bpo-37369: Fix initialization of sys members when launched via an app container (GH-14428)

sys._base_executable is now always defined on all platforms, and can be overridden through configuration.
Also adds test.support.PythonSymlink to encapsulate platform-specific logic for symlinking sys.executable

1 files changed, 56 insertions, 37 deletions

diff --git a/Lib/venv/__init__.py b/Lib/venv/__init__.py
index b64125f..4ab9cc6 100644
--- a/Lib/venv/__init__.py
+++ b/Lib/venv/__init__.py
@@ -112,7 +112,7 @@ class EnvBuilder:
         prompt = self.prompt if self.prompt is not None else context.env_name
         context.prompt = '(%s) ' % prompt
         create_if_needed(env_dir)
-        executable = getattr(sys, '_base_executable', sys.executable)
+        executable = sys._base_executable
         dirname, exename = os.path.split(os.path.abspath(executable))
         context.executable = executable
         context.python_dir = dirname
@@ -163,47 +163,66 @@ class EnvBuilder:
             if self.prompt is not None:
                 f.write(f'prompt = {self.prompt!r}\n')
 
-    def symlink_or_copy(self, src, dst, relative_symlinks_ok=False):
-        """
-        Try symlinking a file, and if that fails, fall back to copying.
-        """
-        force_copy = not self.symlinks
-        if not force_copy:
-            try:
-                if not os.path.islink(dst): # can't link to itself!
+    if os.name != 'nt':
+        def symlink_or_copy(self, src, dst, relative_symlinks_ok=False):
+            """
+            Try symlinking a file, and if that fails, fall back to copying.
+            """
+            force_copy = not self.symlinks
+            if not force_copy:
+                try:
+                    if not os.path.islink(dst): # can't link to itself!
+                        if relative_symlinks_ok:
+                            assert os.path.dirname(src) == os.path.dirname(dst)
+                            os.symlink(os.path.basename(src), dst)
+                        else:
+                            os.symlink(src, dst)
+                except Exception:   # may need to use a more specific exception
+                    logger.warning('Unable to symlink %r to %r', src, dst)
+                    force_copy = True
+            if force_copy:
+                shutil.copyfile(src, dst)
+    else:
+        def symlink_or_copy(self, src, dst, relative_symlinks_ok=False):
+            """
+            Try symlinking a file, and if that fails, fall back to copying.
+            """
+            bad_src = os.path.lexists(src) and not os.path.exists(src)
+            if self.symlinks and not bad_src and not os.path.islink(dst):
+                try:
                     if relative_symlinks_ok:
                         assert os.path.dirname(src) == os.path.dirname(dst)
                         os.symlink(os.path.basename(src), dst)
                     else:
                         os.symlink(src, dst)
-            except Exception:   # may need to use a more specific exception
-                logger.warning('Unable to symlink %r to %r', src, dst)
-                force_copy = True
-        if force_copy:
-            if os.name == 'nt':
-                # On Windows, we rewrite symlinks to our base python.exe into
-                # copies of venvlauncher.exe
-                basename, ext = os.path.splitext(os.path.basename(src))
-                srcfn = os.path.join(os.path.dirname(__file__),
-                                     "scripts",
-                                     "nt",
-                                     basename + ext)
-                # Builds or venv's from builds need to remap source file
-                # locations, as we do not put them into Lib/venv/scripts
-                if sysconfig.is_python_build(True) or not os.path.isfile(srcfn):
-                    if basename.endswith('_d'):
-                        ext = '_d' + ext
-                        basename = basename[:-2]
-                    if basename == 'python':
-                        basename = 'venvlauncher'
-                    elif basename == 'pythonw':
-                        basename = 'venvwlauncher'
-                    src = os.path.join(os.path.dirname(src), basename + ext)
-                else:
-                    src = srcfn
-                if not os.path.exists(src):
-                    logger.warning('Unable to copy %r', src)
                     return
+                except Exception:   # may need to use a more specific exception
+                    logger.warning('Unable to symlink %r to %r', src, dst)
+
+            # On Windows, we rewrite symlinks to our base python.exe into
+            # copies of venvlauncher.exe
+            basename, ext = os.path.splitext(os.path.basename(src))
+            srcfn = os.path.join(os.path.dirname(__file__),
+                                 "scripts",
+                                 "nt",
+                                 basename + ext)
+            # Builds or venv's from builds need to remap source file
+            # locations, as we do not put them into Lib/venv/scripts
+            if sysconfig.is_python_build(True) or not os.path.isfile(srcfn):
+                if basename.endswith('_d'):
+                    ext = '_d' + ext
+                    basename = basename[:-2]
+                if basename == 'python':
+                    basename = 'venvlauncher'
+                elif basename == 'pythonw':
+                    basename = 'venvwlauncher'
+                src = os.path.join(os.path.dirname(src), basename + ext)
+            else:
+                src = srcfn
+            if not os.path.exists(src):
+                if not bad_src:
+                    logger.warning('Unable to copy %r', src)
+                return
 
             shutil.copyfile(src, dst)
 
@@ -251,7 +270,7 @@ class EnvBuilder:
 
             for suffix in suffixes:
                 src = os.path.join(dirname, suffix)
-                if os.path.exists(src):
+                if os.path.lexists(src):
                     copier(src, os.path.join(binpath, suffix))
 
             if sysconfig.is_python_build(True):