bpo-34977: Use venv redirector instead of original python.exe on Windows

Doc/library/venv.rst

@@ -130,7 +130,6 @@ creation according to their needs, the :class:`EnvBuilder` class.
     .. versionadded:: 3.6
        Added the ``prompt`` parameter
 
-
     Creators of third-party virtual environment tools will be free to use the
     provided ``EnvBuilder`` class as a base class.
 
@@ -177,23 +176,27 @@ creation according to their needs, the :class:`EnvBuilder` class.
 
     .. method:: setup_python(context)
 
-        Creates a copy of the Python executable (and, under Windows, DLLs) in
-        the environment. On a POSIX system, if a specific executable
-        ``python3.x`` was used, symlinks to ``python`` and ``python3`` will be
-        created pointing to that executable, unless files with those names
-        already exist.
+        Creates a copy of the Python executable in the environment on POSIX
+        systems. If a specific executable ``python3.x`` was used, symlinks to
+        ``python`` and ``python3`` will be created pointing to that executable,
+        unless files with those names already exist.
 
     .. method:: setup_scripts(context)
 
         Installs activation scripts appropriate to the platform into the virtual
-        environment.
+        environment. On Windows, also installs the ``python[w].exe`` scripts.
 
     .. method:: post_setup(context)
 
         A placeholder method which can be overridden in third party
         implementations to pre-install packages in the virtual environment or
         perform other post-creation steps.
 
+    .. versionchanged:: 3.7.2
+       Windows now uses redirector scripts for ``python[w].exe`` instead of
+       copying the actual binaries, and so :meth:`setup_python` does nothing
+       unless running from a build in the source tree.
+
     In addition, :class:`EnvBuilder` provides this utility method that can be
     called from :meth:`setup_scripts` or :meth:`post_setup` in subclasses to
     assist in installing custom scripts into the virtual environment.

Doc/whatsnew/3.7.rst

@@ -2512,3 +2512,13 @@ In 3.7.1 the :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token
 when provided with input that does not have a trailing new line.  This behavior
 now matches what the C tokenizer does internally.
 (Contributed by Ammar Askar in :issue:`33899`.)
+
+Notable changes in Python 3.7.2
+===============================
+
+In 3.7.2, :mod:`venv` on Windows no longer copies the original binaries, but
+creates redirector scripts named ``python.exe`` and ``pythonw.exe`` instead.
+This resolves a long standing issue where all virtual environments would have
+to be upgraded or recreated with each Python update. However, note that this
+release will still require recreation of virtual environments in order to get
+the new scripts.

Lib/test/test_venv.py

@@ -243,6 +243,7 @@ def test_isolation(self):
             self.assertIn('include-system-site-packages = %s\n' % s, data)
 
     @unittest.skipUnless(can_symlink(), 'Needs symlinks')
+    @unittest.skipIf(os.name == 'nt', 'Symlinks are never used on Windows')
     def test_symlinking(self):
         """
         Test symlinking works as expected

Lib/venv/__init__.py

@@ -64,10 +64,11 @@ def create(self, env_dir):
         self.system_site_packages = False
         self.create_configuration(context)
         self.setup_python(context)
+        if not self.upgrade:
+            self.setup_scripts(context)
         if self.with_pip:
             self._setup_pip(context)
         if not self.upgrade:
-            self.setup_scripts(context)
             self.post_setup(context)
         if true_system_site_packages:
             # We had set it to False before, now
@@ -158,14 +159,6 @@ def create_configuration(self, context):
             f.write('include-system-site-packages = %s\n' % incl)
             f.write('version = %d.%d.%d\n' % sys.version_info[:3])
 
-    if os.name == 'nt':
-        def include_binary(self, f):
-            if f.endswith(('.pyd', '.dll')):
-                result = True
-            else:
-                result = f.startswith('python') and f.endswith('.exe')
-            return result
-
     def symlink_or_copy(self, src, dst, relative_symlinks_ok=False):
         """
         Try symlinking a file, and if that fails, fall back to copying.
@@ -195,9 +188,9 @@ def setup_python(self, context):
         binpath = context.bin_path
         path = context.env_exe
         copier = self.symlink_or_copy
-        copier(context.executable, path)
         dirname = context.python_dir
         if os.name != 'nt':
+            copier(context.executable, path)
             if not os.path.islink(path):
                 os.chmod(path, 0o755)
             for suffix in ('python', 'python3'):
@@ -209,26 +202,22 @@ def setup_python(self, context):
                     if not os.path.islink(path):
                         os.chmod(path, 0o755)
         else:
-            # See bpo-34011. When using a proper install, we should only need to
-            # copy the top-level of DLLs.
-            include = self.include_binary
-            files = [f for f in os.listdir(dirname) if include(f)]
-            for f in files:
-                src = os.path.join(dirname, f)
-                dst = os.path.join(binpath, f)
-                if dst != context.env_exe:  # already done, above
-                    copier(src, dst)
-
-            # When creating from a build directory, we continue to copy all files.
+            # For normal cases, the venvlauncher will be copied from
+            # our scripts folder. For builds, we need to copy it
+            # manually.
             if sysconfig.is_python_build(True):
-                subdir = 'DLLs'
-                dirname = os.path.join(dirname, subdir)
-                if os.path.isdir(dirname):
-                    files = [f for f in os.listdir(dirname) if include(f)]
-                    for f in files:
-                        src = os.path.join(dirname, f)
-                        dst = os.path.join(binpath, f)
-                        copier(src, dst)
+                suffix = '.exe'
+                if context.python_exe.lower().endswith('_d.exe'):
+                    suffix = '_d.exe'
+
+                src = os.path.join(dirname, "venvlauncher" + suffix)
+                dst = os.path.join(binpath, context.python_exe)
+                copier(src, dst)
+
+                src = os.path.join(dirname, "venvwlauncher" + suffix)
+                dst = os.path.join(binpath, "pythonw" + suffix)
+                copier(src, dst)
+
                 # copy init.tcl over
                 for root, dirs, files in os.walk(context.python_dir):
                     if 'init.tcl' in files:
@@ -326,7 +315,7 @@ def install_scripts(self, context, path):
                 dstfile = os.path.join(dstdir, f)
                 with open(srcfile, 'rb') as f:
                     data = f.read()
-                if not srcfile.endswith('.exe'):
+                if not srcfile.endswith(('.exe', '.pdb')):
                     try:
                         data = data.decode('utf-8')
                         data = self.replace_variables(data, context)

Misc/NEWS.d/next/Windows/2018-12-07-10-00-38.bpo-34977.agQJbD.rst

@@ -0,0 +1,2 @@
+venv on Windows will now use a python.exe redirector rather than copying the
+actual binaries from the base environment.

PC/getpathp.c

@@ -536,10 +536,16 @@ static _PyInitError
 get_program_full_path(const _PyCoreConfig *core_config,
                       PyCalculatePath *calculate, _PyPathConfig *config)
 {
+    const wchar_t *pyvenv_launcher;
     wchar_t program_full_path[MAXPATHLEN+1];
     memset(program_full_path, 0, sizeof(program_full_path));
 
-    if (!GetModuleFileNameW(NULL, program_full_path, MAXPATHLEN)) {
+    /* The launcher may need to force the executable path to a
+     * different environment, so override it here. */
+    pyvenv_launcher = _wgetenv(L"__PYVENV_LAUNCHER__");
+    if (pyvenv_launcher && pyvenv_launcher[0]) {
+        wcscpy_s(program_full_path, MAXPATHLEN+1, pyvenv_launcher);
+    } else if (!GetModuleFileNameW(NULL, program_full_path, MAXPATHLEN)) {
         /* GetModuleFileName should never fail when passed NULL */
         return _Py_INIT_ERR("Cannot determine program path");
     }