refactor(@schematics/angular): use type guard based narrowing with TS AST

By leveraging TypeScript's AST type guards, function parameter assumptions and casting can be removed.  Many of these cases caused errors when enabling TypeScript's strict option. This is preliminary work to support enabling full TypeScript strict mode within the project.

Author: clydin

packages/schematics/angular/app-shell/index.ts

@@ -110,11 +110,11 @@ function getBootstrapComponentPath(
   const componentSymbol = arrLiteral.elements[0].getText();
 
   const relativePath = getSourceNodes(moduleSource)
-    .filter(node => node.kind === ts.SyntaxKind.ImportDeclaration)
+    .filter(ts.isImportDeclaration)
     .filter(imp => {
       return findNode(imp, ts.SyntaxKind.Identifier, componentSymbol);
     })
-    .map((imp: ts.ImportDeclaration) => {
+    .map(imp => {
       const pathStringLiteral = imp.moduleSpecifier as ts.StringLiteral;
 
       return pathStringLiteral.text;
@@ -205,8 +205,8 @@ function addRouterModule(mainPath: string): Rule {
 function getMetadataProperty(metadata: ts.Node, propertyName: string): ts.PropertyAssignment {
   const properties = (metadata as ts.ObjectLiteralExpression).properties;
   const property = properties
-    .filter(prop => prop.kind === ts.SyntaxKind.PropertyAssignment)
-    .filter((prop: ts.PropertyAssignment) => {
+    .filter(ts.isPropertyAssignment)
+    .filter((prop) => {
       const name = prop.name;
       switch (name.kind) {
         case ts.SyntaxKind.Identifier:

packages/schematics/angular/utility/ng-ast-utils.ts

@@ -62,11 +62,11 @@ export function findBootstrapModulePath(host: Tree, mainPath: string): string {
   const source = ts.createSourceFile(mainPath, mainText, ts.ScriptTarget.Latest, true);
   const allNodes = getSourceNodes(source);
   const bootstrapModuleRelativePath = allNodes
-    .filter(node => node.kind === ts.SyntaxKind.ImportDeclaration)
+    .filter(ts.isImportDeclaration)
     .filter(imp => {
       return findNode(imp, ts.SyntaxKind.Identifier, bootstrapModule.getText());
     })
-    .map((imp: ts.ImportDeclaration) => {
+    .map(imp => {
       const modulePathStringLiteral = imp.moduleSpecifier as ts.StringLiteral;
 
       return modulePathStringLiteral.text;