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fix(eslint-plugin): [unified-signatures] exempt this from optional parameter overload check #11005

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fix(eslint-plugin): [unified-signatures] exempt this from optional parameter overload check #11005

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e61d6cd
fix(unified-signatures): exempt `this` from optional parameter overlo…
jedwards1211 Mar 28, 2025
1b00350
Merge branch 'main' into fix-10982
jedwards1211 Mar 31, 2025
f4689e4
Merge branch 'main' into fix-10982
jedwards1211 Apr 1, 2025
58fef3a
fix: exempt signatures with `this: void` from unified-signatures
jedwards1211 Apr 1, 2025
181c003
Merge branch 'main' into fix-10982
JoshuaKGoldberg Apr 14, 2025
676857b
Merge branch 'main' into HEAD
kirkwaiblinger Apr 28, 2025
99e300f
lint fix
kirkwaiblinger Apr 28, 2025
f6301ab
remove unsafe type predicate
kirkwaiblinger Apr 28, 2025
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37 changes: 37 additions & 0 deletions packages/eslint-plugin/src/rules/unified-signatures.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -264,6 +264,14 @@
types1: readonly TSESTree.Parameter[],
types2: readonly TSESTree.Parameter[],
): Unify | undefined {
const firstParam1 = types1[0];
const firstParam2 = types2[0];

// exempt signatures with `this: void` from the rule
if (isThisVoidParam(firstParam1) || isThisVoidParam(firstParam2)) {
return undefined;
}

const index = getIndexOfFirstDifference(
types1,
types2,
Expand Down Expand Up @@ -294,6 +302,22 @@
: undefined;
}

function isThisParam(param: TSESTree.Parameter | undefined): boolean {
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FYI/PSA - I changed this not to be a type predicate since it's only valid in the true branch, not the false branch (the function returning false does not imply that param is not a TSESTree.Identifier).

return (
param != null &&
param.type === AST_NODE_TYPES.Identifier &&
param.name === 'this'
);
}

function isThisVoidParam(param: TSESTree.Parameter | undefined) {
return (
isThisParam(param) &&
(param as TSESTree.Identifier).typeAnnotation?.typeAnnotation.type ===
AST_NODE_TYPES.TSVoidKeyword
);
}

/**
* Detect `a(): void` and `a(x: number): void`.
* Returns the parameter declaration (`x: number` in this example) that should be optional/rest, and overload it's a part of.
Expand All @@ -310,6 +334,19 @@
const shorter = sig1.length < sig2.length ? sig1 : sig2;
const shorterSig = sig1.length < sig2.length ? a : b;

const firstParam1 = sig1.at(0);
const firstParam2 = sig2.at(0);
// If one signature has explicit this type and another doesn't, they can't
// be unified.
if (isThisParam(firstParam1) !== isThisParam(firstParam2)) {
return undefined;
}

// exempt signatures with `this: void` from the rule
if (isThisVoidParam(firstParam1) || isThisVoidParam(firstParam2)) {
return undefined;

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}

// If one is has 2+ parameters more than the other, they must all be optional/rest.
// Differ by optional parameters: f() and f(x), f() and f(x, ?y, ...z)
// Not allowed: f() and f(x, y)
Expand Down
83 changes: 83 additions & 0 deletions packages/eslint-plugin/tests/rules/unified-signatures.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -380,6 +380,21 @@ declare function f(x: boolean): unknown;
`,
options: [{ ignoreOverloadsWithDifferentJSDoc: true }],
},
`
function f(): void;
function f(this: {}): void;
function f(this: void | {}): void {}
`,
`
function f(a: boolean): void;
function f(this: {}, a: boolean): void;
function f(this: void | {}, a: boolean): void {}
`,
`
function f(this: void, a: boolean): void;
function f(this: {}, a: boolean): void;
function f(this: void | {}, a: boolean): void {}
`,
],
invalid: [
{
Expand Down Expand Up @@ -1136,5 +1151,73 @@ declare function f(x: boolean): unknown;
],
options: [{ ignoreOverloadsWithDifferentJSDoc: true }],
},
{
code: `
function f(this: {}, a: boolean): void;
function f(this: {}, a: string): void;
function f(this: {}, a: boolean | string): void {}
`,
errors: [
{
column: 22,
line: 3,
messageId: 'singleParameterDifference',
},
],
},
{
code: `
function f(this: {}): void;
function f(this: {}, a: string): void;
function f(this: {}, a?: string): void {}
`,
errors: [
{
column: 22,
line: 3,
messageId: 'omittingSingleParameter',
},
],
},
{
code: `
function f(this: string): void;
function f(this: number): void;
function f(this: string | number): void {}
`,
errors: [
{
column: 12,
data: {
failureStringStart:
'These overloads can be combined into one signature',
type1: 'string',
type2: 'number',
},
line: 3,
messageId: 'singleParameterDifference',
},
],
},
{
code: `
function f(this: string, a: boolean): void;
function f(this: number, a: boolean): void;
function f(this: string | number, a: boolean): void {}
`,
errors: [
{
column: 12,
data: {
failureStringStart:
'These overloads can be combined into one signature',
type1: 'string',
type2: 'number',
},
line: 3,
messageId: 'singleParameterDifference',
},
],
},
],
});