fix #266 and add a unittest for the tag_to_version

Author: RonnyPfannschmidt

CHANGELOG.rst

@@ -6,6 +6,8 @@ v3.0.0
 * switch to src layout (breaking change)
 * no longer alias tag and parsed_version in order to support understanding a version parse failure
 * require parse results to be ScmVersion or None (breaking change)
+* fix #266 by requirin the prefix word to be a word again
+  (breaking change as the bug allowed arbitrary prefixes while the original feature only allowed words")
 
 v2.1.0
 ======

src/setuptools_scm/version.py

@@ -13,6 +13,7 @@
 SEMVER_MINOR = 2
 SEMVER_PATCH = 3
 SEMVER_LEN = 3
+TAG_PREFIX = re.compile(r"^\w+-(.*)")
 
 
 def _pad(iterable, size, padding=None):
@@ -56,14 +57,21 @@ def callable_or_entrypoint(group, callable_or_name):
 
 
 def tag_to_version(tag):
+    """
+    take a tag that might be prefixed with a keyword and return only the version part
+    """
     trace("tag", tag)
     if "+" in tag:
         warnings.warn("tag %r will be stripped of the local component" % tag)
         tag = tag.split("+")[0]
     # lstrip the v because of py2/py3 differences in setuptools
     # also required for old versions of setuptools
-
-    version = tag.rsplit("-", 1)[-1].lstrip("v")
+    prefix_match = TAG_PREFIX.match(tag)
+    if prefix_match is not None:
+        version = prefix_match.group(1)
+    else:
+        version = tag
+    trace("version pre parse", version)
     if VERSION_CLASS is None:
         return version
     version = pkg_parse_version(version)

testing/test_functions.py

@@ -2,7 +2,12 @@
 import sys
 import pkg_resources
 from setuptools_scm import dump_version, get_version, PRETEND_KEY
-from setuptools_scm.version import guess_next_version, meta, format_version
+from setuptools_scm.version import (
+    guess_next_version,
+    meta,
+    format_version,
+    tag_to_version,
+)
 from setuptools_scm.utils import has_command
 
 PY3 = sys.version_info > (2,)
@@ -77,3 +82,16 @@ def test_has_command(recwarn):
     assert not has_command("yadayada_setuptools_aint_ne")
     msg = recwarn.pop()
     assert "yadayada" in str(msg.message)
+
+
+@pytest.mark.parametrize(
+    "tag, expected_version",
+    [
+        ("1.1", "1.1"),
+        ("release-1.1", "1.1"),
+        pytest.param("3.3.1-rc26", "3.3.1rc26", marks=pytest.mark.issue(266)),
+    ],
+)
+def test_tag_to_version(tag, expected_version):
+    version = str(tag_to_version(tag))
+    assert version == expected_version