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* @fileoverview Rule to enforce a particular function style
* @author Nicholas C. Zakas
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../types').Rule.RuleModule} */
module.exports = {
meta: {
dialects: ["javascript", "typescript"],
language: "javascript",
type: "suggestion",
defaultOptions: [
"expression",
{
allowArrowFunctions: false,
allowTypeAnnotation: false,
overrides: {},
},
],
docs: {
description:
"Enforce the consistent use of either `function` declarations or expressions assigned to variables",
recommended: false,
frozen: true,
url: "https://eslint.org/docs/latest/rules/func-style",
},
schema: [
{
enum: ["declaration", "expression"],
},
{
type: "object",
properties: {
allowArrowFunctions: {
type: "boolean",
},
allowTypeAnnotation: {
type: "boolean",
},
overrides: {
type: "object",
properties: {
namedExports: {
enum: ["declaration", "expression", "ignore"],
},
},
additionalProperties: false,
},
},
additionalProperties: false,
},
],
messages: {
expression: "Expected a function expression.",
declaration: "Expected a function declaration.",
},
},
create(context) {
const [style, { allowArrowFunctions, allowTypeAnnotation, overrides }] =
context.options;
const enforceDeclarations = style === "declaration";
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) &&
node.parent.body.some(
member =>
member.type === "TSDeclareFunction" &&
member.id.name === functionName,
)
);
}
const nodesToCheck = {
FunctionDeclaration(node) {
stack.push(false);
if (
!enforceDeclarations &&
node.parent.type !== "ExportDefaultDeclaration" &&
(typeof exportFunctionStyle === "undefined" ||
node.parent.type !== "ExportNamedDeclaration") &&
!isOverloadedFunction(node)
) {
context.report({ node, messageId: "expression" });
}
if (
node.parent.type === "ExportNamedDeclaration" &&
exportFunctionStyle === "expression" &&
!isOverloadedFunction(node)
) {
context.report({ node, messageId: "expression" });
}
},
"FunctionDeclaration:exit"() {
stack.pop();
},
FunctionExpression(node) {
stack.push(false);
if (
enforceDeclarations &&
node.parent.type === "VariableDeclarator" &&
(typeof exportFunctionStyle === "undefined" ||
node.parent.parent.parent.type !==
"ExportNamedDeclaration") &&
!(allowTypeAnnotation && node.parent.id.typeAnnotation)
) {
context.report({
node: node.parent,
messageId: "declaration",
});
}
if (
node.parent.type === "VariableDeclarator" &&
node.parent.parent.parent.type ===
"ExportNamedDeclaration" &&
exportFunctionStyle === "declaration" &&
!(allowTypeAnnotation && node.parent.id.typeAnnotation)
) {
context.report({
node: node.parent,
messageId: "declaration",
});
}
},
"FunctionExpression:exit"() {
stack.pop();
},
"ThisExpression, Super"() {
if (stack.length > 0) {
stack[stack.length - 1] = true;
}
},
};
if (!allowArrowFunctions) {
nodesToCheck.ArrowFunctionExpression = function () {
stack.push(false);
};
nodesToCheck["ArrowFunctionExpression:exit"] = function (node) {
const hasThisOrSuperExpr = stack.pop();
if (
!hasThisOrSuperExpr &&
node.parent.type === "VariableDeclarator"
) {
if (
enforceDeclarations &&
(typeof exportFunctionStyle === "undefined" ||
node.parent.parent.parent.type !==
"ExportNamedDeclaration") &&
!(allowTypeAnnotation && node.parent.id.typeAnnotation)
) {
context.report({
node: node.parent,
messageId: "declaration",
});
}
if (
node.parent.parent.parent.type ===
"ExportNamedDeclaration" &&
exportFunctionStyle === "declaration" &&
!(allowTypeAnnotation && node.parent.id.typeAnnotation)
) {
context.report({
node: node.parent,
messageId: "declaration",
});
}
}
};
}
return nodesToCheck;
},
};
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