Minimize the number of default enabled IMEs part 4

This is a follow up CL for recent attempt to minimize
the number of default enabled IMEs.
- part1: I831502db502f4073c9c2f50ce7705a4e45e2e1e3
- part2: Ife93d909fb8a24471c425c903e2b7048826e17a3
- part3: I6571d464a46453934f0a8f5e79018a67a9a3c845

It turned out that the changes made in part2 and part3 are
a bit overkill, and users will see no software keyboards
in some particular situations. The problem we missed in
the previous CLs is the fact that
InputMethodInfo#isDefault is indeed a locale-dependent
value, hence it may vary depending on the system locale.
Existing unittests also failed to abstract such
locale-dependent nature.

In order to addresses that regression, the selection logic
is a bit widely reorganized in this CL.  Now the logic is
implemented as a series of fallback rules.

Also, unit tests are updated to be able to 1) test the
order of the enabled IMEs, and 2) emulate the
locale-dependent behavior of InputMethodInfo#isDefault
to enrich test cases.

BUG: 17347871
BUG: 18192576
Change-Id: I871ccda787eb0f1099ba3574356c1da4b33681f3

2 files changed, 325 insertions, 166 deletions

diff --git a/core/java/com/android/internal/inputmethod/InputMethodUtils.java b/core/java/com/android/internal/inputmethod/InputMethodUtils.java
index ac915d1..183527c 100644
--- a/core/java/com/android/internal/inputmethod/InputMethodUtils.java
+++ b/core/java/com/android/internal/inputmethod/InputMethodUtils.java
@@ -16,6 +16,8 @@
 
 package com.android.internal.inputmethod;
 
+import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.app.AppOpsManager;
 import android.content.ContentResolver;
 import android.content.Context;
@@ -34,7 +36,9 @@ import android.view.textservice.SpellCheckerInfo;
 import android.view.textservice.TextServicesManager;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 
@@ -115,8 +119,8 @@ public class InputMethodUtils {
     }
 
     /**
-     * @deprecated Use {@link Locale} returned from
-     * {@link #getFallbackLocaleForDefaultIme(ArrayList)} instead.
+     * @deprecated Use {@link #isSystemImeThatHasSubtypeOf(InputMethodInfo, Context, boolean,
+     * Locale, boolean, String)} instead.
      */
     @Deprecated
     public static boolean isSystemImeThatHasEnglishKeyboardSubtype(InputMethodInfo imi) {
@@ -126,25 +130,60 @@ public class InputMethodUtils {
         return containsSubtypeOf(imi, ENGLISH_LOCALE.getLanguage(), SUBTYPE_MODE_KEYBOARD);
     }
 
+    private static boolean isSystemImeThatHasSubtypeOf(final InputMethodInfo imi,
+            final Context context, final boolean checkDefaultAttribute,
+            @Nullable final Locale requiredLocale, final boolean checkCountry,
+            final String requiredSubtypeMode) {
+        if (!isSystemIme(imi)) {
+            return false;
+        }
+        if (checkDefaultAttribute && !imi.isDefault(context)) {
+            return false;
+        }
+        if (!containsSubtypeOf(imi, requiredLocale, checkCountry, requiredSubtypeMode)) {
+            return false;
+        }
+        return true;
+    }
+
+    @Nullable
     public static Locale getFallbackLocaleForDefaultIme(final ArrayList<InputMethodInfo> imis,
             final Context context) {
+        // At first, find the fallback locale from the IMEs that are declared as "default" in the
+        // current locale.  Note that IME developers can declare an IME as "default" only for
+        // some particular locales but "not default" for other locales.
         for (final Locale fallbackLocale : SEARCH_ORDER_OF_FALLBACK_LOCALES) {
             for (int i = 0; i < imis.size(); ++i) {
-                final InputMethodInfo imi = imis.get(i);
-                if (isSystemIme(imi) && imi.isDefault(context) &&
-                        containsSubtypeOf(imi, fallbackLocale, false /* ignoreCountry */,
-                                SUBTYPE_MODE_KEYBOARD)) {
+                if (isSystemImeThatHasSubtypeOf(imis.get(i), context,
+                        true /* checkDefaultAttribute */, fallbackLocale,
+                        true /* checkCountry */, SUBTYPE_MODE_KEYBOARD)) {
+                    return fallbackLocale;
+                }
+            }
+        }
+        // If no fallback locale is found in the above condition, find fallback locales regardless
+        // of the "default" attribute as a last resort.
+        for (final Locale fallbackLocale : SEARCH_ORDER_OF_FALLBACK_LOCALES) {
+            for (int i = 0; i < imis.size(); ++i) {
+                if (isSystemImeThatHasSubtypeOf(imis.get(i), context,
+                        false /* checkDefaultAttribute */, fallbackLocale,
+                        true /* checkCountry */, SUBTYPE_MODE_KEYBOARD)) {
                     return fallbackLocale;
                 }
             }
         }
+        Slog.w(TAG, "Found no fallback locale. imis=" + Arrays.toString(imis.toArray()));
         return null;
     }
 
-    private static boolean isSystemAuxilialyImeThatHasAutomaticSubtype(InputMethodInfo imi) {
+    private static boolean isSystemAuxilialyImeThatHasAutomaticSubtype(final InputMethodInfo imi,
+            final Context context, final boolean checkDefaultAttribute) {
         if (!isSystemIme(imi)) {
             return false;
         }
+        if (checkDefaultAttribute && !imi.isDefault(context)) {
+            return false;
+        }
         if (!imi.isAuxiliaryIme()) {
             return false;
         }
@@ -166,98 +205,184 @@ public class InputMethodUtils {
         }
     }
 
-    public static ArrayList<InputMethodInfo> getDefaultEnabledImes(
-            Context context, boolean isSystemReady, ArrayList<InputMethodInfo> imis) {
-        // OK to store null in fallbackLocale because isImeThatHasSubtypeOf() is null-tolerant.
-        final Locale fallbackLocale = getFallbackLocaleForDefaultIme(imis, context);
+    private static final class InputMethodListBuilder {
+        // Note: We use LinkedHashSet instead of android.util.ArraySet because the enumeration
+        // order can have non-trivial effect in the call sites.
+        @NonNull
+        private final LinkedHashSet<InputMethodInfo> mInputMethodSet = new LinkedHashSet<>();
 
-        if (!isSystemReady) {
-            final ArrayList<InputMethodInfo> retval = new ArrayList<>();
+        public InputMethodListBuilder fillImes(final ArrayList<InputMethodInfo> imis,
+                final Context context, final boolean checkDefaultAttribute,
+                @Nullable final Locale locale, final boolean checkCountry,
+                final String requiredSubtypeMode) {
             for (int i = 0; i < imis.size(); ++i) {
                 final InputMethodInfo imi = imis.get(i);
-                // TODO: We should check isAsciiCapable instead of relying on fallbackLocale.
-                if (isSystemIme(imi) && imi.isDefault(context) &&
-                        isImeThatHasSubtypeOf(imi, fallbackLocale, false /* ignoreCountry */,
-                                SUBTYPE_MODE_KEYBOARD)) {
-                    retval.add(imi);
+                if (isSystemImeThatHasSubtypeOf(imi, context, checkDefaultAttribute, locale,
+                        checkCountry, requiredSubtypeMode)) {
+                    mInputMethodSet.add(imi);
                 }
             }
-            return retval;
+            return this;
         }
 
-        // OK to store null in fallbackLocale because isImeThatHasSubtypeOf() is null-tolerant.
-        final Locale systemLocale = getSystemLocaleFromContext(context);
-        // TODO: Use LinkedHashSet to simplify the code.
-        final ArrayList<InputMethodInfo> retval = new ArrayList<>();
-        boolean systemLocaleKeyboardImeFound = false;
-
-        // First, try to find IMEs with taking the system locale country into consideration.
-        for (int i = 0; i < imis.size(); ++i) {
-            final InputMethodInfo imi = imis.get(i);
-            if (!isSystemIme(imi) || !imi.isDefault(context)) {
-                continue;
-            }
-            final boolean isSystemLocaleKeyboardIme = isImeThatHasSubtypeOf(imi, systemLocale,
-                    false /* ignoreCountry */, SUBTYPE_MODE_KEYBOARD);
-            // TODO: We should check isAsciiCapable instead of relying on fallbackLocale.
-            // TODO: Use LinkedHashSet to simplify the code.
-            if (isSystemLocaleKeyboardIme ||
-                    isImeThatHasSubtypeOf(imi, fallbackLocale, false /* ignoreCountry */,
-                            SUBTYPE_MODE_ANY)) {
-                retval.add(imi);
+        // TODO: The behavior of InputMethodSubtype#overridesImplicitlyEnabledSubtype() should be
+        // documented more clearly.
+        public InputMethodListBuilder fillAuxiliaryImes(final ArrayList<InputMethodInfo> imis,
+                final Context context) {
+            // If one or more auxiliary input methods are available, OK to stop populating the list.
+            for (final InputMethodInfo imi : mInputMethodSet) {
+                if (imi.isAuxiliaryIme()) {
+                    return this;
+                }
             }
-            systemLocaleKeyboardImeFound |= isSystemLocaleKeyboardIme;
-        }
-
-        // System locale country doesn't match any IMEs, try to find IMEs in a country-agnostic
-        // way.
-        if (!systemLocaleKeyboardImeFound) {
+            boolean added = false;
             for (int i = 0; i < imis.size(); ++i) {
                 final InputMethodInfo imi = imis.get(i);
-                if (!isSystemIme(imi) || !imi.isDefault(context)) {
-                    continue;
-                }
-                if (isImeThatHasSubtypeOf(imi, fallbackLocale, false /* ignoreCountry */,
-                        SUBTYPE_MODE_KEYBOARD)) {
-                    // IMEs that have fallback locale are already added in the previous loop. We
-                    // don't need to add them again here.
-                    // TODO: Use LinkedHashSet to simplify the code.
-                    continue;
+                if (isSystemAuxilialyImeThatHasAutomaticSubtype(imi, context,
+                        true /* checkDefaultAttribute */)) {
+                    mInputMethodSet.add(imi);
+                    added = true;
                 }
-                if (isImeThatHasSubtypeOf(imi, systemLocale, true /* ignoreCountry */,
-                        SUBTYPE_MODE_ANY)) {
-                    retval.add(imi);
+            }
+            if (added) {
+                return this;
+            }
+            for (int i = 0; i < imis.size(); ++i) {
+                final InputMethodInfo imi = imis.get(i);
+                if (isSystemAuxilialyImeThatHasAutomaticSubtype(imi, context,
+                        false /* checkDefaultAttribute */)) {
+                    mInputMethodSet.add(imi);
                 }
             }
+            return this;
         }
 
-        // If one or more auxiliary input methods are available, OK to stop populating the list.
-        for (int i = 0; i < retval.size(); ++i) {
-            if (retval.get(i).isAuxiliaryIme()) {
-                return retval;
-            }
+        public boolean isEmpty() {
+            return mInputMethodSet.isEmpty();
         }
-        for (int i = 0; i < imis.size(); ++i) {
-            final InputMethodInfo imi = imis.get(i);
-            if (isSystemAuxilialyImeThatHasAutomaticSubtype(imi)) {
-                retval.add(imi);
-            }
+
+        @NonNull
+        public ArrayList<InputMethodInfo> build() {
+            return new ArrayList<>(mInputMethodSet);
         }
-        return retval;
     }
 
-    public static boolean isImeThatHasSubtypeOf(final InputMethodInfo imi,
-            final Locale locale, final boolean ignoreCountry, final String mode) {
-        if (locale == null) {
-            return false;
-        }
-        return containsSubtypeOf(imi, locale, ignoreCountry, mode);
+    private static InputMethodListBuilder getMinimumKeyboardSetWithoutSystemLocale(
+            final ArrayList<InputMethodInfo> imis, final Context context,
+            @Nullable final Locale fallbackLocale) {
+        // Before the system becomes ready, we pick up at least one keyboard in the following order.
+        // The first user (device owner) falls into this category.
+        // 1. checkDefaultAttribute: true, locale: fallbackLocale, checkCountry: true
+        // 2. checkDefaultAttribute: false, locale: fallbackLocale, checkCountry: true
+        // 3. checkDefaultAttribute: true, locale: fallbackLocale, checkCountry: false
+        // 4. checkDefaultAttribute: false, locale: fallbackLocale, checkCountry: false
+        // TODO: We should check isAsciiCapable instead of relying on fallbackLocale.
+
+        final InputMethodListBuilder builder = new InputMethodListBuilder();
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, fallbackLocale,
+                true /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, false /* checkDefaultAttribute */, fallbackLocale,
+                true /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, fallbackLocale,
+                false /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, false /* checkDefaultAttribute */, fallbackLocale,
+                false /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        Slog.w(TAG, "No software keyboard is found. imis=" + Arrays.toString(imis.toArray())
+                + " fallbackLocale=" + fallbackLocale);
+        return builder;
+    }
+
+    private static InputMethodListBuilder getMinimumKeyboardSetWithSystemLocale(
+            final ArrayList<InputMethodInfo> imis, final Context context,
+            @Nullable final Locale systemLocale, @Nullable final Locale fallbackLocale) {
+        // Once the system becomes ready, we pick up at least one keyboard in the following order.
+        // Secondary users fall into this category in general.
+        // 1. checkDefaultAttribute: true, locale: systemLocale, checkCountry: true
+        // 2. checkDefaultAttribute: true, locale: systemLocale, checkCountry: false
+        // 3. checkDefaultAttribute: true, locale: fallbackLocale, checkCountry: true
+        // 4. checkDefaultAttribute: true, locale: fallbackLocale, checkCountry: false
+        // 5. checkDefaultAttribute: false, locale: fallbackLocale, checkCountry: true
+        // 6. checkDefaultAttribute: false, locale: fallbackLocale, checkCountry: false
+        // TODO: We should check isAsciiCapable instead of relying on fallbackLocale.
+
+        final InputMethodListBuilder builder = new InputMethodListBuilder();
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, systemLocale,
+                true /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, systemLocale,
+                false /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, fallbackLocale,
+                true /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, true /* checkDefaultAttribute */, fallbackLocale,
+                false /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, false /* checkDefaultAttribute */, fallbackLocale,
+                true /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        builder.fillImes(imis, context, false /* checkDefaultAttribute */, fallbackLocale,
+                false /* checkCountry */, SUBTYPE_MODE_KEYBOARD);
+        if (!builder.isEmpty()) {
+            return builder;
+        }
+        Slog.w(TAG, "No software keyboard is found. imis=" + Arrays.toString(imis.toArray())
+                + " systemLocale=" + systemLocale + " fallbackLocale=" + fallbackLocale);
+        return builder;
+    }
+
+    public static ArrayList<InputMethodInfo> getDefaultEnabledImes(final Context context,
+            final boolean isSystemReady, final ArrayList<InputMethodInfo> imis) {
+        final Locale fallbackLocale = getFallbackLocaleForDefaultIme(imis, context);
+        if (!isSystemReady) {
+            // When the system is not ready, the system locale is not stable and reliable. Hence
+            // we will pick up IMEs that support software keyboard based on the fallback locale.
+            // Also pick up suitable IMEs regardless of the software keyboard support.
+            // (e.g. Voice IMEs)
+            return getMinimumKeyboardSetWithoutSystemLocale(imis, context, fallbackLocale)
+                    .fillImes(imis, context, true /* checkDefaultAttribute */, fallbackLocale,
+                            true /* checkCountry */, SUBTYPE_MODE_ANY)
+                    .build();
+        }
+
+        // When the system is ready, we will primarily rely on the system locale, but also keep
+        // relying on the fallback locale as a last resort.
+        // Also pick up suitable IMEs regardless of the software keyboard support (e.g. Voice IMEs),
+        // then pick up suitable auxiliary IMEs when necessary (e.g. Voice IMEs with "automatic"
+        // subtype)
+        final Locale systemLocale = getSystemLocaleFromContext(context);
+        return getMinimumKeyboardSetWithSystemLocale(imis, context, systemLocale, fallbackLocale)
+                .fillImes(imis, context, true /* checkDefaultAttribute */, systemLocale,
+                        true /* checkCountry */, SUBTYPE_MODE_ANY)
+                .fillAuxiliaryImes(imis, context)
+                .build();
     }
 
     /**
-     * @deprecated Use {@link #isSystemIme(InputMethodInfo)} and
-     * {@link InputMethodInfo#isDefault(Context)} and
-     * {@link #isImeThatHasSubtypeOf(InputMethodInfo, Locale, boolean, String))} instead.
+     * @deprecated Use {@link #isSystemImeThatHasSubtypeOf(InputMethodInfo, Context, boolean,
+     * Locale, boolean, String)} instead.
      */
     @Deprecated
     public static boolean isValidSystemDefaultIme(
@@ -285,22 +410,25 @@ public class InputMethodUtils {
     }
 
     public static boolean containsSubtypeOf(final InputMethodInfo imi,
-            final Locale locale, final boolean ignoreCountry, final String mode) {
+            @Nullable final Locale locale, final boolean checkCountry, final String mode) {
+        if (locale == null) {
+            return false;
+        }
         final int N = imi.getSubtypeCount();
         for (int i = 0; i < N; ++i) {
             final InputMethodSubtype subtype = imi.getSubtypeAt(i);
-            if (ignoreCountry) {
-                final Locale subtypeLocale = new Locale(getLanguageFromLocaleString(
-                        subtype.getLocale()));
-                if (!subtypeLocale.getLanguage().equals(locale.getLanguage())) {
-                    continue;
-                }
-            } else {
+            if (checkCountry) {
                 // TODO: Use {@link Locale#toLanguageTag()} and
                 // {@link Locale#forLanguageTag(languageTag)} instead.
                 if (!TextUtils.equals(subtype.getLocale(), locale.toString())) {
                     continue;
                 }
+            } else {
+                final Locale subtypeLocale = new Locale(getLanguageFromLocaleString(
+                        subtype.getLocale()));
+                if (!subtypeLocale.getLanguage().equals(locale.getLanguage())) {
+                    continue;
+                }
             }
             if (mode == SUBTYPE_MODE_ANY || TextUtils.isEmpty(mode) ||
                     mode.equalsIgnoreCase(subtype.getMode())) {
@@ -465,19 +593,9 @@ public class InputMethodUtils {
         return applicableSubtypes;
     }
 
-    private static List<InputMethodSubtype> getEnabledInputMethodSubtypeList(
-            Context context, InputMethodInfo imi, List<InputMethodSubtype> enabledSubtypes,
-            boolean allowsImplicitlySelectedSubtypes) {
-        if (allowsImplicitlySelectedSubtypes && enabledSubtypes.isEmpty()) {
-            enabledSubtypes = InputMethodUtils.getImplicitlyApplicableSubtypesLocked(
-                    context.getResources(), imi);
-        }
-        return InputMethodSubtype.sort(context, 0, imi, enabledSubtypes);
-    }
-
     /**
      * Returns the language component of a given locale string.
-     * TODO: Use {@link Locale#toLanguageTag()} and {@link Locale#forLanguageTag(languageTag)}
+     * TODO: Use {@link Locale#toLanguageTag()} and {@link Locale#forLanguageTag(String)}
      */
     public static String getLanguageFromLocaleString(String locale) {
         final int idx = locale.indexOf('_');
diff --git a/core/tests/inputmethodtests/src/android/os/InputMethodTest.java b/core/tests/inputmethodtests/src/android/os/InputMethodTest.java
index 577dd64..1557918 100644
--- a/core/tests/inputmethodtests/src/android/os/InputMethodTest.java
+++ b/core/tests/inputmethodtests/src/android/os/InputMethodTest.java
@@ -33,6 +33,7 @@ import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Objects;
 
 public class InputMethodTest extends InstrumentationTestCase {
     private static final boolean IS_AUX = true;
@@ -46,84 +47,104 @@ public class InputMethodTest extends InstrumentationTestCase {
     private static final Locale LOCALE_EN_IN = new Locale("en", "IN");
     private static final Locale LOCALE_HI = new Locale("hi");
     private static final Locale LOCALE_JA_JP = new Locale("ja", "JP");
+    private static final Locale LOCALE_ZH_CN = new Locale("zh", "CN");
+    private static final Locale LOCALE_ZH_TW = new Locale("zh", "TW");
     private static final String SUBTYPE_MODE_KEYBOARD = "keyboard";
     private static final String SUBTYPE_MODE_VOICE = "voice";
 
     @SmallTest
     public void testVoiceImes() throws Exception {
         // locale: en_US
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_US, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_US, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_US, IS_SYSTEM_READY,
-                "DummyDefaultAutoVoiceIme", "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_US, IS_SYSTEM_READY,
-                "DummyNonDefaultAutoVoiceIme0", "DummyNonDefaultAutoVoiceIme1",
-                "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_US,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_US,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_US,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_US,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyNonDefaultAutoVoiceIme0",
+                "DummyNonDefaultAutoVoiceIme1");
 
         // locale: en_GB
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_GB, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_GB, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_GB, IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_GB, IS_SYSTEM_READY,
-                "DummyNonDefaultAutoVoiceIme0", "DummyNonDefaultAutoVoiceIme1",
-                "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_GB,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_GB,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_EN_GB,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_EN_GB,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyNonDefaultAutoVoiceIme0",
+                "DummyNonDefaultAutoVoiceIme1");
 
         // locale: ja_JP
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_JA_JP, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_JA_JP, !IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme");
-        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_JA_JP, IS_SYSTEM_READY,
-                "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
-        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_JA_JP, IS_SYSTEM_READY,
-                "DummyNonDefaultAutoVoiceIme0", "DummyNonDefaultAutoVoiceIme1",
-                "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_JA_JP,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_JA_JP,
+                !IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme");
+        assertDefaultEnabledImes(getImesWithDefaultVoiceIme(), LOCALE_JA_JP,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyDefaultAutoVoiceIme");
+        assertDefaultEnabledImes(getImesWithoutDefaultVoiceIme(), LOCALE_JA_JP,
+                IS_SYSTEM_READY, "DummyDefaultEnKeyboardIme", "DummyNonDefaultAutoVoiceIme0",
+                "DummyNonDefaultAutoVoiceIme1");
     }
 
     @SmallTest
     public void testKeyboardImes() throws Exception {
         // locale: en_US
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_US, !IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.latin");
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_US, IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.voice", "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rUS"), LOCALE_EN_US,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rUS"), LOCALE_EN_US,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.latin",
+                "com.android.apps.inputmethod.voice");
 
         // locale: en_GB
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_GB, !IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.latin");
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_GB, IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.voice", "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rGB"), LOCALE_EN_GB,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rGB"), LOCALE_EN_GB,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.latin",
+                "com.android.apps.inputmethod.voice");
 
         // locale: en_IN
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_IN, !IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.latin");
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_EN_IN, IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.voice", "com.android.apps.inputmethod.latin",
-                "com.android.apps.inputmethod.hindi");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rIN"), LOCALE_EN_IN,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("en-rIN"), LOCALE_EN_IN,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.hindi",
+                "com.android.apps.inputmethod.latin", "com.android.apps.inputmethod.voice");
 
         // locale: hi
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_HI, !IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.latin");
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_HI, IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.voice", "com.android.apps.inputmethod.latin",
-                "com.android.apps.inputmethod.hindi");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("hi"), LOCALE_HI,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("hi"), LOCALE_HI,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.hindi",
+                "com.android.apps.inputmethod.latin", "com.android.apps.inputmethod.voice");
 
         // locale: ja_JP
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_JA_JP, !IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.latin");
-        assertDefaultEnabledImes(getSamplePreinstalledImes(), LOCALE_JA_JP, IS_SYSTEM_READY,
-                "com.android.apps.inputmethod.voice", "com.android.apps.inputmethod.latin",
-                "com.android.apps.inputmethod.japanese");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("ja-rJP"), LOCALE_JA_JP,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("ja-rJP"), LOCALE_JA_JP,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.japanese",
+                "com.android.apps.inputmethod.voice");
+
+        // locale: zh_CN
+        assertDefaultEnabledImes(getSamplePreinstalledImes("zh-rCN"), LOCALE_ZH_CN,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("zh-rCN"), LOCALE_ZH_CN,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.pinyin",
+                "com.android.apps.inputmethod.voice");
+
+        // locale: zh_TW
+        // Note: In this case, no IME is suitable for the system locale. Hence we will pick up a
+        // fallback IME regardless of the "default" attribute.
+        assertDefaultEnabledImes(getSamplePreinstalledImes("zh-rTW"), LOCALE_ZH_TW,
+                !IS_SYSTEM_READY, "com.android.apps.inputmethod.latin");
+        assertDefaultEnabledImes(getSamplePreinstalledImes("zh-rTW"), LOCALE_ZH_TW,
+                IS_SYSTEM_READY, "com.android.apps.inputmethod.latin",
+                "com.android.apps.inputmethod.voice");
     }
 
     @SmallTest
     public void testParcelable() throws Exception {
-        final ArrayList<InputMethodInfo> originalList = getSamplePreinstalledImes();
+        final ArrayList<InputMethodInfo> originalList = getSamplePreinstalledImes("en-rUS");
         final List<InputMethodInfo> clonedList = cloneViaParcel(originalList);
         assertNotNull(clonedList);
         final List<InputMethodInfo> clonedClonedList = cloneViaParcel(clonedList);
@@ -139,11 +160,14 @@ public class InputMethodTest extends InstrumentationTestCase {
     }
 
     private void assertDefaultEnabledImes(final ArrayList<InputMethodInfo> preinstalledImes,
-            final Locale systemLocale, final boolean isSystemReady, String... imeNames) {
+            final Locale systemLocale, final boolean isSystemReady, String... expectedImeNames) {
         final Context context = getInstrumentation().getTargetContext();
-        assertEquals(new HashSet<String>(Arrays.asList(imeNames)),
-                getPackageNames(callGetDefaultEnabledImesUnderWithLocale(context,
-                        isSystemReady, preinstalledImes, systemLocale)));
+        final String[] actualImeNames = getPackageNames(callGetDefaultEnabledImesUnderWithLocale(
+                context, isSystemReady, preinstalledImes, systemLocale));
+        assertEquals(expectedImeNames.length, actualImeNames.length);
+        for (int i = 0; i < expectedImeNames.length; ++i) {
+            assertEquals(expectedImeNames[i], actualImeNames[i]);
+        }
     }
 
     private static List<InputMethodInfo> cloneViaParcel(final List<InputMethodInfo> list) {
@@ -172,11 +196,10 @@ public class InputMethodTest extends InstrumentationTestCase {
         }
     }
 
-    private HashSet<String> getPackageNames(final ArrayList<InputMethodInfo> imis) {
-        final HashSet<String> packageNames = new HashSet<>();
-        for (final InputMethodInfo imi : imis) {
-            final String actualPackageName = imi.getPackageName();
-            packageNames.add(actualPackageName);
+    private String[] getPackageNames(final ArrayList<InputMethodInfo> imis) {
+        final String[] packageNames = new String[imis.size()];
+        for (int i = 0; i < imis.size(); ++i) {
+            packageNames[i] = imis.get(i).getPackageName();
         }
         return packageNames;
     }
@@ -278,21 +301,34 @@ public class InputMethodTest extends InstrumentationTestCase {
         return preinstalledImes;
     }
 
-    private static ArrayList<InputMethodInfo> getSamplePreinstalledImes() {
+    private static boolean contains(final String[] textList, final String textToBeChecked) {
+        if (textList == null) {
+            return false;
+        }
+        for (final String text : textList) {
+            if (Objects.equals(textToBeChecked, text)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private static ArrayList<InputMethodInfo> getSamplePreinstalledImes(final String localeString) {
         ArrayList<InputMethodInfo> preinstalledImes = new ArrayList<>();
 
         // a dummy Voice IME
         {
+            final boolean isDefaultIme = false;
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             subtypes.add(createDummyInputMethodSubtype("", SUBTYPE_MODE_VOICE, IS_AUX,
                     IS_AUTO, !IS_ASCII_CAPABLE));
             preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.voice",
-                    "com.android.inputmethod.voice", "DummyVoiceIme", IS_AUX, IS_DEFAULT,
+                    "com.android.inputmethod.voice", "DummyVoiceIme", IS_AUX, isDefaultIme,
                     subtypes));
         }
-
         // a dummy Hindi IME
         {
+            final boolean isDefaultIme = contains(new String[]{ "hi", "en-rIN" }, localeString);
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             // TODO: This subtype should be marked as IS_ASCII_CAPABLE
             subtypes.add(createDummyInputMethodSubtype("en_IN", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
@@ -300,32 +336,36 @@ public class InputMethodTest extends InstrumentationTestCase {
             subtypes.add(createDummyInputMethodSubtype("hi", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, !IS_ASCII_CAPABLE));
             preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.hindi",
-                    "com.android.inputmethod.hindi", "DummyHindiIme", !IS_AUX, IS_DEFAULT,
+                    "com.android.inputmethod.hindi", "DummyHindiIme", !IS_AUX, isDefaultIme,
                     subtypes));
         }
 
         // a dummy Pinyin IME
         {
+            final boolean isDefaultIme = contains(new String[]{ "zh-rCN" }, localeString);
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             subtypes.add(createDummyInputMethodSubtype("zh_CN", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, !IS_ASCII_CAPABLE));
-            preinstalledImes.add(createDummyInputMethodInfo("ccom.android.apps.inputmethod.pinyin",
-                    "com.android.apps.inputmethod.pinyin", "DummyPinyinIme", !IS_AUX, IS_DEFAULT,
+            preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.pinyin",
+                    "com.android.apps.inputmethod.pinyin", "DummyPinyinIme", !IS_AUX, isDefaultIme,
                     subtypes));
         }
 
-        // a dummy Korian IME
+        // a dummy Korean IME
         {
+            final boolean isDefaultIme = contains(new String[]{ "ko" }, localeString);
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             subtypes.add(createDummyInputMethodSubtype("ko", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, !IS_ASCII_CAPABLE));
             preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.korean",
-                    "com.android.apps.inputmethod.korean", "DummyKorianIme", !IS_AUX, IS_DEFAULT,
+                    "com.android.apps.inputmethod.korean", "DummyKoreanIme", !IS_AUX, isDefaultIme,
                     subtypes));
         }
 
         // a dummy Latin IME
         {
+            final boolean isDefaultIme = contains(
+                    new String[]{ "en-rUS", "en-rGB", "en-rIN", "en", "hi" }, localeString);
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             subtypes.add(createDummyInputMethodSubtype("en_US", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, IS_ASCII_CAPABLE));
@@ -336,12 +376,13 @@ public class InputMethodTest extends InstrumentationTestCase {
             subtypes.add(createDummyInputMethodSubtype("hi", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, IS_ASCII_CAPABLE));
             preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.latin",
-                    "com.android.apps.inputmethod.latin", "DummyLatinIme", !IS_AUX, IS_DEFAULT,
+                    "com.android.apps.inputmethod.latin", "DummyLatinIme", !IS_AUX, isDefaultIme,
                     subtypes));
         }
 
         // a dummy Japanese IME
         {
+            final boolean isDefaultIme = contains(new String[]{ "ja", "ja-rJP" }, localeString);
             final ArrayList<InputMethodSubtype> subtypes = new ArrayList<InputMethodSubtype>();
             subtypes.add(createDummyInputMethodSubtype("ja", SUBTYPE_MODE_KEYBOARD, !IS_AUX,
                     !IS_AUTO, !IS_ASCII_CAPABLE));
@@ -349,7 +390,7 @@ public class InputMethodTest extends InstrumentationTestCase {
                     !IS_AUTO, !IS_ASCII_CAPABLE));
             preinstalledImes.add(createDummyInputMethodInfo("com.android.apps.inputmethod.japanese",
                     "com.android.apps.inputmethod.japanese", "DummyJapaneseIme", !IS_AUX,
-                    IS_DEFAULT, subtypes));
+                    isDefaultIme, subtypes));
         }
 
         return preinstalledImes;