fix(compiler-cli): suppress unnecessary optional chain for indexed ac…

…cesses

TypeScript's type system does not include `undefined` in the type of an indexed
access, whereas array index accesses may be expected to be out-of-bounds.
This commit updates the extended diagnostic for unnecessary optional chains to
ignore indexed accesses.

Closes angular#46918

packages/compiler-cli/src/ngtsc/typecheck/extended/checks/optional_chain_not_nullable/index.ts

@@ -27,9 +27,12 @@ class OptionalChainNotNullableCheck extends
   override visitNode(
       ctx: TemplateContext<ErrorCode.OPTIONAL_CHAIN_NOT_NULLABLE>, component: ts.ClassDeclaration,
       node: TmplAstNode|AST): NgTemplateDiagnostic<ErrorCode.OPTIONAL_CHAIN_NOT_NULLABLE>[] {
-    if (!(node instanceof SafeCall) && !(node instanceof SafePropertyRead) &&
-        !(node instanceof SafeKeyedRead))
+    if (!(node instanceof SafeCall) && !(node instanceof SafePropertyRead)) {
+      // Note: `SafeKeyedRead` is also ignored here because TypeScript does not include `undefined`
+      // in the type of an indexed access, leading to potentially false positives for out-of-bounds
+      // accesses of arrays.
       return [];
+    }
 
     const symbolLeft = ctx.templateTypeChecker.getSymbolOfNode(node.receiver, component);
     if (symbolLeft === null || symbolLeft.kind !== SymbolKind.Expression) {

packages/compiler-cli/src/ngtsc/typecheck/extended/test/checks/optional_chain_not_nullable/optional_chain_not_nullable_spec.ts

@@ -68,7 +68,10 @@ runInEachFileSystem(() => {
       expect(getSourceCodeForDiagnostic(diags[0])).toBe(`bar`);
     });
 
-    it('should produce optional chain warning for indexed access', () => {
+    // Using indexed access syntax is not reported as a warning as TypeScript's type system
+    // does not include `undefined` in the type of an indexed access, whereas array index
+    // accesses may be expected to be out-of-bounds.
+    it('should not produce optional chain warning for indexed access', () => {
       const fileName = absoluteFrom('/main.ts');
       const {program, templateTypeChecker} = setup([{
         fileName,
@@ -83,11 +86,7 @@ runInEachFileSystem(() => {
           templateTypeChecker, program.getTypeChecker(), [optionalChainNotNullableFactory],
           {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
-      expect(diags.length).toBe(1);
-      expect(diags[0].category).toBe(ts.DiagnosticCategory.Warning);
-      expect(diags[0].code).toBe(ngErrorCode(ErrorCode.OPTIONAL_CHAIN_NOT_NULLABLE));
-      expect(diags[0].messageText).toContain(`the '?.' operator can be safely removed`);
-      expect(getSourceCodeForDiagnostic(diags[0])).toBe(`var1?.['bar']`);
+      expect(diags.length).toBe(0);
     });
 
     it('should produce optional chain warning for method call', () => {