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feat: ignore overloaded function declarations in func-style rule #19755

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Merged
merged 7 commits into from
May 27, 2025
Merged

feat: ignore overloaded function declarations in func-style rule #19755

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2a23382
feat: ignore overloaded function declarations in func-style rule
sethamus May 23, 2025
5449f62
Merge branch 'main' into ignore-overloaded-function-declarations
sethamus May 23, 2025
61ea43d
fix CI
sethamus May 23, 2025
9b088a4
refactor
sethamus May 25, 2025
ff26693
add more tests
sethamus May 26, 2025
9dfcb5e
refactor
sethamus May 26, 2025
baf6230
add tests
sethamus May 26, 2025
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18 changes: 18 additions & 0 deletions docs/src/rules/func-style.md
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,24 @@ const foo1 = () => {};

:::

Overloaded function declarations are not reported as errors by this rule. These are functions that have multiple declarations with the same name but different parameter types or return types (commonly used in TypeScript to provide type information for different ways of calling the same function).

Examples of **correct** TypeScript code for this rule with the default `"expression"` option:

::: correct

```ts
/*eslint func-style: ["error", "expression"]*/

function process(value: string): string;
function process(value: number): number;
function process(value: unknown) {
return value;
}
```

:::

### declaration

Examples of **incorrect** code for this rule with the `"declaration"` option:
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43 changes: 41 additions & 2 deletions lib/rules/func-style.js
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Expand Up @@ -65,6 +65,43 @@ module.exports = {
const { namedExports: exportFunctionStyle } = overrides;
const stack = [];

/**
* Checks if a function declaration is part of an overloaded function
* @param {ASTNode} node The function declaration node to check
* @returns {boolean} True if the function is overloaded
*/
function isOverloadedFunction(node) {
const functionName = node.id.name;

if (node.parent.type === "ExportNamedDeclaration") {
return node.parent.parent.body.some(
member =>
member.type === "ExportNamedDeclaration" &&
member.declaration?.type === "TSDeclareFunction" &&
member.declaration.id.name === functionName,
);
}

if (node.parent.type === "SwitchCase") {
return node.parent.parent.cases.some(switchCase =>
switchCase.consequent.some(
member =>
member.type === "TSDeclareFunction" &&
member.id.name === functionName,
),
);
}

return (
Array.isArray(node.parent.body) &&
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There's still no test that would hit this. I think those tests should have the "expression"` option.

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Aside from labeled function declarations, which was caught by CI (hence this check), I can't think of any other scenario where node.parent.body wouldn't be an array.

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The tests you added in 9b088a4 would hit this, but with options: ["expression"].

Another example of a function declaration where node.parent.body is not an array could be if (foo) function bar() {} (just needs sourceType: "script" to be a valid syntax).

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@sethamus sethamus May 26, 2025 •
edited
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Oh right I misunderstood your previous comments, sorry about that.

node.parent.body.some(
member =>
member.type === "TSDeclareFunction" &&
member.id.name === functionName,
)
);
}

const nodesToCheck = {
FunctionDeclaration(node) {
stack.push(false);
Expand All @@ -73,14 +110,16 @@ module.exports = {
!enforceDeclarations &&
node.parent.type !== "ExportDefaultDeclaration" &&
(typeof exportFunctionStyle === "undefined" ||
node.parent.type !== "ExportNamedDeclaration")
node.parent.type !== "ExportNamedDeclaration") &&
!isOverloadedFunction(node)
) {
context.report({ node, messageId: "expression" });
}

if (
node.parent.type === "ExportNamedDeclaration" &&
exportFunctionStyle === "expression"
exportFunctionStyle === "expression" &&
!isOverloadedFunction(node)
) {
context.report({ node, messageId: "expression" });
}
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