fix(compiler-cli): enable nullish coalescing check only with strictNullChecks (#44862)

TypeScript configures `strictNullChecks` to be disabled by default, so the nullish
coalescing check should follow the same default. The rule actively depends on
`strictNullChecks`, as TypeScript doesn't include `null`/`undefined` in its types
otherwise so the check wouldn't have a way to differentiate between them.

This commit also takes the `strict` flag into account when `strictNullChecks` itself
is not configured.

PR Close #44862

Author: JoostK

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

@@ -66,7 +66,9 @@ export const factory: TemplateCheckFactory<
   name: ExtendedTemplateDiagnosticName.NULLISH_COALESCING_NOT_NULLABLE,
   create: (options: NgCompilerOptions) => {
     // Require `strictNullChecks` to be enabled.
-    if (options.strictNullChecks === false) {
+    const strictNullChecks =
+        options.strictNullChecks === undefined ? !!options.strict : !!options.strictNullChecks;
+    if (!strictNullChecks) {
       return null;
     }
 

packages/compiler-cli/src/ngtsc/typecheck/extended/test/checks/nullish_coalescing_not_nullable/nullish_coalescing_not_nullable_spec.ts

@@ -28,13 +28,24 @@ runInEachFileSystem(() => {
 
     it('should return a check if `strictNullChecks` is enabled', () => {
       expect(nullishCoalescingNotNullableFactory.create({strictNullChecks: true})).toBeDefined();
-      expect(nullishCoalescingNotNullableFactory.create({})).not.toBeNull();  // Defaults enabled.
     });
 
+    it('should return a check if `strictNullChecks` is not configured but `strict` is enabled',
+       () => {
+         expect(nullishCoalescingNotNullableFactory.create({strict: true})).toBeDefined();
+       });
+
     it('should not return a check if `strictNullChecks` is disabled', () => {
       expect(nullishCoalescingNotNullableFactory.create({strictNullChecks: false})).toBeNull();
+      expect(nullishCoalescingNotNullableFactory.create({})).toBeNull();  // Defaults disabled.
     });
 
+    it('should not return a check if `strict` is enabled but `strictNullChecks` is disabled',
+       () => {
+         expect(nullishCoalescingNotNullableFactory.create({strict: true, strictNullChecks: false}))
+             .toBeNull();
+       });
+
     it('should produce nullish coalescing warning', () => {
       const fileName = absoluteFrom('/main.ts');
       const {program, templateTypeChecker} = setup([{
@@ -48,7 +59,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(1);
       expect(diags[0].category).toBe(ts.DiagnosticCategory.Warning);
@@ -69,7 +80,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(0);
     });
@@ -87,7 +98,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(0);
     });
@@ -105,7 +116,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(0);
     });
@@ -123,7 +134,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(0);
     });
@@ -152,7 +163,7 @@ runInEachFileSystem(() => {
          const component = getClass(sf, 'TestCmp');
          const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
              templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-             {} /* options */);
+             {strictNullChecks: true} /* options */);
          const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
          expect(diags.length).toBe(1);
          expect(diags[0].category).toBe(ts.DiagnosticCategory.Warning);
@@ -185,7 +196,7 @@ runInEachFileSystem(() => {
       const component = getClass(sf, 'TestCmp');
       const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
           templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-          {} /* options */);
+          {strictNullChecks: true} /* options */);
       const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
       expect(diags.length).toBe(0);
     });
@@ -210,7 +221,7 @@ runInEachFileSystem(() => {
          const component = getClass(sf, 'TestCmp');
          const extendedTemplateChecker = new ExtendedTemplateCheckerImpl(
              templateTypeChecker, program.getTypeChecker(), [nullishCoalescingNotNullableFactory],
-             {} /* options */);
+             {strictNullChecks: true} /* options */);
          const diags = extendedTemplateChecker.getDiagnosticsForComponent(component);
          expect(diags.length).toBe(0);
        });
@@ -232,6 +243,7 @@ runInEachFileSystem(() => {
           program.getTypeChecker(),
           [nullishCoalescingNotNullableFactory],
           {
+            strictNullChecks: true,
             extendedDiagnostics: {
               checks: {
                 nullishCoalescingNotNullable: DiagnosticCategoryLabel.Error,