Support refs/users/self for the GET branch rest endpoint

A user may fetch the magic branch refs/users/self and this branch is
resolved to the user branch of the calling user
> git fetch origin refs/users/self

This change adds support for this magic ref to the GET Branch rest
endpoint. This only works if the repository is All-Users.

Change-Id: I2d56a8896e0b701351e10e22ba6012ed28d53117

Documentation/rest-api-projects.txt

@@ -1702,7 +1702,9 @@ List all branches that match regex `t.*1`:
 'GET /projects/link:#project-name[\{project-name\}]/branches/link:#branch-id[\{branch-id\}]'
 --
 
-Retrieves a branch of a project.
+Retrieves a branch of a project. For the "All-Users" repository, the magic
+branch "refs/users/self" is automatically resolved to the user branch of the
+calling user.
 
 .Request
 ----

java/com/google/gerrit/entities/RefNames.java

@@ -255,6 +255,10 @@ public class RefNames {
     return ref.startsWith(REFS_USERS);
   }
 
+  public static boolean isRefsUsersSelf(String ref, boolean isAllUsers) {
+    return isAllUsers && REFS_USERS_SELF.equals(ref);
+  }
+
   /**
    * Whether the ref is a group branch that stores NoteDb data of a group. Returns {@code true} for
    * all refs that start with {@code refs/groups/}.

java/com/google/gerrit/server/api/projects/BranchApiImpl.java

@@ -16,6 +16,7 @@ package com.google.gerrit.server.api.projects;
 
 import static com.google.gerrit.server.api.ApiUtil.asRestApiException;
 
+import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.extensions.api.projects.BranchApi;
 import com.google.gerrit.extensions.api.projects.BranchInfo;
 import com.google.gerrit.extensions.api.projects.BranchInput;
@@ -126,6 +127,10 @@ public class BranchApiImpl implements BranchApi {
 
   private BranchResource resource()
       throws RestApiException, IOException, PermissionBackendException {
-    return branches.parse(project, IdString.fromDecoded(ref));
+    String refName = ref;
+    if (RefNames.isRefsUsersSelf(ref, project.getProjectState().isAllUsers())) {
+      refName = RefNames.refsUsers(project.getUser().getAccountId());
+    }
+    return branches.parse(project, IdString.fromDecoded(refName));
   }
 }

java/com/google/gerrit/server/git/receive/ReceiveCommits.java

@@ -21,6 +21,7 @@ import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.common.flogger.LazyArgs.lazy;
 import static com.google.gerrit.entities.RefNames.REFS_CHANGES;
 import static com.google.gerrit.entities.RefNames.isConfigRef;
+import static com.google.gerrit.entities.RefNames.isRefsUsersSelf;
 import static com.google.gerrit.git.ObjectIds.abbreviateName;
 import static com.google.gerrit.server.change.HashtagsUtil.cleanupHashtag;
 import static com.google.gerrit.server.git.MultiProgressMonitor.UNKNOWN;
@@ -1080,7 +1081,7 @@ class ReceiveCommits {
   private ReceiveCommand wrapReceiveCommand(ReceiveCommand cmd, Task progress) {
     String refname = cmd.getRefName();
 
-    if (projectState.isAllUsers() && RefNames.REFS_USERS_SELF.equals(cmd.getRefName())) {
+    if (isRefsUsersSelf(cmd.getRefName(), projectState.isAllUsers())) {
       refname = RefNames.refsUsers(user.getAccountId());
       logger.atFine().log("Swapping out command for %s to %s", RefNames.REFS_USERS_SELF, refname);
     }

java/com/google/gerrit/server/restapi/project/ListBranches.java

@@ -143,7 +143,11 @@ public class ListBranches implements RestReadView<ProjectResource> {
   BranchInfo toBranchInfo(BranchResource rsrc)
       throws IOException, ResourceNotFoundException, PermissionBackendException {
     try (Repository db = repoManager.openRepository(rsrc.getNameKey())) {
-      Ref r = db.exactRef(rsrc.getRef());
+      String refName = rsrc.getRef();
+      if (RefNames.isRefsUsersSelf(refName, rsrc.getProjectState().isAllUsers())) {
+        refName = RefNames.refsUsers(rsrc.getUser().getAccountId());
+      }
+      Ref r = db.exactRef(refName);
       if (r == null) {
         throw new ResourceNotFoundException();
       }

javatests/com/google/gerrit/acceptance/rest/project/GetBranchIT.java

@@ -262,9 +262,12 @@ public class GetBranchIT extends AbstractDaemonTest {
     requestScopeOperations.setApiUser(user.id());
     assertBranchFound(allUsers, RefNames.refsUsers(user.id()));
 
-    // TODO: every user can see the own user ref via the magic ref/users/self ref
-    // requestScopeOperations.setApiUser(user.id());
-    // assertBranchFound(allUsers, RefNames.REFS_USERS_SELF);
+    // every user can see the own user ref via the magic ref/users/self ref. For this special case,
+    // the branch in the request is refs/users/self, but the response contains the actual
+    // refs/users/$sharded_id/$id
+    BranchInfo branchInfo =
+        gApi.projects().name(allUsers.get()).branch(RefNames.REFS_USERS_SELF).get();
+    assertThat(branchInfo.ref).isEqualTo(RefNames.refsUsers(user.id()));
   }
 
   @Test