fix(client): fix detection of Angular context after string interpolation

This probably still has its own issues but seems to be at least an improvement over
past scanner issues.

It may be good to spend more time on the correctness of this or just
`ts.createSourceFile`. This previously wasn't done due to perfomance
concerns.

fixes angular#1872

client/src/embedded_support.ts

@@ -77,8 +77,23 @@ function isPropertyAssignmentToStringOrStringInArray(
   let lastTokenText: string|undefined;
   let unclosedBraces = 0;
   let unclosedBrackets = 0;
+  let unclosedTaggedTemplates = 0;
   let propertyAssignmentContext = false;
+
+  function isTemplateStartOfTaggedTemplate() {
+    return token === ts.SyntaxKind.NoSubstitutionTemplateLiteral ||
+        token === ts.SyntaxKind.TemplateHead;
+  }
+
   while (token !== ts.SyntaxKind.EndOfFileToken && scanner.getStartPos() < offset) {
+    if (isTemplateStartOfTaggedTemplate()) {
+      unclosedTaggedTemplates++;
+    }
+    if (token === ts.SyntaxKind.CloseBraceToken && unclosedTaggedTemplates > 0) {
+      // https://github.com/Microsoft/TypeScript/issues/20055
+      token = scanner.reScanTemplateToken(/*isTaggedTemplate*/ true);
+      unclosedTaggedTemplates--;
+    }
     if (lastToken === ts.SyntaxKind.Identifier && lastTokenText !== undefined &&
         propertyAssignmentNames.includes(lastTokenText) && token === ts.SyntaxKind.ColonToken) {
       propertyAssignmentContext = true;

client/src/tests/embedded_support_spec.ts

@@ -38,6 +38,21 @@ describe('embedded language support', () => {
     it('at end of template', () => {
       test(`template: '<div></div>¦'`, isInsideInlineTemplateRegion, true);
     });
+
+    it('works for inline templates after a template string', () => {
+      test(
+          'const x = `${""}`;\n' +
+              'template: `hello ¦world`',
+          isInsideInlineTemplateRegion, true);
+    });
+
+    it('works for inline templates after a tagged template string inside tagged template string',
+       () => {
+         test(
+             'const x = `${`${""}`}`;\n' +
+                 'template: `hello ¦world`',
+             isInsideInlineTemplateRegion, true);
+       });
   });
 
   describe('isInsideAngularContext', () => {
@@ -112,4 +127,4 @@ function extractCursorInfo(textWithCursor: string): {cursor: number, text: strin
     cursor,
     text: textWithCursor.substr(0, cursor) + textWithCursor.substr(cursor + 1),
   };
-}
+}