refactor(forms): improve typing on min & max (angular#65212)

If we're calling `min` on a path that's guaranteed to be `number` we
don't want to make the users validator function handle the `null` or
`string` cases.

This uncovered an issue in the `SchemaTreePath` type which needed to be
fixed by preventing the model type from being distributed over.

PR Close angular#65212

Author: mmalerba

goldens/public-api/forms/signals/index.api.md

@@ -335,7 +335,7 @@ export class MetadataKey<TValue> {
 export const MIN: AggregateMetadataKey<number | undefined, number | undefined>;
 
 // @public
-export function min<TPathKind extends PathKind = PathKind.Root>(path: SchemaPath<number | string | null, SchemaPathRules.Supported, TPathKind>, minValue: number | LogicFn<number | string | null, number | undefined, TPathKind>, config?: BaseValidatorConfig<number | string | null, TPathKind>): void;
+export function min<TValue extends number | string | null, TPathKind extends PathKind = PathKind.Root>(path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>, minValue: number | LogicFn<TValue, number | undefined, TPathKind>, config?: BaseValidatorConfig<TValue, TPathKind>): void;
 
 // @public
 export const MIN_LENGTH: AggregateMetadataKey<number | undefined, number | undefined>;
@@ -505,7 +505,7 @@ export namespace SchemaPathRules {
 }
 
 // @public
-export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> = (TModel extends AbstractControl ? CompatSchemaPath<TModel, TPathKind> : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) & (TModel extends AbstractControl ? unknown : TModel extends Array<any> ? unknown : TModel extends Record<string, any> ? {
+export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> = ([TModel] extends [AbstractControl] ? CompatSchemaPath<TModel, TPathKind> : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) & (TModel extends AbstractControl ? unknown : TModel extends Array<any> ? unknown : TModel extends Record<string, any> ? {
     [K in keyof TModel]: MaybeSchemaPathTree<TModel[K], PathKind.Child>;
 } : unknown);
 

packages/forms/signals/src/api/types.ts

@@ -405,23 +405,25 @@ export type CompatSchemaPath<
  *
  * @experimental 21.0.0
  */
-export type SchemaPathTree<
-  TModel,
-  TPathKind extends PathKind = PathKind.Root,
-> = (TModel extends AbstractControl
-  ? CompatSchemaPath<TModel, TPathKind>
-  : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) &
-  // Subpaths
-  (TModel extends AbstractControl
-    ? unknown
-    : // Array paths have no subpaths
-      TModel extends Array<any>
+export type SchemaPathTree<TModel, TPathKind extends PathKind = PathKind.Root> =
+  // Note: We use `[TModel]` here to avoid distributing over a union type model.
+  // (e.g. if we have a model of `number | string`, we want a `SchemaPath<number | string>`,
+  // not a `SchemaPath<number> | SchemaPath<string>`.
+  // See https://typescriptlang.org/docs/handbook/2/conditional-types.html#distributive-conditional-types)
+  ([TModel] extends [AbstractControl]
+    ? CompatSchemaPath<TModel, TPathKind>
+    : SchemaPath<TModel, SchemaPathRules.Supported, TPathKind>) &
+    // Subpaths
+    (TModel extends AbstractControl
       ? unknown
-      : // Object subfields
-        TModel extends Record<string, any>
-        ? {[K in keyof TModel]: MaybeSchemaPathTree<TModel[K], PathKind.Child>}
-        : // Primitive or other type - no subpaths
-          unknown);
+      : // Array paths have no subpaths
+        TModel extends Array<any>
+        ? unknown
+        : // Object subfields
+          TModel extends Record<string, any>
+          ? {[K in keyof TModel]: MaybeSchemaPathTree<TModel[K], PathKind.Child>}
+          : // Primitive or other type - no subpaths
+            unknown);
 
 /**
  * Helper type for defining `FieldPath`. Given a type `TValue` that may include `undefined`, it

packages/forms/signals/src/api/validators/min.ts

@@ -29,10 +29,13 @@ import {BaseValidatorConfig, getOption, isEmpty} from './util';
  * @category validation
  * @experimental 21.0.0
  */
-export function min<TPathKind extends PathKind = PathKind.Root>(
-  path: SchemaPath<number | string | null, SchemaPathRules.Supported, TPathKind>,
-  minValue: number | LogicFn<number | string | null, number | undefined, TPathKind>,
-  config?: BaseValidatorConfig<number | string | null, TPathKind>,
+export function min<
+  TValue extends number | string | null,
+  TPathKind extends PathKind = PathKind.Root,
+>(
+  path: SchemaPath<TValue, SchemaPathRules.Supported, TPathKind>,
+  minValue: number | LogicFn<TValue, number | undefined, TPathKind>,
+  config?: BaseValidatorConfig<TValue, TPathKind>,
 ) {
   const MIN_MEMO = metadata(path, (ctx) =>
     computed(() => (typeof minValue === 'number' ? minValue : minValue(ctx))),

packages/forms/signals/test/node/api/validators/min.spec.ts

@@ -59,7 +59,7 @@ describe('min validator', () => {
         (p) => {
           min(p.age, 5, {
             error: ({value}) => {
-              return customError({kind: 'special-min', message: value()?.toString()});
+              return customError({kind: 'special-min', message: value().toString()});
             },
           });
         },
@@ -84,7 +84,7 @@ describe('min validator', () => {
             error: ({value}) => {
               return {
                 kind: 'special-min',
-                message: value()?.toString(),
+                message: value().toString(),
               };
             },
           });
@@ -130,7 +130,7 @@ describe('min validator', () => {
             error: ({value, valueOf}) => {
               return valueOf(p.name) === 'disabled'
                 ? []
-                : customError({kind: 'special-min', message: value()?.toString()});
+                : customError({kind: 'special-min', message: value().toString()});
             },
           });
         },

packages/forms/signals/test/node/field_node.spec.ts

@@ -13,7 +13,6 @@ import {
   applyEach,
   customError,
   disabled,
-  SchemaPath,
   form,
   hidden,
   readonly,
@@ -23,6 +22,7 @@ import {
   Schema,
   schema,
   SchemaOrSchemaFn,
+  SchemaPath,
   SchemaPathTree,
   validate,
   validateTree,
@@ -1228,7 +1228,7 @@ describe('FieldNode', () => {
     });
 
     it('should error on resolving predefined schema path that is not part of the form', () => {
-      let otherP: SchemaPath<any>;
+      let otherP: SchemaPath<string>;
       const s = schema<string>((p) => (otherP = p));
       SchemaImpl.rootCompile(s);