fix: support TSFunctionType in getFunctionHeadLoc (#21335)

fix: correct `max-params` report location for TS function types

Author: xbinaryx

lib/rules/utils/ast-utils.js

@@ -2394,6 +2394,8 @@ module.exports = {
 	 *              ^^^^^^^^^^^^^^^^^^^^^
 	 * - `class A { foo = (a, b) => {} }`
 	 *              ^^^^^^
+	 * - `type F = (a, b) => void`
+	 *                    ^^
 	 * @param {ASTNode} node The function node to get.
 	 * @param {SourceCode} sourceCode The source code object to get tokens.
 	 * @returns {string} The location of the function node for reporting.
@@ -2418,6 +2420,14 @@ module.exports = {
 				isArrowToken,
 			);
 
+			start = arrowToken.loc.start;
+			end = arrowToken.loc.end;
+		} else if (node.type === "TSFunctionType") {
+			const arrowToken = sourceCode.getTokenBefore(
+				node.returnType.typeAnnotation,
+				isArrowToken,
+			);
+
 			start = arrowToken.loc.start;
 			end = arrowToken.loc.end;
 		} else {

tests/lib/rules/max-params.js

@@ -328,14 +328,124 @@ ruleTesterTypeScript.run("max-params", rule, {
   declare function makeDate(m: number, d: number, y: number): Date;
 		`,
 			options: [{ max: 1 }],
-			errors: [{ messageId: "exceed" }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function 'makeDate'", count: 3, max: 1 },
+					line: 2,
+					column: 3,
+					endLine: 2,
+					endColumn: 28,
+				},
+			],
 		},
 		{
 			code: `
   type sum = (a: number, b: number) => number;
 		`,
 			options: [{ max: 1 }],
-			errors: [{ messageId: "exceed" }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 2,
+					column: 37,
+					endLine: 2,
+					endColumn: 39,
+				},
+			],
+		},
+		{
+			code: "let f: (a: number, b: number) => number;",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 31,
+					endLine: 1,
+					endColumn: 33,
+				},
+			],
+		},
+		{
+			code: "interface I { m: (a: number, b: number) => number; }",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 41,
+					endLine: 1,
+					endColumn: 43,
+				},
+			],
+		},
+		{
+			code: "function g(cb: (a: number, b: number) => number) {}",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 39,
+					endLine: 1,
+					endColumn: 41,
+				},
+			],
+		},
+		{
+			code: "declare function g(): (a: number, b: number) => number;",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 46,
+					endLine: 1,
+					endColumn: 48,
+				},
+			],
+		},
+		{
+			code: "type F = <T>(a: T, b: T) => T;",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 26,
+					endLine: 1,
+					endColumn: 28,
+				},
+			],
+		},
+		{
+			code: "type F = (a: number, b: number) => (c: number, d: number) => number;",
+			options: [{ max: 1 }],
+			errors: [
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 33,
+					endLine: 1,
+					endColumn: 35,
+				},
+				{
+					messageId: "exceed",
+					data: { name: "Function", count: 2, max: 1 },
+					line: 1,
+					column: 59,
+					endLine: 1,
+					endColumn: 61,
+				},
+			],
 		},
 		{
 			code: `function foo(this: unknown[], a, b, c) {}`,

tests/lib/rules/utils/ast-utils.js

@@ -1257,6 +1257,44 @@ describe("ast-utils", () => {
 				);
 			});
 		});
+
+		it('should return the location of the `=>` token for "type F = (a, b) => void".', () => {
+			const expectedLoc = {
+				start: { line: 1, column: 16 },
+				end: { line: 1, column: 18 },
+			};
+
+			linter.verify(
+				"type F = (a, b) => void",
+				{
+					files: ["**/*.ts"],
+					languageOptions: {
+						parser: require("@typescript-eslint/parser"),
+					},
+					plugins: {
+						test: {
+							rules: {
+								checker: {
+									create: mustCall(() => ({
+										TSFunctionType: mustCall(node => {
+											assert.deepStrictEqual(
+												astUtils.getFunctionHeadLoc(
+													node,
+													linter.getSourceCode(),
+												),
+												expectedLoc,
+											);
+										}),
+									})),
+								},
+							},
+						},
+					},
+					rules: { "test/checker": "error" },
+				},
+				"test.ts",
+			);
+		});
 	});
 
 	describe("isEmptyBlock", () => {