bot_update: Refactor branch to detach and checkout.

Refactor _git_checkout to use information from
get_target_branch_and_revision to know what branch to checkout after
cloning.

Bug: 1104182
Change-Id: Ib3ba57ca0b6803f172b85121c2a4b123f17bfb8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2303291Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

recipes/recipe_modules/bot_update/resources/bot_update.py

@@ -588,54 +588,30 @@ def get_total_disk_space():
     return (total, free)
 
 
-def _get_target_branch_and_revision(solution_name, git_url, revisions):
-  normalized_name = solution_name.strip('/')
-  if normalized_name in revisions:
-    configured = revisions[normalized_name]
-  elif git_url in revisions:
-    configured = revisions[git_url]
+def get_target_branch_and_revision(solution_name, git_url, revisions):
+  solution_name = solution_name.strip('/')
+  configured = revisions.get(solution_name) or revisions.get(git_url)
+
+  if configured is None or COMMIT_HASH_RE.match(configured):
+    # TODO(crbug.com/1104182): Get the default branch instead of assuming
+    # 'master'.
+    branch = 'origin/master'
+    revision = configured or 'HEAD'
+    return branch, revision
+  elif ':' in configured:
+    branch, revision = configured.split(':', 1)
   else:
-    return 'master', 'HEAD'
-
-  parts = configured.split(':', 1)
-  if len(parts) == 2:
-    # Support for "branch:revision" syntax.
-    return parts
-  if COMMIT_HASH_RE.match(configured):
-    return 'master', configured
-  return configured, 'HEAD'
-
-
-def get_target_pin(solution_name, git_url, revisions):
-  """Returns revision to be checked out if it is pinned, else None."""
-  _, revision = _get_target_branch_and_revision(
-      solution_name, git_url, revisions)
-  if COMMIT_HASH_RE.match(revision):
-    return revision
-  return None
+    branch = configured
+    revision = 'HEAD'
 
+  if branch.startswith('refs/heads/'):
+    branch = 'refs/remotes/origin/' + branch[len('refs/heads/'):]
+  elif branch.startswith('refs/branch-heads/'):
+    branch = 'refs/remotes/branch-heads/' + branch[len('refs/branch-heads/'):]
+  elif not branch.startswith(('refs/', 'origin/')):
+    branch = 'origin/' + branch
 
-def force_solution_revision(solution_name, git_url, revisions, cwd):
-  branch, revision = _get_target_branch_and_revision(
-      solution_name, git_url, revisions)
-  if revision and revision.upper() != 'HEAD':
-    treeish = revision
-  else:
-    # TODO(machenbach): This won't work with branch-heads, as Gerrit's
-    # destination branch would be e.g. refs/branch-heads/123. But here
-    # we need to pass refs/remotes/branch-heads/123 to check out.
-    # This will also not work if somebody passes a local refspec like
-    # refs/heads/master. It needs to translate to refs/remotes/origin/master
-    # first. See also https://crbug.com/740456 .
-    if branch.startswith(('refs/', 'origin/')):
-      treeish = branch
-    else:
-      treeish = 'origin/' + branch
-
-  # Note that -- argument is necessary to ensure that git treats `treeish`
-  # argument as revision or ref, and not as a file/directory which happens to
-  # have the exact same name.
-  git('checkout', '--force', treeish, '--', cwd=cwd)
+  return branch, revision
 
 
 def _has_in_git_cache(revision_sha1, refs, git_cache_dir, url):
@@ -720,8 +696,10 @@ def _git_checkout(sln, sln_dir, revisions, refs, no_fetch_tags, git_cache_dir,
         'GIT_TRACE_PERFORMANCE': 'true',
     }
 
+  branch, revision = get_target_branch_and_revision(name, url, revisions)
+  pin = revision if COMMIT_HASH_RE.match(revision) else None
+
   # Step 1: populate/refresh cache, if necessary.
-  pin = get_target_pin(name, url, revisions)
   if not pin:
     # Refresh only once.
     git(*populate_cmd, env=env)
@@ -775,7 +753,10 @@ def _git_checkout(sln, sln_dir, revisions, refs, no_fetch_tags, git_cache_dir,
         # to master in contrast with the non-clone case, which results in a
         # detached HEAD. This prevents fetching the default branch so detach the
         # HEAD after cloning.
-        git('checkout', 'HEAD', '--detach', cwd=sln_dir)
+        # Note that the '--' argument is needed to ensure that git treats
+        # 'pin or branch' as revision or ref, and not as file/directory which
+        # happens to have the exact same name.
+        git('checkout', pin or branch, '--detach', '--', cwd=sln_dir)
         _git_disable_gc(sln_dir)
       else:
         _git_disable_gc(sln_dir)
@@ -792,7 +773,10 @@ def _git_checkout(sln, sln_dir, revisions, refs, no_fetch_tags, git_cache_dir,
       if sys.platform.startswith('win'):
         _maybe_break_locks(sln_dir, tries=3)
 
-      force_solution_revision(name, url, revisions, sln_dir)
+      # Note that the '--' argument is needed to ensure that git treats
+      # 'pin or branch' as revision or ref, and not as file/directory which
+      # happens to have the exact same name.
+      git('checkout', '--force', pin or branch, '--', cwd=sln_dir)
       git('clean', '-dff', cwd=sln_dir)
       return
     except SubprocessFailed as e: