fix(eslint-plugin): [explicit-function-return-types] fix false positi…

…ve on default parameters (#9045) [explicit-function-return-types] default parameters where a type annotation is present should count as typed function expressions fix #8950 Co-authored-by: auvred <61150013+auvred@users.noreply.github.com>
typescript-eslint · May 13, 2024 · 8acb8d4 · 8acb8d4
1 parent 7ce6acd
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diff --git a/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts b/packages/eslint-plugin/src/util/explicitReturnTypeUtils.ts
@@ -87,12 +87,22 @@ function isTypedParent(
   return (
     isTypeAssertion(parent) ||
     isVariableDeclaratorWithTypeAnnotation(parent) ||
+    isDefaultFunctionParameterWithTypeAnnotation(parent) ||
     isPropertyDefinitionWithTypeAnnotation(parent) ||
     isFunctionArgument(parent, callee) ||
     isTypedJSX(parent)
   );
 }
 
+function isDefaultFunctionParameterWithTypeAnnotation(
+  node: TSESTree.Node,
+): boolean {
+  return (
+    node.type === AST_NODE_TYPES.AssignmentPattern &&
+    node.left.typeAnnotation != null
+  );
+}
+
 /**
  * Checks if a node belongs to:
  * ```

diff --git a/packages/eslint-plugin/tests/rules/explicit-function-return-type.test.ts b/packages/eslint-plugin/tests/rules/explicit-function-return-type.test.ts
@@ -770,7 +770,32 @@ class Bar {
 }
       `,
     },
+    {
+      code: `
+type CallBack = () => void;
+
+function f(gotcha: CallBack = () => {}): void {}
+      `,
+      options: [{ allowTypedFunctionExpressions: true }],
+    },
+    {
+      code: `
+type CallBack = () => void;
+
+const f = (gotcha: CallBack = () => {}): void => {};
+      `,
+      options: [{ allowTypedFunctionExpressions: true }],
+    },
+    {
+      code: `
+type ObjectWithCallback = { callback: () => void };
+
+const f = (gotcha: ObjectWithCallback = { callback: () => {} }): void => {};
+      `,
+      options: [{ allowTypedFunctionExpressions: true }],
+    },
   ],
+
   invalid: [
     {
       code: `
@@ -1940,5 +1965,54 @@ let foo = (() => () => {})()();
         },
       ],
     },
+    {
+      code: `
+type CallBack = () => void;
+
+function f(gotcha: CallBack = () => {}): void {}
+      `,
+      options: [{ allowTypedFunctionExpressions: false }],
+      errors: [
+        {
+          messageId: 'missingReturnType',
+          line: 4,
+          column: 34,
+          endLine: 4,
+          endColumn: 36,
+        },
+      ],
+    },
+    {
+      code: `
+type CallBack = () => void;
+
+const f = (gotcha: CallBack = () => {}): void => {};
+      `,
+      options: [{ allowTypedFunctionExpressions: false }],
+      errors: [
+        {
+          messageId: 'missingReturnType',
+          line: 4,
+          column: 34,
+          endLine: 4,
+          endColumn: 36,
+        },
+      ],
+    },
+    {
+      code: `
+type ObjectWithCallback = { callback: () => void };
+
+const f = (gotcha: ObjectWithCallback = { callback: () => {} }): void => {};
+      `,
+      options: [{ allowTypedFunctionExpressions: false }],
+      errors: [
+        {
+          messageId: 'missingReturnType',
+          line: 4,
+          column: 43,
+        },
+      ],
+    },
   ],
 });