Combination of intersections/partials causes invalid nested object type to not report error

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🔎 Search Terms

partial nested object type

🕗 Version & Regression Information

This changed between versions 4.5.5 and 4.6.4. It reproduces in all versions since 4.6.4 (including nightly)

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💻 Code

type OverridesInput = {
    someProp?: 'A' | 'B'
}

const foo: Partial<{something: any}> & {variables: {
    overrides?: OverridesInput;
} & Partial<{
    overrides?: OverridesInput;
}>} = {variables: {overrides: false}};

🙁 Actual behavior

There is no error on the overrides field in the object. Changing the type of foo slightly (removing one of the intersections) causes the error to appear correctly, but this unique combination of types produces no error. Does not matter what the contents of OverridesInput is, nor what the content inside the outer partial (currently {something: any}) is. Additionally, the following all produce the error correctly:

type OverridesInput = {
    someProp?: 'A' | 'B'
}

const foo: {variables: {
    overrides?: OverridesInput;
} & Partial<{
    overrides?: OverridesInput;
}>} = {variables: {overrides: false}};

type OverridesInput = {
    someProp?: 'A' | 'B'
}

const foo: Partial<{something: any}> & {variables: {
    overrides?: OverridesInput;
}} = {variables: {overrides: false}};

type OverridesInput = {
    someProp?: 'A' | 'B'
}

const foo: Partial<{something: any}> & {variables: Partial<{
    overrides?: OverridesInput;
}>} = {variables: {overrides: false}};

🙂 Expected behavior

There should be an error on the overrides field of the object since false is not assignable to OverridesInput | undefined.

type OverridesInput = {
    someProp?: 'A' | 'B'
}

const foo: Partial<{something: any}> & {variables: {
    overrides?: OverridesInput;
} & Partial<{
    overrides?: OverridesInput;
// @ts-expect-error
}>} = {variables: {overrides: false}};

This was a little easier for me to read.

interface Unrelated { _?: any }

// Identical but distinct types.
interface VariablesA { overrides?: OverridesInput; }
interface VariablesB { overrides?: OverridesInput; }

const foo: Unrelated & { variables: VariablesA & VariablesB } = {
    variables: {
        // Should be an error here:
        overrides: false
    }
};

I would've expected some weak type checking on this one.

The change between release-4.4 and main occurred at 44e827b.

Anders Hejlsberg (@ahejlsberg)

Anders Hejlsberg (@ahejlsberg) thoughts? This changed in #47738

The issue here is that when the target in a relation is an intersection, common property checks are only performed at the top level. For example:

type A1 = { x: { a?: string } };
type B1 = { x: { b?: string } };
type C1 = { x: { c: string } };

const ab1: A1 & B1 = {} as C1;  // No error

type A2 = { a?: string };
type B2 = { b?: string };
type C2 = { c: string };

const ab2: A2 & B2 = {} as C2;  // Error

We definitely should error in both of the examples above.

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Combination of intersections/partials causes invalid nested object type to not report error #51043

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🙂 Expected behavior

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Combination of intersections/partials causes invalid nested object type to not report error #51043

Description

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Activity

RyanCavanaugh commented on Oct 4, 2022

DanielRosenwasser commented on Oct 4, 2022

typescript-bot commented on Oct 5, 2022

RyanCavanaugh commented on Oct 5, 2022

ahejlsberg commented on Oct 11, 2022

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