gh-100247: Fix py.exe launcher not using entire shebang command for finding custom commands (GH-100944)

4 files changed, 154 insertions, 94 deletions

diff --git a/Doc/using/windows.rst b/Doc/using/windows.rst
index fdbe4c1..69bca4d 100644
--- a/Doc/using/windows.rst
+++ b/Doc/using/windows.rst
@@ -831,7 +831,7 @@ To allow shebang lines in Python scripts to be portable between Unix and
 Windows, this launcher supports a number of 'virtual' commands to specify
 which interpreter to use.  The supported virtual commands are:
 
-* ``/usr/bin/env python``
+* ``/usr/bin/env``
 * ``/usr/bin/python``
 * ``/usr/local/bin/python``
 * ``python``
@@ -868,14 +868,28 @@ minor version. I.e. ``/usr/bin/python3.7-32`` will request usage of the
 
 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
-behaviour of the Unix ``env`` program, which performs a :envvar:`PATH` search.
+executable :envvar:`PATH` for a Python executable matching the name provided
+as the first argument. This corresponds to the behaviour of the Unix ``env``
+program, which performs a :envvar:`PATH` search.
 If an executable matching the first argument after the ``env`` command cannot
-be found, it will be handled as described below. Additionally, the environment
-variable :envvar:`PYLAUNCHER_NO_SEARCH_PATH` may be set (to any value) to skip
-this additional search.
+be found, but the argument starts with ``python``, it will be handled as
+described for the other virtual commands.
+The environment variable :envvar:`PYLAUNCHER_NO_SEARCH_PATH` may be set
+(to any value) to skip this search of :envvar:`PATH`.
+
+Shebang lines that do not match any of these patterns are looked up in the
+``[commands]`` section of the launcher's :ref:`.INI file <launcher-ini>`.
+This may be used to handle certain commands in a way that makes sense for your
+system. The name of the command must be a single argument (no spaces),
+and the value substituted is the full path to the executable (no arguments
+may be added).
 
-Shebang lines that do not match any of these patterns are treated as **Windows**
+.. code-block:: ini
+
+   [commands]
+   /bin/sh=C:\Program Files\Bash\bash.exe
+
+Any commands not found in the .INI file are treated as **Windows** executable
 paths that are absolute or relative to the directory containing the script file.
 This is a convenience for Windows-only scripts, such as those generated by an
 installer, since the behavior is not compatible with Unix-style shells.
@@ -898,15 +912,16 @@ Then Python will be started with the ``-v`` option
 Customization
 -------------
 
+.. _launcher-ini:
+
 Customization via INI files
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 Two .ini files will be searched by the launcher - ``py.ini`` in the current
-user's "application data" directory (i.e. the directory returned by calling the
-Windows function ``SHGetFolderPath`` with ``CSIDL_LOCAL_APPDATA``) and ``py.ini`` in the
-same directory as the launcher. The same .ini files are used for both the
-'console' version of the launcher (i.e. py.exe) and for the 'windows' version
-(i.e. pyw.exe).
+user's application data directory (``%LOCALAPPDATA%`` or ``$env:LocalAppData``)
+and ``py.ini`` in the same directory as the launcher. The same .ini files are
+used for both the 'console' version of the launcher (i.e. py.exe) and for the
+'windows' version (i.e. pyw.exe).
 
 Customization specified in the "application directory" will have precedence over
 the one next to the executable, so a user, who may not have write access to the
diff --git a/Lib/test/test_launcher.py b/Lib/test/test_launcher.py
index 47152d4..351a638 100644
--- a/Lib/test/test_launcher.py
+++ b/Lib/test/test_launcher.py
@@ -67,12 +67,17 @@ TEST_PY_ENV = dict(
 )
 
 
-TEST_PY_COMMANDS = "\n".join([
+TEST_PY_DEFAULTS = "\n".join([
     "[defaults]",
-    *[f"{k[3:].lower()}={v}" for k, v in TEST_PY_ENV.items()]
+    *[f"{k[3:].lower()}={v}" for k, v in TEST_PY_ENV.items()],
 ])
 
 
+TEST_PY_COMMANDS = "\n".join([
+    "[commands]",
+    "test-command=TEST_EXE.exe",
+])
+
 def create_registry_data(root, data):
     def _create_registry_data(root, key, value):
         if isinstance(value, dict):
@@ -429,21 +434,21 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertTrue(data["env.tag"].startswith("2."), data["env.tag"])
 
     def test_py_default(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             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):
+        with self.py_ini(TEST_PY_DEFAULTS):
             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):
+        with self.py_ini(TEST_PY_DEFAULTS):
             data = self.run_py(["-3", "-arg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
         self.assertEqual("3.100-arm64", data["SearchInfo.tag"])
@@ -468,7 +473,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual("X.Y-arm64.exe -X fake_arg_for_test -arg", data["stdout"].strip())
 
     def test_py_default_short_argv0(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             for argv0 in ['"py.exe"', 'py.exe', '"py"', 'py']:
                 with self.subTest(argv0):
                     data = self.run_py(["--version"], argv=f'{argv0} --version')
@@ -518,7 +523,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertNotEqual(data2["SearchInfo.lowPriorityTag"], "True")
 
     def test_py_shebang(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python -prearg") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -526,7 +531,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(f"X.Y.exe -prearg {script} -postarg", data["stdout"].strip())
 
     def test_python_shebang(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! python -prearg") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -534,7 +539,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         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.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python2 -prearg") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -542,7 +547,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         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.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python3 -prearg") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -550,7 +555,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(f"X.Y-arm64.exe -X fake_arg_for_test -prearg {script} -postarg", data["stdout"].strip())
 
     def test_py_shebang_nl(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python -prearg\n") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -558,7 +563,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(f"X.Y.exe -prearg {script} -postarg", data["stdout"].strip())
 
     def test_py2_shebang_nl(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python2 -prearg\n") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -566,7 +571,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(f"X.Y-32.exe -prearg {script} -postarg", data["stdout"].strip())
 
     def test_py3_shebang_nl(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python3 -prearg\n") as script:
                 data = self.run_py([script, "-postarg"])
         self.assertEqual("PythonTestSuite", data["SearchInfo.company"])
@@ -574,7 +579,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(f"X.Y-arm64.exe -X fake_arg_for_test -prearg {script} -postarg", data["stdout"].strip())
 
     def test_py_shebang_short_argv0(self):
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script("#! /usr/bin/python -prearg") as script:
                 # Override argv to only pass "py.exe" as the command
                 data = self.run_py([script, "-postarg"], argv=f'"py.exe" "{script}" -postarg')
@@ -591,7 +596,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
 
     def test_search_path(self):
         stem = Path(sys.executable).stem
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script(f"#! /usr/bin/env {stem} -prearg") as script:
                 data = self.run_py(
                     [script, "-postarg"],
@@ -602,7 +607,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
     def test_search_path_exe(self):
         # Leave the .exe on the name to ensure we don't add it a second time
         name = Path(sys.executable).name
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script(f"#! /usr/bin/env {name} -prearg") as script:
                 data = self.run_py(
                     [script, "-postarg"],
@@ -612,7 +617,7 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
 
     def test_recursive_search_path(self):
         stem = self.get_py_exe().stem
-        with self.py_ini(TEST_PY_COMMANDS):
+        with self.py_ini(TEST_PY_DEFAULTS):
             with self.script(f"#! /usr/bin/env {stem}") as script:
                 data = self.run_py(
                     [script],
@@ -673,3 +678,21 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
             f'"{script.parent}\\some\\ random app" -witharg {script}',
             data["stdout"].strip(),
         )
+
+    def test_literal_shebang_command(self):
+        with self.py_ini(TEST_PY_COMMANDS):
+            with self.script('#! test-command arg1') as script:
+                data = self.run_py([script])
+        self.assertEqual(
+            f"TEST_EXE.exe arg1 {script}",
+            data["stdout"].strip(),
+        )
+
+    def test_literal_shebang_invalid_template(self):
+        with self.script('#! /usr/bin/not-python arg1') as script:
+            data = self.run_py([script])
+        expect = script.parent / "/usr/bin/not-python"
+        self.assertEqual(
+            f"{expect} arg1 {script}",
+            data["stdout"].strip(),
+        )
diff --git a/Misc/NEWS.d/next/Windows/2023-01-11-14-42-11.gh-issue-100247.YfEmSz.rst b/Misc/NEWS.d/next/Windows/2023-01-11-14-42-11.gh-issue-100247.YfEmSz.rst
new file mode 100644
index 0000000..7bfcbd7
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2023-01-11-14-42-11.gh-issue-100247.YfEmSz.rst
@@ -0,0 +1,2 @@
+Restores support for the :file:`py.exe` launcher finding shebang commands in
+its configuration file using the full command name.
diff --git a/PC/launcher2.c b/PC/launcher2.c
index 9b3db04..8371c60 100644
--- a/PC/launcher2.c
+++ b/PC/launcher2.c
@@ -16,6 +16,7 @@
 #include <stdio.h>
 #include <stdbool.h>
 #include <tchar.h>
+#include <assert.h>
 
 #define MS_WINDOWS
 #include "patchlevel.h"
@@ -37,6 +38,7 @@
 #define RC_INSTALLING       111
 #define RC_NO_PYTHON_AT_ALL 112
 #define RC_NO_SHEBANG       113
+#define RC_RECURSIVE_SHEBANG 114
 
 static FILE * log_fp = NULL;
 
@@ -702,16 +704,23 @@ _decodeShebang(SearchInfo *search, const char *buffer, int bufferLength, bool on
 
 
 bool
-_shebangStartsWith(const wchar_t *buffer, int bufferLength, const wchar_t *prefix, const wchar_t **rest)
+_shebangStartsWith(const wchar_t *buffer, int bufferLength, const wchar_t *prefix, const wchar_t **rest, int *firstArgumentLength)
 {
     int prefixLength = (int)wcsnlen_s(prefix, MAXLEN);
-    if (bufferLength < prefixLength) {
+    if (bufferLength < prefixLength || !_startsWithArgument(buffer, bufferLength, prefix, prefixLength)) {
         return false;
     }
     if (rest) {
         *rest = &buffer[prefixLength];
     }
-    return _startsWithArgument(buffer, bufferLength, prefix, prefixLength);
+    if (firstArgumentLength) {
+        int i = prefixLength;
+        while (i < bufferLength && !isspace(buffer[i])) {
+            i += 1;
+        }
+        *firstArgumentLength = i - prefixLength;
+    }
+    return true;
 }
 
 
@@ -723,26 +732,27 @@ searchPath(SearchInfo *search, const wchar_t *shebang, int shebangLength)
     }
 
     wchar_t *command;
-    if (!_shebangStartsWith(shebang, shebangLength, L"/usr/bin/env ", &command)) {
+    int commandLength;
+    if (!_shebangStartsWith(shebang, shebangLength, L"/usr/bin/env ", &command, &commandLength)) {
         return RC_NO_SHEBANG;
     }
 
-    wchar_t filename[MAXLEN];
-    int lastDot = 0;
-    int commandLength = 0;
-    while (commandLength < MAXLEN && command[commandLength] && !isspace(command[commandLength])) {
-        if (command[commandLength] == L'.') {
-            lastDot = commandLength;
-        }
-        filename[commandLength] = command[commandLength];
-        commandLength += 1;
-    }
-
     if (!commandLength || commandLength == MAXLEN) {
         return RC_BAD_VIRTUAL_PATH;
     }
 
-    filename[commandLength] = L'\0';
+    int lastDot = commandLength;
+    while (lastDot > 0 && command[lastDot] != L'.') {
+        lastDot -= 1;
+    }
+    if (!lastDot) {
+        lastDot = commandLength;
+    }
+
+    wchar_t filename[MAXLEN];
+    if (wcsncpy_s(filename, MAXLEN, command, lastDot)) {
+        return RC_BAD_VIRTUAL_PATH;
+    }
 
     const wchar_t *ext = L".exe";
     // If the command already has an extension, we do not want to add it again
@@ -780,7 +790,7 @@ searchPath(SearchInfo *search, const wchar_t *shebang, int shebangLength)
     if (GetModuleFileNameW(NULL, filename, MAXLEN) &&
         0 == _comparePath(filename, -1, buffer, -1)) {
         debug(L"# ignoring recursive shebang command\n");
-        return RC_NO_SHEBANG;
+        return RC_RECURSIVE_SHEBANG;
     }
 
     wchar_t *buf = allocSearchInfoBuffer(search, n + 1);
@@ -994,73 +1004,78 @@ checkShebang(SearchInfo *search)
         return exitCode;
     }
 
-    // Handle some known, case-sensitive shebang templates
+    // Handle some known, case-sensitive shebangs
     const wchar_t *command;
     int commandLength;
+    // Each template must end with "python"
     static const wchar_t *shebangTemplates[] = {
-        L"/usr/bin/env ",
-        L"/usr/bin/",
-        L"/usr/local/bin/",
+        L"/usr/bin/env python",
+        L"/usr/bin/python",
+        L"/usr/local/bin/python",
         L"python",
         NULL
     };
 
     for (const wchar_t **tmpl = shebangTemplates; *tmpl; ++tmpl) {
-        if (_shebangStartsWith(shebang, shebangLength, *tmpl, &command)) {
-            commandLength = 0;
-            // Normally "python" is the start of the command, but we also need it
-            // as a shebang prefix for back-compat. We move the command marker back
-            // if we match on that one.
-            if (0 == wcscmp(*tmpl, L"python")) {
-                command -= 6;
-            }
-            while (command[commandLength] && !isspace(command[commandLength])) {
-                commandLength += 1;
-            }
-            if (!commandLength) {
-            } else if (_findCommand(search, command, commandLength)) {
+        // Just to make sure we don't mess this up in the future
+        assert(0 == wcscmp(L"python", (*tmpl) + wcslen(*tmpl) - 6));
+
+        if (_shebangStartsWith(shebang, shebangLength, *tmpl, &command, &commandLength)) {
+            // Search for "python{command}" overrides. All templates end with
+            // "python", so we prepend it by jumping back 6 characters
+            if (_findCommand(search, &command[-6], commandLength + 6)) {
                 search->executableArgs = &command[commandLength];
                 search->executableArgsLength = shebangLength - commandLength;
                 debug(L"# Treating shebang command '%.*s' as %s\n",
-                    commandLength, command, search->executablePath);
-            } else if (_shebangStartsWith(command, commandLength, L"python", NULL)) {
-                search->tag = &command[6];
-                search->tagLength = commandLength - 6;
-                // If we had 'python3.12.exe' then we want to strip the suffix
-                // off of the tag
-                if (search->tagLength > 4) {
-                    const wchar_t *suffix = &search->tag[search->tagLength - 4];
-                    if (0 == _comparePath(suffix, 4, L".exe", -1)) {
-                        search->tagLength -= 4;
-                    }
-                }
-                // If we had 'python3_d' then we want to strip the '_d' (any
-                // '.exe' is already gone)
-                if (search->tagLength > 2) {
-                    const wchar_t *suffix = &search->tag[search->tagLength - 2];
-                    if (0 == _comparePath(suffix, 2, L"_d", -1)) {
-                        search->tagLength -= 2;
-                    }
+                    commandLength + 6, &command[-6], search->executablePath);
+                return 0;
+            }
+
+            search->tag = command;
+            search->tagLength = commandLength;
+            // If we had 'python3.12.exe' then we want to strip the suffix
+            // off of the tag
+            if (search->tagLength > 4) {
+                const wchar_t *suffix = &search->tag[search->tagLength - 4];
+                if (0 == _comparePath(suffix, 4, L".exe", -1)) {
+                    search->tagLength -= 4;
                 }
-                search->oldStyleTag = true;
-                search->executableArgs = &command[commandLength];
-                search->executableArgsLength = shebangLength - commandLength;
-                if (search->tag && search->tagLength) {
-                    debug(L"# Treating shebang command '%.*s' as 'py -%.*s'\n",
-                        commandLength, command, search->tagLength, search->tag);
-                } else {
-                    debug(L"# Treating shebang command '%.*s' as 'py'\n",
-                        commandLength, command);
+            }
+            // If we had 'python3_d' then we want to strip the '_d' (any
+            // '.exe' is already gone)
+            if (search->tagLength > 2) {
+                const wchar_t *suffix = &search->tag[search->tagLength - 2];
+                if (0 == _comparePath(suffix, 2, L"_d", -1)) {
+                    search->tagLength -= 2;
                 }
+            }
+            search->oldStyleTag = true;
+            search->executableArgs = &command[commandLength];
+            search->executableArgsLength = shebangLength - commandLength;
+            if (search->tag && search->tagLength) {
+                debug(L"# Treating shebang command '%.*s' as 'py -%.*s'\n",
+                    commandLength, command, search->tagLength, search->tag);
             } else {
-                debug(L"# Found shebang command but could not execute it: %.*s\n",
+                debug(L"# Treating shebang command '%.*s' as 'py'\n",
                     commandLength, command);
             }
-            // search is done by this point
             return 0;
         }
     }
 
+    // Unrecognised executables are first tried as command aliases
+    commandLength = 0;
+    while (commandLength < shebangLength && !isspace(shebang[commandLength])) {
+        commandLength += 1;
+    }
+    if (_findCommand(search, shebang, commandLength)) {
+        search->executableArgs = &shebang[commandLength];
+        search->executableArgsLength = shebangLength - commandLength;
+        debug(L"# Treating shebang command '%.*s' as %s\n",
+            commandLength, shebang, search->executablePath);
+        return 0;
+    }
+
     // Unrecognised commands are joined to the script's directory and treated
     // as the executable path
     return _useShebangAsExecutable(search, shebang, shebangLength);
@@ -2407,7 +2422,12 @@ performSearch(SearchInfo *search, EnvironmentInfo **envs)
     // Check for a shebang line in our script file
     // (or return quickly if no script file was specified)
     exitCode = checkShebang(search);
-    if (exitCode) {
+    switch (exitCode) {
+    case 0:
+    case RC_NO_SHEBANG:
+    case RC_RECURSIVE_SHEBANG:
+        break;
+    default:
         return exitCode;
     }