Add InputMethodSubtype#getCanonicalizedLanguageTag()

This is a preparation for implementing Subtype-keyed physical keyboard
layout switching.

This CL introduces an @hide method

   InputMethodSubtype#getCanonicalizedLanguageTag()

so that later CLs can be written by obtaining canonicalized BCP 47
Language Tags from InputMethodSubtype.

See test cases to see how it works.

Bug: 252816846
Test: atest FrameworksCoreTests:InputMethodSubtypeTest
Change-Id: I5276642ba83fb708e95591da9bc7fefe2810b170

core/java/android/view/inputmethod/InputMethodSubtype.java

@@ -16,6 +16,7 @@
 
 package android.view.inputmethod;
 
+import android.annotation.AnyThread;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.content.Context;
@@ -23,6 +24,7 @@ import android.content.pm.ApplicationInfo;
 import android.content.res.Configuration;
 import android.icu.text.DisplayContext;
 import android.icu.text.LocaleDisplayNames;
+import android.icu.util.ULocale;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.text.TextUtils;
@@ -89,6 +91,14 @@ public final class InputMethodSubtype implements Parcelable {
     private volatile Locale mCachedLocaleObj;
     private volatile HashMap<String, String> mExtraValueHashMapCache;
 
+    /**
+     * A volatile cache to optimize {@link #getCanonicalizedLanguageTag()}.
+     *
+     * <p>{@code null} means that the initial evaluation is not yet done.</p>
+     */
+    @Nullable
+    private volatile String mCachedCanonicalizedLanguageTag;
+
     /**
      * InputMethodSubtypeBuilder is a builder class of InputMethodSubtype.
      * This class is designed to be used with
@@ -391,6 +401,37 @@ public final class InputMethodSubtype implements Parcelable {
         }
     }
 
+    /**
+     * Returns a canonicalized BCP 47 Language Tag initialized with {@link #getLocaleObject()}.
+     *
+     * <p>This has an internal cache mechanism.  Subsequent calls are in general cheap and fast.</p>
+     *
+     * @return a canonicalized BCP 47 Language Tag initialized with {@link #getLocaleObject()}. An
+     *         empty string if {@link #getLocaleObject()} returns {@code null} or an empty
+     *         {@link Locale} object.
+     * @hide
+     */
+    @AnyThread
+    @NonNull
+    public String getCanonicalizedLanguageTag() {
+        final String cachedValue = mCachedCanonicalizedLanguageTag;
+        if (cachedValue != null) {
+            return cachedValue;
+        }
+
+        String result = null;
+        final Locale locale = getLocaleObject();
+        if (locale != null) {
+            final String langTag = locale.toLanguageTag();
+            if (!TextUtils.isEmpty(langTag)) {
+                result = ULocale.createCanonical(ULocale.forLanguageTag(langTag)).toLanguageTag();
+            }
+        }
+        result = TextUtils.emptyIfNull(result);
+        mCachedCanonicalizedLanguageTag = result;
+        return result;
+    }
+
     /**
      * @return The mode of the subtype.
      */

core/tests/coretests/src/android/view/inputmethod/InputMethodSubtypeTest.java

@@ -20,8 +20,10 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
+import android.annotation.Nullable;
 import android.os.Parcel;
 import android.view.inputmethod.InputMethodSubtype.InputMethodSubtypeBuilder;
 
@@ -125,6 +127,36 @@ public class InputMethodSubtypeTest {
         assertEquals("he", clonedSubtypeHe.getLocale());
     }
 
+    @Test
+    public void testCanonicalizedLanguageTagObjectCache() {
+        final InputMethodSubtype subtype = createSubtypeUsingLanguageTag("en-US");
+        // Verify that the returned object is cached and any subsequent call should return the same
+        // object, which is strictly guaranteed if the method gets called only on a single thread.
+        assertSame(subtype.getCanonicalizedLanguageTag(), subtype.getCanonicalizedLanguageTag());
+    }
+
+    @Test
+    public void testCanonicalizedLanguageTag() {
+        verifyCanonicalizedLanguageTag("en", "en");
+        verifyCanonicalizedLanguageTag("en-US", "en-US");
+        verifyCanonicalizedLanguageTag("en-Latn-US-t-k0-qwerty", "en-Latn-US-t-k0-qwerty");
+
+        verifyCanonicalizedLanguageTag("en-us", "en-US");
+        verifyCanonicalizedLanguageTag("EN-us", "en-US");
+
+        verifyCanonicalizedLanguageTag(null, "");
+        verifyCanonicalizedLanguageTag("", "");
+
+        verifyCanonicalizedLanguageTag("und", "und");
+        verifyCanonicalizedLanguageTag("apparently invalid language tag!!!", "und");
+    }
+
+    private void verifyCanonicalizedLanguageTag(
+            @Nullable String languageTag, @Nullable String expectedLanguageTag) {
+        final InputMethodSubtype subtype = createSubtypeUsingLanguageTag(languageTag);
+        assertEquals(subtype.getCanonicalizedLanguageTag(), expectedLanguageTag);
+    }
+
     private static InputMethodSubtype cloneViaParcel(final InputMethodSubtype original) {
         Parcel parcel = null;
         try {