Bump pyparsing, update usages and update UT

Support `pyparsing` 2 and 3.

Related changes in `pyparsing==3.0.0`:
- `originalTextFor` -> `original_text_for`
- `stringEnd` -> `string_end`
- `stringStart` -> `string_start`

Implemented according to this suggestion:
pypa#480 (comment)

Determine which attributres to import according to
`pyparsing.__version__`, and import pyparsing 2 attributes as 3.

Update UT: `test_parseexception_error_msg` to check for either
`string_end` or `stringEnd` in exception message.

packaging/markers.py

@@ -5,6 +5,7 @@
 import operator
 import os
 import platform
+import pyparsing
 import sys
 from typing import Any, Callable, Dict, List, Optional, Tuple, Union
 
@@ -16,10 +17,21 @@
     ParseResults,
     QuotedString,
     ZeroOrMore,
-    stringEnd,
-    stringStart,
 )
 
+# To support pyparsing 2 and 3
+if pyparsing.__version__.startswith("2."):
+    from pyparsing import (
+        stringEnd as string_end,
+        stringStart as string_start,
+    )
+else:
+    from pyparsing import (
+        string_end,
+        string_start,
+    )
+
+
 from .specifiers import InvalidSpecifier, Specifier
 
 __all__ = [
@@ -135,7 +147,7 @@ def serialize(self) -> str:
 MARKER_ATOM = MARKER_ITEM | Group(LPAREN + MARKER_EXPR + RPAREN)
 MARKER_EXPR << MARKER_ATOM + ZeroOrMore(BOOLOP + MARKER_EXPR)
 
-MARKER = stringStart + MARKER_EXPR + stringEnd
+MARKER = string_start + MARKER_EXPR + string_end
 
 
 def _coerce_parse_result(results: Union[ParseResults, List[Any]]) -> List[Any]:

packaging/requirements.py

@@ -2,6 +2,7 @@
 # 2.0, and the BSD License. See the LICENSE file in the root of this repository
 # for complete details.
 
+import pyparsing
 import re
 import string
 import urllib.parse
@@ -15,14 +16,25 @@
     Regex,
     Word,
     ZeroOrMore,
-    originalTextFor,
-    stringEnd,
-    stringStart,
 )
 
 from .markers import MARKER_EXPR, Marker
 from .specifiers import LegacySpecifier, Specifier, SpecifierSet
 
+# To support pyparsing 2 and 3
+if pyparsing.__version__.startswith("2."):
+    from pyparsing import (
+        originalTextFor as original_text_for,
+        stringEnd as string_end,
+        stringStart as string_start,
+    )
+else:
+    from pyparsing import (
+        original_text_for,
+        string_end,
+        string_start,
+    )
+
 
 class InvalidRequirement(ValueError):
     """
@@ -63,10 +75,10 @@ class InvalidRequirement(ValueError):
 _VERSION_SPEC = Optional((LPAREN + VERSION_MANY + RPAREN) | VERSION_MANY)
 _VERSION_SPEC.setParseAction(lambda s, l, t: t._raw_spec or "")
 
-VERSION_SPEC = originalTextFor(_VERSION_SPEC)("specifier")
+VERSION_SPEC = original_text_for(_VERSION_SPEC)("specifier")
 VERSION_SPEC.setParseAction(lambda s, l, t: t[1])
 
-MARKER_EXPR = originalTextFor(MARKER_EXPR())("marker")
+MARKER_EXPR = original_text_for(MARKER_EXPR())("marker")
 MARKER_EXPR.setParseAction(
     lambda s, l, t: Marker(s[t._original_start : t._original_end])
 )
@@ -78,7 +90,7 @@ class InvalidRequirement(ValueError):
 
 NAMED_REQUIREMENT = NAME + Optional(EXTRAS) + (URL_AND_MARKER | VERSION_AND_MARKER)
 
-REQUIREMENT = stringStart + NAMED_REQUIREMENT + stringEnd
+REQUIREMENT = string_start + NAMED_REQUIREMENT + string_end
 # pyparsing isn't thread safe during initialization, so we do it eagerly, see
 # issue #104
 REQUIREMENT.parseString("x[]")

setup.py

@@ -48,7 +48,7 @@
     author=about["__author__"],
     author_email=about["__email__"],
     python_requires=">=3.6",
-    install_requires=["pyparsing>=2.0.2,<3"],  # Needed to avoid issue #91
+    install_requires=["pyparsing>=2.0.2"],  # Needed to avoid issue #91
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",

tests/test_requirements.py

@@ -192,4 +192,4 @@ def test_sys_platform_linux_in(self):
     def test_parseexception_error_msg(self):
         with pytest.raises(InvalidRequirement) as e:
             Requirement("toto 42")
-        assert "Expected stringEnd" in str(e.value)
+        assert "Expected string_end" in str(e.value)