Fix #78: clear error when a configured branch does not exist

- git_checkout detects 'remote branch not found' clone failures and raises a
  message naming the package, branch and URL, pointing at the mx.ini setting.
- git_switch_branch and git_merge_rbranch raise the same clear GitError instead
  of logging a terse 'No such branch' and calling sys.exit(1), so the update path
  behaves consistently with checkout.
- The worker reports expected WCErrors as a plain error message and keeps the full
  traceback at debug level only.

Author: jensens

CHANGES.md

@@ -13,6 +13,11 @@
   with a `# managed by mxdev` marker and prunes managed entries that are no longer
   configured, while leaving user-defined sources untouched. [jensens]
 
+- Fix #78: Give a clear, actionable error when a configured `branch` does not exist on the
+  remote (e.g. it was deleted), naming the package, branch and URL and pointing at the
+  `mx.ini` setting, on both checkout and update. Expected VCS errors are no longer reported
+  with a full Python traceback (the traceback is kept at debug level). [jensens]
+
 
 ## 5.3.2 (2026-05-30)
 

src/mxdev/vcs/common.py

@@ -426,11 +426,14 @@ def worker(working_copies: WorkingCopies, the_queue: queue.Queue) -> None:
             return
         try:
             output = action(**kwargs)
-        except WCError:
+        except WCError as e:
             with output_lock:
                 for lvl, msg in wc._output:
                     lvl(msg)
-                logger.exception("Can not execute action!")
+                # WCError is an expected operational failure: show a clean,
+                # actionable message and keep the full traceback for debug only.
+                logger.error("%s", e)
+                logger.debug("Traceback for the error above:", exc_info=True)
                 working_copies.errors = True
         else:
             with output_lock:

src/mxdev/vcs/git.py

@@ -15,6 +15,14 @@ class GitError(common.WCError):
     pass
 
 
+def _branch_not_found_message(name: str, branch: str, url: str) -> str:
+    """Build a clear, actionable error for a configured branch that is missing."""
+    return (
+        f"Branch '{branch}' for package '{name}' does not exist at '{url}'. "
+        f"Check the 'branch' setting for [{name}] in your mx.ini."
+    )
+
+
 class GitWorkingCopy(common.BaseWorkingCopy):
     """The git working copy.
 
@@ -117,8 +125,7 @@ def git_merge_rbranch(self, stdout_in: str, stderr_in: str, accept_missing: bool
             if accept_missing:
                 logger.info("No such branch %r", branch)
                 return (stdout_in, stderr_in)
-            logger.error("No such branch %r", branch)
-            sys.exit(1)
+            raise GitError(_branch_not_found_message(self.source["name"], branch, self.source["url"]))
 
         rbp = self._remote_branch_prefix
         cmd = self.run_git(["merge", f"{rbp}/{branch}"], cwd=path)
@@ -151,6 +158,9 @@ def git_checkout(self, **kwargs) -> str | None:
         cmd = self.run_git(args)
         stdout, stderr = cmd.communicate()
         if cmd.returncode != 0:
+            branch = self.source.get("branch")
+            if branch and "not found in upstream" in stderr:
+                raise GitError(_branch_not_found_message(name, branch, url))
             raise GitError(f"git cloning of '{name}' failed.\n{stderr}")
         if "rev" in self.source:
             stdout, stderr = self.git_switch_branch(stdout, stderr)
@@ -206,8 +216,7 @@ def git_switch_branch(self, stdout_in: str, stderr_in: str, accept_missing: bool
             self.output((logger.info, f"No such branch {branch}"))
             return (stdout_in + stdout, stderr_in + stderr)
         else:
-            self.output((logger.error, f"No such branch {branch}"))
-            sys.exit(1)
+            raise GitError(_branch_not_found_message(self.source["name"], branch, self.source["url"]))
         # runs the checkout with predetermined arguments
         cmd = self.run_git(argv, cwd=path)
         stdout, stderr = cmd.communicate()

tests/test_common.py

@@ -525,7 +525,9 @@ def update(self, **kwargs):
     common.worker(working_copies, test_queue)
 
     assert working_copies.errors is True
-    assert "Can not execute action!" in caplog.text
+    # The actual error message is shown (no generic message / traceback noise).
+    assert "Test error" in caplog.text
+    assert "Can not execute action!" not in caplog.text
 
 
 def test_worker_with_bytes_output(mocker):

tests/test_git_additional.py

@@ -275,6 +275,7 @@ def test_git_merge_rbranch_missing_branch_accept():
 
 def test_git_merge_rbranch_missing_branch_no_accept():
     """Test git_merge_rbranch with missing branch and accept_missing=False."""
+    from mxdev.vcs.git import GitError
     from mxdev.vcs.git import GitWorkingCopy
 
     with patch("mxdev.vcs.common.which", return_value="/usr/bin/git"):
@@ -293,9 +294,12 @@ def test_git_merge_rbranch_missing_branch_no_accept():
         mock_process.communicate.return_value = ("* main\n  develop\n", "")
 
         with patch.object(wc, "run_git", return_value=mock_process):
-            with pytest.raises(SystemExit):
+            with pytest.raises(GitError) as excinfo:
                 wc.git_merge_rbranch("", "", accept_missing=False)
 
+    assert "Branch 'nonexistent' for package 'test-package' does not exist" in str(excinfo.value)
+    assert "Check the 'branch' setting for [test-package] in your mx.ini" in str(excinfo.value)
+
 
 def test_git_merge_rbranch_merge_failure():
     """Test git_merge_rbranch handles merge failure."""
@@ -888,6 +892,7 @@ def test_git_switch_branch_failure():
 
 def test_git_switch_branch_missing_no_accept():
     """Test git_switch_branch with missing branch and accept_missing=False."""
+    from mxdev.vcs.git import GitError
     from mxdev.vcs.git import GitWorkingCopy
 
     with patch("mxdev.vcs.common.which", return_value="/usr/bin/git"):
@@ -905,8 +910,12 @@ def test_git_switch_branch_missing_no_accept():
         mock_process.communicate.return_value = ("* main\n", "")
 
         with patch.object(wc, "run_git", return_value=mock_process):
-            with pytest.raises(SystemExit):
-                wc.git_switch_branch("", "", accept_missing=False)
+            with patch.object(wc, "git_version", return_value=(2, 30, 0)):
+                with pytest.raises(GitError) as excinfo:
+                    wc.git_switch_branch("", "", accept_missing=False)
+
+    assert "Branch 'nonexistent' for package 'test-package' does not exist" in str(excinfo.value)
+    assert "Check the 'branch' setting for [test-package] in your mx.ini" in str(excinfo.value)
 
 
 def test_git_switch_branch_missing_accept():