fix(eslint-plugin): [typedef] support "for..in", "for..of" (typescript-eslint#787)

octogonz · bradzacher · commit 39e41b56ca26 · 2019-08-01T17:57:04.000-07:00
diff --git a/packages/eslint-plugin/src/rules/typedef.ts b/packages/eslint-plugin/src/rules/typedef.ts
@@ -142,7 +142,32 @@ export default util.createRule<[Options], MessageIds>({
           options[OptionKeys.VariableDeclaration] &&
           !node.id.typeAnnotation
         ) {
-          report(node, getNodeName(node.id));
+          // Are we inside a context that does not allow type annotations?
+          let typeAnnotationRequired = true;
+
+          let current: TSESTree.Node | undefined = node.parent;
+          while (current) {
+            switch (current.type) {
+              case AST_NODE_TYPES.VariableDeclaration:
+                // Keep looking upwards
+                current = current.parent;
+                break;
+              case AST_NODE_TYPES.ForOfStatement:
+              case AST_NODE_TYPES.ForInStatement:
+                // Stop traversing and don't report an error
+                typeAnnotationRequired = false;
+                current = undefined;
+                break;
+              default:
+                // Stop traversing
+                current = undefined;
+                break;
+            }
+          }
+
+          if (typeAnnotationRequired) {
+            report(node, getNodeName(node.id));
+          }
         }
       },
     };
diff --git a/packages/eslint-plugin/tests/rules/typedef.test.ts b/packages/eslint-plugin/tests/rules/typedef.test.ts
@@ -198,6 +198,31 @@ ruleTester.run('typedef', rule, {
         },
       ],
     },
+    // Contexts where TypeScript doesn't allow annotations
+    {
+      code: `for (x of [1, 2, 3]) { }`,
+      options: [
+        {
+          variableDeclaration: true,
+        },
+      ],
+    },
+    {
+      code: `for (const x in {}) { }`,
+      options: [
+        {
+          variableDeclaration: true,
+        },
+      ],
+    },
+    {
+      code: `try { } catch (e) { }`,
+      options: [
+        {
+          variableDeclaration: true,
+        },
+      ],
+    },
   ],
   invalid: [
     // Array destructuring
