Consolidate relative symlink creation. (#2667)

This is work towards #2658 which will need to tackle falling back from
symlinks when there are insufficient permissions to create them.

pex/common.py

@@ -619,7 +619,7 @@ def symlink(
         self._ensure_parent(dst)
         abs_src = os.path.realpath(src)
         abs_dst = os.path.realpath(os.path.join(self.chroot, dst))
-        safe_symlink(os.path.relpath(abs_src, os.path.dirname(abs_dst)), abs_dst)
+        safe_relative_symlink(abs_src, abs_dst)
 
     def write(
         self,
@@ -768,7 +768,7 @@ def iter_files():
                 write_entry(filename, arcname)
 
 
-def relative_symlink(
+def safe_relative_symlink(
     src,  # type: Text
     dst,  # type: Text
 ):
@@ -779,6 +779,7 @@ def relative_symlink(
     :param dst: The path to create the symlink at.
     """
     dst_parent = os.path.dirname(dst)
+    safe_mkdir(dst_parent)
     rel_src = os.path.relpath(src, dst_parent)
     safe_symlink(rel_src, dst)
 
@@ -831,7 +832,7 @@ def iter_copytree(
                 yield src_entry, dst_entry
             try:
                 if copy_mode is CopyMode.SYMLINK:
-                    relative_symlink(src_entry, dst_entry)
+                    safe_relative_symlink(src_entry, dst_entry)
                 elif is_dir:
                     os.mkdir(dst_entry)
                 else:

pex/pep_376.py

@@ -14,8 +14,15 @@
 from fileinput import FileInput
 
 from pex import hashing
-from pex.common import CopyMode, is_pyc_dir, is_pyc_file, safe_mkdir, safe_open
-from pex.fs import safe_link, safe_symlink
+from pex.common import (
+    CopyMode,
+    is_pyc_dir,
+    is_pyc_file,
+    safe_mkdir,
+    safe_open,
+    safe_relative_symlink,
+)
+from pex.fs import safe_link
 from pex.interpreter import PythonInterpreter
 from pex.typing import TYPE_CHECKING, cast
 from pex.util import CacheHelper
@@ -413,10 +420,7 @@ def _reinstall_site_packages(
                     if copy_mode is CopyMode.SYMLINK and not (
                         src_entry.endswith(".dist-info") and os.path.isdir(src_entry)
                     ):
-                        dst_parent = os.path.dirname(dst_entry)
-                        safe_mkdir(dst_parent)
-                        rel_src = os.path.relpath(src_entry, dst_parent)
-                        safe_symlink(rel_src, dst_entry)
+                        safe_relative_symlink(src_entry, dst_entry)
                         traverse.discard(path)
                     elif is_dir:
                         safe_mkdir(dst_entry)

pex/resolver.py

@@ -17,12 +17,11 @@
 from pex.atomic_directory import AtomicDirectory, atomic_directory
 from pex.auth import PasswordEntry
 from pex.cache.dirs import BuiltWheelDir, CacheDir
-from pex.common import pluralize, safe_mkdir, safe_mkdtemp, safe_open
+from pex.common import pluralize, safe_mkdir, safe_mkdtemp, safe_open, safe_relative_symlink
 from pex.compatibility import url_unquote, urlparse
 from pex.dependency_configuration import DependencyConfiguration
 from pex.dist_metadata import DistMetadata, Distribution, Requirement, is_wheel
 from pex.fingerprinted_distribution import FingerprintedDistribution
-from pex.fs import safe_symlink
 from pex.jobs import Raise, SpawnedJob, execute_parallel, iter_map_parallel
 from pex.network_configuration import NetworkConfiguration
 from pex.orderedset import OrderedSet
@@ -572,10 +571,9 @@ def finalize_install(self, install_requests):
                 # Note: Create a relative path symlink between the two directories so that the
                 # PEX_ROOT can be used within a chroot environment where the prefix of the path may
                 # change between programs running inside and outside of the chroot.
-                source_path = os.path.join(atomic_dir.work_dir, self.request.wheel_file)
-                start_dir = os.path.dirname(source_path)
-                relative_target_path = os.path.relpath(self.install_chroot, start_dir)
-                safe_symlink(relative_target_path, source_path)
+                safe_relative_symlink(
+                    self.install_chroot, os.path.join(atomic_dir.work_dir, self.request.wheel_file)
+                )
 
         return self._iter_resolved_distributions(install_requests, fingerprint=wheel_dir_hash)