Type Alias DeepMergeStrict<Left, Right>

DeepMergeStrict: Simplify<
    Left extends (infer U)[]
        ? DeepMergeStrict<U, Right>[]
        : Left extends ReadonlyArray<infer U>
            ? ReadonlyArray<DeepMergeStrict<U, Right>>
            : Left extends object
                ? Right extends object
                    ? {
                        [K in keyof Left]: K extends keyof Right
                            ? DeepMergeStrict<Left[K], Right[K]>
                            : DeepMergeStrict<Left[K], Right>
                    } & { [K in Exclude<keyof Right, keyof Left>]: Right[K] }
                    : Left
                : Left,
>

type A = { a: { x: { foo: true } } };
type B = { a: { x: { foo: number, bar: string } } };
type Merged = DeepMergeStrict< A, B >;
// { a: { x: { foo: true, bar: string } } }
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