bpo-45211: Add _Py_IsStdlibDir().

Include/internal/pycore_pathconfig.h

@@ -8,6 +8,8 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
+#include <stdbool.h>
+
 typedef struct _PyPathConfig {
     /* Full path to the Python program */
     wchar_t *program_full_path;
@@ -67,6 +69,11 @@ extern PyStatus _PyConfig_WritePathConfig(const PyConfig *config);
 extern void _Py_DumpPathConfig(PyThreadState *tstate);
 extern PyObject* _PyPathConfig_AsDict(void);
 
+
+/* locating the stdlib */
+
+extern bool _Py_IsStdlibDir(const wchar_t *stdlibdir, bool checkpyc);
+
 #ifdef __cplusplus
 }
 #endif

Modules/getpath.c

@@ -109,10 +109,6 @@ extern "C" {
 #error "PREFIX, EXEC_PREFIX, VERSION and VPATH macros must be defined"
 #endif
 
-#ifndef LANDMARK
-#define LANDMARK L"os.py"
-#endif
-
 #define BUILD_LANDMARK L"Modules/Setup.local"
 
 #define PATHLEN_ERR() _PyStatus_ERR("path configuration: path too long")
@@ -325,33 +321,7 @@ absolutize(wchar_t **path_p)
 static PyStatus
 ismodule(const wchar_t *path, int *result)
 {
-    wchar_t *filename = joinpath2(path, LANDMARK);
-    if (filename == NULL) {
-        return _PyStatus_NO_MEMORY();
-    }
-
-    if (isfile(filename)) {
-        PyMem_RawFree(filename);
-        *result = 1;
-        return _PyStatus_OK();
-    }
-
-    /* Check for the compiled version of prefix. */
-    size_t len = wcslen(filename);
-    wchar_t *pyc = PyMem_RawMalloc((len + 2) * sizeof(wchar_t));
-    if (pyc == NULL) {
-        PyMem_RawFree(filename);
-        return _PyStatus_NO_MEMORY();
-    }
-
-    memcpy(pyc, filename, len * sizeof(wchar_t));
-    pyc[len] = L'c';
-    pyc[len + 1] = L'\0';
-    *result = isfile(pyc);
-
-    PyMem_RawFree(filename);
-    PyMem_RawFree(pyc);
-
+    *result = _Py_IsStdlibDir(path, true) ? 1 : 0;
     return _PyStatus_OK();
 }
 

PC/getpathp.c

@@ -85,6 +85,7 @@
 #include "pycore_fileutils.h"     // _Py_add_relfile()
 #include "osdefs.h"               // SEP, ALTSEP
 #include <wchar.h>
+#include <stdbool.h>
 
 #ifndef MS_WINDOWS
 #error getpathp.c should only be built on Windows
@@ -209,33 +210,6 @@ exists(const wchar_t *filename)
 }
 
 
-/* Is module -- check for .pyc too.
-   Assumes 'filename' MAXPATHLEN+1 bytes long -
-   may extend 'filename' by one character. */
-static int
-ismodule(wchar_t *filename)
-{
-    size_t n;
-
-    if (exists(filename)) {
-        return 1;
-    }
-
-    /* Check for the compiled version of prefix. */
-    n = wcsnlen_s(filename, MAXPATHLEN+1);
-    if (n < MAXPATHLEN) {
-        int exist = 0;
-        filename[n] = L'c';
-        filename[n + 1] = L'\0';
-        exist = exists(filename);
-        // Drop the 'c' we just added.
-        filename[n] = L'\0';
-        return exist;
-    }
-    return 0;
-}
-
-
 /* Add a path component, by appending stuff to buffer.
    buffer must have at least MAXPATHLEN + 1 bytes allocated, and contain a
    NUL-terminated string with no more than MAXPATHLEN characters (not counting
@@ -269,18 +243,6 @@ canonicalize(wchar_t *buffer, const wchar_t *path)
     return _PyStatus_OK();
 }
 
-static int
-is_stdlibdir(wchar_t *stdlibdir)
-{
-    wchar_t *filename = stdlibdir;
-#ifndef LANDMARK
-#  define LANDMARK L"os.py"
-#endif
-    /* join() ensures 'landmark' can not overflow prefix if too long. */
-    join(filename, LANDMARK);
-    return ismodule(filename);
-}
-
 /* assumes argv0_path is MAXPATHLEN+1 bytes long, already \0 term'd.
    assumption provided by only caller, calculate_path() */
 static int
@@ -299,7 +261,7 @@ search_for_prefix(wchar_t *prefix, const wchar_t *argv0_path)
         /* Due to reduce() and our initial value, this result
            is guaranteed to fit. */
         wcscpy(&stdlibdir[wcslen(prefix) + 1], L"lib");
-        if (is_stdlibdir(stdlibdir)) {
+        if (_Py_IsStdlibDir(stdlibdir, true)) {
             return 1;
         }
         reduce(prefix);

Python/pathconfig.c

@@ -6,6 +6,7 @@
 #include "pycore_fileutils.h"
 #include "pycore_pathconfig.h"
 #include "pycore_pymem.h"         // _PyMem_SetDefaultAllocator()
+#include <stdbool.h>
 #include <wchar.h>
 #ifdef MS_WINDOWS
 #  include <windows.h>            // GetFullPathNameW(), MAX_PATH
@@ -813,6 +814,55 @@ _Py_FindEnvConfigValue(FILE *env_file, const wchar_t *key,
     return _PyStatus_OK();
 }
 
+
+/* locating the stdlib */
+
+static int
+file_exists(const wchar_t *filename)
+{
+#ifdef MS_WINDOWS
+    return GetFileAttributesW(filename) != 0xFFFFFFFF;
+#else
+    struct stat buf;
+    return _Py_wstat(filename, &buf) == 0 && S_ISREG(buf.st_mode);
+#endif
+}
+
+/* Decide if the given directory hold the stdlib. */
+bool
+_Py_IsStdlibDir(const wchar_t *stdlibdir, bool checkpyc)
+{
+    // Build the filename to look for.
+    wchar_t filename[MAXPATHLEN + 1];
+    assert(stdlibdir != NULL);
+#ifdef MS_WINDOWS
+    wcscpy_s(filename, MAXPATHLEN + 1, stdlibdir);
+#else
+    wcscpy(filename, stdlibdir);
+#endif
+#ifndef LANDMARK
+#define LANDMARK L"os.py"
+#endif
+    _Py_add_relfile(filename, LANDMARK, MAXPATHLEN + 1);
+
+    // Check if the file exists.
+    if (file_exists(filename)) {
+        return true;
+    }
+
+    // Check for the compiled version. */
+    size_t len = wcslen(filename);
+    if (checkpyc && len < MAXPATHLEN) {
+        filename[len] = 'c';
+        filename[len + 1] = '\0';
+        if (file_exists(filename)) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 #ifdef __cplusplus
 }
 #endif