typescript-eslint · bradzacher · Feb 2, 2020 · Jan 31, 2020
diff --git a/packages/eslint-plugin/docs/rules/explicit-module-boundary-types.md b/packages/eslint-plugin/docs/rules/explicit-module-boundary-types.md
@@ -65,13 +65,26 @@ The rule accepts an options object with the following properties:
 
 ```ts
 type Options = {
-  // if true, type annotations are also allowed on the variable of a function expression rather than on the function directly
+  /**
+   * If true, type annotations are also allowed on the variable of a function expression
+   * rather than on the function arguments/return value directly.
+   */
   allowTypedFunctionExpressions?: boolean;
-  // if true, functions immediately returning another function expression will not be checked
+  /**
+   * If true, functions immediately returning another function expression will not
+   * require an explicit return value annotation.
+   * You must still type the parameters of the function.
+   */
   allowHigherOrderFunctions?: boolean;
-  // if true, body-less arrow functions are allowed to return an object as const
+  /**
+   * If true, body-less arrow functions that return an `as const` type assertion will not
+   * require an explicit return value annotation.
+   * You must still type the parameters of the function.
+   */
   allowDirectConstAssertionInArrowFunctions?: boolean;
-  // an array of function/method names that will not be checked
+  /**
+   * An array of function/method names that will not have their arguments or their return values checked.
+   */
   allowedNames?: string[];
 };
 
@@ -118,6 +131,8 @@ export let funcExpr = function() {
 export let objectProp = {
   foo: () => 1,
 };
+
+export const foo = bar => {};
 ```
 
 Examples of additional **correct** code for this rule with `{ allowTypedFunctionExpressions: true }`:
@@ -146,6 +161,9 @@ export let objectPropAs = {
 export let objectPropCast = <ObjectType>{
   foo: () => 1,
 };
+
+type FooType = (bar: string) => void;
+export const foo: FooType = bar => {};
 ```
 
 ### `allowHigherOrderFunctions`
@@ -158,6 +176,10 @@ export var arrowFn = () => () => {};
 export function fn() {
   return function() {};
 }
+
+export function foo(outer) {
+  return function(inner): void {};
+}
 ```
 
 Examples of **correct** code for this rule with `{ allowHigherOrderFunctions: true }`:
@@ -168,17 +190,15 @@ export var arrowFn = () => (): void => {};
 export function fn() {
   return function(): void {};
 }
+
+export function foo(outer: string) {
+  return function(inner: string): void {};
+}
 ```
 
 ### `allowDirectConstAssertionInArrowFunctions`
 
-Examples of additional **correct** code for this rule with `{ allowDirectConstAssertionInArrowFunctions: true }`:
-
-```ts
-export const func = (value: number) => ({ type: 'X', value } as const);
-```
-
-Examples of additional **incorrect** code for this rule with `{ allowDirectConstAssertionInArrowFunctions: true }`:
+Examples of **incorrect** code for this rule with `{ allowDirectConstAssertionInArrowFunctions: true }`:
 
 ```ts
 export const func = (value: number) => ({ type: 'X', value });
@@ -187,15 +207,34 @@ export const foo = () => {
     bar: true,
   } as const;
 };
+export const bar = () => 1;
+export const baz = arg => arg as const;
+```
+
+Examples of **correct** code for this rule with `{ allowDirectConstAssertionInArrowFunctions: true }`:
+
+```ts
+export const func = (value: number) => ({ type: 'X', value } as const);
+export const foo = () =>
+  ({
+    bar: true,
+  } as const);
+export const bar = () => 1 as const;
+export const baz = (arg: string) => arg as const;
 ```
 
 ### `allowedNames`
 
 You may pass function/method names you would like this rule to ignore, like so:
 
-```cjson
+```json
 {
-    "@typescript-eslint/explicit-module-boundary-types": ["error", { "allowedName": ["ignoredFunctionName", "ignoredMethodName"] }]
+  "@typescript-eslint/explicit-module-boundary-types": [
+    "error",
+    {
+      "allowedName": ["ignoredFunctionName", "ignoredMethodName"]
+    }
+  ]
 }
 ```
 

diff --git a/packages/eslint-plugin/src/rules/explicit-module-boundary-types.ts b/packages/eslint-plugin/src/rules/explicit-module-boundary-types.ts
@@ -6,6 +6,7 @@ import * as util from '../util';
 import {
   checkFunctionExpressionReturnType,
   checkFunctionReturnType,
+  isTypedFunctionExpression,
 } from '../util/explicitReturnTypeUtils';
 
 type Options = [
@@ -178,7 +179,11 @@ export default util.createRule<Options, MessageIds>({
           return;
         }
 
-        if (isAllowedName(node.parent) || isUnexported(node)) {
+        if (
+          isAllowedName(node.parent) ||
+          isUnexported(node) ||
+          isTypedFunctionExpression(node, options)
+        ) {
           return;
         }
 

diff --git a/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts b/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts
@@ -5,6 +5,7 @@ import {
   AST_TOKEN_TYPES,
 } from '@typescript-eslint/experimental-utils';
 import { isTypeAssertion, isConstructor, isSetter } from './astUtils';
+import { nullThrows, NullThrowsReasons } from './nullThrows';
 
 type FunctionNode =
   | TSESTree.ArrowFunctionExpression
@@ -264,6 +265,26 @@ function checkFunctionReturnType(
   report(getReporLoc(node, sourceCode));
 }
 
+function isTypedFunctionExpression(
+  node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression,
+  options: Options,
+): boolean {
+  const parent = nullThrows(node.parent, NullThrowsReasons.MissingParent);
+
+  if (!options.allowTypedFunctionExpressions) {
+    return false;
+  }
+
+  return (
+    isTypeAssertion(parent) ||
+    isVariableDeclaratorWithTypeAnnotation(parent) ||
+    isClassPropertyWithTypeAnnotation(parent) ||
+    isPropertyOfObjectWithType(parent) ||
+    isFunctionArgument(parent, node) ||
+    isConstructorArgument(parent)
+  );
+}
+
 /**
  * Checks if a function declaration/expression has a return type.
  */
@@ -273,36 +294,25 @@ function checkFunctionExpressionReturnType(
   sourceCode: TSESLint.SourceCode,
   report: (loc: TSESTree.SourceLocation) => void,
 ): void {
-  // Should always have a parent; checking just in case
-  /* istanbul ignore else */ if (node.parent) {
-    if (options.allowTypedFunctionExpressions) {
-      if (
-        isTypeAssertion(node.parent) ||
-        isVariableDeclaratorWithTypeAnnotation(node.parent) ||
-        isClassPropertyWithTypeAnnotation(node.parent) ||
-        isPropertyOfObjectWithType(node.parent) ||
-        isFunctionArgument(node.parent, node) ||
-        isConstructorArgument(node.parent)
-      ) {
-        return;
-      }
-    }
+  if (isTypedFunctionExpression(node, options)) {
+    return;
+  }
 
-    if (
-      options.allowExpressions &&
-      node.parent.type !== AST_NODE_TYPES.VariableDeclarator &&
-      node.parent.type !== AST_NODE_TYPES.MethodDefinition &&
-      node.parent.type !== AST_NODE_TYPES.ExportDefaultDeclaration &&
-      node.parent.type !== AST_NODE_TYPES.ClassProperty
-    ) {
-      return;
-    }
+  const parent = nullThrows(node.parent, NullThrowsReasons.MissingParent);
+  if (
+    options.allowExpressions &&
+    parent.type !== AST_NODE_TYPES.VariableDeclarator &&
+    parent.type !== AST_NODE_TYPES.MethodDefinition &&
+    parent.type !== AST_NODE_TYPES.ExportDefaultDeclaration &&
+    parent.type !== AST_NODE_TYPES.ClassProperty
+  ) {
+    return;
   }
 
   // https://github.com/typescript-eslint/typescript-eslint/issues/653
   if (
-    node.type === AST_NODE_TYPES.ArrowFunctionExpression &&
     options.allowDirectConstAssertionInArrowFunctions &&
+    node.type === AST_NODE_TYPES.ArrowFunctionExpression &&
     returnsConstAssertionDirectly(node)
   ) {
     return;
@@ -311,4 +321,8 @@ function checkFunctionExpressionReturnType(
   checkFunctionReturnType(node, options, sourceCode, report);
 }
 
-export { checkFunctionReturnType, checkFunctionExpressionReturnType };
+export {
+  checkFunctionReturnType,
+  checkFunctionExpressionReturnType,
+  isTypedFunctionExpression,
+};