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RFC: Enforce Interfaces having at least one implementing Object #1377

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RFC: Enforce Interfaces having at least one implementing Object #1377

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10 changes: 8 additions & 2 deletions src/type/__tests__/validation-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1205,7 +1205,7 @@ describe('Type System: Interface fields must have output types', () => {
]);
});

it('accepts an interface not implemented by at least one object', () => {
it('rejects an interface not implemented by at least one object', () => {
const schema = buildSchema(`
type Query {
test: SomeInterface
Expand All @@ -1215,7 +1215,13 @@ describe('Type System: Interface fields must have output types', () => {
foo: String
}
`);
expect(validateSchema(schema)).to.deep.equal([]);
expect(validateSchema(schema)).to.deep.equal([
{
message:
'Interface SomeInterface must be implemented by at least one Object type.',
locations: [{ line: 6, column: 7 }],
},
]);
});
});

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18 changes: 18 additions & 0 deletions src/type/validate.js
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Original file line number Diff line number Diff line change
Expand Up @@ -257,6 +257,9 @@ function validateTypes(context: SchemaValidationContext): void {
} else if (isInterfaceType(type)) {
// Ensure fields are valid.
validateFields(context, type);

// Ensure Interfaces include at least 1 Object type.
validateInterfaces(context, type);
} else if (isUnionType(type)) {
// Ensure Unions include valid member types.
validateUnionMembers(context, type);
Expand Down Expand Up @@ -364,6 +367,21 @@ function validateObjectInterfaces(
});
}

function validateInterfaces(
context: SchemaValidationContext,
iface: GraphQLInterfaceType,
): void {
const possibleTypes = context.schema.getPossibleTypes(iface);

if (possibleTypes.length === 0) {
context.reportError(
`Interface ${iface.name} must be implemented ` +
`by at least one Object type.`,
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Should we maybe expand the error message a little?

Interface ${iface.name} must be implemented by at least one Object type. An interface that does not have any implementation can never be instantiated.

iface.astNode,
);
}
}

function validateObjectImplementsInterface(
context: SchemaValidationContext,
object: GraphQLObjectType,
Expand Down