experiments: fix --all-tags/--all-branches bug (#4612)

* brancher: add sha_only option to omit branch/tag names

* experiments: resolve branches/tags into commit objects during `exp show`

dvc/repo/brancher.py

@@ -4,7 +4,12 @@ from dvc.tree.local import LocalTree
 
 
 def brancher(  # noqa: E302
-    self, revs=None, all_branches=False, all_tags=False, all_commits=False
+    self,
+    revs=None,
+    all_branches=False,
+    all_tags=False,
+    all_commits=False,
+    sha_only=False,
 ):
     """Generator that iterates over specified revisions.
 
@@ -13,6 +18,7 @@ def brancher(  # noqa: E302
         all_branches (bool): iterate over all available branches.
         all_commits (bool): iterate over all commits.
         all_tags (bool): iterate over all available tags.
+        sha_only (bool): only return git SHA for a revision.
 
     Yields:
         str: the display name for the currently selected tree, it could be:
@@ -53,6 +59,9 @@ def brancher(  # noqa: E302
                 # ignore revs that don't contain repo root
                 # (i.e. revs from before a subdir=True repo was init'ed)
                 if self.tree.exists(self.root_dir):
-                    yield ", ".join(names)
+                    if sha_only:
+                        yield sha
+                    else:
+                        yield ", ".join(names)
     finally:
         self.tree = saved_tree

dvc/repo/experiments/show.py

@@ -17,7 +17,7 @@ def _collect_experiment(repo, branch, stash=False, sha_only=True):
         if rev == "workspace":
             res["timestamp"] = None
         else:
-            commit = repo.scm.repo.rev_parse(rev)
+            commit = _resolve_commit(repo, rev)
             res["timestamp"] = datetime.fromtimestamp(commit.committed_date)
 
         configs = _collect_configs(repo)
@@ -44,6 +44,15 @@ def _collect_experiment(repo, branch, stash=False, sha_only=True):
     return res
 
 
+def _resolve_commit(repo, rev):
+    from git.objects.tag import TagObject
+
+    commit = repo.scm.repo.rev_parse(rev)
+    if isinstance(commit, TagObject):
+        commit = commit.object
+    return commit
+
+
 @locked
 def show(
     repo,
@@ -65,6 +74,7 @@ def show(
             all_branches=all_branches,
             all_tags=all_tags,
             all_commits=all_commits,
+            sha_only=True,
         )
     )