fix(ios): nomatch event firing on iOS 18+

Author: jamsch

README.md

@@ -237,7 +237,9 @@ ExpoSpeechRecognitionModule.start({
   // The maximum number of alternative transcriptions to return.
   maxAlternatives: 1,
   // [Default: false] Continuous recognition.
-  // If false on iOS, recognition will run until no speech is detected for 3 seconds.
+  // If false:
+  //    - on iOS 17-, recognition will run until no speech is detected for 3 seconds.
+  //    - on iOS 18+ and Android, recognition will run until a final result is received.
   // Not supported on Android 12 and below.
   continuous: true,
   // [Default: false] Prevent device from sending audio over the network. Only enabled if the device supports it.

ios/ExpoSpeechRecognitionModule.swift

@@ -41,6 +41,14 @@ public class ExpoSpeechRecognitionModule: Module {
   // This is a temporary workaround until the issue is fixed in a future iOS release
   var hasSeenFinalResult: Bool = false
 
+  // Hack for iOS 18 to avoid sending a "nomatch" event after the final-final result
+  // Example event order emitted in iOS 18:
+  // [
+  //   { isFinal: false, transcripts: ["actually", "final", "results"], metadata: { duration: 1500 } },
+  //   { isFinal: true, transcripts: [] }
+  // ]
+  var previousResult: SFSpeechRecognitionResult?
+
   public func definition() -> ModuleDefinition {
     // Sets the name of the module that JavaScript code will use to refer to the module. Takes a string as an argument.
     // Can be inferred from module's class name, but it's recommended to set it explicitly for clarity.
@@ -130,6 +138,9 @@ public class ExpoSpeechRecognitionModule: Module {
         do {
           let currentLocale = await speechRecognizer?.getLocale()
 
+          // Reset the previous result
+          self?.previousResult = nil
+
           // Re-create the speech recognizer when locales change
           if self.speechRecognizer == nil || currentLocale != options.lang {
             guard let locale = resolveLocale(localeIdentifier: options.lang) else {
@@ -358,12 +369,14 @@ public class ExpoSpeechRecognitionModule: Module {
 
   func sendErrorAndStop(error: String, message: String) {
     hasSeenFinalResult = false
+    previousResult = nil
     sendEvent("error", ["error": error, "message": message])
     sendEvent("end")
   }
 
   func handleEnd() {
     hasSeenFinalResult = false
+    previousResult = nil
     sendEvent("end")
   }
 
@@ -422,11 +435,19 @@ public class ExpoSpeechRecognitionModule: Module {
     }
 
     if isFinal && results.isEmpty {
-      // https://developer.mozilla.org/en-US/docs/Web/API/SpeechRecognition/nomatch_event
-      // The nomatch event of the Web Speech API is fired
-      // when the speech recognition service returns a final result with no significant recognition.
-      sendEvent("nomatch")
-      return
+      // Hack for iOS 18 to avoid sending a "nomatch" event after the final-final result
+      var previousResultWasFinal = false
+      if #available(iOS 18.0, *), let previousResult = previousResult {
+        previousResultWasFinal = previousResult.speechRecognitionMetadata?.speechDuration ?? 0 > 0
+      }
+
+      if !previousResultWasFinal || previousResult?.transcriptions.isEmpty {
+        // https://developer.mozilla.org/en-US/docs/Web/API/SpeechRecognition/nomatch_event
+        // The nomatch event of the Web Speech API is fired
+        // when the speech recognition service returns a final result with no significant recognition.
+        sendEvent("nomatch")
+        return
+      }
     }
 
     sendEvent(
@@ -436,6 +457,8 @@ public class ExpoSpeechRecognitionModule: Module {
         "results": results.map { $0.toDictionary() },
       ]
     )
+
+    previousResult = result
   }
 
   func handleRecognitionError(_ error: Error) {

src/ExpoSpeechRecognitionModule.types.ts

@@ -149,7 +149,10 @@ export type ExpoSpeechRecognitionOptions = {
    *
    * Not supported on Android 12 and below.
    *
-   * If false on iOS, recognition will run until no speech is detected for 3 seconds.
+   * If false, the behaviors are the following:
+   *
+   *   - on iOS 17-, recognition will run until no speech is detected for 3 seconds.
+   *   - on iOS 18+ and Android, recognition will run until a result with `isFinal: true` is received.
    */
   continuous?: boolean;
   /** [Default: false] Prevent device from sending audio over the network. Only enabled if the device supports it.