1 files changed, 70 insertions, 0 deletions
diff --git a/dhpython/markers.py b/dhpython/markers.py
new file mode 100644
index 0000000..a0a3e55
--- /dev/null
+++ b/dhpython/markers.py
@@ -0,0 +1,70 @@
+# Copyright © 2022 Stefano Rivera <stefanor@debian.org>
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+"""
+Handle Environment Markers
+https://www.python.org/dev/peps/pep-0508/#environment-markers
+
+TODO: Ideally replace with the packaging library, but the API is currently
+private: https://github.com/pypa/packaging/issues/496
+"""
+
+import re
+
+
+SIMPLE_ENV_MARKER_RE = re.compile(r'''
+    (?P<marker>[a-z_]+)
+    \s*
+    (?P<op><=?|>=?|[=!~]=|===)
+    \s*
+    (?P<quote>['"])
+    (?P<value>.*)  # Could contain additional markers
+    (?P=quote)
+    ''', re.VERBOSE)
+COMPLEX_ENV_MARKER_RE = re.compile(r'''
+    (?:\s|\))
+    (?:and|or)
+    (?:\s|\()
+    ''', re.VERBOSE)
+
+
+class ComplexEnvironmentMarker(Exception):
+    pass
+
+
+def parse_environment_marker(marker):
+    """Parse a simple marker of <= 1 environment restriction"""
+    marker = marker.strip()
+    if marker.startswith('(') and marker.endswith(')'):
+        marker = marker[1:-1].strip()
+
+    m = COMPLEX_ENV_MARKER_RE.search(marker)
+    if m:
+        raise ComplexEnvironmentMarker()
+
+    m = SIMPLE_ENV_MARKER_RE.match(marker)
+    if not m:
+        raise ComplexEnvironmentMarker()
+
+    return (
+        m.group('marker'),
+        m.group('op'),
+        m.group('value'),
+    )