restore support for windows 7

this backports the windows 7 compatible fix for bpo-39401 from pythongh-18234,
originally authored by Steve Dower, and removes explicit dependencies on
pathcch.

Author: Hoikas

PC/getpathp.c

@@ -250,14 +250,43 @@ ismodule(wchar_t *filename, int update_filename)
    stuff as fits will be appended.
 */
 
+
+static int _PathCchCombineEx_Initialized = 0;
+typedef HRESULT(__stdcall *PPathCchCombineEx) (PWSTR pszPathOut, size_t cchPathOut,
+                                               PCWSTR pszPathIn, PCWSTR pszMore,
+                                               unsigned long dwFlags);
+static PPathCchCombineEx _PathCchCombineEx;
+
 static void
 join(wchar_t *buffer, const wchar_t *stuff)
 {
-    if (FAILED(PathCchCombineEx(buffer, MAXPATHLEN+1, buffer, stuff, 0))) {
-        Py_FatalError("buffer overflow in getpathp.c's join()");
+    if (_PathCchCombineEx_Initialized == 0) {
+        HMODULE pathapi = LoadLibraryExW(L"api-ms-win-core-path-l1-1-0.dll", NULL,
+                                         LOAD_LIBRARY_SEARCH_SYSTEM32);
+        if (pathapi) {
+            _PathCchCombineEx = (PPathCchCombineEx)GetProcAddress(pathapi, "PathCchCombineEx");
+        }
+        else {
+            _PathCchCombineEx = NULL;
+        }
+        _PathCchCombineEx_Initialized = 1;
+    }
+    if (_PathCchCombineEx) {
+        if (FAILED(_PathCchCombineEx(buffer, MAXPATHLEN+1, buffer, stuff, 0))) {
+            Py_FatalError("buffer overflow in getpathp.c's join()");
+        }
+    } else {
+        if (!PathCombineW(buffer, buffer, stuff)) {
+            Py_FatalError("buffer overflow in getpathp.c's join()");
+        }
     }
 }
 
+static int _PathCchCanonicalizeEx_Initialized = 0;
+typedef HRESULT(__stdcall *PPathCchCanonicalizeEx) (PWSTR pszPathOut, size_t cchPathOut,
+    PCWSTR pszPathIn, unsigned long dwFlags);
+static PPathCchCanonicalizeEx _PathCchCanonicalizeEx;
+
 /* Call PathCchCanonicalizeEx(path): remove navigation elements such as "."
    and ".." to produce a direct, well-formed path. */
 static PyStatus
@@ -267,8 +296,26 @@ canonicalize(wchar_t *buffer, const wchar_t *path)
         return _PyStatus_NO_MEMORY();
     }
 
-    if (FAILED(PathCchCanonicalizeEx(buffer, MAXPATHLEN + 1, path, 0))) {
-        return INIT_ERR_BUFFER_OVERFLOW();
+    if (_PathCchCanonicalizeEx_Initialized == 0) {
+        HMODULE pathapi = LoadLibraryExW(L"api-ms-win-core-path-l1-1-0.dll", NULL,
+                                         LOAD_LIBRARY_SEARCH_SYSTEM32);
+        if (pathapi) {
+            _PathCchCanonicalizeEx = (PPathCchCanonicalizeEx)GetProcAddress(pathapi, "PathCchCanonicalizeEx");
+        }
+        else {
+            _PathCchCanonicalizeEx = NULL;
+        }
+        _PathCchCanonicalizeEx_Initialized = 1;
+    }
+    if (_PathCchCanonicalizeEx) {
+        if (FAILED(_PathCchCanonicalizeEx(buffer, MAXPATHLEN + 1, path, 0))) {
+            return INIT_ERR_BUFFER_OVERFLOW();
+        }
+    }
+    else {
+        if (!PathCanonicalizeW(buffer, path)) {
+            return INIT_ERR_BUFFER_OVERFLOW();
+        }
     }
     return _PyStatus_OK();
 }

PC/pyconfig.h

@@ -136,8 +136,8 @@ WIN32 is still required for the locale module.
 
 /* set the version macros for the windows headers */
 /* Python 3.9+ requires Windows 8 or greater */
-#define Py_WINVER 0x0602 /* _WIN32_WINNT_WIN8 */
-#define Py_NTDDI NTDDI_WIN8
+#define Py_WINVER 0x0601 /* _WIN32_WINNT_WIN7 */
+#define Py_NTDDI NTDDI_WIN7
 
 /* We only set these values when building Python - we don't want to force
    these values on extensions, as that will affect the prototypes and

PCbuild/pythoncore.vcxproj

@@ -106,7 +106,7 @@
       <PreprocessorDefinitions Condition="$(IncludeExternals)">_Py_HAVE_ZLIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>
     <Link>
-      <AdditionalDependencies>version.lib;shlwapi.lib;ws2_32.lib;pathcch.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>version.lib;shlwapi.lib;ws2_32.lib;%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
   </ItemDefinitionGroup>
   <ItemGroup>