bpo-46566: Add new py.exe launcher implementation (GH-32062)

Doc/using/windows.rst

@@ -817,6 +817,13 @@ minor version. I.e. ``/usr/bin/python2.7-32`` will request usage of the
    by the "-64" suffix. Furthermore it is possible to specify a major and
    architecture without minor (i.e. ``/usr/bin/python3-64``).
 
+.. versionchanged:: 3.11
+
+   The "-64" suffix is deprecated, and now implies "any architecture that is
+   not provably i386/32-bit". To request a specific environment, use the new
+   ``-V:<TAG>`` argument with the complete tag.
+
+
 The ``/usr/bin/env`` form of shebang line has one further special property.
 Before looking for installed Python interpreters, this form will search the
 executable :envvar:`PATH` for a Python executable. This corresponds to the
@@ -937,13 +944,65 @@ For example:
 Diagnostics
 -----------
 
-If an environment variable ``PYLAUNCH_DEBUG`` is set (to any value), the
+If an environment variable :envvar:`PYLAUNCHER_DEBUG` is set (to any value), the
 launcher will print diagnostic information to stderr (i.e. to the console).
 While this information manages to be simultaneously verbose *and* terse, it
 should allow you to see what versions of Python were located, why a
 particular version was chosen and the exact command-line used to execute the
-target Python.
+target Python. It is primarily intended for testing and debugging.
 
+Dry Run
+-------
+
+If an environment variable :envvar:`PYLAUNCHER_DRYRUN` is set (to any value),
+the launcher will output the command it would have run, but will not actually
+launch Python. This may be useful for tools that want to use the launcher to
+detect and then launch Python directly. Note that the command written to
+standard output is always encoded using UTF-8, and may not render correctly in
+the console.
+
+Install on demand
+-----------------
+
+If an environment variable :envvar:`PYLAUNCHER_ALLOW_INSTALL` is set (to any
+value), and the requested Python version is not installed but is available on
+the Microsoft Store, the launcher will attempt to install it. This may require
+user interaction to complete, and you may need to run the command again.
+
+An additional :envvar:`PYLAUNCHER_ALWAYS_INSTALL` variable causes the launcher
+to always try to install Python, even if it is detected. This is mainly intended
+for testing (and should be used with :envvar:`PYLAUNCHER_DRYRUN`).
+
+Return codes
+------------
+
+The following exit codes may be returned by the Python launcher. Unfortunately,
+there is no way to distinguish these from the exit code of Python itself.
+
+The names of codes are as used in the sources, and are only for reference. There
+is no way to access or resolve them apart from reading this page. Entries are
+listed in alphabetical order of names.
+
++-------------------+-------+-----------------------------------------------+
+| Name              | Value | Description                                   |
++===================+=======+===============================================+
+| RC_BAD_VENV_CFG   | 107   | A :file:`pyvenv.cfg` was found but is corrupt.|
++-------------------+-------+-----------------------------------------------+
+| RC_CREATE_PROCESS | 101   | Failed to launch Python.                      |
++-------------------+-------+-----------------------------------------------+
+| RC_INSTALLING     | 111   | An install was started, but the command will  |
+|                   |       | need to be re-run after it completes.         |
++-------------------+-------+-----------------------------------------------+
+| RC_INTERNAL_ERROR | 109   | Unexpected error. Please report a bug.        |
++-------------------+-------+-----------------------------------------------+
+| RC_NO_COMMANDLINE | 108   | Unable to obtain command line from the        |
+|                   |       | operating system.                             |
++-------------------+-------+-----------------------------------------------+
+| RC_NO_PYTHON      | 103   | Unable to locate the requested version.       |
++-------------------+-------+-----------------------------------------------+
+| RC_NO_VENV_CFG    | 106   | A :file:`pyvenv.cfg` was required but not     |
+|                   |       | found.                                        |
++-------------------+-------+-----------------------------------------------+
 
 
 .. _windows_finding_modules:

Lib/test/test_launcher.py

@@ -0,0 +1,423 @@
+import contextlib
+import itertools
+import os
+import re
+import subprocess
+import sys
+import sysconfig
+import tempfile
+import textwrap
+import unittest
+from pathlib import Path
+from test import support
+
+if sys.platform != "win32":
+    raise unittest.SkipTest("test only applies to Windows")
+
+# Get winreg after the platform check
+import winreg
+
+
+PY_EXE = "py.exe"
+if sys.executable.casefold().endswith("_d.exe".casefold()):
+    PY_EXE = "py_d.exe"
+
+# Registry data to create. On removal, everything beneath top-level names will
+# be deleted.
+TEST_DATA = {
+    "PythonTestSuite": {
+        "DisplayName": "Python Test Suite",
+        "SupportUrl": "https://www.python.org/",
+        "3.100": {
+            "DisplayName": "X.Y version",
+            "InstallPath": {
+                None: sys.prefix,
+                "ExecutablePath": "X.Y.exe",
+            }
+        },
+        "3.100-32": {
+            "DisplayName": "X.Y-32 version",
+            "InstallPath": {
+                None: sys.prefix,
+                "ExecutablePath": "X.Y-32.exe",
+            }
+        },
+        "3.100-arm64": {
+            "DisplayName": "X.Y-arm64 version",
+            "InstallPath": {
+                None: sys.prefix,
+                "ExecutablePath": "X.Y-arm64.exe",
+                "ExecutableArguments": "-X fake_arg_for_test",
+            }
+        },
+        "ignored": {
+            "DisplayName": "Ignored because no ExecutablePath",
+            "InstallPath": {
+                None: sys.prefix,
+            }
+        },
+    }
+}
+
+TEST_PY_COMMANDS = textwrap.dedent("""
+    [defaults]
+    py_python=PythonTestSuite/3.100
+    py_python2=PythonTestSuite/3.100-32
+    py_python3=PythonTestSuite/3.100-arm64
+""")
+
+
+def create_registry_data(root, data):
+    def _create_registry_data(root, key, value):
+        if isinstance(value, dict):
+            # For a dict, we recursively create keys
+            with winreg.CreateKeyEx(root, key) as hkey:
+                for k, v in value.items():
+                    _create_registry_data(hkey, k, v)
+        elif isinstance(value, str):
+            # For strings, we set values. 'key' may be None in this case
+            winreg.SetValueEx(root, key, None, winreg.REG_SZ, value)
+        else:
+            raise TypeError("don't know how to create data for '{}'".format(value))
+
+    for k, v in data.items():
+        _create_registry_data(root, k, v)
+
+
+def enum_keys(root):
+    for i in itertools.count():
+        try:
+            yield winreg.EnumKey(root, i)
+        except OSError as ex:
+            if ex.winerror == 259:
+                break
+            raise
+
+
+def delete_registry_data(root, keys):
+    ACCESS = winreg.KEY_WRITE | winreg.KEY_ENUMERATE_SUB_KEYS
+    for key in list(keys):
+        with winreg.OpenKey(root, key, access=ACCESS) as hkey:
+            delete_registry_data(hkey, enum_keys(hkey))
+        winreg.DeleteKey(root, key)
+
+
+def is_installed(tag):
+    key = rf"Software\Python\PythonCore\{tag}\InstallPath"
+    for root, flag in [
+        (winreg.HKEY_CURRENT_USER, 0),
+        (winreg.HKEY_LOCAL_MACHINE, winreg.KEY_WOW64_64KEY),
+        (winreg.HKEY_LOCAL_MACHINE, winreg.KEY_WOW64_32KEY),
+    ]:
+        try:
+            winreg.CloseKey(winreg.OpenKey(root, key, access=winreg.KEY_READ | flag))
+            return True
+        except OSError:
+            pass
+    return False
+
+
+class PreservePyIni:
+    def __init__(self, path, content):
+        self.path = Path(path)
+        self.content = content
+        self._preserved = None
+
+    def __enter__(self):
+        try:
+            self._preserved = self.path.read_bytes()
+        except FileNotFoundError:
+            self._preserved = None
+        self.path.write_text(self.content, encoding="utf-16")
+
+    def __exit__(self, *exc_info):
+        if self._preserved is None:
+            self.path.unlink()
+        else:
+            self.path.write_bytes(self._preserved)
+
+
+class RunPyMixin:
+    py_exe = None
+
+    @classmethod
+    def find_py(cls):
+        py_exe = None
+        if sysconfig.is_python_build(True):
+            py_exe = Path(sys.executable).parent / PY_EXE
+        else:
+            for p in os.getenv("PATH").split(";"):
+                if p:
+                    py_exe = Path(p) / PY_EXE
+                    if py_exe.is_file():
+                        break
+        if not py_exe:
+            raise unittest.SkipTest(
+                "cannot locate '{}' for test".format(PY_EXE)
+            )
+        return py_exe
+
+    def run_py(self, args, env=None, allow_fail=False, expect_returncode=0):
+        if not self.py_exe:
+            self.py_exe = self.find_py()
+
+        env = {**os.environ, **(env or {}), "PYLAUNCHER_DEBUG": "1", "PYLAUNCHER_DRYRUN": "1"}
+        with subprocess.Popen(
+            [self.py_exe, *args],
+            env=env,
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        ) as p:
+            p.stdin.close()
+            p.wait(10)
+            out = p.stdout.read().decode("utf-8", "replace")
+            err = p.stderr.read().decode("ascii", "replace")
+        if p.returncode != expect_returncode and support.verbose and not allow_fail:
+            print("++ COMMAND ++")
+            print([self.py_exe, *args])
+            print("++ STDOUT ++")
+            print(out)
+            print("++ STDERR ++")
+            print(err)
+        if allow_fail and p.returncode != expect_returncode:
+            raise subprocess.CalledProcessError(p.returncode, [self.py_exe, *args], out, err)
+        else:
+            self.assertEqual(expect_returncode, p.returncode)
+        data = {
+            s.partition(":")[0]: s.partition(":")[2].lstrip()
+            for s in err.splitlines()
+            if not s.startswith("#") and ":" in s
+        }
+        data["stdout"] = out
+        data["stderr"] = err
+        return data
+
+    def py_ini(self, content):
+        if not self.py_exe:
+            self.py_exe = self.find_py()
+        return PreservePyIni(self.py_exe.with_name("py.ini"), content)
+
+    @contextlib.contextmanager
+    def script(self, content, encoding="utf-8"):
+        file = Path(tempfile.mktemp(dir=os.getcwd()) + ".py")
+        file.write_text(content, encoding=encoding)
+        try:
+            yield file
+        finally:
+            file.unlink()
+
+
+class TestLauncher(unittest.TestCase, RunPyMixin):
+    @classmethod
+    def setUpClass(cls):
+        with winreg.CreateKey(winreg.HKEY_CURRENT_USER, rf"Software\Python") as key:
+            create_registry_data(key, TEST_DATA)
+
+        if support.verbose:
+            p = subprocess.check_output("reg query HKCU\\Software\\Python /s")
+            print(p.decode('mbcs'))
+
+
+    @classmethod
+    def tearDownClass(cls):
+        with winreg.OpenKey(winreg.HKEY_CURRENT_USER, rf"Software\Python", access=winreg.KEY_WRITE | winreg.KEY_ENUMERATE_SUB_KEYS) as key:
+            delete_registry_data(key, TEST_DATA)
+
+
+    def test_version(self):
+        data = self.run_py(["-0"])
+        self.assertEqual(self.py_exe, Path(data["argv0"]))
+        self.assertEqual(sys.version.partition(" ")[0], data["version"])
+
+    def test_help_option(self):
+        data = self.run_py(["-h"])
+        self.assertEqual("True", data["SearchInfo.help"])
+
+    def test_list_option(self):
+        for opt, v1, v2 in [
+            ("-0", "True", "False"),
+            ("-0p", "False", "True"),
+            ("--list", "True", "False"),
+            ("--list-paths", "False", "True"),
+        ]:
+            with self.subTest(opt):
+                data = self.run_py([opt])
+                self.assertEqual(v1, data["SearchInfo.list"])
+                self.assertEqual(v2, data["SearchInfo.listPaths"])
+
+    def test_list(self):
+        data = self.run_py(["--list"])
+        found = {}
+        expect = {}
+        for line in data["stdout"].splitlines():
+            m = re.match(r"\s*(.+?)\s+(.+)$", line)
+            if m:
+                found[m.group(1)] = m.group(2)
+        for company in TEST_DATA:
+            company_data = TEST_DATA[company]
+            tags = [t for t in company_data if isinstance(company_data[t], dict)]
+            for tag in tags:
+                arg = f"-V:{company}/{tag}"
+                expect[arg] = company_data[tag]["DisplayName"]
+            expect.pop(f"-V:{company}/ignored", None)
+
+        actual = {k: v for k, v in found.items() if k in expect}
+        try:
+            self.assertDictEqual(expect, actual)
+        except:
+            if support.verbose:
+                print("*** STDOUT ***")
+                print(data["stdout"])
+            raise
+
+    def test_list_paths(self):
+        data = self.run_py(["--list-paths"])
+        found = {}
+        expect = {}
+        for line in data["stdout"].splitlines():
+            m = re.match(r"\s*(.+?)\s+(.+)$", line)
+            if m:
+                found[m.group(1)] = m.group(2)
+        for company in TEST_DATA:
+            company_data = TEST_DATA[company]
+            tags = [t for t in company_data if isinstance(company_data[t], dict)]
+            for tag in tags:
+                arg = f"-V:{company}/{tag}"
+                install = company_data[tag]["InstallPath"]
+                try:
+                    expect[arg] = install["ExecutablePath"]
+                    try:
+                        expect[arg] += " " + install["ExecutableArguments"]
+                    except KeyError:
+                        pass
+                except KeyError:
+                    expect[arg] = str(Path(install[None]) / Path(sys.executable).name)
+
+            expect.pop(f"-V:{company}/ignored", None)
+
+        actual = {k: v for k, v in found.items() if k in expect}
+        try:
+            self.assertDictEqual(expect, actual)
+        except:
+            if support.verbose:
+                print("*** STDOUT ***")
+                print(data["stdout"])
+            raise
+
+    def test_filter_to_company(self):
+        company = "PythonTestSuite"
+        data = self.run_py([f"-V:{company}/"])
+        self.assertEqual("X.Y.exe", data["LaunchCommand"])
+        self.assertEqual(company, data["env.company"])
+        self.assertEqual("3.100", data["env.tag"])
+
+    def test_filter_to_tag(self):
+        company = "PythonTestSuite"
+        data = self.run_py([f"-V:3.100"])
+        self.assertEqual("X.Y.exe", data["LaunchCommand"])
+        self.assertEqual(company, data["env.company"])
+        self.assertEqual("3.100", data["env.tag"])
+
+        data = self.run_py([f"-V:3.100-3"])
+        self.assertEqual("X.Y-32.exe", data["LaunchCommand"])
+        self.assertEqual(company, data["env.company"])
+        self.assertEqual("3.100-32", data["env.tag"])
+
+        data = self.run_py([f"-V:3.100-a"])
+        self.assertEqual("X.Y-arm64.exe -X fake_arg_for_test", data["LaunchCommand"])
+        self.assertEqual(company, data["env.company"])
+        self.assertEqual("3.100-arm64", data["env.tag"])
+
+    def test_filter_to_company_and_tag(self):
+        company = "PythonTestSuite"
+        data = self.run_py([f"-V:{company}/3.1"])
+        self.assertEqual("X.Y.exe", data["LaunchCommand"])
+        self.assertEqual(company, data["env.company"])
+        self.assertEqual("3.100", data["env.tag"])
+
+    def test_search_major_3(self):
+        try:
+            data = self.run_py(["-3"], allow_fail=True)
+        except subprocess.CalledProcessError:
+            raise unittest.SkipTest("requires at least one Python 3.x install")
+        self.assertEqual("PythonCore", data["env.company"])
+        self.assertTrue(data["env.tag"].startswith("3."), data["env.tag"])
+
+    def test_search_major_3_32(self):
+        try:
+            data = self.run_py(["-3-32"], allow_fail=True)
+        except subprocess.CalledProcessError:
+            if not any(is_installed(f"3.{i}-32") for i in range(5, 11)):
+                raise unittest.SkipTest("requires at least one 32-bit Python 3.x install")
+            raise
+        self.assertEqual("PythonCore", data["env.company"])
+        self.assertTrue(data["env.tag"].startswith("3."), data["env.tag"])
+        self.assertTrue(data["env.tag"].endswith("-32"), data["env.tag"])
+
+    def test_search_major_2(self):
+        try:
+            data = self.run_py(["-2"], allow_fail=True)
+        except subprocess.CalledProcessError:
+            if not is_installed("2.7"):
+                raise unittest.SkipTest("requires at least one Python 2.x install")
+        self.assertEqual("PythonCore", data["env.company"])
+        self.assertTrue(data["env.tag"].startswith("2."), data["env.tag"])
+
+    def test_py_default(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            data = self.run_py(["-arg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100", data["SearchInfo.tag"])
+        self.assertEqual("X.Y.exe -arg", data["stdout"].strip())
+
+    def test_py2_default(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            data = self.run_py(["-2", "-arg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-32", data["SearchInfo.tag"])
+        self.assertEqual("X.Y-32.exe -arg", data["stdout"].strip())
+
+    def test_py3_default(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            data = self.run_py(["-3", "-arg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-arm64", data["SearchInfo.tag"])
+        self.assertEqual("X.Y-arm64.exe -X fake_arg_for_test -arg", data["stdout"].strip())
+
+    def test_py_shebang(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python -prearg") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y.exe -prearg {script} -postarg", data["stdout"].strip())
+
+    def test_py2_shebang(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python2 -prearg") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-32", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y-32.exe -prearg {script} -postarg", data["stdout"].strip())
+
+    def test_py3_shebang(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script("#! /usr/bin/env python3 -prearg") as script:
+                data = self.run_py([script, "-postarg"])
+        self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
+        self.assertEqual("3.100-arm64", data["SearchInfo.tag"])
+        self.assertEqual(f"X.Y-arm64.exe -X fake_arg_for_test -prearg {script} -postarg", data["stdout"].strip())
+
+    def test_install(self):
+        data = self.run_py(["-V:3.10"], env={"PYLAUNCHER_ALWAYS_INSTALL": "1"}, expect_returncode=111)
+        cmd = data["stdout"].strip()
+        # If winget is runnable, we should find it. Otherwise, we'll be trying
+        # to open the Store.
+        try:
+            subprocess.check_call(["winget.exe", "--version"])
+        except FileNotFoundError:
+            self.assertIn("ms-windows-store://", cmd)
+        else:
+            self.assertIn("winget.exe", cmd)
+        self.assertIn("9PJPW5LDXLZ5", cmd)

Misc/NEWS.d/next/Windows/2022-03-23-12-51-46.bpo-46566.4x4a7e.rst

@@ -0,0 +1,6 @@
+Upgraded :ref:`launcher` to support a new ``-V:company/tag`` argument for
+full :pep:`514` support and to detect ARM64 installs. The ``-64`` suffix on
+arguments is deprecated, but still selects any non-32-bit install. Setting
+:envvar:`PYLAUNCHER_ALLOW_INSTALL` and specifying a version that is not
+installed will attempt to install the requested version from the Microsoft
+Store.

PC/launcher-usage.txt

@@ -0,0 +1,31 @@
+Python Launcher for Windows Version %s
+
+usage:
+%s [launcher-args] [python-args] [script [script-args]]
+
+Launcher arguments:
+-2     : Launch the latest Python 2.x version
+-3     : Launch the latest Python 3.x version
+-X.Y   : Launch the specified Python version
+
+The above default to an architecture native runtime, but will select any
+available. Add a "-32" to the argument to only launch 32-bit runtimes,
+or add "-64" to omit 32-bit runtimes (this latter option is deprecated).
+
+To select a specific runtime, use the -V: options.
+
+-V:TAG         : Launch a Python runtime with the specified tag
+-V:COMPANY/TAG : Launch a Python runtime from the specified company and
+                 with the specified tag
+
+-0  --list       : List the available pythons
+-0p --list-paths : List with paths
+
+If no options are given but a script is specified, the script is checked for a
+shebang line. Otherwise, an active virtual environment or global default will
+be selected.
+
+See https://docs.python.org/using/windows.html#python-launcher-for-windows for
+additional configuration.
+
+The following help text is from Python:

PC/pylauncher.rc

@@ -25,6 +25,9 @@
 7 ICON DISCARDABLE "icons\setup.ico" 
 #endif
 
+1 USAGE "launcher-usage.txt"
+
+
 /////////////////////////////////////////////////////////////////////////////
 //
 // Version

PCbuild/pylauncher.vcxproj

@@ -76,7 +76,7 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
   <PropertyGroup Label="Configuration">
     <ConfigurationType>Application</ConfigurationType>
-    <CharacterSet>MultiByte</CharacterSet>
+    <CharacterSet>Unicode</CharacterSet>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">
@@ -95,12 +95,12 @@
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
     </ClCompile>
     <Link>
-      <AdditionalDependencies>version.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>shell32.lib;pathcch.lib;%(AdditionalDependencies)</AdditionalDependencies>
       <SubSystem>Console</SubSystem>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>
-    <ClCompile Include="..\PC\launcher.c" />
+    <ClCompile Include="..\PC\launcher2.c" />
   </ItemGroup>
   <ItemGroup>
     <None Include="..\PC\launcher.ico" />

PCbuild/pywlauncher.vcxproj

@@ -95,12 +95,12 @@
       <RuntimeLibrary>MultiThreaded</RuntimeLibrary>
     </ClCompile>
     <Link>
-      <AdditionalDependencies>version.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>shell32.lib;pathcch.lib;%(AdditionalDependencies)</AdditionalDependencies>
       <SubSystem>Windows</SubSystem>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>
-    <ClCompile Include="..\PC\launcher.c" />
+    <ClCompile Include="..\PC\launcher2.c" />
   </ItemGroup>
   <ItemGroup>
     <None Include="..\PC\launcher.ico" />

Tools/msi/launcher/launcher.wixproj

@@ -8,6 +8,7 @@
         <DefineConstants>UpgradeCode=1B68A0EC-4DD3-5134-840E-73854B0863F1;SuppressUpgradeTable=1;$(DefineConstants)</DefineConstants>
         <IgnoreCommonWxlTemplates>true</IgnoreCommonWxlTemplates>
         <SuppressICEs>ICE80</SuppressICEs>
+        <_Rebuild>Build</_Rebuild>
     </PropertyGroup>
     <Import Project="..\msi.props" />
     <ItemGroup>
@@ -19,17 +20,26 @@
         <EmbeddedResource Include="*.wxl" />
     </ItemGroup>
 
-    <Target Name="_EnsurePyEx86" Condition="!Exists('$(BuildPath32)py.exe')" BeforeTargets="PrepareForBuild">
+    <Target Name="_MarkAsRebuild" BeforeTargets="BeforeRebuild">
-        <MSBuild Projects="$(PySourcePath)PCbuild\pylauncher.vcxproj" Properties="Platform=Win32" />
+      <PropertyGroup>
+        <_Rebuild>Rebuild</_Rebuild>
+      </PropertyGroup>
     </Target>
-    <Target Name="_EnsurePywEx86" Condition="!Exists('$(BuildPath32)pyw.exe')" BeforeTargets="PrepareForBuild">
+
-        <MSBuild Projects="$(PySourcePath)PCbuild\pywlauncher.vcxproj" Properties="Platform=Win32" />
+    <Target Name="_EnsurePyEx86" Condition="!Exists('$(BuildPath32)py.exe') or '$(_Rebuild)' == 'Rebuild'" BeforeTargets="PrepareForBuild">
+        <MSBuild Projects="$(PySourcePath)PCbuild\pylauncher.vcxproj" Properties="Platform=Win32" Targets="$(_Rebuild)" />
     </Target>
-    <Target Name="_EnsurePyShellExt86" Condition="!Exists('$(BuildPath32)pyshellext.dll')" BeforeTargets="PrepareForBuild">
+    <Target Name="_EnsurePywEx86" Condition="!Exists('$(BuildPath32)pyw.exe') or '$(_Rebuild)' == 'Rebuild'" BeforeTargets="PrepareForBuild">
-        <MSBuild Projects="$(PySourcePath)PCbuild\pyshellext.vcxproj" Properties="Platform=Win32" />
+        <MSBuild Projects="$(PySourcePath)PCbuild\pywlauncher.vcxproj" Properties="Platform=Win32" Targets="$(_Rebuild)" />
     </Target>
-    <Target Name="_EnsurePyShellExt64" Condition="!Exists('$(BuildPath64)pyshellext.dll')" BeforeTargets="PrepareForBuild">
+    <Target Name="_EnsurePyShellExt86" Condition="!Exists('$(BuildPath32)pyshellext.dll') or '$(_Rebuild)' == 'Rebuild'" BeforeTargets="PrepareForBuild">
-        <MSBuild Projects="$(PySourcePath)PCbuild\pyshellext.vcxproj" Properties="Platform=x64" />
+        <MSBuild Projects="$(PySourcePath)PCbuild\pyshellext.vcxproj" Properties="Platform=Win32" Targets="$(_Rebuild)" />
+    </Target>
+    <Target Name="_EnsurePyShellExt64" Condition="!Exists('$(BuildPath64)pyshellext.dll') or '$(_Rebuild)' == 'Rebuild'" BeforeTargets="PrepareForBuild">
+        <MSBuild Projects="$(PySourcePath)PCbuild\pyshellext.vcxproj" Properties="Platform=x64" Targets="$(_Rebuild)" />
+    </Target>
+    <Target Name="_EnsurePyShellExtARM64" Condition="!Exists('$(BuildPathARM64)pyshellext.dll') or '$(_Rebuild)' == 'Rebuild'" BeforeTargets="PrepareForBuild">
+        <MSBuild Projects="$(PySourcePath)PCbuild\pyshellext.vcxproj" Properties="Platform=ARM64" Targets="$(_Rebuild)" />
     </Target>
     
     <Import Project="..\msi.targets" />

Tools/msi/launcher/launcher_files.wxs

@@ -33,6 +33,15 @@
                     <Class Id="{BEA218D2-6950-497B-9434-61683EC065FE}" Advertise="no" Context="InprocServer32" ThreadingModel="apartment" />
                 </File>
             </Component>
+            <!--
+            Currently unclear how to detect ARM64 device at this point.
+            In any case, the shell extension doesn't appear to work, so installing a non-functional
+            pyshellext_amd64.dll for a different platform isn't any worse.
+            <Component Id="pyshellext_arm64.dll" Directory="LauncherInstallDirectory" Guid="{C591963D-7FC6-4FCE-8642-5E01E6B8848F}">
+                <File Id="pyshellext_arm64.dll" Name="pyshellext.arm64.dll" Source="!(bindpath.BuildARM64)\pyshellext.dll">
+                    <Class Id="{BEA218D2-6950-497B-9434-61683EC065FE}" Advertise="no" Context="InprocServer32" ThreadingModel="apartment" />
+                </File>
+            </Component>-->
         </ComponentGroup>
     </Fragment>
 </Wix>