ChangeUtil: Fix findChanges for anonymous users

In I7710befa I didn't realize the user provider was a
Provider<IdentifiedUser>, which caused a ProvisionException when
anonymous users tried to use the REST API to look up changes by
something other than a number. This wasn't noticed sooner because it
didn't affect the web UI, which exclusively uses change numbers.

Change to Provider<CurrentUser> and use asIdentifiedUser only at the
sites where an IdentifiedUser is needed. This will throw a different
unchecked exception type on failure (UnsupportedOperationException
instead of ProvisionException), but callers aren't depending on that.

Add a test, during which I also discovered a bug in the implementation
of AbstractDaemonTest#setApiUserAnonymous. That wasn't already causing
failures because the only user was using it to avoid some side effects
that "may" have happened.

Change-Id: Idbad114d6f5a61167d6fda32ee0093558491cf8e

gerrit-acceptance-framework/src/test/java/com/google/gerrit/acceptance/AbstractDaemonTest.java

@@ -468,7 +468,8 @@ public abstract class AbstractDaemonTest {
   }
 
   protected Context setApiUserAnonymous() {
-    return atrScope.newContext(reviewDbProvider, null, anonymousUser.get());
+    return atrScope.set(
+        atrScope.newContext(reviewDbProvider, null, anonymousUser.get()));
   }
 
   protected static Gson newGson() {

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/api/change/ChangeIT.java

@@ -792,6 +792,27 @@ public class ChangeIT extends AbstractDaemonTest {
     assertThat(rev2.pushCertificate.key).isNull();
   }
 
+  @Test
+  public void anonymousRestApi() throws Exception {
+    setApiUserAnonymous();
+    PushOneCommit.Result r = createChange();
+
+    ChangeInfo info = gApi.changes().id(r.getChangeId()).get();
+    assertThat(info.changeId).isEqualTo(r.getChangeId());
+
+    String triplet = project.get() + "~master~" + r.getChangeId();
+    info = gApi.changes().id(triplet).get();
+    assertThat(info.changeId).isEqualTo(r.getChangeId());
+
+    info = gApi.changes().id(info._number).get();
+    assertThat(info.changeId).isEqualTo(r.getChangeId());
+
+    exception.expect(AuthException.class);
+    gApi.changes()
+        .id(triplet)
+        .current()
+        .review(ReviewInput.approve());
+  }
 
   private static Iterable<Account.Id> getReviewers(
       Collection<AccountInfo> r) {

gerrit-server/src/main/java/com/google/gerrit/server/ChangeUtil.java

@@ -177,7 +177,7 @@ public class ChangeUtil {
     return subject;
   }
 
-  private final Provider<IdentifiedUser> user;
+  private final Provider<CurrentUser> user;
   private final Provider<ReviewDb> db;
   private final Provider<InternalChangeQuery> queryProvider;
   private final ChangeControl.GenericFactory changeControlFactory;
@@ -192,7 +192,7 @@ public class ChangeUtil {
   private final StarredChangesUtil starredChangesUtil;
 
   @Inject
-  ChangeUtil(Provider<IdentifiedUser> user,
+  ChangeUtil(Provider<CurrentUser> user,
       Provider<ReviewDb> db,
       Provider<InternalChangeQuery> queryProvider,
       ChangeControl.GenericFactory changeControlFactory,
@@ -238,7 +238,7 @@ public class ChangeUtil {
       RevCommit commitToRevert =
           revWalk.parseCommit(ObjectId.fromString(patch.getRevision().get()));
 
-      PersonIdent authorIdent = user.get()
+      PersonIdent authorIdent = user.get().asIdentifiedUser()
           .newCommitterIdent(myIdent.getWhen(), myIdent.getTimeZone());
 
       if (commitToRevert.getParentCount() == 0) {