-  if (path.tail instanceof BoundEventAst) {
-    // TODO: Determine the type of the event parameter based on the Observable<T> or EventEmitter<T>
-    // of the event.
-    result = [{name: '$event', kind: 'variable', type: info.query.getBuiltinType(BuiltinType.Any)}];
+function getEventDeclaration(
+    info: DiagnosticTemplateInfo, path: TemplateAstPath): SymbolDeclaration|undefined {
+  const event = path.tail;
+  if (!(event instanceof BoundEventAst)) {
+    // No event available in this context.
+    return;
   }
-  return result;
+
+  const genericEvent: SymbolDeclaration = {
+    name: '$event',
+    kind: 'variable',
+    type: info.query.getBuiltinType(BuiltinType.Any),
+  };
+
+  const outputSymbol = findOutputBinding(event, path, info.query);
+  if (!outputSymbol) {
+    // The `$event` variable doesn't belong to an output, so its type can't be refined.
+    // TODO: type `$event` variables in bindings to DOM events.
+    return genericEvent;
+  }
+
+  // The raw event type is wrapped in a generic, like EventEmitter<T> or Observable<T>.
+  const ta = outputSymbol.typeArguments();
+  if (!ta || ta.length !== 1) return genericEvent;
+  const eventType = ta[0];
+
+  return {...genericEvent, type: eventType};
 }
 
+/**
+ * Returns the symbols available in a particular scope of a template.
+ * @param info parsed template information
+ * @param path path of template nodes narrowing to the context the expression scope should be
+ * derived for.
+ */
 export function getExpressionScope(
     info: DiagnosticTemplateInfo, path: TemplateAstPath): SymbolTable {
   let result = info.members;
   const references = getReferences(info);
   const variables = getVarDeclarations(info, path);
-  const events = getEventDeclaration(info, path);
-  if (references.length || variables.length || events.length) {
+  const event = getEventDeclaration(info, path);
+  if (references.length || variables.length || event) {
     const referenceTable = info.query.createSymbolTable(references);
     const variableTable = info.query.createSymbolTable(variables);
-    const eventsTable = info.query.createSymbolTable(events);
+    const eventsTable = info.query.createSymbolTable(event ? [event] : []);
     result = info.query.mergeSymbolTable([result, referenceTable, variableTable, eventsTable]);
   }
   return result;

diff --git a/packages/language-service/src/locate_symbol.ts b/packages/language-service/src/locate_symbol.ts
@@ -109,7 +109,7 @@ function locateSymbol(ast: TemplateAst, path: TemplateAstPath, info: AstResult):
         visitVariable(ast) {},
         visitEvent(ast) {
           if (!attributeValueSymbol()) {
-            symbol = findOutputBinding(info, path, ast);
+            symbol = findOutputBinding(ast, path, info.template.query);
             symbol = symbol && new OverrideKindSymbol(symbol, DirectiveKind.EVENT);
             span = spanOf(ast);
           }

diff --git a/packages/language-service/src/utils.ts b/packages/language-service/src/utils.ts
@@ -11,7 +11,7 @@ import * as ts from 'typescript';
 
 import {AstResult, SelectorInfo} from './common';
 import {DiagnosticTemplateInfo} from './expression_diagnostics';
-import {Span, Symbol} from './types';
+import {Span, Symbol, SymbolQuery} from './types';
 
 export interface SpanHolder {
   sourceSpan: ParseSourceSpan;
@@ -268,14 +268,14 @@ export function invertMap(obj: {[name: string]: string}): {[name: string]: strin
  * @param path narrowing
  */
 export function findOutputBinding(
-    info: AstResult, path: TemplateAstPath, binding: BoundEventAst): Symbol|undefined {
+    binding: BoundEventAst, path: TemplateAstPath, query: SymbolQuery): Symbol|undefined {
   const element = path.first(ElementAst);
   if (element) {
     for (const directive of element.directives) {
       const invertedOutputs = invertMap(directive.directive.outputs);
       const fieldName = invertedOutputs[binding.name];
       if (fieldName) {
-        const classSymbol = info.template.query.getTypeSymbol(directive.directive.type.reference);
+        const classSymbol = query.getTypeSymbol(directive.directive.type.reference);
         if (classSymbol) {
           return classSymbol.members().get(fieldName);
         }

diff --git a/packages/language-service/test/completions_spec.ts b/packages/language-service/test/completions_spec.ts
@@ -753,6 +753,23 @@ describe('completions', () => {
       expectContain(completions, CompletionKind.VARIABLE, ['$event']);
     });
   });
+
+  describe('$event completions', () => {
+    it('should suggest $event in event bindings', () => {
+      mockHost.override(TEST_TEMPLATE, `<div (click)="myClick(~{cursor});"></div>`);
+      const marker = mockHost.getLocationMarkerFor(TEST_TEMPLATE, 'cursor');
+      const completions = ngLS.getCompletionsAtPosition(TEST_TEMPLATE, marker.start);
+      expectContain(completions, CompletionKind.VARIABLE, ['$event']);
+    });
+
+    it('should suggest $event completions in output bindings', () => {
+      mockHost.override(TEST_TEMPLATE, `<div string-model (modelChange)="$event.~{cursor}"></div>`);
+      const marker = mockHost.getLocationMarkerFor(TEST_TEMPLATE, 'cursor');
+      const completions = ngLS.getCompletionsAtPosition(TEST_TEMPLATE, marker.start);
+      // Expect string properties
+      expectContain(completions, CompletionKind.METHOD, ['charAt', 'substring']);
+    });
+  });
 });
 
 function expectContain(

diff --git a/packages/language-service/test/diagnostics_spec.ts b/packages/language-service/test/diagnostics_spec.ts
@@ -311,16 +311,14 @@ describe('diagnostics', () => {
 
   describe('with $event', () => {
     it('should accept an event', () => {
-      const fileName = '/app/test.ng';
-      mockHost.override(fileName, '<div (click)="myClick($event)">Click me!</div>');
-      const diagnostics = ngLS.getSemanticDiagnostics(fileName);
+      mockHost.override(TEST_TEMPLATE, '<div (click)="myClick($event)">Click me!</div>');
+      const diagnostics = ngLS.getSemanticDiagnostics(TEST_TEMPLATE);
       expect(diagnostics).toEqual([]);
     });
 
     it('should reject it when not in an event binding', () => {
-      const fileName = '/app/test.ng';
-      const content = mockHost.override(fileName, '<div [tabIndex]="$event"></div>');
-      const diagnostics = ngLS.getSemanticDiagnostics(fileName) !;
+      const content = mockHost.override(TEST_TEMPLATE, '<div [tabIndex]="$event"></div>');
+      const diagnostics = ngLS.getSemanticDiagnostics(TEST_TEMPLATE) !;
       expect(diagnostics.length).toBe(1);
       const {messageText, start, length} = diagnostics[0];
       expect(messageText)
@@ -330,6 +328,17 @@ describe('diagnostics', () => {
       expect(start).toBe(content.lastIndexOf(keyword));
       expect(length).toBe(keyword.length);
     });
+
+    it('should reject invalid properties on an event type', () => {
+      const content = mockHost.override(
+          TEST_TEMPLATE, '<div string-model (modelChange)="$event.notSubstring()"></div>');
+      const diagnostics = ngLS.getSemanticDiagnostics(TEST_TEMPLATE) !;
+      expect(diagnostics.length).toBe(1);
+      const {messageText, start, length} = diagnostics[0];
+      expect(messageText).toBe(`Unknown method 'notSubstring'`);
+      expect(start).toBe(content.indexOf('$event'));
+      expect(length).toBe('$event.notSubstring()'.length);
+    });
   });
 
   it('should not crash with a incomplete *ngFor', () => {