fix(forms): improve error message for invalid value accessors (#22731)

Signed-off-by: Dirk Luijk <mail@dirkluijk.nl>

PR Close #22731

packages/forms/src/directives/shared.ts

@@ -187,9 +187,13 @@ export function selectValueAccessor(
     dir: NgControl, valueAccessors: ControlValueAccessor[]): ControlValueAccessor|null {
   if (!valueAccessors) return null;
 
+  if (!Array.isArray(valueAccessors))
+    _throwError(dir, 'Value accessor was not provided as an array for form control with');
+
   let defaultAccessor: ControlValueAccessor|undefined = undefined;
   let builtinAccessor: ControlValueAccessor|undefined = undefined;
   let customAccessor: ControlValueAccessor|undefined = undefined;
+
   valueAccessors.forEach((v: ControlValueAccessor) => {
     if (v.constructor === DefaultValueAccessor) {
       defaultAccessor = v;

packages/forms/test/directives_spec.ts

@@ -55,6 +55,12 @@ function asyncValidator(expected: any, timeout = 0) {
         it('should throw when given an empty array',
            () => { expect(() => selectValueAccessor(dir, [])).toThrowError(); });
 
+        it('should throw when accessor is not provided as array', () => {
+          expect(() => selectValueAccessor(dir, {} as any[]))
+              .toThrowError(
+                  `Value accessor was not provided as an array for form control with unspecified name attribute`);
+        });
+
         it('should return the default value accessor when no other provided',
            () => { expect(selectValueAccessor(dir, [defaultAccessor])).toEqual(defaultAccessor); });
 

packages/forms/test/spies.ts

@@ -16,6 +16,6 @@ export class SpyChangeDetectorRef extends SpyObject {
   }
 }
 
-export class SpyNgControl extends SpyObject {}
+export class SpyNgControl extends SpyObject { path = []; }
 
 export class SpyValueAccessor extends SpyObject { writeValue: any; }