feat(compiler): support a non-null postfix assert (#16672)

Template expressions can now use a post-fix `!` operator
that asserts the target of the operator is not null. This is
similar to the TypeScript non-null assert operator. Expressions
generated in factories will be generated with the non-null assert
operator.

Closes: #10855

packages/compiler-cli/src/diagnostics/expression_type.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {AST, AstVisitor, Binary, BindingPipe, Chain, Conditional, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, PrefixNot, PropertyRead, PropertyWrite, Quote, SafeMethodCall, SafePropertyRead, visitAstChildren} from '@angular/compiler';
+import {AST, AstVisitor, Binary, BindingPipe, Chain, Conditional, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, NonNullAssert, PrefixNot, PropertyRead, PropertyWrite, Quote, SafeMethodCall, SafePropertyRead, visitAstChildren} from '@angular/compiler';
 
 import {BuiltinType, Signature, Span, Symbol, SymbolQuery, SymbolTable} from './symbols';
 
@@ -283,6 +283,11 @@ export class AstType implements AstVisitor {
     return this.query.getBuiltinType(BuiltinType.Boolean);
   }
 
+  visitNonNullAssert(ast: NonNullAssert) {
+    const expressionType = this.getType(ast.expression);
+    return this.query.getNonNullableType(expressionType);
+  }
+
   visitPropertyRead(ast: PropertyRead) {
     return this.resolvePropertyRead(this.getType(ast.receiver), ast);
   }

packages/compiler-cli/test/diagnostics/expression_diagnostics_spec.ts

@@ -135,6 +135,8 @@ describe('expression diagnostics', () => {
      () => reject(`<div>{{maybe_person.name.first}}`, 'The expression might be null'));
   it('should accept a safe accss to an undefined field',
      () => accept(`<div>{{maybe_person?.name.first}}</div>`));
+  it('should accept a type assert to an undefined field',
+     () => accept(`<div>{{maybe_person!.name.first}}</div>`));
   it('should accept a # reference', () => accept(`
           <form #f="ngForm" novalidate>
             <input name="first" ngModel required #first="ngModel">