From 24120164a93ba2c2016d8740a475d671da055f85 Mon Sep 17 00:00:00 2001
From: Saugat Pachhai <suagatchhetri@outlook.com>
Date: Tue, 21 Jan 2020 20:28:53 +0545
Subject: [PATCH 1/4] gc: change option to use single remove flags

---
 dvc/command/gc.py | 51 +++++++++++++++++++++--------------------------
 dvc/repo/gc.py    |  8 +++++---
 2 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/dvc/command/gc.py b/dvc/command/gc.py
index 7cbffc537c..4aaf516423 100644
--- a/dvc/command/gc.py
+++ b/dvc/command/gc.py
@@ -9,19 +9,28 @@
 
 logger = logging.getLogger(__name__)
 
+supported_removal_filters = ("commits", "branches", "tags")
+
 
 class CmdGC(CmdBase):
     def run(self):
-        msg = "This will remove all cache except items used in "
 
+        msg = "This will remove all cache except items used in "
         msg += "the working tree"
-        if self.args.all_commits:
+
+        self.args.remove = self.args.remove or []
+
+        if "commits" not in self.args.remove:
             msg += " and all git commits"
-        elif self.args.all_branches and self.args.all_tags:
+
+        if (
+            "branches" not in self.args.remove
+            and "tags" not in self.args.remove
+        ):
             msg += " and all git branches and tags"
-        elif self.args.all_branches:
+        elif "branches" not in self.args.remove:
             msg += " and all git branches"
-        elif self.args.all_tags:
+        elif "tags" not in self.args.remove:
             msg += " and all git tags"
 
         if self.args.repos:
@@ -39,9 +48,9 @@ def run(self):
             return 1
 
         self.repo.gc(
-            all_branches=self.args.all_branches,
-            all_tags=self.args.all_tags,
-            all_commits=self.args.all_commits,
+            all_branches="branches" in self.args.remove,
+            all_tags="tags" in self.args.remove,
+            all_commits="commits" in self.args.remove,
             cloud=self.args.cloud,
             remote=self.args.remote,
             force=self.args.force,
@@ -64,26 +73,6 @@ def add_parser(subparsers, parent_parser):
         help=GC_HELP,
         formatter_class=argparse.RawDescriptionHelpFormatter,
     )
-    gc_parser.add_argument(
-        "-a",
-        "--all-branches",
-        action="store_true",
-        default=False,
-        help="Keep data files for the tips of all git branches.",
-    )
-    gc_parser.add_argument(
-        "-T",
-        "--all-tags",
-        action="store_true",
-        default=False,
-        help="Keep data files for all git tags.",
-    )
-    gc_parser.add_argument(
-        "--all-commits",
-        action="store_true",
-        default=False,
-        help=argparse.SUPPRESS,
-    )
     gc_parser.add_argument(
         "-c",
         "--cloud",
@@ -94,6 +83,12 @@ def add_parser(subparsers, parent_parser):
     gc_parser.add_argument(
         "-r", "--remote", help="Remote storage to collect garbage in."
     )
+    gc_parser.add_argument(
+        "--remove",
+        nargs="*",
+        choices=supported_removal_filters,
+        help="Available choices for remove: %(choices)s",
+    )
     gc_parser.add_argument(
         "-f",
         "--force",
diff --git a/dvc/repo/gc.py b/dvc/repo/gc.py
index e55a34dc3f..d732f44758 100644
--- a/dvc/repo/gc.py
+++ b/dvc/repo/gc.py
@@ -2,6 +2,7 @@
 
 from . import locked
 from dvc.cache import NamedCache
+from dvc.scm import NoSCM
 
 
 logger = logging.getLogger(__name__)
@@ -41,12 +42,13 @@ def gc(
 
         used = NamedCache()
         for repo in all_repos + [self]:
+            has_scm = not isinstance(repo.scm, NoSCM)
             used.update(
                 repo.used_cache(
-                    all_branches=all_branches,
+                    all_branches=not all_branches and has_scm,
                     with_deps=with_deps,
-                    all_tags=all_tags,
-                    all_commits=all_commits,
+                    all_tags=not all_tags and has_scm,
+                    all_commits=not all_commits and has_scm,
                     remote=remote,
                     force=force,
                     jobs=jobs,

From b9838b76d836a2ef32c6ca1cf1701c60923cd371 Mon Sep 17 00:00:00 2001
From: Saugat Pachhai <suagatchhetri@outlook.com>
Date: Thu, 23 Jan 2020 10:14:46 +0545
Subject: [PATCH 2/4] fixup! brancher: do not get tree if there's no revs

---
 dvc/command/gc.py    |  4 +---
 dvc/repo/__init__.py |  2 ++
 dvc/repo/brancher.py | 12 +++++++++++-
 dvc/repo/gc.py       | 25 +++++++++++++++++--------
 4 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/dvc/command/gc.py b/dvc/command/gc.py
index 4aaf516423..b43c86bf59 100644
--- a/dvc/command/gc.py
+++ b/dvc/command/gc.py
@@ -48,9 +48,7 @@ def run(self):
             return 1
 
         self.repo.gc(
-            all_branches="branches" in self.args.remove,
-            all_tags="tags" in self.args.remove,
-            all_commits="commits" in self.args.remove,
+            remove=self.args.remove,
             cloud=self.args.cloud,
             remote=self.args.remote,
             force=self.args.force,
diff --git a/dvc/repo/__init__.py b/dvc/repo/__init__.py
index 9d0a506a87..1a2ee06df9 100644
--- a/dvc/repo/__init__.py
+++ b/dvc/repo/__init__.py
@@ -223,6 +223,7 @@ def used_cache(
         force=False,
         jobs=None,
         recursive=False,
+        exclude_revs=None,
     ):
         """Get the stages related to the given target and collect
         the `info` of its outputs.
@@ -245,6 +246,7 @@ def used_cache(
             all_branches=all_branches,
             all_tags=all_tags,
             all_commits=all_commits,
+            exclude_revs=exclude_revs,
         ):
             targets = targets or [None]
 
diff --git a/dvc/repo/brancher.py b/dvc/repo/brancher.py
index 955b135135..bc83d98dc5 100644
--- a/dvc/repo/brancher.py
+++ b/dvc/repo/brancher.py
@@ -4,7 +4,12 @@
 
 
 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,
+    exclude_revs=None,
 ):
     """Generator that iterates over specified revisions.
 
@@ -26,6 +31,7 @@ def brancher(  # noqa: E302
 
     saved_tree = self.tree
     revs = revs or []
+    exclude_revs = exclude_revs or []
 
     scm = self.scm
 
@@ -41,9 +47,13 @@ def brancher(  # noqa: E302
         if all_tags:
             revs.extend(scm.list_tags())
 
+    excluded_shas = [scm.resolve_rev(rev) for rev in exclude_revs]
+
     try:
         if revs:
             for sha, names in group_by(scm.resolve_rev, revs).items():
+                if sha in excluded_shas:
+                    continue
                 self.tree = scm.get_tree(sha)
                 yield ", ".join(names)
     finally:
diff --git a/dvc/repo/gc.py b/dvc/repo/gc.py
index d732f44758..9c57d419ae 100644
--- a/dvc/repo/gc.py
+++ b/dvc/repo/gc.py
@@ -2,7 +2,6 @@
 
 from . import locked
 from dvc.cache import NamedCache
-from dvc.scm import NoSCM
 
 
 logger = logging.getLogger(__name__)
@@ -17,12 +16,10 @@ def _do_gc(typ, func, clist):
 @locked
 def gc(
     self,
-    all_branches=False,
+    remove=None,
     cloud=False,
     remote=None,
     with_deps=False,
-    all_tags=False,
-    all_commits=False,
     force=False,
     jobs=None,
     repos=None,
@@ -31,6 +28,7 @@ def gc(
     from dvc.repo import Repo
 
     all_repos = []
+    remove = remove or []
 
     if repos:
         all_repos = [Repo(path) for path in repos]
@@ -42,16 +40,27 @@ def gc(
 
         used = NamedCache()
         for repo in all_repos + [self]:
-            has_scm = not isinstance(repo.scm, NoSCM)
+            exclude_revs = (
+                repo.scm.list_branches()
+                if {"commits", "branches"} - set(remove)
+                else []
+            )
+            exclude_revs += (
+                repo.scm.list_tags()
+                if {"tags", "commits"} - set(remove)
+                else []
+            )
+
             used.update(
                 repo.used_cache(
-                    all_branches=not all_branches and has_scm,
+                    all_branches="branches" not in remove,
                     with_deps=with_deps,
-                    all_tags=not all_tags and has_scm,
-                    all_commits=not all_commits and has_scm,
+                    all_tags="tags" not in remove,
+                    all_commits="commits" not in remove,
                     remote=remote,
                     force=force,
                     jobs=jobs,
+                    exclude_revs=exclude_revs,
                 )
             )
 

From 13c3338c3a56f8ea7dd56c32a941f0100592d328 Mon Sep 17 00:00:00 2001
From: Saugat Pachhai <suagatchhetri@outlook.com>
Date: Thu, 23 Jan 2020 17:10:20 +0545
Subject: [PATCH 3/4] temp: try to exclude some hashes

---
 dvc/repo/gc.py | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/dvc/repo/gc.py b/dvc/repo/gc.py
index 9c57d419ae..58ba4b51dd 100644
--- a/dvc/repo/gc.py
+++ b/dvc/repo/gc.py
@@ -41,22 +41,17 @@ def gc(
         used = NamedCache()
         for repo in all_repos + [self]:
             exclude_revs = (
-                repo.scm.list_branches()
-                if {"commits", "branches"} - set(remove)
-                else []
-            )
-            exclude_revs += (
-                repo.scm.list_tags()
-                if {"tags", "commits"} - set(remove)
-                else []
+                repo.scm.list_branches() if "branches" in remove else []
             )
+            exclude_revs += repo.scm.list_tags() if "tags" in remove else []
+            all_commits = "commits" not in remove and not bool(exclude_revs)
 
             used.update(
                 repo.used_cache(
-                    all_branches="branches" not in remove,
+                    all_branches="branches" not in remove and not all_commits,
                     with_deps=with_deps,
-                    all_tags="tags" not in remove,
-                    all_commits="commits" not in remove,
+                    all_tags="tags" not in remove and not all_commits,
+                    all_commits=all_commits,
                     remote=remote,
                     force=force,
                     jobs=jobs,

From 3c07c4248ec4e7b12901f19afa571523048f7e7c Mon Sep 17 00:00:00 2001
From: Ruslan Kuprieiev <kupruser@gmail.com>
Date: Sun, 26 Jan 2020 21:32:38 +0200
Subject: [PATCH 4/4] gc: rework implementation

---
 dvc/command/gc.py             | 56 +++++++++++++++++++----------------
 dvc/repo/__init__.py          |  2 --
 dvc/repo/brancher.py          | 17 ++++-------
 dvc/repo/gc.py                | 18 ++++-------
 dvc/scm/base.py               |  4 ++-
 dvc/scm/git/__init__.py       | 14 +++++++--
 scripts/completion/dvc.bash   |  2 +-
 scripts/completion/dvc.zsh    |  4 +--
 tests/func/test_gc.py         | 18 ++++++++---
 tests/unit/command/test_gc.py | 39 ++++++++++++++++++++++++
 tests/unit/scm/test_git.py    | 13 ++++++++
 11 files changed, 126 insertions(+), 61 deletions(-)
 create mode 100644 tests/unit/command/test_gc.py

diff --git a/dvc/command/gc.py b/dvc/command/gc.py
index b43c86bf59..9e7f84680a 100644
--- a/dvc/command/gc.py
+++ b/dvc/command/gc.py
@@ -9,29 +9,21 @@
 
 logger = logging.getLogger(__name__)
 
-supported_removal_filters = ("commits", "branches", "tags")
-
 
 class CmdGC(CmdBase):
     def run(self):
-
-        msg = "This will remove all cache except items used in "
-        msg += "the working tree"
-
-        self.args.remove = self.args.remove or []
-
-        if "commits" not in self.args.remove:
-            msg += " and all git commits"
-
-        if (
-            "branches" not in self.args.remove
-            and "tags" not in self.args.remove
-        ):
-            msg += " and all git branches and tags"
-        elif "branches" not in self.args.remove:
-            msg += " and all git branches"
-        elif "tags" not in self.args.remove:
-            msg += " and all git tags"
+        msg = (
+            "This will remove all cache except items used in the working tree"
+            "{tags}{history}{branches}{history}"
+        ).format(
+            tags="" if self.args.remove_all_tags else "and all git tags",
+            branches=""
+            if self.args.remove_all_branches
+            else "and all git branches",
+            history=""
+            if self.args.remove_all_history
+            else "and their history",
+        )
 
         if self.args.repos:
             msg += " of the current and the following repos:"
@@ -48,7 +40,9 @@ def run(self):
             return 1
 
         self.repo.gc(
-            remove=self.args.remove,
+            remove_all_tags=self.args.remove_all_tags,
+            remove_all_branches=self.args.remove_all_branches,
+            remove_all_history=self.args.remove_all_history,
             cloud=self.args.cloud,
             remote=self.args.remote,
             force=self.args.force,
@@ -82,10 +76,22 @@ def add_parser(subparsers, parent_parser):
         "-r", "--remote", help="Remote storage to collect garbage in."
     )
     gc_parser.add_argument(
-        "--remove",
-        nargs="*",
-        choices=supported_removal_filters,
-        help="Available choices for remove: %(choices)s",
+        "--remove-all-tags",
+        action="store_true",
+        default=False,
+        help="Remove cache for all git tags.",
+    )
+    gc_parser.add_argument(
+        "--remove-all-branches",
+        action="store_true",
+        default=False,
+        help="Remove cache for all git branches.",
+    )
+    gc_parser.add_argument(
+        "--remove-all-history",
+        action="store_true",
+        default=False,
+        help="Remove cache for all history of all branches and tags.",
     )
     gc_parser.add_argument(
         "-f",
diff --git a/dvc/repo/__init__.py b/dvc/repo/__init__.py
index 1a2ee06df9..9d0a506a87 100644
--- a/dvc/repo/__init__.py
+++ b/dvc/repo/__init__.py
@@ -223,7 +223,6 @@ def used_cache(
         force=False,
         jobs=None,
         recursive=False,
-        exclude_revs=None,
     ):
         """Get the stages related to the given target and collect
         the `info` of its outputs.
@@ -246,7 +245,6 @@ def used_cache(
             all_branches=all_branches,
             all_tags=all_tags,
             all_commits=all_commits,
-            exclude_revs=exclude_revs,
         ):
             targets = targets or [None]
 
diff --git a/dvc/repo/brancher.py b/dvc/repo/brancher.py
index bc83d98dc5..5a95257e24 100644
--- a/dvc/repo/brancher.py
+++ b/dvc/repo/brancher.py
@@ -4,12 +4,7 @@
 
 
 def brancher(  # noqa: E302
-    self,
-    revs=None,
-    all_branches=False,
-    all_tags=False,
-    all_commits=False,
-    exclude_revs=None,
+    self, revs=None, all_branches=False, all_tags=False, all_commits=False
 ):
     """Generator that iterates over specified revisions.
 
@@ -31,7 +26,6 @@ def brancher(  # noqa: E302
 
     saved_tree = self.tree
     revs = revs or []
-    exclude_revs = exclude_revs or []
 
     scm = self.scm
 
@@ -39,7 +33,10 @@ def brancher(  # noqa: E302
     yield "working tree"
 
     if all_commits:
-        revs = scm.list_all_commits()
+        revs = scm.list_all_commits(
+            exclude_all_tags=not all_tags,
+            exclude_all_branches=not all_branches,
+        )
     else:
         if all_branches:
             revs.extend(scm.list_branches())
@@ -47,13 +44,9 @@ def brancher(  # noqa: E302
         if all_tags:
             revs.extend(scm.list_tags())
 
-    excluded_shas = [scm.resolve_rev(rev) for rev in exclude_revs]
-
     try:
         if revs:
             for sha, names in group_by(scm.resolve_rev, revs).items():
-                if sha in excluded_shas:
-                    continue
                 self.tree = scm.get_tree(sha)
                 yield ", ".join(names)
     finally:
diff --git a/dvc/repo/gc.py b/dvc/repo/gc.py
index 58ba4b51dd..fc38bf147a 100644
--- a/dvc/repo/gc.py
+++ b/dvc/repo/gc.py
@@ -16,7 +16,9 @@ def _do_gc(typ, func, clist):
 @locked
 def gc(
     self,
-    remove=None,
+    remove_all_tags=False,
+    remove_all_branches=False,
+    remove_all_history=False,
     cloud=False,
     remote=None,
     with_deps=False,
@@ -28,7 +30,6 @@ def gc(
     from dvc.repo import Repo
 
     all_repos = []
-    remove = remove or []
 
     if repos:
         all_repos = [Repo(path) for path in repos]
@@ -40,22 +41,15 @@ def gc(
 
         used = NamedCache()
         for repo in all_repos + [self]:
-            exclude_revs = (
-                repo.scm.list_branches() if "branches" in remove else []
-            )
-            exclude_revs += repo.scm.list_tags() if "tags" in remove else []
-            all_commits = "commits" not in remove and not bool(exclude_revs)
-
             used.update(
                 repo.used_cache(
-                    all_branches="branches" not in remove and not all_commits,
                     with_deps=with_deps,
-                    all_tags="tags" not in remove and not all_commits,
-                    all_commits=all_commits,
+                    all_branches=not remove_all_branches,
+                    all_tags=not remove_all_tags,
+                    all_commits=not remove_all_history,
                     remote=remote,
                     force=force,
                     jobs=jobs,
-                    exclude_revs=exclude_revs,
                 )
             )
 
diff --git a/dvc/scm/base.py b/dvc/scm/base.py
index 412731ca89..34c72aba52 100644
--- a/dvc/scm/base.py
+++ b/dvc/scm/base.py
@@ -115,7 +115,9 @@ def list_tags(self):  # pylint: disable=no-self-use
         """Returns a list of available tags in the repo."""
         return []
 
-    def list_all_commits(self):  # pylint: disable=no-self-use
+    def list_all_commits(
+        self, exclude_all_tags=False, exclude_all_branches=False
+    ):  # pylint: disable=no-self-use
         """Returns a list of commits in the repo."""
         return []
 
diff --git a/dvc/scm/git/__init__.py b/dvc/scm/git/__init__.py
index 3872c8e72e..8ffc842a2f 100644
--- a/dvc/scm/git/__init__.py
+++ b/dvc/scm/git/__init__.py
@@ -244,8 +244,18 @@ def list_branches(self):
     def list_tags(self):
         return [t.name for t in self.repo.tags]
 
-    def list_all_commits(self):
-        return [c.hexsha for c in self.repo.iter_commits("--all")]
+    def list_all_commits(
+        self, exclude_all_tags=False, exclude_all_branches=False
+    ):
+        args = []
+        if exclude_all_tags:
+            args.extend(["--exclude", "refs/tags/*"])
+        if exclude_all_branches:
+            args.extend(["--exclude", "refs/heads/*"])
+        # NOTE: order matters, `--exclude` needs to be before `--all` in order
+        # to affect it.
+        args.append("--all")
+        return self.repo.git.rev_list(*args).splitlines()
 
     def _install_hook(self, name, cmd):
         command = (
diff --git a/scripts/completion/dvc.bash b/scripts/completion/dvc.bash
index 2af965a67d..5c9ea3c4ff 100644
--- a/scripts/completion/dvc.bash
+++ b/scripts/completion/dvc.bash
@@ -26,7 +26,7 @@ _dvc_diff='-t --target'
 _dvc_fetch='-j --jobs -r --remote -a --all-branches -T --all-tags -d --with-deps -R --recursive $(compgen -G *.dvc)'
 _dvc_get_url=''
 _dvc_get='-o --out --rev --show-url'
-_dvc_gc='-a --all-branches -T --all-tags -c --cloud -r --remote -f --force -p --projects -j --jobs'
+_dvc_gc='--remove-all-branches --remove-all-tags --remove-all-history -c --cloud -r --remote -f --force -p --projects -j --jobs'
 _dvc_import_url='-f --file'
 _dvc_import='-o --out --rev'
 _dvc_init='--no-scm -f --force'
diff --git a/scripts/completion/dvc.zsh b/scripts/completion/dvc.zsh
index 32bdef47ff..3b6911c450 100644
--- a/scripts/completion/dvc.zsh
+++ b/scripts/completion/dvc.zsh
@@ -124,8 +124,8 @@ _dvc_get=(
 )
 
 _dvc_gc=(
-  {-a,--all-branches}"[Keep data files for the tips of all git branches.]"
-  {-T,--all-tags}"[Keep data files for all git tags.]"
+  "--remove-all-branches[Keep data files for the tips of all git branches.]"
+  "--remove-all-tags[Keep data files for all git tags.]"
   {-c,--cloud}"[Collect garbage in remote repository.]"
   {-r,--remote}"[Remote storage to collect garbage in.]:Remote repository:"
   {-f,--force}"[Force garbage collection - automatically agree to all prompts.]:Repos:_files"
diff --git a/tests/func/test_gc.py b/tests/func/test_gc.py
index 41c4f2204a..fd29ea8ef8 100644
--- a/tests/func/test_gc.py
+++ b/tests/func/test_gc.py
@@ -92,16 +92,26 @@ def test(self):
 
         self._check_cache(4)
 
-        self.dvc.gc(all_tags=True, all_branches=True)
+        self.dvc.gc()
+        self._check_cache(4)
 
+        self.dvc.gc(remove_all_history=True)
         self._check_cache(3)
 
-        self.dvc.gc(all_tags=False, all_branches=True)
+        self.dvc.gc(remove_all_tags=True)
+        self._check_cache(3)
 
+        self.dvc.gc(remove_all_branches=True)
         self._check_cache(2)
 
-        self.dvc.gc(all_tags=True, all_branches=False)
+        self.dvc.gc(remove_all_branches=True, remove_all_tags=True)
+        self._check_cache(2)
 
+        self.dvc.gc(
+            remove_all_branches=True,
+            remove_all_tags=True,
+            remove_all_history=True,
+        )
         self._check_cache(1)
 
 
@@ -183,7 +193,7 @@ def test_all_commits(tmp_dir, scm, dvc):
     tmp_dir.dvc_gen("testfile", "workspace")
 
     n = _count_files(dvc.cache.local.cache_dir)
-    dvc.gc(all_commits=True)
+    dvc.gc()
 
     # Only one uncommitted file should go away
     assert _count_files(dvc.cache.local.cache_dir) == n - 1
diff --git a/tests/unit/command/test_gc.py b/tests/unit/command/test_gc.py
new file mode 100644
index 0000000000..a390c8f29b
--- /dev/null
+++ b/tests/unit/command/test_gc.py
@@ -0,0 +1,39 @@
+from dvc.cli import parse_args
+from dvc.command.gc import CmdGC
+
+
+def test_gc(mocker):
+    cli_args = parse_args(
+        [
+            "gc",
+            "--remove-all-tags",
+            "--remove-all-branches",
+            "--remove-all-history",
+            "--cloud",
+            "--remote",
+            "myremote",
+            "--force",
+            "--jobs",
+            "10",
+            "--projects",
+            "/some/path",
+            "/some/other/path",
+        ]
+    )
+    assert cli_args.func == CmdGC
+
+    cmd = cli_args.func(cli_args)
+    m = mocker.patch("dvc.repo.Repo.gc")
+
+    assert cmd.run() == 0
+
+    m.assert_called_once_with(
+        remove_all_tags=True,
+        remove_all_branches=True,
+        remove_all_history=True,
+        cloud=True,
+        remote="myremote",
+        force=True,
+        jobs=10,
+        repos=["/some/path", "/some/other/path"],
+    )
diff --git a/tests/unit/scm/test_git.py b/tests/unit/scm/test_git.py
index 2874da16b5..40f08dab4c 100644
--- a/tests/unit/scm/test_git.py
+++ b/tests/unit/scm/test_git.py
@@ -15,3 +15,16 @@ def test_belongs_to_scm_true_on_git_internal(self):
     def test_belongs_to_scm_false(self):
         path = os.path.join("some", "non-.git", "file")
         self.assertFalse(self.dvc.scm.belongs_to_scm(path))
+
+
+def test_list_all_commits_detached_head(tmp_dir, scm):
+    tmp_dir.scm_gen({"first": "first"}, commit="first")
+    tmp_dir.scm_gen({"second": "second"}, commit="second")
+    scm.branch("branch_second")
+    scm.checkout("branch_third", create_new=True)
+    tmp_dir.scm_gen({"third": "third"}, commit="third")
+    scm.checkout("branch_second")
+    assert len(scm.list_all_commits()) == 3
+    # deleting the branch so that `third` commit gets lost
+    scm.repo.git.branch("branch_third", D=True)
+    assert len(scm.list_all_commits()) == 2