ConditionalPickDeep: Fix returning {} instead of never when no keys match (#1360)

Author: derodero24

source/conditional-pick-deep.d.ts

@@ -74,7 +74,7 @@ type BooleanPick = ConditionalPickDeep<Example, boolean | undefined>;
 //=> {c: {e: {g?: boolean}; j: boolean}}
 
 type NumberPick = ConditionalPickDeep<Example, number>;
-//=> {}
+//=> never
 
 type StringOrBooleanPick = ConditionalPickDeep<Example, string | boolean>;
 //=> {
@@ -99,11 +99,13 @@ export type ConditionalPickDeep<
 	Type,
 	Condition,
 	Options extends ConditionalPickDeepOptions = {},
-> = _ConditionalPickDeep<
+> = _NeverIfEmpty<_ConditionalPickDeep<
 	Type,
 	Condition,
 	ApplyDefaultOptions<ConditionalPickDeepOptions, DefaultConditionalPickDeepOptions, Options>
->;
+>>;
+
+type _NeverIfEmpty<Type> = Type extends EmptyObject ? never : Type;
 
 type _ConditionalPickDeep<
 	Type,

test-d/conditional-pick-deep.ts

@@ -102,7 +102,15 @@ declare const emptyPick: ConditionalPickDeep<Example, 'abcdefg'>;
 expectType<{never: never}>(emptyPick);
 
 declare const emptyEqualityPick: ConditionalPickDeep<Example, 'abcdefg', {condition: 'equality'}>;
-expectType<{}>(emptyEqualityPick);
+expectType<never>(emptyEqualityPick);
+
+// Returns `never` when no keys match the condition
+declare const noMatchingKeys: ConditionalPickDeep<{a: string; b: number}, boolean>;
+expectType<never>(noMatchingKeys);
+
+// Union with no common properties
+declare const unionNoCommon: ConditionalPickDeep<{a: string} | {b: string}, string>;
+expectType<{a: string} | {b: string}>(unionNoCommon);
 
 declare const stringOrBooleanPick: ConditionalPickDeep<Example, string | boolean>;
 expectType<{