Allow setting lock task features without setting packages

Fixes: 278121754
Test: MixedDeviceOwnerTest#testLockTaskAfterReboot
Change-Id: Ib2fe11f927d2085b8bc50f86ef0c3681b9472291

core/java/android/app/admin/LockTaskPolicy.java

@@ -38,6 +38,7 @@ public final class LockTaskPolicy extends PolicyValue<LockTaskPolicy> {
     /**
      * @hide
      */
+    // We default on the power button menu, in order to be consistent with pre-P behaviour
     public static final int DEFAULT_LOCK_TASK_FLAG =
             DevicePolicyManager.LOCK_TASK_FEATURE_GLOBAL_ACTIONS;
 
@@ -72,18 +73,28 @@ public final class LockTaskPolicy extends PolicyValue<LockTaskPolicy> {
     /**
      * @hide
      */
-    public LockTaskPolicy(@NonNull Set<String> packages) {
-        Objects.requireNonNull(packages);
-        mPackages.addAll(packages);
+    public LockTaskPolicy(@Nullable Set<String> packages) {
+        if (packages != null) {
+            mPackages.addAll(packages);
+        }
         setValue(this);
     }
 
     /**
      * @hide
      */
-    public LockTaskPolicy(@NonNull Set<String> packages, int flags) {
-        Objects.requireNonNull(packages);
-        mPackages = new HashSet<>(packages);
+    public LockTaskPolicy(int flags) {
+        mFlags = flags;
+        setValue(this);
+    }
+
+    /**
+     * @hide
+     */
+    public LockTaskPolicy(@Nullable Set<String> packages, int flags) {
+        if (packages != null) {
+            mPackages.addAll(packages);
+        }
         mFlags = flags;
         setValue(this);
     }

services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java

@@ -14744,24 +14744,24 @@ public class DevicePolicyManagerService extends IDevicePolicyManager.Stub {
             synchronized (getLockObject()) {
                 enforcingAdmin = enforceCanCallLockTaskLocked(who, caller.getPackageName());
             }
-            if (packages.length == 0) {
+            LockTaskPolicy currentPolicy = mDevicePolicyEngine.getLocalPolicySetByAdmin(
+                    PolicyDefinition.LOCK_TASK,
+                    enforcingAdmin,
+                    caller.getUserId());
+            LockTaskPolicy policy;
+            if (currentPolicy == null) {
+                policy = new LockTaskPolicy(Set.of(packages));
+            } else {
+                policy = new LockTaskPolicy(currentPolicy);
+                policy.setPackages(Set.of(packages));
+            }
+            if (policy.getPackages().isEmpty()
+                    && policy.getFlags() == DevicePolicyManager.LOCK_TASK_FEATURE_NONE) {
                 mDevicePolicyEngine.removeLocalPolicy(
                         PolicyDefinition.LOCK_TASK,
                         enforcingAdmin,
                         caller.getUserId());
             } else {
-                LockTaskPolicy currentPolicy = mDevicePolicyEngine.getLocalPolicySetByAdmin(
-                        PolicyDefinition.LOCK_TASK,
-                        enforcingAdmin,
-                        caller.getUserId());
-                LockTaskPolicy policy;
-                if (currentPolicy == null) {
-                    policy = new LockTaskPolicy(Set.of(packages));
-                } else {
-                    policy = new LockTaskPolicy(currentPolicy);
-                    policy.setPackages(Set.of(packages));
-                }
-
                 mDevicePolicyEngine.setLocalPolicy(
                         PolicyDefinition.LOCK_TASK,
                         enforcingAdmin,
@@ -14876,18 +14876,26 @@ public class DevicePolicyManagerService extends IDevicePolicyManager.Stub {
                     PolicyDefinition.LOCK_TASK,
                     enforcingAdmin,
                     caller.getUserId());
+            LockTaskPolicy policy;
             if (currentPolicy == null) {
-                throw new IllegalArgumentException("Can't set a lock task flags without setting "
-                        + "lock task packages first.");
+                policy = new LockTaskPolicy(flags);
+            } else {
+                policy = new LockTaskPolicy(currentPolicy);
+                policy.setFlags(flags);
+            }
+            if (policy.getPackages().isEmpty()
+                    && policy.getFlags() == DevicePolicyManager.LOCK_TASK_FEATURE_NONE) {
+                mDevicePolicyEngine.removeLocalPolicy(
+                        PolicyDefinition.LOCK_TASK,
+                        enforcingAdmin,
+                        caller.getUserId());
+            } else {
+                mDevicePolicyEngine.setLocalPolicy(
+                        PolicyDefinition.LOCK_TASK,
+                        enforcingAdmin,
+                        policy,
+                        caller.getUserId());
             }
-            LockTaskPolicy policy = new LockTaskPolicy(currentPolicy);
-            policy.setFlags(flags);
-
-            mDevicePolicyEngine.setLocalPolicy(
-                    PolicyDefinition.LOCK_TASK,
-                    enforcingAdmin,
-                    policy,
-                    caller.getUserId());
         } else {
             Objects.requireNonNull(who, "ComponentName is null");
             synchronized (getLockObject()) {

services/devicepolicy/java/com/android/server/devicepolicy/LockTaskPolicySerializer.java

@@ -42,10 +42,6 @@ final class LockTaskPolicySerializer extends PolicySerializer<LockTaskPolicy> {
     void saveToXml(PolicyKey policyKey, TypedXmlSerializer serializer,
             @NonNull LockTaskPolicy value) throws IOException {
         Objects.requireNonNull(value);
-        if (value.getPackages() == null || value.getPackages().isEmpty()) {
-            throw new IllegalArgumentException("Error saving LockTaskPolicy to file, lock task "
-                    + "packages must be present");
-        }
         serializer.attribute(
                 /* namespace= */ null,
                 ATTR_PACKAGES,