[Page] Allow for non-primary page action

UNRELEASED.md

@@ -19,6 +19,7 @@ Use [the changelog guidelines](https://git.io/polaris-changelog-guidelines) to f
 - Fixed `Modal` setting an invalid `id` on `aria-labelledby` when no `title` is set ([#2115](https://github.com/Shopify/polaris-react/pull/2115))
 - Fixed error warnings in `Card` and `RollupActions` tests ([#2125](https://github.com/Shopify/polaris-react/pull/2125))
 - Added default accessibility label from `ResourceItem` ([#2097](https://github.com/Shopify/polaris-react/pull/2097))
+- Reverted `Page.primaryAction` forcing `primary` to be `true` ([#2137](https://github.com/Shopify/polaris-react/pull/2137))
 
 ### Documentation
 

src/components/Page/components/Header/Header.tsx

@@ -114,11 +114,13 @@ export class Header extends React.PureComponent<HeaderProps, State> {
       />
     );
 
+    const primary =
+      primaryAction &&
+      (primaryAction.primary === undefined ? true : primaryAction.primary);
+
     const primaryActionMarkup = primaryAction ? (
       <div className={styles.PrimaryActionWrapper}>
-        {buttonsFrom(primaryAction, {
-          primary: true,
-        })}
+        {buttonsFrom(primaryAction, {primary})}
       </div>
     ) : null;
 

src/components/Page/components/Header/tests/Header.test.tsx

@@ -87,7 +87,7 @@ describe('<Header />', () => {
   });
 
   describe('primaryAction', () => {
-    it('renders a button based on the given action', () => {
+    it('renders a `primary` button based on the given action', () => {
       const primaryAction: HeaderPrimaryAction = {
         content: 'Click me!',
       };
@@ -99,6 +99,20 @@ describe('<Header />', () => {
       const expectedButton = buttonsFrom(primaryAction, {primary: true});
       expect(header.contains(expectedButton)).toBeTruthy();
     });
+
+    it('renders a regular button based on the given action when primary is set to false', () => {
+      const primaryAction: HeaderPrimaryAction = {
+        content: 'Click me!',
+        primary: false,
+      };
+
+      const header = mountWithAppProvider(
+        <Header {...mockProps} primaryAction={primaryAction} />,
+      );
+
+      const expectedButton = buttonsFrom(primaryAction, {primary: false});
+      expect(header.contains(expectedButton)).toBeTruthy();
+    });
   });
 
   describe('pagination', () => {