fix: prevent prerelase from creating a bump when there are no commits

Closes #281

Author: woile

commitizen/commands/bump.py

@@ -112,6 +112,13 @@ def __call__(self):  # noqa: C901
         if increment is None:
             increment = self.find_increment(commits)
 
+        # It may happen that there are commits, but they are not elegible
+        # for an increment, this generate a problem when using prerelease (#281)
+        if prerelease and increment is None:
+            raise NoCommitsFoundError(
+                "[NO_COMMITS_FOUND]\n" "No commits found to generate a pre-release."
+            )
+
         # Increment is removed when current and next version
         # are expected to be prereleases.
         if prerelease and current_version_instance.is_prerelease:

tests/commands/test_bump_command.py

@@ -358,3 +358,29 @@ def test_bump_with_changelog_config(mocker, changelog_path, config_path):
         out = f.read()
     assert out.startswith("#")
     assert "0.2.0" in out
+
+
+def test_prevent_prerelease_when_no_increment_detected(
+    mocker, capsys, tmp_commitizen_project
+):
+    create_file_and_commit("feat: new file")
+
+    testargs = ["cz", "bump", "--yes"]
+    mocker.patch.object(sys, "argv", testargs)
+
+    cli.main()
+    out, _ = capsys.readouterr()
+
+    assert "0.2.0" in out
+
+    create_file_and_commit("test: new file")
+    testargs = ["cz", "bump", "-pr", "beta"]
+    mocker.patch.object(sys, "argv", testargs)
+
+    with pytest.raises(NoCommitsFoundError) as excinfo:
+        cli.main()
+
+    expected_error_message = (
+        "[NO_COMMITS_FOUND]\n" "No commits found to generate a pre-release."
+    )
+    assert expected_error_message in str(excinfo.value)