frontend/eslint-rules.mjs

const readability = {
	create(context) {
		const filename = context.filename;

		function checkParameters(node) {
			const last = node.params.at(-1);
			if (
				last?.type === "Identifier"
				&& !last.optional
				&& last.typeAnnotation?.typeAnnotation.type === "TSUnionType"
				&& last.typeAnnotation.typeAnnotation.types.some(
					type => type.type === "TSUndefinedKeyword",
				)
			)
				context.report({ messageId: "optional", node: last });
		}

		return {
			ArrowFunctionExpression: checkParameters,
			CallExpression(node) {
				if (
					node.callee.type === "MemberExpression"
					&& ["refine", "superRefine"].includes(node.callee.property.name)
					&& !filename.endsWith(".schema.ts")
				)
					context.report({ messageId: "schema", node });
			},
			FunctionDeclaration: checkParameters,
			FunctionExpression: checkParameters,
			ImportDeclaration(node) {
				if (
					node.source.value === "zod"
					&& node.importKind !== "type"
					&& !filename.endsWith(".schema.ts")
				)
					context.report({ messageId: "schema", node });
			},
			JSXOpeningElement(node) {
				if (
					!filename.includes("/packages/icons/")
					&& node.name.type === "JSXIdentifier"
					&& /^(?:svg|path|circle|ellipse|rect|polygon|polyline|line|g|defs|use|symbol)$/.test(
						node.name.name,
					)
				)
					context.report({ messageId: "svg", node });
			},
			TSUnionType(node) {
				const complex
					= node.types.length > 2
						|| node.types.some(type => type.type === "TSTypeLiteral");

				if (
					complex
					&& node.types.some(
						(type, index) =>
							index > 0
							&& type.loc.start.line === node.types[index - 1].loc.end.line,
					)
				)
					context.report({ messageId: "union", node });
			},
			VariableDeclarator(node) {
				if (
					!/^[A-Z]/.test(node.id.name ?? "")
					|| node.init?.type !== "ArrowFunctionExpression"
					|| node.init.body.type !== "BlockStatement"
				)
					return;

				for (const statement of node.init.body.body) {
					if (statement.type === "FunctionDeclaration")
						context.report({ messageId: "helper", node: statement });

					else if (statement.type === "VariableDeclaration") {
						for (const declaration of statement.declarations) {
							if (
								["ArrowFunctionExpression", "FunctionExpression"].includes(
									declaration.init?.type,
								)
							)
								context.report({ messageId: "helper", node: declaration });
						}
					}
				}
			},
		};
	},
	meta: {
		messages: {
			helper:
				"Move helpers outside components; actions belong to the ViewModel.",
			optional:
				"Use an optional trailing parameter instead of a union with undefined.",
			schema: "Declare Zod schemas in a dedicated *.schema.ts file.",
			svg: "Own SVG markup in packages/icons, and import its public component.",
			union: "Put complex union members on separate lines.",
		},
		schema: [],
		type: "suggestion",
	},
};

function isComponent(node) {
	const pending = [node];

	while (pending.length > 0) {
		const child = pending.pop();
		if (!child) continue;

		switch (child.type) {
			case "JSXElement": {
				return true;
			}

			case "JSXFragment": {
				return true;
			}

			case "JSXExpressionContainer": {
				pending.push(child.expression);
				continue;
			}

			case "LogicalExpression": {
				pending.push(child.right);
				continue;
			}

			case "ConditionalExpression": {
				pending.push(child.consequent, child.alternate);
				continue;
			}
		}
	}

	return false;
}

const jsxSpacing = {
	create(context) {
		function check(node) {
			let previous;

			for (const child of node.children) {
				if (child.type === "JSXText" && !child.value.trim()) continue;
				if (isComponent(child)) {
					if (previous) {
						const gap = context.sourceCode.text.slice(
							previous.range[1],
							child.range[0],
						);

						if (!/\n\s*\n/.test(gap))
							context.report({
								fix: fixer => fixer.insertTextAfter(previous, "\n"),
								messageId: "space",
								node: child,
							});
					}

					previous = child;
				}
				else previous = undefined;
			}
		}

		return { JSXElement: check, JSXFragment: check };
	},
	meta: {
		fixable: "whitespace",
		messages: { space: "Separate sibling JSX components with a blank line." },
		schema: [],
		type: "layout",
	},
};

export default { rules: { "jsx-spacing": jsxSpacing, readability } };