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feat(eslint-plugin): [unbound-method] report property signatures with function types #11682

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feat(eslint-plugin): [unbound-method] report property signatures with function types #11682

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10 changes: 10 additions & 0 deletions packages/eslint-plugin/src/rules/unbound-method.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -328,6 +328,15 @@ function checkIfMethod(
}
return checkMethod(assignee as ts.FunctionExpression, ignoreStatic);
}
case ts.SyntaxKind.PropertySignature: {
const type = (valueDeclaration as ts.PropertySignature).type;
if (type?.kind !== ts.SyntaxKind.FunctionType) {
return {
dangerous: false,
};
}
return checkMethod(type as ts.FunctionTypeNode, ignoreStatic);
}
case ts.SyntaxKind.MethodDeclaration:
case ts.SyntaxKind.MethodSignature: {
return checkMethod(
Expand All @@ -343,6 +352,7 @@ function checkIfMethod(
function checkMethod(
valueDeclaration:
| ts.FunctionExpression
| ts.FunctionTypeNode
| ts.MethodDeclaration
| ts.MethodSignature,
ignoreStatic: boolean,
Expand Down
96 changes: 94 additions & 2 deletions packages/eslint-plugin/tests/rules/unbound-method.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -463,7 +463,11 @@ class Foo {
type foo = new ({ unbound }: Foo) => void;
`,
'const { unbound } = { unbound: () => {} };',
'function foo({ unbound }: { unbound: () => void } = { unbound: () => {} }) {}',
`
function foo(
{ unbound }: { unbound: (this: void) => void } = { unbound: () => {} },
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@ronami ronami Oct 5, 2025

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To my understanding, this previously valid test is in fact invalid without a this: void parameter type.

) {}
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/1866
`
class BaseClass {
Expand All @@ -480,6 +484,30 @@ class OtherClass extends BaseClass {
const oc = new OtherClass();
oc.superLogThis();
`,
`
interface Foo {
bound: (this: void) => number;
}

declare const foo: Foo;
foo.bound;
`,
`
interface Foo {
bound: (this: void) => number;
}

declare const foo: Foo;
const { bound } = foo;
`,
`
type Foo = {
bound: (this: void) => number;
};

declare const foo: Foo;
const { bound } = foo;
`,
],
invalid: [
{
Expand Down Expand Up @@ -965,7 +993,7 @@ function foo({ unbound }: { unbound: () => string } | Foo) {}
errors: [
{
line: 5,
messageId: 'unbound',
messageId: 'unboundWithoutThisAnnotation',
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@ronami ronami Oct 5, 2025 •
edited
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This is interesting, it seems the rule iterates on union types and reports the first violation:

typescript-eslint/packages/eslint-plugin/src/rules/unbound-method.ts

Lines 263 to 275 in 7f5fed7

for (const intersectionPart of tsutils
.unionConstituents(services.getTypeAtLocation(node))
.flatMap(unionPart =>
tsutils.intersectionConstituents(unionPart),
)) {
const reported = checkIfMethodAndReport(
property.key,
intersectionPart.getProperty(property.key.name),
);
if (reported) {
break;
}
}

In this case, the union starts with { unbound: () => string }, with Foo being second. Currently, { unbound: () => string } doesn't report, which causes the report to come from Foo.

This PR made it so { unbound: () => string } does trigger a report, which changes the error message accordingly.

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@ronami ronami Oct 5, 2025

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Somewhat related: #11683.

},
],
},
Expand Down Expand Up @@ -1252,5 +1280,69 @@ const f = objectLiteral.f;
},
],
},
{
code: `
interface Foo {
bound: () => number;
}

declare const foo: Foo;
foo.bound;
`,
errors: [
{
line: 7,
messageId: 'unboundWithoutThisAnnotation',
},
],
},
{
code: `
interface Foo {
bound: () => number;
}

declare const foo: Foo;
const { bound } = foo;
`,
errors: [
{
line: 7,
messageId: 'unboundWithoutThisAnnotation',
},
],
},
{
code: `
interface Foo {
bound: (this: Foo) => number;
}

declare const foo: Foo;
foo.bound;
`,
errors: [
{
line: 7,
messageId: 'unbound',
},
],
},
{
code: `
type Foo = {
bound: () => number;
};

declare const foo: Foo;
foo.bound;
`,
errors: [
{
line: 7,
messageId: 'unboundWithoutThisAnnotation',
},
],
},
],
});
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