fix: use first dropdown option as the default value (#2465)

Fixes a problem where the default state for a dropdown would be `null`
even though the UI would show option 1 as selected.

We fix this by using option 1 as the default state value if nothing is
specified.

packages/examples/packages/interactive-ui/src/index.test.tsx

@@ -76,7 +76,9 @@ describe('onRpcRequest', () => {
       const resultScreen = await response.getInterface();
 
       expect(resultScreen).toRender(
-        <Result values={{ 'example-input': '', 'example-dropdown': '' }} />,
+        <Result
+          values={{ 'example-input': '', 'example-dropdown': 'option1' }}
+        />,
       );
       await resultScreen.ok();
 

packages/snaps-controllers/coverage.json

@@ -1,6 +1,6 @@
 {
-  "branches": 91.59,
-  "functions": 96.76,
+  "branches": 91.64,
+  "functions": 96.77,
   "lines": 97.89,
   "statements": 97.57
 }

packages/snaps-controllers/src/interface/utils.test.tsx

@@ -232,6 +232,22 @@ describe('constructState', () => {
     });
   });
 
+  it('sets default value for root level dropdown', () => {
+    const element = (
+      <Box>
+        <Dropdown name="foo">
+          <Option value="option1">Option 1</Option>
+          <Option value="option2">Option 2</Option>
+        </Dropdown>
+      </Box>
+    );
+
+    const result = constructState({}, element);
+    expect(result).toStrictEqual({
+      foo: 'option1',
+    });
+  });
+
   it('supports root level dropdowns', () => {
     const element = (
       <Box>
@@ -248,6 +264,26 @@ describe('constructState', () => {
     });
   });
 
+  it('sets default value for dropdowns in forms', () => {
+    const element = (
+      <Box>
+        <Form name="form">
+          <Field label="foo">
+            <Dropdown name="foo">
+              <Option value="option1">Option 1</Option>
+              <Option value="option2">Option 2</Option>
+            </Dropdown>
+          </Field>
+        </Form>
+      </Box>
+    );
+
+    const result = constructState({}, element);
+    expect(result).toStrictEqual({
+      form: { foo: 'option1' },
+    });
+  });
+
   it('supports dropdowns in forms', () => {
     const element = (
       <Box>

packages/snaps-controllers/src/interface/utils.ts

@@ -11,6 +11,7 @@ import type {
   FieldElement,
   InputElement,
   JSXElement,
+  OptionElement,
 } from '@metamask/snaps-sdk/jsx';
 import { isJSXElementUnsafe } from '@metamask/snaps-sdk/jsx';
 import {
@@ -48,6 +49,26 @@ export function assertNameIsUnique(state: InterfaceState, name: string) {
   );
 }
 
+/**
+ * Construct default state for a component.
+ *
+ * This function is meant to be used inside constructInputState to account
+ * for component specific defaults and will not override the component value or existing form state.
+ *
+ * @param element - The input element.
+ * @returns The default state for the specific component, if any.
+ */
+function constructComponentSpecificDefaultState(
+  element: InputElement | DropdownElement,
+) {
+  if (element.type === 'Dropdown') {
+    const children = getJsxChildren(element) as OptionElement[];
+    return children[0].props.value;
+  }
+
+  return null;
+}
+
 /**
  * Construct the state for an input field.
  *
@@ -59,7 +80,12 @@ function constructInputState(
   oldState: InterfaceState,
   element: InputElement | DropdownElement,
 ) {
-  return element.props.value ?? oldState[element.props.name] ?? null;
+  return (
+    element.props.value ??
+    oldState[element.props.name] ??
+    constructComponentSpecificDefaultState(element) ??
+    null
+  );
 }
 
 /**
@@ -77,7 +103,12 @@ function constructFormInputState(
 ) {
   const oldFormState = oldState[form] as FormState;
   const oldInputState = oldFormState?.[component.props.name];
-  return component.props.value ?? oldInputState ?? null;
+  return (
+    component.props.value ??
+    oldInputState ??
+    constructComponentSpecificDefaultState(component) ??
+    null
+  );
 }
 
 /**