1 files changed, 37 insertions, 37 deletions
diff --git a/setuptools/_vendor/packaging/version.py b/setuptools/_vendor/packaging/version.py
index e76e9607..8d779a48 100644
--- a/setuptools/_vendor/packaging/version.py
+++ b/setuptools/_vendor/packaging/version.py
@@ -21,7 +21,7 @@ from ._structures import Infinity
 
 
 __all__ = [
-    "parse", "Version", "LegacyVersion", "InvalidVersion",
+    "parse", "Version", "LegacyVersion", "InvalidVersion", "VERSION_PATTERN"
 ]
 
 
@@ -156,44 +156,44 @@ def _legacy_cmpkey(version):
 
     return epoch, parts
 
+# Deliberately not anchored to the start and end of the string, to make it
+# easier for 3rd party code to reuse
+VERSION_PATTERN = r"""
+    v?
+    (?:
+        (?:(?P<epoch>[0-9]+)!)?                           # epoch
+        (?P<release>[0-9]+(?:\.[0-9]+)*)                  # release segment
+        (?P<pre>                                          # pre-release
+            [-_\.]?
+            (?P<pre_l>(a|b|c|rc|alpha|beta|pre|preview))
+            [-_\.]?
+            (?P<pre_n>[0-9]+)?
+        )?
+        (?P<post>                                         # post release
+            (?:-(?P<post_n1>[0-9]+))
+            |
+            (?:
+                [-_\.]?
+                (?P<post_l>post|rev|r)
+                [-_\.]?
+                (?P<post_n2>[0-9]+)?
+            )
+        )?
+        (?P<dev>                                          # dev release
+            [-_\.]?
+            (?P<dev_l>dev)
+            [-_\.]?
+            (?P<dev_n>[0-9]+)?
+        )?
+    )
+    (?:\+(?P<local>[a-z0-9]+(?:[-_\.][a-z0-9]+)*))?       # local version
+"""
+
 
 class Version(_BaseVersion):
 
     _regex = re.compile(
-        r"""
-        ^
-        \s*
-        v?
-        (?:
-            (?:(?P<epoch>[0-9]+)!)?                           # epoch
-            (?P<release>[0-9]+(?:\.[0-9]+)*)                  # release segment
-            (?P<pre>                                          # pre-release
-                [-_\.]?
-                (?P<pre_l>(a|b|c|rc|alpha|beta|pre|preview))
-                [-_\.]?
-                (?P<pre_n>[0-9]+)?
-            )?
-            (?P<post>                                         # post release
-                (?:-(?P<post_n1>[0-9]+))
-                |
-                (?:
-                    [-_\.]?
-                    (?P<post_l>post|rev|r)
-                    [-_\.]?
-                    (?P<post_n2>[0-9]+)?
-                )
-            )?
-            (?P<dev>                                          # dev release
-                [-_\.]?
-                (?P<dev_l>dev)
-                [-_\.]?
-                (?P<dev_n>[0-9]+)?
-            )?
-        )
-        (?:\+(?P<local>[a-z0-9]+(?:[-_\.][a-z0-9]+)*))?       # local version
-        \s*
-        $
-        """,
+        r"^\s*" + VERSION_PATTERN + r"\s*$",
         re.VERBOSE | re.IGNORECASE,
     )
 
@@ -297,8 +297,8 @@ def _parse_letter_version(letter, number):
             letter = "a"
         elif letter == "beta":
             letter = "b"
-        elif letter in ["rc", "pre", "preview"]:
-            letter = "c"
+        elif letter in ["c", "pre", "preview"]:
+            letter = "rc"
 
         return letter, int(number)
     if not letter and number: