fix(ngcc): avoid warning when reflecting on index signature member (#33198)

Previously, when `ngcc` was reflecting on class members it did not
account for the fact that a member could be of the kind
`IndexSignature`. This can happen, for example, on abstract classes (as
is the case for [JsonCallbackContext][1]).

Trying to reflect on such members (and failing to recognize their kind),
resulted in warnings, such as:
```
Warning: Unknown member type: "[key: string]: (data: any) => void;
```

While these warnings are harmless, they can be confusing and worrisome
for users.

This commit avoids such warnings by detecting class members of the
`IndexSignature` kind and ignoring them.

[1]: https://github.com/angular/angular/blob/4659cc26e/packages/common/http/src/jsonp.ts#L39

PR Close #33198

packages/compiler-cli/ngcc/src/host/esm2015_host.ts

@@ -1778,7 +1778,10 @@ function isNamedDeclaration(node: ts.Declaration): node is ts.NamedDeclaration&
 
 function isClassMemberType(node: ts.Declaration): node is ts.ClassElement|
     ts.PropertyAccessExpression|ts.BinaryExpression {
-  return ts.isClassElement(node) || isPropertyAccess(node) || ts.isBinaryExpression(node);
+  return (ts.isClassElement(node) || isPropertyAccess(node) || ts.isBinaryExpression(node)) &&
+      // Additionally, ensure `node` is not an index signature, for example on an abstract class:
+      // `abstract class Foo { [key: string]: any; }`
+      !ts.isIndexSignatureDeclaration(node);
 }
 
 /**

packages/compiler-cli/ngcc/test/host/esm2015_host_spec.ts

@@ -46,6 +46,7 @@ runInEachFileSystem(() => {
     let TYPINGS_DTS_FILES: TestFile[];
     let MODULE_WITH_PROVIDERS_PROGRAM: TestFile[];
     let NAMESPACED_IMPORT_FILE: TestFile;
+    let INDEX_SIGNATURE_PROP_FILE: TestFile;
 
     beforeEach(() => {
       _ = absoluteFrom;
@@ -690,6 +691,15 @@ runInEachFileSystem(() => {
     ];
     `
       };
+
+      INDEX_SIGNATURE_PROP_FILE = {
+        name: _('/index_signature_prop.d.ts'),
+        contents: `
+          abstract class IndexSignatureClass {
+            [key: string]: any;
+          }
+        `,
+      };
     });
 
     describe('getDecoratorsOfDeclaration()', () => {
@@ -941,6 +951,20 @@ runInEachFileSystem(() => {
         expect(staticProperty.value !.getText()).toEqual(`'static'`);
       });
 
+      it('should ignore index signature properties', () => {
+        loadTestFiles([INDEX_SIGNATURE_PROP_FILE]);
+        const logger = new MockLogger();
+        const {program} = makeTestBundleProgram(INDEX_SIGNATURE_PROP_FILE.name);
+        const host = new Esm2015ReflectionHost(logger, false, program.getTypeChecker());
+        const classNode = getDeclaration(
+            program, INDEX_SIGNATURE_PROP_FILE.name, 'IndexSignatureClass',
+            isNamedClassDeclaration);
+        const members = host.getMembersOfClass(classNode);
+
+        expect(members).toEqual([]);
+        expect(logger.logs.warn).toEqual([]);
+      });
+
       it('should throw if the symbol is not a class', () => {
         loadTestFiles([FOO_FUNCTION_FILE]);
         const {program} = makeTestBundleProgram(FOO_FUNCTION_FILE.name);