fix(core): use Capacitor safe-area CSS variables on older WebViews (#30865)

Issue number: internal

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

The safe area variables are only reliant on `env` variables that are
provided by devices.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

Capacitor 8 has released [safe area variable
fallbacks](https://capacitorjs.com/docs/apis/system-bars#android-note)
to provide consistent behaviors with older Android devices:

> Due to a [bug](https://issues.chromium.org/issues/40699457) in some
older versions of Android WebView (< 140), correct safe area values are
not available via the safe-area-inset-x CSS env variables. This plugin
will inject the correct inset values into a new CSS variable(s) named
--safe-area-inset-x that you can use as a fallback in your frontend
styles.

- Updated safe area variables to use the fallbacks provided by
Capacitor.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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  2. Update the BREAKING.md file with the breaking change.
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## Other information

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screenshots of how the component looks before and after the change. -->

Dev build: `8.7.13-dev.11765920447.1a01ab8b`

---------

Co-authored-by: Brandy Smith <[email protected]>

Author: thetaPC

core/src/components/app/test/safe-area/app.e2e.ts

@@ -18,20 +18,66 @@ configs({ directions: ['ltr'] }).forEach(({ config, title, screenshot }) => {
 
       await expect(page).toHaveScreenshot(screenshot(`app-${screenshotModifier}-diff`));
     };
+
     test.beforeEach(async ({ page }) => {
       await page.goto(`/src/components/app/test/safe-area`, config);
     });
-    test('should not have visual regressions with action sheet', async ({ page }) => {
-      await testOverlay(page, '#show-action-sheet', 'ionActionSheetDidPresent', 'action-sheet');
-    });
-    test('should not have visual regressions with menu', async ({ page }) => {
-      await testOverlay(page, '#show-menu', 'ionDidOpen', 'menu');
-    });
-    test('should not have visual regressions with picker', async ({ page }) => {
-      await testOverlay(page, '#show-picker', 'ionPickerDidPresent', 'picker');
+
+    test.describe(title('Ionic safe area variables'), () => {
+      test.beforeEach(async ({ page }) => {
+        const htmlTag = page.locator('html');
+        const hasSafeAreaClass = await htmlTag.evaluate((el) => el.classList.contains('safe-area'));
+
+        expect(hasSafeAreaClass).toBe(true);
+      });
+
+      test('should not have visual regressions with action sheet', async ({ page }) => {
+        await testOverlay(page, '#show-action-sheet', 'ionActionSheetDidPresent', 'action-sheet');
+      });
+      test('should not have visual regressions with menu', async ({ page }) => {
+        await testOverlay(page, '#show-menu', 'ionDidOpen', 'menu');
+      });
+      test('should not have visual regressions with picker', async ({ page }) => {
+        await testOverlay(page, '#show-picker', 'ionPickerDidPresent', 'picker');
+      });
+      test('should not have visual regressions with toast', async ({ page }) => {
+        await testOverlay(page, '#show-toast', 'ionToastDidPresent', 'toast');
+      });
     });
-    test('should not have visual regressions with toast', async ({ page }) => {
-      await testOverlay(page, '#show-toast', 'ionToastDidPresent', 'toast');
+
+    test.describe(title('Capacitor safe area variables'), () => {
+      test('should use safe-area-inset vars when safe-area class is not defined', async ({ page }) => {
+        await page.evaluate(() => {
+          const html = document.documentElement;
+
+          // Remove the safe area class
+          html.classList.remove('safe-area');
+
+          // Set the safe area inset variables
+          html.style.setProperty('--safe-area-inset-top', '10px');
+          html.style.setProperty('--safe-area-inset-bottom', '20px');
+          html.style.setProperty('--safe-area-inset-left', '30px');
+          html.style.setProperty('--safe-area-inset-right', '40px');
+        });
+
+        const top = await page.evaluate(() =>
+          getComputedStyle(document.documentElement).getPropertyValue('--ion-safe-area-top').trim()
+        );
+        const bottom = await page.evaluate(() =>
+          getComputedStyle(document.documentElement).getPropertyValue('--ion-safe-area-bottom').trim()
+        );
+        const left = await page.evaluate(() =>
+          getComputedStyle(document.documentElement).getPropertyValue('--ion-safe-area-left').trim()
+        );
+        const right = await page.evaluate(() =>
+          getComputedStyle(document.documentElement).getPropertyValue('--ion-safe-area-right').trim()
+        );
+
+        expect(top).toBe('10px');
+        expect(bottom).toBe('20px');
+        expect(left).toBe('30px');
+        expect(right).toBe('40px');
+      });
     });
   });
 });

core/src/css/core.scss

@@ -252,10 +252,12 @@ html.plt-ios.plt-hybrid, html.plt-ios.plt-pwa {
 
 @supports (padding-top: env(safe-area-inset-top)) {
   html {
-    --ion-safe-area-top: env(safe-area-inset-top);
-    --ion-safe-area-bottom: env(safe-area-inset-bottom);
-    --ion-safe-area-left: env(safe-area-inset-left);
-    --ion-safe-area-right: env(safe-area-inset-right);
+    // `--safe-area-inset-*` are set by Capacitor
+    // @see https://capacitorjs.com/docs/apis/system-bars#android-note
+    --ion-safe-area-top: var(--safe-area-inset-top, env(safe-area-inset-top));
+    --ion-safe-area-bottom: var(--safe-area-inset-bottom, env(safe-area-inset-bottom));
+    --ion-safe-area-left: var(--safe-area-inset-left, env(safe-area-inset-left));
+    --ion-safe-area-right: var(--safe-area-inset-right, env(safe-area-inset-right));
   }
 }