Extra environment marker should evaluate correctly.

packaging/markers.py

@@ -14,6 +14,7 @@
 
 from ._compat import string_types
 from .specifiers import Specifier, InvalidSpecifier
+from .utils import safe_extra
 
 
 __all__ = [
@@ -126,6 +127,20 @@ def serialize(self):
 MARKER_VAR = VARIABLE | MARKER_VALUE
 
 MARKER_ITEM = Group(MARKER_VAR + MARKER_OP + MARKER_VAR)
+
+# Special parsing rules apply for markers that evaluate extras.
+EXTRA_VARIABLE = L('extra')
+EXTRA_VARIABLE.setParseAction(lambda s, l, t: Variable(t[0]))
+
+EXTRA_OP = (L("==") | L("===")) | L("!=")
+EXTRA_OP.setParseAction(lambda s, l, t: Op(t[0]))
+
+EXTRA_VALUE = QuotedString("'") | QuotedString('"')
+EXTRA_VALUE.setParseAction(lambda s, l, t: Value(safe_extra(t[0])))
+
+EXTRA_ITEM = Group(EXTRA_VARIABLE + EXTRA_OP + EXTRA_VALUE)
+
+MARKER_ITEM = EXTRA_ITEM | MARKER_ITEM
 MARKER_ITEM.setParseAction(lambda s, l, t: tuple(t[0]))
 
 LPAREN = L("(").suppress()
@@ -297,5 +312,9 @@ def evaluate(self, environment=None):
         current_environment = default_environment()
         if environment is not None:
             current_environment.update(environment)
+        if current_environment.get('extra'):
+            current_environment['extra'] = safe_extra(
+                current_environment['extra']
+            )
 
         return _evaluate_markers(self._markers, current_environment)

packaging/utils.py

@@ -12,3 +12,12 @@
 def canonicalize_name(name):
     # This is taken from PEP 503.
     return _canonicalize_regex.sub("-", name).lower()
+
+
+def safe_extra(extra):
+    """Convert an arbitrary string to a standard 'extra' name
+
+    Any runs of non-alphanumeric characters are replaced with a single '_',
+    and the result is always lowercased.
+    """
+    return re.sub('[^A-Za-z0-9.-]+', '_', extra).lower()

tests/test_markers.py

@@ -303,6 +303,11 @@ def test_extra_with_no_extra_in_environment(self):
                 {"extra": "security"},
                 True,
             ),
+            (
+                "extra == 'SECURITY'",
+                {"extra": "security"},
+                True,
+            ),
         ],
     )
     def test_evaluates(self, marker_string, environment, expected):