CodeOwnerResolver: Return Optional from resolve method rather than Stream

The resolve method either returns a stream with exactly one code owner
or an empty stream. It's easier and more readable to just return an
Optional. Returning a stream is a left-over from when the resolve method
was resolving "*" to all users.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I1a575727855e72dfea876facf142ef4534982315

java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolver.java

diff --git a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolver.java b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolver.java
index ad239f0..c6b5f55 100644
--- a/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolver.java
+++ b/java/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolver.java
@@ -45,7 +45,6 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.stream.Stream;
 
 /** Class to resolve {@link CodeOwnerReference}s to {@link CodeOwner}s. */
 public class CodeOwnerResolver {
@@ -188,7 +187,9 @@
                   }
                   return true;
                 })
-            .flatMap(this::resolve)
+            .map(this::resolve)
+            .filter(Optional::isPresent)
+            .map(Optional::get)
             .collect(toImmutableSet());
     return CodeOwnerResolverResult.create(codeOwners, ownedByAllUsers.get());
   }
@@ -233,34 +234,34 @@
    * @return the {@link CodeOwner} for the code owner reference if it was resolved, otherwise {@link
    *     Optional#empty()}
    */
-  public Stream<CodeOwner> resolve(CodeOwnerReference codeOwnerReference) {
+  public Optional<CodeOwner> resolve(CodeOwnerReference codeOwnerReference) {
     String email = requireNonNull(codeOwnerReference, "codeOwnerReference").email();
     logger.atFine().log("resolving code owner reference %s", codeOwnerReference);
 
     if (!isEmailDomainAllowed(email)) {
       logger.atFine().log("domain of email %s is not allowed", email);
-      return Stream.of();
+      return Optional.empty();
     }
 
     Optional<AccountState> accountState =
         lookupEmail(email).flatMap(accountId -> lookupAccount(accountId, email));
     if (!accountState.isPresent()) {
       logger.atFine().log("no account for email %s", email);
-      return Stream.of();
+      return Optional.empty();
     }
     if (!accountState.get().account().isActive()) {
       logger.atFine().log("account for email %s is inactive", email);
-      return Stream.of();
+      return Optional.empty();
     }
     if (enforceVisibility && !isVisible(accountState.get(), email)) {
       logger.atFine().log(
           "account %d or email %s not visible", accountState.get().account().id().get(), email);
-      return Stream.of();
+      return Optional.empty();
     }
 
     CodeOwner codeOwner = CodeOwner.create(accountState.get().account().id());
     logger.atFine().log("resolved to code owner %s", codeOwner);
-    return Stream.of(codeOwner);
+    return Optional.of(codeOwner);
   }
 
   /** Whether the given account can be seen. */

java/com/google/gerrit/plugins/codeowners/restapi/RenameEmail.java

diff --git a/java/com/google/gerrit/plugins/codeowners/restapi/RenameEmail.java b/java/com/google/gerrit/plugins/codeowners/restapi/RenameEmail.java
index e8092b3..0ed505b 100644
--- a/java/com/google/gerrit/plugins/codeowners/restapi/RenameEmail.java
+++ b/java/com/google/gerrit/plugins/codeowners/restapi/RenameEmail.java
@@ -14,13 +14,10 @@
 
 package com.google.gerrit.plugins.codeowners.restapi;
 
-import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static java.util.Objects.requireNonNull;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Strings;
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Iterables;
 import com.google.gerrit.entities.Account;
 import com.google.gerrit.extensions.restapi.AuthException;
 import com.google.gerrit.extensions.restapi.BadRequestException;
@@ -158,19 +155,14 @@
     }
   }
 
-  private Account.Id resolveEmail(String email)
-      throws ResourceConflictException, UnprocessableEntityException {
+  private Account.Id resolveEmail(String email) throws UnprocessableEntityException {
     requireNonNull(email, "email");
 
-    ImmutableSet<CodeOwner> codeOwners =
-        codeOwnerResolver.resolve(CodeOwnerReference.create(email)).collect(toImmutableSet());
-    if (codeOwners.isEmpty()) {
+    Optional<CodeOwner> codeOwner = codeOwnerResolver.resolve(CodeOwnerReference.create(email));
+    if (!codeOwner.isPresent()) {
       throw new UnprocessableEntityException(String.format("cannot resolve email %s", email));
     }
-    if (codeOwners.size() > 1) {
-      throw new ResourceConflictException(String.format("email %s is ambigious", email));
-    }
-    return Iterables.getOnlyElement(codeOwners).accountId();
+    return codeOwner.get().accountId();
   }
 
   /**

javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolverTest.java

diff --git a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolverTest.java b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolverTest.java
index 6e19e28..cefe297 100644
--- a/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolverTest.java
+++ b/javatests/com/google/gerrit/plugins/codeowners/backend/CodeOwnerResolverTest.java
@@ -34,8 +34,8 @@
 import com.google.inject.Key;
 import com.google.inject.Provider;
 import java.nio.file.Paths;
+import java.util.Optional;
 import java.util.Set;
-import java.util.stream.Stream;
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.Repository;
 import org.junit.Before;
@@ -89,14 +89,14 @@
 
   @Test
   public void resolveCodeOwnerReferenceForEmail() throws Exception {
-    Stream<CodeOwner> codeOwner =
+    Optional<CodeOwner> codeOwner =
         codeOwnerResolver.get().resolve(CodeOwnerReference.create(admin.email()));
-    assertThat(codeOwner).onlyElement().hasAccountIdThat().isEqualTo(admin.id());
+    assertThat(codeOwner).value().hasAccountIdThat().isEqualTo(admin.id());
   }
 
   @Test
   public void cannotResolveCodeOwnerReferenceForStarAsEmail() throws Exception {
-    Stream<CodeOwner> codeOwner =
+    Optional<CodeOwner> codeOwner =
         codeOwnerResolver
             .get()
             .resolve(CodeOwnerReference.create(CodeOwnerResolver.ALL_USERS_WILDCARD));
@@ -160,14 +160,14 @@
 
     // admin has the "Modify Account" global capability and hence can see the secondary email of the
     // user account.
-    Stream<CodeOwner> codeOwner =
+    Optional<CodeOwner> codeOwner =
         codeOwnerResolver.get().resolve(CodeOwnerReference.create(secondaryEmail));
-    assertThat(codeOwner).onlyElement().hasAccountIdThat().isEqualTo(user.id());
+    assertThat(codeOwner).value().hasAccountIdThat().isEqualTo(user.id());
 
     // user can see its own secondary email.
     requestScopeOperations.setApiUser(user.id());
     codeOwner = codeOwnerResolver.get().resolve(CodeOwnerReference.create(secondaryEmail));
-    assertThat(codeOwner).onlyElement().hasAccountIdThat().isEqualTo(user.id());
+    assertThat(codeOwner).value().hasAccountIdThat().isEqualTo(user.id());
   }
 
   @Test
@@ -297,9 +297,9 @@
     assertThat(codeOwnerResolver.get().resolve(adminCodeOwnerReference)).isEmpty();
 
     // if visibility is not enforced the code owner reference can be resolved regardless
-    Stream<CodeOwner> codeOwner =
+    Optional<CodeOwner> codeOwner =
         codeOwnerResolver.get().enforceVisibility(false).resolve(adminCodeOwnerReference);
-    assertThat(codeOwner).onlyElement().hasAccountIdThat().isEqualTo(admin.id());
+    assertThat(codeOwner).value().hasAccountIdThat().isEqualTo(admin.id());
   }
 
   @Test
@@ -311,13 +311,13 @@
 
     // admin is the current user and can see the account
     assertThat(codeOwnerResolver.get().resolve(CodeOwnerReference.create(user.email())))
-        .isNotEmpty();
+        .isPresent();
     assertThat(
             codeOwnerResolver
                 .get()
                 .forUser(identifiedUserFactory.create(admin.id()))
                 .resolve(CodeOwnerReference.create(user.email())))
-        .isNotEmpty();
+        .isPresent();
 
     // user2 cannot see the account
     assertThat(