fix(rtl): allow :host to use rtl() (#28353)

Issue number: N/A

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

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

While working on a safe area padding mixin, I realized that `rtl()`
wasn't being applied for `:host` when using Firefox or Safari. This is
happening because the syntax for `:dir()` is wrong. The placement needs
to be updated for Firefox and Safari to register it.

```scss
:host {
   @include rtl() { // <- won't work
      // styles
   }
}

// generates
:host-context([dir=rtl]) {
  // styles
}

:host:dir(rtl) { // <- wrong syntax
   // styles
}
```

```scss
:host(.class) {
   @include rtl() { // <- won't work
      // styles
   }
}

// generates
:host-context([dir=rtl]):host(.class) {
  // styles
}

:host-context([dir=rtl]).class {
   // styles
}

:host(.class):dir(rtl) { // <- wrong syntax
   // styles
}
```

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

I updated `rtl()` to use `:dir()` as the `addHostSelector` in the
`add-root-selector` function. This generates all the correct selectors
for Firefox and Safari. However, `:dir()` does not have the structure of
`:host-context()` so I had to add a new parameter to `add-root-selector`
to determine whether to use `:host-context()` or not. I set the default
to `true` since the function originally used `:host-context()`.

An extra win is that the updated function will be ready for when
`:host-context()` can be removed from the codebase.


```diff
:host {
   @include rtl() { // <- works
      // styles
   }
}

// generates
:host-context([dir=rtl]) {
  // styles
}

-  :host:dir(rtl) {
+  :host(:dir(rtl)) {
   // styles
}
```

```diff
:host(.class) {
   @include rtl() { // <- works
      // styles
   }
}

// generates
:host-context([dir=rtl]):host(.class) {
  padding-right: 40px;
}

:host-context([dir=rtl]).class {
   // styles
}

-  :host(.class):dir(rtl) {
+  :host(.class:dir(rtl)) {
   // styles
}
```

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

N/A

---------

Co-authored-by: ionitron <hi@ionicframework.com>

core/src/themes/ionic.functions.string.scss

@@ -85,9 +85,15 @@
 // Add Root Selector
 // --------------------------------------------------------------------------------
 // Adds a root selector using host based on the selector passed
+// $root: The selector that needs to be updated to include the $addHostSelector.
+// - Example: ion-button
+// $addHostSelector: The selector that is used to add the host to the $root selector.
+// - Example: [dir=rtl]
+// $useHostContext: Whether to use host-context or not. Defaults to true.
 // --------------------------------------------------------------------------------
 
-@function add-root-selector($root, $addHostSelector) {
+
+@function add-root-selector($root, $addHostSelector, $useHostContext: true) {
   $selectors: str-split($root, ",");
 
   $list: ();
@@ -95,14 +101,21 @@
   @each $selector in $selectors {
     // If the selector contains :host( it means it is targeting a class on the host
     // element so we need to change how we target it:
+    // Example with `useHostContext=true`
     // @include add-root-selector(":host(.fixed)", "[dir=rtl]")
     // --> :host-context([dir=rtl]):host(.fixed)
     // --> :host-context([dir=rtl]).fixed
+    // ---
+    // Example with `useHostContext=false`
+    // @include add-root(":host(.fixed)", ":dir(rtl)", false)
+    // --> :host(.fixed:dir(rtl))
     @if str-contains($selector, ":host(") {
-      // @include add-root-selector(":host(.fixed)", "[dir=rtl]")
-      // --> :host-context([dir=rtl]):host(.fixed)
-      $shadow-element: str-replace($selector, ":host(", ":host-context(#{$addHostSelector}):host(");
-      $list: append($list, $shadow-element, comma);
+      @if $useHostContext {
+        // @include add-root-selector(":host(.fixed)", "[dir=rtl]")
+        // --> :host-context([dir=rtl]):host(.fixed)
+        $shadow-element: str-replace($selector, ":host(", ":host-context(#{$addHostSelector}):host(");
+        $list: append($list, $shadow-element, comma);
+      }
 
       $new-element: ();
       $elements: str-split($selector, " ");
@@ -117,19 +130,28 @@
           $scoped-element: str-replace($scoped-element, ")", "");
           $scoped-element: str-replace($scoped-element, ":host(", "");
 
-          // Add the class back inside of host with the rtl selector:
-          // .fixed -> :host-context([dir=rtl]).fixed
-          $scoped-element: str-replace($scoped-element, $scoped-element, ":host-context(#{$addHostSelector})#{$scoped-element}");
-
+          // Add the class back inside of host with the addHostSelector:
+          @if $useHostContext {
+            // .fixed -> :host-context([dir=rtl]).fixed
+            $scoped-element: str-replace($scoped-element, $scoped-element, ":host-context(#{$addHostSelector})#{$scoped-element}");
+          } @else {
+            // .fixed -> :host(.fixed:dir(rtl))
+            $scoped-element: str-replace($scoped-element, $scoped-element, ":host(#{$scoped-element}#{$addHostSelector})");
+          }
+          
           // @include add-root-selector(":host(.fixed)", "[dir=rtl]")
           // --> :host-context([dir=rtl]).fixed
+          // @include add-root(":host(.fixed)", ":dir(rtl)", false)
+          // --> :host(.fixed:dir(rtl))
           $new-element: append($new-element, $scoped-element, space);
         } @else {
-          // Add back any selectors that followed the host after transforming the
-          // first selector:
-          // :host(.fixed) ::slotted(ion-icon)
+          // Add back any selectors that followed the host
+          // after transforming the first selector:
+          // @include add-root-selector(":host(.fixed) ::slotted(ion-icon)", "[dir=rtl]")
           // --> :host-context([dir=rtl]):host(.fixed) ::slotted(ion-icon)
           // --> :host-context([dir=rtl]).fixed ::slotted(ion-icon)
+          // @include add-root(":host(.fixed) ::slotted(ion-icon)", ":dir(rtl)", false)
+          // --> :host(.fixed:dir(rtl)) ::slotted(ion-icon)
           $new-element: append($new-element, $element, space);
         }
       }
@@ -140,24 +162,38 @@
     // element so we can change it to look for host-context
     // @include add-root-selector(":host", "[dir=rtl]")
     // --> :host-context([dir=rtl])
-    // --> :host:dir(rtl)
+    // @include add-root(":host", ":dir(rtl)", false)
+    // --> :host(:dir(rtl))
     } @else if str-contains($selector, ":host") {
       $new-element: ();
       $elements: str-split($selector, " ");
 
       @each $element in $elements {
         @if str-contains($element, ":host") {
+          $updated-element: '';
+
           // Replace the :host with the addHostSelector:
-          // :host -> :host-context([dir=rtl])
-          $updated-element: str-replace($element, ":host", ":host-context(#{$addHostSelector})");
+          @if $useHostContext {
+            // :host -> :host-context([dir=rtl])
+            $updated-element: str-replace($element, ":host", ":host-context(#{$addHostSelector})");
+          } @else {
+            // :host -> :host(:dir(rtl))
+            $updated-element: str-replace($element, ":host", ":host(#{$addHostSelector})");
+          }
 
           // Add the final selector after all transformations:
-          // :host -> :host-context([dir=rtl])
+          // @include add-root-selector(":host", "[dir=rtl]")
+          // --> :host-context([dir=rtl])
+          // @include add-root(":host", ":dir(rtl)", false)
+          // --> :host(:dir(rtl))
           $new-element: append($new-element, $updated-element, space);
         } @else {
-          // Add back any selectors that followed the host after transforming the
-          // first selector:
-          // :host ::slotted(ion-icon) -> :host-context([dir=rtl]) ::slotted(ion-icon)
+          // Add back any selectors that followed the host
+          // after transforming the first selector:
+          // @include add-root-selector(":host ::slotted(ion-icon)", "[dir=rtl]")
+          // --> :host-context([dir=rtl]) ::slotted(ion-icon)
+          // @include add-root(":host ::slotted(ion-icon)", ":dir(rtl)", false)
+          // --> :host(:dir(rtl)) ::slotted(ion-icon)
           $new-element: append($new-element, $element, space);
         }
       }
@@ -168,9 +204,15 @@
     // @include add-root-selector("ion-component", "[dir=rtl]")
     // --> :host-context([dir=rtl]) ion-component
     // --> [dir=rtl] ion-component
+    // @include add-root("ion-component", ":dir(rtl)", false)
+    // --> ion-component:dir(rtl)
     } @else {
-      $list: append($list, "#{$addHostSelector} #{$selector}", comma);
-      $list: append($list, ":host-context(#{$addHostSelector}) #{$selector}", comma);
+      @if ($useHostContext) {
+        $list: append($list, ":host-context(#{$addHostSelector}) #{$selector}", comma);
+        $list: append($list, "#{$addHostSelector} #{$selector}", comma);
+      } @else {
+        $list: append($list, "#{$selector}#{$addHostSelector}", comma);
+      }
     }
   }
 

core/src/themes/ionic.mixins.scss

@@ -242,17 +242,13 @@
     // - Firefox doesn't support `:host-context()`, but does support `:dir()`.
     // - Safari doesn't support `:host-context()`, but Safari 16.4+ supports `:dir()`
     // @link https://webkit.org/blog/13966/webkit-features-in-safari-16-4/
-    @each $selector in $rootSplit {
-      $dirSelector: "#{$selector}:dir(rtl)";
-      // Group the selectors back into a single selector to optimize the output.
-      $dirSelectors: append($dirSelectors, $dirSelector, comma);
-    }
+    // -- However, there is a Webkit bug on v16 that prevents `:dir()` from working when
+    // -- the app direction is changed dynamically. v17+ works fine.
+    // -- @link https://bugs.webkit.org/show_bug.cgi?id=257133
 
     // Supported by Firefox.
-    @if length($dirSelectors) > 0 {
-      @at-root #{$dirSelectors} {
-        @content;
-      }
+    @at-root #{add-root-selector($root, ":dir(rtl)", false)} {
+      @content;
     }
   }
 }