chore: add exported-function-args-maximum Deno Style Guide linter plugin

_tools/lint_plugin.ts

@@ -310,5 +310,45 @@
         };
       },
     },
+    // https://docs.deno.com/runtime/contributing/style_guide/#exported-functions%3A-max-2-args%2C-put-the-rest-into-an-options-object
+    "exported-function-args-maximum": {
+      create(context) {
+        return {
+          ExportNamedDeclaration(node) {
+            const declaration = node.declaration;
+            if (declaration?.type !== "FunctionDeclaration") return;
+            const params = declaration.params;
+            const id = declaration.id;
+            if (params.length < 3) return;
+            if (params.length === 3) {
+              const param = params.at(-1)!;
+
+              switch (param.type) {
+                case "Identifier":
+                  if (param.name === "options") return;
+                  break;
+                case "AssignmentPattern": {
+                  if (param.right.type === "ObjectExpression") return;
+                  break;
+                }
+              }
+              return context.report({
+                node: id ?? declaration,
+                message:
+                  "Third argument of export function is not an options object.",
+                hint:
+                  "Export functions can have 0-2 required arguments, plus (if necessary) an options object (so max 3 total).",
+              });
+            }
+            context.report({
+              node: id ?? declaration,
+              message: "Exported function has more than three arguments.",
+              hint:
+                "Export functions can have 0-2 required arguments, plus (if necessary) an options object (so max 3 total).",
+            });
+          },
+        };
+      },
+    },
   },
 } satisfies Deno.lint.Plugin;

_tools/lint_plugin_test.ts

@@ -310,3 +310,60 @@ new CustomError("Can't parse input");
     ],
   );
 });
+
+Deno.test("deno-style-guide/exported-function-args-maximum", {
+  ignore: !Deno.version.deno.startsWith("2"),
+}, () => {
+  // Good
+  assertLintPluginDiagnostics(
+    `
+function foo() {
+}
+function foo(bar: unknown) {
+}
+function foo(bar: unknown, baz: unknown) {
+}
+function foo(bar: unknown, baz: unknown, options: Record<string, unknown>) {
+}
+function foo(bar: unknown, baz: unknown, bat: unknown, bay: unknown) {
+}
+export function foo() {
+}
+export function foo(bar: unknown) {
+}
+export function foo(bar: unknown, baz: unknown) {
+}
+export function foo(bar: unknown, baz: unknown, options: Record<string, unknown>) {
+}
+    `,
+    [],
+  );
+
+  // Bad
+  assertLintPluginDiagnostics(
+    `
+export function foo(bar: unknown, baz: unknown, bat: unknown) {
+}
+export function foo(bar: unknown, baz: unknown, bat: unknown, options: Record<string, unknown>) {
+}
+`,
+    [
+      {
+        fix: [],
+        hint:
+          "Export functions can have 0-2 required arguments, plus (if necessary) an options object (so max 3 total).",
+        id: "deno-style-guide/exported-function-args-maximum",
+        message: "Third argument of export function is not an options object.",
+        range: [17, 20],
+      },
+      {
+        fix: [],
+        hint:
+          "Export functions can have 0-2 required arguments, plus (if necessary) an options object (so max 3 total).",
+        id: "deno-style-guide/exported-function-args-maximum",
+        message: "Exported function has more than three arguments.",
+        range: [83, 86],
+      },
+    ],
+  );
+});

assert/almost_equals.ts

@@ -29,6 +29,7 @@ import { AssertionError } from "./assertion_error.ts";
  * default is one hundred thousandth of a percent of the expected value.
  * @param msg The optional message to include in the error.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertAlmostEquals(
   actual: number,
   expected: number,

assert/array_includes.ts

@@ -27,6 +27,7 @@ export type ArrayLikeArg<T> = ArrayLike<T> & object;
  * @param expected The array-like object to check for.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertArrayIncludes<T>(
   actual: ArrayLikeArg<T>,
   expected: ArrayLikeArg<T>,

assert/equals.ts

@@ -41,6 +41,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertEquals<T>(
   actual: T,
   expected: T,

assert/greater.ts

@@ -21,6 +21,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertGreater<T>(actual: T, expected: T, msg?: string) {
   if (actual > expected) return;
 

assert/greater_or_equal.ts

@@ -21,6 +21,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertGreaterOrEqual<T>(
   actual: T,
   expected: T,

assert/instance_of.ts

@@ -25,6 +25,7 @@ export type GetConstructorType<T extends AnyConstructor> = InstanceType<T>;
  * @param expectedType The expected class constructor.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertInstanceOf<
   // deno-lint-ignore no-explicit-any
   T extends abstract new (...args: any[]) => any,

assert/is_error.ts

@@ -26,6 +26,7 @@ import { stripAnsiCode } from "@std/internal/styles";
  * @param msgMatches The optional string or RegExp to assert in the error message.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertIsError<E extends Error = Error>(
   error: unknown,
   // deno-lint-ignore no-explicit-any

assert/less.ts

@@ -20,6 +20,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertLess<T>(actual: T, expected: T, msg?: string) {
   if (actual < expected) return;
 

assert/less_or_equal.ts

@@ -21,6 +21,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertLessOrEqual<T>(
   actual: T,
   expected: T,

assert/match.ts

@@ -18,6 +18,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected pattern to match.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertMatch(
   actual: string,
   expected: RegExp,

assert/not_equals.ts

@@ -24,6 +24,7 @@ import { format } from "@std/internal/format";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertNotEquals<T>(actual: T, expected: T, msg?: string) {
   if (!equal(actual, expected)) {
     return;

assert/not_instance_of.ts

@@ -20,6 +20,7 @@ import { assertFalse } from "./false.ts";
  * @param unexpectedType The class constructor to check against.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertNotInstanceOf<A, T>(
   actual: A,
   // deno-lint-ignore no-explicit-any

assert/not_match.ts

@@ -18,6 +18,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to not match.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertNotMatch(
   actual: string,
   expected: RegExp,

assert/not_strict_equals.ts

@@ -24,6 +24,7 @@ import { format } from "@std/internal/format";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertNotStrictEquals<T>(
   actual: T,
   expected: T,

assert/object_match.ts

@@ -29,6 +29,7 @@ import { assertEquals } from "./equals.ts";
  * @param expected The expected value to match.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertObjectMatch(
   // deno-lint-ignore no-explicit-any
   actual: Record<PropertyKey, any>,

assert/rejects.ts

@@ -53,6 +53,7 @@ export function assertRejects<E extends Error = Error>(
   msgIncludes?: string,
   msg?: string,
 ): Promise<E>;
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export async function assertRejects<E extends Error = Error>(
   fn: () => PromiseLike<unknown>,
   errorClassOrMsg?:

assert/strict_equals.ts

@@ -29,6 +29,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected value to compare.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertStrictEquals<T>(
   actual: unknown,
   expected: T,

assert/string_includes.ts

@@ -18,6 +18,7 @@ import { AssertionError } from "./assertion_error.ts";
  * @param expected The expected string to check for inclusion.
  * @param msg The optional message to display if the assertion fails.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertStringIncludes(
   actual: string,
   expected: string,

assert/throws.ts

@@ -56,6 +56,7 @@ export function assertThrows<E extends Error = Error>(
   msgIncludes?: string,
   msg?: string,
 ): E;
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function assertThrows<E extends Error = Error>(
   fn: () => unknown,
   errorClassOrMsg?:

async/_util.ts

@@ -1,6 +1,7 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
 // This module is browser compatible.
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function exponentialBackoffWithJitter(
   cap: number,
   base: number,

async/pool.ts

@@ -36,6 +36,7 @@ const ERROR_WHILE_MAPPING_MESSAGE =
  * @param iteratorFn The function to call for every item of the array.
  * @returns The async iterator with the transformed values.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function pooledMap<T, R>(
   poolLimit: number,
   array: Iterable<T> | AsyncIterable<T>,

bytes/copy.ts

@@ -40,6 +40,7 @@
  * Defining an offset will start copying at the specified index in the
  * destination array.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function copy(src: Uint8Array, dst: Uint8Array, offset = 0): number {
   offset = Math.max(0, Math.min(offset, dst.byteLength));
   const dstBytesAvailable = dst.byteLength - offset;

bytes/includes_needle.ts

@@ -39,6 +39,7 @@ import { indexOfNeedle } from "./index_of_needle.ts";
  * ```
  * The search will start at the specified index in the source array.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function includesNeedle(
   source: Uint8Array,
   needle: Uint8Array,

bytes/index_of_needle.ts

@@ -44,6 +44,7 @@
  * Defining a start index will begin the search at the specified index in the
  * source array.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function indexOfNeedle(
   source: Uint8Array,
   needle: Uint8Array,

bytes/last_index_of_needle.ts

@@ -41,6 +41,7 @@
  * Defining a start index will begin the search at the specified index in the
  * source array.
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function lastIndexOfNeedle(
   source: Uint8Array,
   needle: Uint8Array,

cbor/_common_encode.ts

@@ -60,6 +60,7 @@ export function calcEncodingSize(x: CborType): number {
   return size + calcHeaderSize(pairs);
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function encode(
   input: CborType,
   output: Uint8Array,

collections/reduce_groups.ts

@@ -36,6 +36,7 @@ import { mapValues } from "./map_values.ts";
  * });
  * ```
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function reduceGroups<T, A>(
   record: Readonly<Record<string, ReadonlyArray<T>>>,
   reducer: (accumulator: A, current: T) => A,

collections/running_reduce.ts

@@ -26,6 +26,7 @@
  * assertEquals(sumSteps, [1, 3, 6, 10, 15]);
  * ```
  */
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function runningReduce<T, O>(
   array: readonly T[],
   reducer: (accumulator: O, current: T, currentIndex: number) => O,

csv/_io.ts

@@ -56,6 +56,7 @@ export interface LineReader {
   isEOF(): boolean;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export async function parseRecord(
   fullLine: string,
   reader: LineReader,
@@ -201,6 +202,7 @@ export async function parseRecord(
   return result;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function createBareQuoteErrorMessage(
   zeroBasedRecordStartLine: number,
   zeroBasedLine: number,
@@ -212,6 +214,7 @@ export function createBareQuoteErrorMessage(
     zeroBasedColumn + 1
   }: bare " in non-quoted-field`;
 }
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function createQuoteErrorMessage(
   zeroBasedRecordStartLine: number,
   zeroBasedLine: number,
@@ -224,6 +227,7 @@ export function createQuoteErrorMessage(
   }: extraneous or missing " in quoted-field`;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function convertRowToObject(
   row: readonly string[],
   headers: readonly string[],

encoding/_common16.ts

@@ -29,6 +29,7 @@ export function calcSizeHex(originalSize: number): number {
   return originalSize * 2;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function encode(
   buffer: Uint8Array_,
   i: number,
@@ -43,6 +44,7 @@ export function encode(
   return o;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function decode(
   buffer: Uint8Array_,
   i: number,

encoding/_common32.ts

@@ -53,6 +53,7 @@ export function calcSizeBase32(rawSize: number): number {
   return ((rawSize + 4) / 5 | 0) * 8;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function encode(
   buffer: Uint8Array_,
   i: number,
@@ -128,6 +129,7 @@ export function encode(
   return o;
 }
 
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
 export function decode(
   buffer: Uint8Array_,
   i: number,