gh-101467: Correct py.exe handling of prefix matches and cases when only one runtime is installed (GH-101468)

4 files changed, 114 insertions, 18 deletions

diff --git a/Doc/using/windows.rst b/Doc/using/windows.rst
index bd09666..1c4e41c 100644
--- a/Doc/using/windows.rst
+++ b/Doc/using/windows.rst
@@ -743,22 +743,47 @@ command::
 
   py -2
 
-You should find the latest version of Python 3.x starts.
-
 If you see the following error, you do not have the launcher installed::
 
   'py' is not recognized as an internal or external command,
   operable program or batch file.
 
-Per-user installations of Python do not add the launcher to :envvar:`PATH`
-unless the option was selected on installation.
-
 The command::
 
   py --list
 
 displays the currently installed version(s) of Python.
 
+The ``-x.y`` argument is the short form of the ``-V:Company/Tag`` argument,
+which allows selecting a specific Python runtime, including those that may have
+come from somewhere other than python.org. Any runtime registered by following
+:pep:`514` will be discoverable. The ``--list`` command lists all available
+runtimes using the ``-V:`` format.
+
+When using the ``-V:`` argument, specifying the Company will limit selection to
+runtimes from that provider, while specifying only the Tag will select from all
+providers. Note that omitting the slash implies a tag::
+
+  # Select any '3.*' tagged runtime
+  py -V:3
+
+  # Select any 'PythonCore' released runtime
+  py -V:PythonCore/
+
+  # Select PythonCore's latest Python 3 runtime
+  py -V:PythonCore/3
+
+The short form of the argument (``-3``) only ever selects from core Python
+releases, and not other distributions. However, the longer form (``-V:3``) will
+select from any.
+
+The Company is matched on the full string, case-insenitive. The Tag is matched
+oneither the full string, or a prefix, provided the next character is a dot or a
+hyphen. This allows ``-V:3.1`` to match ``3.1-32``, but not ``3.10``. Tags are
+sorted using numerical ordering (``3.10`` is newer than ``3.1``), but are
+compared using text (``-V:3.01`` does not match ``3.1``).
+
+
 Virtual environments
 ^^^^^^^^^^^^^^^^^^^^
 
diff --git a/Lib/test/test_launcher.py b/Lib/test/test_launcher.py
index 351a638..2f35eaf 100644
--- a/Lib/test/test_launcher.py
+++ b/Lib/test/test_launcher.py
@@ -56,7 +56,17 @@ TEST_DATA = {
                 None: sys.prefix,
             }
         },
-    }
+    },
+    "PythonTestSuite1": {
+        "DisplayName": "Python Test Suite Single",
+        "3.100": {
+            "DisplayName": "Single Interpreter",
+            "InstallPath": {
+                None: sys.prefix,
+                "ExecutablePath": sys.executable,
+            }
+        }
+    },
 }
 
 
@@ -206,6 +216,7 @@ class RunPyMixin:
             **{k.upper(): v for k, v in os.environ.items() if k.upper() not in ignore},
             "PYLAUNCHER_DEBUG": "1",
             "PYLAUNCHER_DRYRUN": "1",
+            "PYLAUNCHER_LIMIT_TO_COMPANY": "",
             **{k.upper(): v for k, v in (env or {}).items()},
         }
         if not argv:
@@ -388,23 +399,33 @@ class TestLauncher(unittest.TestCase, RunPyMixin):
         self.assertEqual(company, data["env.company"])
         self.assertEqual("3.100", data["env.tag"])
 
-        data = self.run_py([f"-V:3.100-3"])
+        data = self.run_py([f"-V:3.100-32"])
         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"])
+        data = self.run_py([f"-V:3.100-arm64"])
         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"])
+        data = self.run_py([f"-V:{company}/3.1"], expect_returncode=103)
+
+        data = self.run_py([f"-V:{company}/3.100"])
         self.assertEqual("X.Y.exe", data["LaunchCommand"])
         self.assertEqual(company, data["env.company"])
         self.assertEqual("3.100", data["env.tag"])
 
+    def test_filter_with_single_install(self):
+        company = "PythonTestSuite1"
+        data = self.run_py(
+            [f"-V:Nonexistent"],
+            env={"PYLAUNCHER_LIMIT_TO_COMPANY": company},
+            expect_returncode=103,
+        )
+
     def test_search_major_3(self):
         try:
             data = self.run_py(["-3"], allow_fail=True)
diff --git a/Misc/NEWS.d/next/Windows/2023-01-31-16-50-07.gh-issue-101467.ye9t-L.rst b/Misc/NEWS.d/next/Windows/2023-01-31-16-50-07.gh-issue-101467.ye9t-L.rst
new file mode 100644
index 0000000..4d4da05
--- /dev/null
+++ b/Misc/NEWS.d/next/Windows/2023-01-31-16-50-07.gh-issue-101467.ye9t-L.rst
@@ -0,0 +1,3 @@
+The ``py.exe`` launcher now correctly filters when only a single runtime is
+installed. It also correctly handles prefix matches on tags so that ``-3.1``
+does not match ``3.11``, but would still match ``3.1-32``.
diff --git a/PC/launcher2.c b/PC/launcher2.c
index 2052a2f..beeb2ae 100644
--- a/PC/launcher2.c
+++ b/PC/launcher2.c
@@ -295,6 +295,30 @@ _startsWithArgument(const wchar_t *x, int xLen, const wchar_t *y, int yLen)
 }
 
 
+// Unlike regular startsWith, this function requires that the following
+// character is either NULL (that is, the entire string matches) or is one of
+// the characters in 'separators'.
+bool
+_startsWithSeparated(const wchar_t *x, int xLen, const wchar_t *y, int yLen, const wchar_t *separators)
+{
+    if (!x || !y) {
+        return false;
+    }
+    yLen = yLen < 0 ? (int)wcsnlen_s(y, MAXLEN) : yLen;
+    xLen = xLen < 0 ? (int)wcsnlen_s(x, MAXLEN) : xLen;
+    if (xLen < yLen) {
+        return false;
+    }
+    if (xLen == yLen) {
+        return 0 == _compare(x, xLen, y, yLen);
+    }
+    return separators &&
+        0 == _compare(x, yLen, y, yLen) &&
+        wcschr(separators, x[yLen]) != NULL;
+}
+
+
+
 /******************************************************************************\
  ***                               HELP TEXT                                ***
 \******************************************************************************/
@@ -409,6 +433,9 @@ typedef struct {
     bool listPaths;
     // if true, display help message before contiuning
     bool help;
+    // if set, limits search to registry keys with the specified Company
+    // This is intended for debugging and testing only
+    const wchar_t *limitToCompany;
     // dynamically allocated buffers to free later
     struct _SearchInfoBuffer *_buffer;
 } SearchInfo;
@@ -489,6 +516,7 @@ dumpSearchInfo(SearchInfo *search)
     DEBUG_BOOL(list);
     DEBUG_BOOL(listPaths);
     DEBUG_BOOL(help);
+    DEBUG(limitToCompany);
 #undef DEBUG_BOOL
 #undef DEBUG_2
 #undef DEBUG
@@ -1606,6 +1634,10 @@ registrySearch(const SearchInfo *search, EnvironmentInfo **result, HKEY root, in
             }
             break;
         }
+        if (search->limitToCompany && 0 != _compare(search->limitToCompany, -1, buffer, cchBuffer)) {
+            debug(L"# Skipping %s due to PYLAUNCHER_LIMIT_TO_COMPANY\n", buffer);
+            continue;
+        }
         HKEY subkey;
         if (ERROR_SUCCESS == RegOpenKeyExW(root, buffer, 0, KEY_READ, &subkey)) {
             exitCode = _registrySearchTags(search, result, subkey, sortKey, buffer, fallbackArch);
@@ -1884,6 +1916,11 @@ collectEnvironments(const SearchInfo *search, EnvironmentInfo **result)
         }
     }
 
+    if (search->limitToCompany) {
+        debug(L"# Skipping APPX search due to PYLAUNCHER_LIMIT_TO_COMPANY\n");
+        return 0;
+    }
+
     for (struct AppxSearchInfo *info = APPX_SEARCH; info->familyName; ++info) {
         exitCode = appxSearch(search, result, info->familyName, info->tag, info->sortKey);
         if (exitCode && exitCode != RC_NO_PYTHON) {
@@ -2053,12 +2090,15 @@ _companyMatches(const SearchInfo *search, const EnvironmentInfo *env)
 
 
 bool
-_tagMatches(const SearchInfo *search, const EnvironmentInfo *env)
+_tagMatches(const SearchInfo *search, const EnvironmentInfo *env, int searchTagLength)
 {
-    if (!search->tag || !search->tagLength) {
+    if (searchTagLength < 0) {
+        searchTagLength = search->tagLength;
+    }
+    if (!search->tag || !searchTagLength) {
         return true;
     }
-    return _startsWith(env->tag, -1, search->tag, search->tagLength);
+    return _startsWithSeparated(env->tag, -1, search->tag, searchTagLength, L".-");
 }
 
 
@@ -2095,7 +2135,7 @@ _selectEnvironment(const SearchInfo *search, EnvironmentInfo *env, EnvironmentIn
         }
 
         if (!search->oldStyleTag) {
-            if (_companyMatches(search, env) && _tagMatches(search, env)) {
+            if (_companyMatches(search, env) && _tagMatches(search, env, -1)) {
                 // Because of how our sort tree is set up, we will walk up the
                 // "prev" side and implicitly select the "best" best. By
                 // returning straight after a match, we skip the entire "next"
@@ -2120,7 +2160,7 @@ _selectEnvironment(const SearchInfo *search, EnvironmentInfo *env, EnvironmentIn
                 }
             }
 
-            if (_startsWith(env->tag, -1, search->tag, tagLength)) {
+            if (_tagMatches(search, env, tagLength)) {
                 if (exclude32Bit && _is32Bit(env)) {
                     debug(L"# Excluding %s/%s because it looks like 32bit\n", env->company, env->tag);
                 } else if (only32Bit && !_is32Bit(env)) {
@@ -2147,10 +2187,6 @@ selectEnvironment(const SearchInfo *search, EnvironmentInfo *root, EnvironmentIn
         *best = NULL;
         return RC_NO_PYTHON_AT_ALL;
     }
-    if (!root->next && !root->prev) {
-        *best = root;
-        return 0;
-    }
 
     EnvironmentInfo *result = NULL;
     int exitCode = _selectEnvironment(search, root, &result);
@@ -2560,6 +2596,17 @@ process(int argc, wchar_t ** argv)
         debug(L"argv0: %s\nversion: %S\n", argv[0], PY_VERSION);
     }
 
+    DWORD len = GetEnvironmentVariableW(L"PYLAUNCHER_LIMIT_TO_COMPANY", NULL, 0);
+    if (len > 1) {
+        wchar_t *limitToCompany = allocSearchInfoBuffer(&search, len);
+        search.limitToCompany = limitToCompany;
+        if (0 == GetEnvironmentVariableW(L"PYLAUNCHER_LIMIT_TO_COMPANY", limitToCompany, len)) {
+            exitCode = RC_INTERNAL_ERROR;
+            winerror(0, L"Failed to read PYLAUNCHER_LIMIT_TO_COMPANY variable");
+            goto abort;
+        }
+    }
+
     search.originalCmdLine = GetCommandLineW();
 
     exitCode = performSearch(&search, &envs);