fix: fix no-unused-vars with with default type in GenericType (#411)

Author: HsuTing

src/rules/useFlowType.js

@@ -4,33 +4,43 @@ const create = (context) => {
   const markTypeAsUsed = (node) => {
     context.markVariableAsUsed(node.id.name);
   };
+  const markTypeAsUsedWithGenericType = (node) => {
+    let typeId;
+    let scope;
+    let variable;
+
+    if (node.id.type === 'Identifier') {
+      typeId = node.id;
+    } else if (node.id.type === 'QualifiedTypeIdentifier') {
+      typeId = node.id;
+      do {
+        typeId = typeId.qualification;
+      } while (typeId.qualification);
+    }
+
+    for (scope = context.getScope(); scope; scope = scope.upper) {
+      variable = scope.set.get(typeId.name);
+      if (variable && variable.defs.length) {
+        context.markVariableAsUsed(typeId.name);
+        break;
+      }
+    }
+  };
 
   return {
     DeclareClass: markTypeAsUsed,
     DeclareFunction: markTypeAsUsed,
     DeclareModule: markTypeAsUsed,
     DeclareVariable: markTypeAsUsed,
-    GenericTypeAnnotation (node) {
-      let typeId;
-      let scope;
-      let variable;
-
-      if (node.id.type === 'Identifier') {
-        typeId = node.id;
-      } else if (node.id.type === 'QualifiedTypeIdentifier') {
-        typeId = node.id;
-        do {
-          typeId = typeId.qualification;
-        } while (typeId.qualification);
-      }
-
-      for (scope = context.getScope(); scope; scope = scope.upper) {
-        variable = scope.set.get(typeId.name);
-        if (variable && variable.defs.length) {
-          context.markVariableAsUsed(typeId.name);
-          break;
+    GenericTypeAnnotation: markTypeAsUsedWithGenericType,
+    TypeParameterDeclaration (node) {
+      node.params.forEach((param) => {
+        if (param.default && param.default.typeParameters) {
+          param.default.typeParameters.params.forEach((typeParameterNode) => {
+            markTypeAsUsedWithGenericType(typeParameterNode);
+          });
         }
-      }
+      });
     }
   };
 };

tests/rules/assertions/useFlowType.js

@@ -34,6 +34,12 @@ const VALID_WITH_USE_FLOW_TYPE = [
     errors: [
       '\'A\' is defined but never used.'
     ]
+  },
+  {
+    code: 'import type A from "a"; type X<B = ComponentType<A>> = { b: B }; let x: X; console.log(x);',
+    errors: [
+      '\'A\' is defined but never used.'
+    ]
   }
 ];