fix(web): prevents selection-clear for pure layer-switching multitaps

common/web/input-processor/src/text/inputProcessor.ts

@@ -107,8 +107,20 @@ export default class InputProcessor {
       if(keyEvent.baseTranscriptionToken) {
         const transcription = this.contextCache.get(keyEvent.baseTranscriptionToken);
         if(transcription) {
-          // Restores full context, including deadkeys in their exact pre-keystroke state.
-          outputTarget.restoreTo(transcription.preInput);
+          // Has there been a context change at any point during the multitap?  If so, we need
+          // to revert it.  If not, we assume it's a layer-change multitap, in which case
+          // no such reset is needed.
+          if(!isEmptyTransform(transcription.transform) || !transcription.preInput.isEqual(Mock.from(outputTarget))) {
+            // Restores full context, including deadkeys in their exact pre-keystroke state.
+            outputTarget.restoreTo(transcription.preInput);
+          }
+          /*
+            else:
+            1. We don't need to restore the original context, as it's already
+               in-place.
+            2. Restoring anyway would obliterate any selected text, which is bad
+               if this is a purely-layer-switching multitap.  (#11230)
+          */
         } else {
           console.warn('The base context for the multitap could not be found');
         }

common/web/keyboard-processor/src/text/outputTarget.ts

@@ -446,6 +446,17 @@ export class Mock extends OutputTarget {
     this.text = this.getTextBeforeCaret() + s;
   }
 
+  /**
+   * Indicates if this Mock represents an identical context to that of another Mock.
+   *
+   * Does not currently validate a match for deadkeys.
+   * @param other
+   * @returns
+   */
+  isEqual(other: Mock) {
+    return this.text == other.text && this.selStart == other.selStart && this.selEnd == other.selEnd;
+  }
+
   doInputEvent() {
     // Mock isn't backed by an element, so it won't have any event listeners.
   }