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OneOf Inhabitability #4564

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OneOf Inhabitability #4564

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994512e
check oneof inhabitability
jbellenger Feb 17, 2026
ba19546
Detect uninhabitable input types formed by OneOf and non-OneOf cycles
jbellenger Feb 28, 2026
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272 changes: 264 additions & 8 deletions src/type/__tests__/validation-test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -924,7 +924,7 @@ describe('Type System: Input Objects must have fields', () => {
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Invalid circular reference. The Input Object SomeInputObject references itself in the non-null field SomeInputObject.nonNullSelf.',
'Input Object SomeInputObject references itself via the required fields: SomeInputObject.nonNullSelf.',
locations: [{ line: 7, column: 9 }],
},
]);
Expand Down Expand Up @@ -952,13 +952,31 @@ describe('Type System: Input Objects must have fields', () => {
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Invalid circular reference. The Input Object SomeInputObject references itself via the non-null fields: SomeInputObject.startLoop, AnotherInputObject.nextInLoop, YetAnotherInputObject.closeLoop.',
'Input Object SomeInputObject references itself via the required fields: SomeInputObject.startLoop, AnotherInputObject.nextInLoop, YetAnotherInputObject.closeLoop.',
locations: [
{ line: 7, column: 9 },
{ line: 11, column: 9 },
{ line: 15, column: 9 },
],
},
{
message:
'Input Object AnotherInputObject references itself via the required fields: AnotherInputObject.nextInLoop, YetAnotherInputObject.closeLoop, SomeInputObject.startLoop.',
locations: [
{ line: 11, column: 9 },
{ line: 15, column: 9 },
{ line: 7, column: 9 },
],
},
{
message:
'Input Object YetAnotherInputObject references itself via the required fields: YetAnotherInputObject.closeLoop, SomeInputObject.startLoop, AnotherInputObject.nextInLoop.',
locations: [
{ line: 15, column: 9 },
{ line: 7, column: 9 },
{ line: 11, column: 9 },
],
},
]);
});

Expand Down Expand Up @@ -986,24 +1004,28 @@ describe('Type System: Input Objects must have fields', () => {
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Invalid circular reference. The Input Object SomeInputObject references itself via the non-null fields: SomeInputObject.startLoop, AnotherInputObject.closeLoop.',
'Input Object SomeInputObject references itself via the required fields: SomeInputObject.startLoop, AnotherInputObject.closeLoop.',
locations: [
{ line: 7, column: 9 },
{ line: 11, column: 9 },
],
},
{
message:
'Invalid circular reference. The Input Object AnotherInputObject references itself via the non-null fields: AnotherInputObject.startSecondLoop, YetAnotherInputObject.closeSecondLoop.',
'Input Object AnotherInputObject references itself via the required fields: AnotherInputObject.closeLoop, SomeInputObject.startLoop.',
locations: [
{ line: 12, column: 9 },
{ line: 16, column: 9 },
{ line: 11, column: 9 },
{ line: 7, column: 9 },
],
},
{
message:
'Invalid circular reference. The Input Object YetAnotherInputObject references itself in the non-null field YetAnotherInputObject.nonNullSelf.',
locations: [{ line: 17, column: 9 }],
'Input Object YetAnotherInputObject references itself via the required fields: YetAnotherInputObject.closeSecondLoop, AnotherInputObject.closeLoop, SomeInputObject.startLoop.',
locations: [
{ line: 16, column: 9 },
{ line: 11, column: 9 },
{ line: 7, column: 9 },
],
},
]);
});
Expand Down Expand Up @@ -2409,6 +2431,240 @@ describe('Type System: OneOf Input Object fields must be nullable', () => {
});
});

describe('Type System: Input Objects must not have unbreakable cycles', () => {
it('accepts a OneOf Input Object with a scalar field', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
a: Int
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a OneOf Input Object with a recursive list field', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
a: [A!]
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a OneOf Input Object referencing a non-OneOf input object', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
}

input B {
x: Int
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a OneOf/OneOf cycle with a scalar escape', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
escape: Int
}

input B @oneOf {
a: A
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a OneOf/non-OneOf cycle with a nullable escape', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
}

input B {
a: A
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('rejects a self-referencing OneOf type with no escapes', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
self: A
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Input Object A references itself via the required fields: A.self.',
locations: [{ line: 7, column: 9 }],
},
]);
});

it('rejects a mixed OneOf/non-OneOf cycle with no escapes', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
}

input B {
a: A!
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Input Object A references itself via the required fields: A.b, B.a.',
locations: [
{ line: 7, column: 9 },
{ line: 11, column: 9 },
],
},
{
message:
'Input Object B references itself via the required fields: B.a, A.b.',
locations: [
{ line: 11, column: 9 },
{ line: 7, column: 9 },
],
},
]);
});

it('accepts a OneOf/non-OneOf with scalar escape', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
escape: Int
}

input B {
a: A!
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a non-OneOf/non-OneOf cycle with a nullable escape', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A {
b: B!
}

input B {
a: A
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('accepts a non-OneOf/non-OneOf cycle with a list escape', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A {
b: [B!]!
}

input B {
a: A!
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([]);
});

it('rejects a larger mixed OneOf/non-OneOf cycle with no escapes', () => {
const schema = buildSchema(`
type Query {
test(arg: A): Int
}

input A @oneOf {
b: B
}

input B {
c: C!
}

input C @oneOf {
a: A
}
`);
expectJSON(validateSchema(schema)).toDeepEqual([
{
message:
'Input Object A references itself via the required fields: A.b, B.c, C.a.',
locations: [
{ line: 7, column: 9 },
{ line: 11, column: 9 },
{ line: 15, column: 9 },
],
},
{
message:
'Input Object B references itself via the required fields: B.c, C.a, A.b.',
locations: [
{ line: 11, column: 9 },
{ line: 15, column: 9 },
{ line: 7, column: 9 },
],
},
{
message:
'Input Object C references itself via the required fields: C.a, A.b, B.c.',
locations: [
{ line: 15, column: 9 },
{ line: 7, column: 9 },
{ line: 11, column: 9 },
],
},
]);
});
});

describe('Objects must adhere to Interface they implement', () => {
it('accepts an Object which implements an Interface', () => {
const schema = buildSchema(`
Expand Down
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