gh-117201: Handle leading // for posixpath.commonpath

Lib/posixpath.py

@@ -515,19 +515,20 @@ def relpath(path, start=None):
         raise
 
 
-# Return the longest common sub-path of the sequence of paths given as input.
+# Return the longest common sub-path of the iterable of paths given as input.
 # The paths are not normalized before comparing them (this is the
 # responsibility of the caller). Any trailing separator is stripped from the
 # returned path.
 
 def commonpath(paths):
-    """Given a sequence of path names, returns the longest common sub-path."""
+    """Given an iterable of path names, returns the longest common sub-path."""
 
-    paths = tuple(map(os.fspath, paths))
+    paths = tuple(paths)
 
     if not paths:
-        raise ValueError('commonpath() arg is an empty sequence')
+        raise ValueError('commonpath() arg is an empty iterable')
 
+    _, roots, paths = zip(*map(splitroot, paths))
     if isinstance(paths[0], bytes):
         sep = b'/'
         curdir = b'.'
@@ -536,12 +537,11 @@ def commonpath(paths):
         curdir = '.'
 
     try:
+        prefix = min(roots)
         split_paths = [path.split(sep) for path in paths]
 
-        try:
-            isabs, = set(p[:1] == sep for p in paths)
-        except ValueError:
-            raise ValueError("Can't mix absolute and relative paths") from None
+        if not prefix and any(roots):
+            raise ValueError("Can't mix absolute and relative paths")
 
         split_paths = [[c for c in s if c and c != curdir] for s in split_paths]
         s1 = min(split_paths)
@@ -552,7 +552,6 @@ def commonpath(paths):
                 common = s1[:i]
                 break
 
-        prefix = sep if isabs else sep[:0]
         return prefix + sep.join(common)
     except (TypeError, AttributeError):
         genericpath._check_arg_types('commonpath', *paths)

Lib/test/test_posixpath.py

@@ -700,20 +700,32 @@ def check(paths, expected):
                              os.fsencode(expected))
         def check_error(exc, paths):
             self.assertRaises(exc, posixpath.commonpath, paths)
+            self.assertRaises(exc, posixpath.commonpath, paths[::-1])
             self.assertRaises(exc, posixpath.commonpath,
                               [os.fsencode(p) for p in paths])
+            self.assertRaises(exc, posixpath.commonpath,
+                              [os.fsencode(p) for p in paths[::-1]])
 
         self.assertRaises(TypeError, posixpath.commonpath, None)
         self.assertRaises(ValueError, posixpath.commonpath, [])
         self.assertRaises(ValueError, posixpath.commonpath, iter([]))
         check_error(ValueError, ['/usr', 'usr'])
-        check_error(ValueError, ['usr', '/usr'])
+        check_error(ValueError, ['//usr', 'usr'])
+        check_error(ValueError, ['///usr', 'usr'])
+        check_error(ValueError, ['//usr', '/usr', 'usr'])
 
+        # gh-117201: Handle leading slashes
         check(['/usr/local'], '/usr/local')
+        check(['//usr/local'], '//usr/local')
+        check(['///usr/local'], '/usr/local')
+        check(['/usr/local', '//usr/local'], '/usr/local')
+        check(['//usr/local', '//usr/local'], '//usr/local')
+        check(['///usr/local', '//usr/local'], '/usr/local')
+
         check(['/usr/local', '/usr/local'], '/usr/local')
         check(['/usr/local/', '/usr/local'], '/usr/local')
         check(['/usr/local/', '/usr/local/'], '/usr/local')
-        check(['/usr//local', '//usr/local'], '/usr/local')
+        check(['/usr//local', '/usr/local'], '/usr/local')
         check(['/usr/./local', '/./usr/local'], '/usr/local')
         check(['/', '/dev'], '/')
         check(['/usr', '/dev'], '/')
@@ -736,18 +748,9 @@ def check_error(exc, paths):
         check(['', 'spam/alot'], '')
         check_error(ValueError, ['', '/spam/alot'])
 
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          [b'/usr/lib/', '/usr/lib/python3'])
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          [b'/usr/lib/', 'usr/lib/python3'])
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          [b'usr/lib/', '/usr/lib/python3'])
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          ['/usr/lib/', b'/usr/lib/python3'])
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          ['/usr/lib/', b'usr/lib/python3'])
-        self.assertRaises(TypeError, posixpath.commonpath,
-                          ['usr/lib/', b'/usr/lib/python3'])
+        check_error(TypeError, [b'/usr/lib/', '/usr/lib/python3'])
+        check_error(TypeError, [b'/usr/lib/', 'usr/lib/python3'])
+        check_error(TypeError, [b'usr/lib/', '/usr/lib/python3'])
 
 
 class PosixCommonTest(test_genericpath.CommonTest, unittest.TestCase):

Misc/NEWS.d/next/Core and Builtins/2024-03-26-20-20-36.gh-issue-117201.qaS7em.rst

@@ -0,0 +1 @@
+Handle leading ``//`` for :func:`posixpath.commonpath` using :func:`posixpath.splitroot`.