Make aliases relative symlinks (#1610)

docs/changelog/1596.feature.rst

@@ -0,0 +1 @@
+When aliasing interpreters, use relative symlinks - by :user:`asottile`.

src/virtualenv/create/via_global_ref/builtin/ref.py

@@ -7,8 +7,8 @@
 
 from six import add_metaclass
 
-from virtualenv.info import PY3, fs_is_case_sensitive, fs_supports_symlink
-from virtualenv.util.path import copy, link, make_exe, symlink
+from virtualenv.info import fs_is_case_sensitive, fs_supports_symlink
+from virtualenv.util.path import copy, make_exe, symlink
 from virtualenv.util.six import ensure_text
 
 
@@ -95,9 +95,6 @@ def run(self, creator, symlinks):
             method(self.src, dst)
 
 
-alias_via = link if PY3 else (symlink if PathRef.FS_SUPPORTS_SYMLINK else copy)
-
-
 class ExePathRefToDest(PathRefToDest, ExePathRef):
     def __init__(self, src, targets, dest, must_copy=False):
         ExePathRef.__init__(self, src)
@@ -119,5 +116,8 @@ def run(self, creator, symlinks):
             link_file = bin_dir / extra
             if link_file.exists():
                 link_file.unlink()
-            alias_via(dest, link_file)
+            if symlinks:
+                link_file.symlink_to(self.base)
+            else:
+                copy(self.src, link_file)
             make_exe(link_file)

src/virtualenv/util/path/__init__.py

@@ -2,11 +2,10 @@
 
 from ._pathlib import Path
 from ._permission import make_exe
-from ._sync import copy, copytree, ensure_dir, link, symlink
+from ._sync import copy, copytree, ensure_dir, symlink
 
 __all__ = (
     "ensure_dir",
-    "link",
     "symlink",
     "copy",
     "copytree",

src/virtualenv/util/path/_sync.py

@@ -4,14 +4,11 @@
 import os
 import shutil
 
-from six import PY2, PY3
+from six import PY2
 
 from virtualenv.info import IS_CPYTHON, IS_WIN
 from virtualenv.util.six import ensure_text
 
-if PY3:
-    from os import link as os_link
-
 if PY2 and IS_CPYTHON and IS_WIN:  # CPython2 on Windows supports unicode paths if passed as unicode
     norm = lambda src: ensure_text(str(src))  # noqa
 else:
@@ -62,12 +59,6 @@ def copytree(src, dest):
             shutil.copy(src_f, dest_f)
 
 
-def link(src, dest):
-    ensure_safe_to_do(src, dest)
-    logging.debug("hard link %s", _Debug(src, dest.name))
-    os_link(norm(src), norm(dest))
-
-
 class _Debug(object):
     def __init__(self, src, dest):
         self.src = src
@@ -83,8 +74,6 @@ def __str__(self):
     "ensure_dir",
     "symlink",
     "copy",
-    "link",
     "symlink",
-    "link",
     "copytree",
 )

tests/unit/create/test_creator.py

@@ -170,6 +170,26 @@ def list_to_str(iterable):
 
         assert common, "\n".join(difflib.unified_diff(list_to_str(sys_path), list_to_str(system_sys_path)))
 
+    # test that the python executables in the bin directory are either:
+    # - files
+    # - absolute symlinks outside of the venv
+    # - relative symlinks inside of the venv
+    if sys.platform == "win32":
+        exes = ("python.exe",)
+    else:
+        # TODO: also test "python{}.{}" once fixed
+        exes = ("python", "python{}".format(sys.version_info[0]))
+    for exe in exes:
+        exe_path = result.creator.bin_dir / exe
+        assert exe_path.exists()
+        if not exe_path.is_symlink():  # option 1: a real file
+            continue  # it was a file
+        link = os.readlink(str(exe_path))
+        if not os.path.isabs(link):  # option 2: a relative symlink
+            continue
+        # option 3: an absolute symlink, should point outside the venv
+        assert not link.startswith(str(result.creator.dest))
+
 
 @pytest.mark.skipif(not CURRENT.has_venv, reason="requires interpreter with venv")
 def test_venv_fails_not_inline(tmp_path, capsys, mocker):