feat(compiler): support safe keyed read expressions (#41911)

Currently we support safe property (`a?.b`) and method (`a?.b()`) accesses, but we don't handle safe keyed reads (`a?.[0]`) which is inconsistent. These changes expand the compiler in order to support safe key read expressions as well.

PR Close #41911

packages/compiler-cli/src/ngtsc/typecheck/src/expression.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {AST, AstVisitor, ASTWithSource, Binary, BindingPipe, Chain, Conditional, EmptyExpr, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, NonNullAssert, PrefixNot, PropertyRead, PropertyWrite, Quote, SafeMethodCall, SafePropertyRead, ThisReceiver, Unary} from '@angular/compiler';
+import {AST, AstVisitor, ASTWithSource, Binary, BindingPipe, Chain, Conditional, EmptyExpr, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, NonNullAssert, PrefixNot, PropertyRead, PropertyWrite, Quote, SafeKeyedRead, SafeMethodCall, SafePropertyRead, ThisReceiver, Unary} from '@angular/compiler';
 import * as ts from 'typescript';
 
 import {TypeCheckingConfig} from '../api';
@@ -156,7 +156,7 @@ class AstTranslator implements AstVisitor {
   }
 
   visitKeyedRead(ast: KeyedRead): ts.Expression {
-    const receiver = wrapForDiagnostics(this.translate(ast.obj));
+    const receiver = wrapForDiagnostics(this.translate(ast.receiver));
     const key = this.translate(ast.key);
     const node = ts.createElementAccess(receiver, key);
     addParseSpanInfo(node, ast.sourceSpan);
@@ -164,7 +164,7 @@ class AstTranslator implements AstVisitor {
   }
 
   visitKeyedWrite(ast: KeyedWrite): ts.Expression {
-    const receiver = wrapForDiagnostics(this.translate(ast.obj));
+    const receiver = wrapForDiagnostics(this.translate(ast.receiver));
     const left = ts.createElementAccess(receiver, this.translate(ast.key));
     // TODO(joost): annotate `left` with the span of the element access, which is not currently
     //  available on `ast`.
@@ -330,6 +330,30 @@ class AstTranslator implements AstVisitor {
     addParseSpanInfo(node, ast.sourceSpan);
     return node;
   }
+
+  visitSafeKeyedRead(ast: SafeKeyedRead): ts.Expression {
+    const receiver = wrapForDiagnostics(this.translate(ast.receiver));
+    const key = this.translate(ast.key);
+    let node: ts.Expression;
+
+    // The form of safe property reads depends on whether strictness is in use.
+    if (this.config.strictSafeNavigationTypes) {
+      // "a?.[...]" becomes (null as any ? a![...] : undefined)
+      const expr = ts.createElementAccess(ts.createNonNullExpression(receiver), key);
+      addParseSpanInfo(expr, ast.sourceSpan);
+      node = ts.createParen(ts.createConditional(NULL_AS_ANY, expr, UNDEFINED));
+    } else if (VeSafeLhsInferenceBugDetector.veWillInferAnyFor(ast)) {
+      // "a?.[...]" becomes (a as any)[...]
+      node = ts.createElementAccess(tsCastToAny(receiver), key);
+    } else {
+      // "a?.[...]" becomes (a!.[...] as any)
+      const expr = ts.createElementAccess(ts.createNonNullExpression(receiver), key);
+      addParseSpanInfo(expr, ast.sourceSpan);
+      node = tsCastToAny(expr);
+    }
+    addParseSpanInfo(node, ast.sourceSpan);
+    return node;
+  }
 }
 
 /**
@@ -348,8 +372,9 @@ class AstTranslator implements AstVisitor {
 class VeSafeLhsInferenceBugDetector implements AstVisitor {
   private static SINGLETON = new VeSafeLhsInferenceBugDetector();
 
-  static veWillInferAnyFor(ast: SafeMethodCall|SafePropertyRead) {
-    return ast.receiver.visit(VeSafeLhsInferenceBugDetector.SINGLETON);
+  static veWillInferAnyFor(ast: SafeMethodCall|SafePropertyRead|SafeKeyedRead) {
+    const visitor = VeSafeLhsInferenceBugDetector.SINGLETON;
+    return ast instanceof SafeKeyedRead ? ast.receiver.visit(visitor) : ast.receiver.visit(visitor);
   }
 
   visitUnary(ast: Unary): boolean {
@@ -418,4 +443,7 @@ class VeSafeLhsInferenceBugDetector implements AstVisitor {
   visitSafePropertyRead(ast: SafePropertyRead): boolean {
     return false;
   }
+  visitSafeKeyedRead(ast: SafeKeyedRead): boolean {
+    return false;
+  }
 }

packages/compiler-cli/src/ngtsc/typecheck/test/diagnostics_spec.ts

@@ -412,6 +412,35 @@ runInEachFileSystem(() => {
 
         expect(messages).toEqual([]);
       });
+
+      it('does not produce diagnostic for safe keyed access', () => {
+        const messages =
+            diagnose(`<div [class.red-text]="person.favoriteColors?.[0] === 'red'"></div>`, `
+              export class TestComponent {
+                person: {
+                  favoriteColors?: string[];
+                };
+              }`);
+
+        expect(messages).toEqual([]);
+      });
+
+      it('infers a safe keyed read as undefined', () => {
+        const messages = diagnose(`<div (click)="log(person.favoriteColors?.[0])"></div>`, `
+          export class TestComponent {
+            person: {
+              favoriteColors?: string[];
+            };
+
+            log(color: string) {
+              console.log(color);
+            }
+          }`);
+
+        expect(messages).toEqual([
+          `TestComponent.html(1, 19): Argument of type 'string | undefined' is not assignable to parameter of type 'string'.`
+        ]);
+      });
     });
 
     it('computes line and column offsets', () => {

packages/compiler-cli/src/ngtsc/typecheck/test/test_utils.ts

@@ -44,6 +44,7 @@ export function typescriptLibDts(): TestFile {
         call(...args: any[]): any;
       }
       declare interface Array<T> {
+        [index: number]: T;
         length: number;
       }
       declare interface String {

packages/compiler-cli/src/ngtsc/typecheck/test/type_check_block_spec.ts

@@ -997,12 +997,13 @@ describe('type check blocks', () => {
     });
 
     describe('config.strictSafeNavigationTypes', () => {
-      const TEMPLATE = `{{a?.b}} {{a?.method()}}`;
+      const TEMPLATE = `{{a?.b}} {{a?.method()}} {{a?.[0]}}`;
 
       it('should use undefined for safe navigation operations when enabled', () => {
         const block = tcb(TEMPLATE, DIRECTIVES);
         expect(block).toContain('(null as any ? (((ctx).a))!.method() : undefined)');
         expect(block).toContain('(null as any ? (((ctx).a))!.b : undefined)');
+        expect(block).toContain('(null as any ? (((ctx).a))![0] : undefined)');
       });
       it('should use an \'any\' type for safe navigation operations when disabled', () => {
         const DISABLED_CONFIG:
@@ -1010,15 +1011,17 @@ describe('type check blocks', () => {
         const block = tcb(TEMPLATE, DIRECTIVES, DISABLED_CONFIG);
         expect(block).toContain('((((ctx).a))!.method() as any)');
         expect(block).toContain('((((ctx).a))!.b as any)');
+        expect(block).toContain('(((((ctx).a))![0] as any)');
       });
     });
 
     describe('config.strictSafeNavigationTypes (View Engine bug emulation)', () => {
-      const TEMPLATE = `{{a.method()?.b}} {{a()?.method()}}`;
+      const TEMPLATE = `{{a.method()?.b}} {{a()?.method()}} {{a.method()?.[0]}}`;
       it('should check the presence of a property/method on the receiver when enabled', () => {
         const block = tcb(TEMPLATE, DIRECTIVES);
         expect(block).toContain('(null as any ? ((((ctx).a)).method())!.b : undefined)');
         expect(block).toContain('(null as any ? ((ctx).a())!.method() : undefined)');
+        expect(block).toContain('(null as any ? ((((ctx).a)).method())![0] : undefined)');
       });
       it('should not check the presence of a property/method on the receiver when disabled', () => {
         const DISABLED_CONFIG:
@@ -1026,6 +1029,7 @@ describe('type check blocks', () => {
         const block = tcb(TEMPLATE, DIRECTIVES, DISABLED_CONFIG);
         expect(block).toContain('(((((ctx).a)).method()) as any).b');
         expect(block).toContain('(((ctx).a()) as any).method()');
+        expect(block).toContain('(((((ctx).a)).method()) as any)[0]');
       });
     });