patch 8.2.4875: MS-Windows: some .exe files are not recognized

Problem:    MS-Windows: some .exe files are not recognized.
Solution:   Parse APPEXECLINK junctions. (closes #10302)

src/os_mswin.c

@@ -439,6 +439,27 @@ slash_adjust(char_u *p)
 #define _wstat _wstat64
 #define _fstat _fstat64
 
+    static int
+read_reparse_point(const WCHAR *name, char_u *buf, DWORD *buf_len)
+{
+    HANDLE h;
+    BOOL ok;
+
+    h = CreateFileW(name, FILE_READ_ATTRIBUTES,
+	    FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+	    OPEN_EXISTING,
+	    FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
+	    NULL);
+    if (h == INVALID_HANDLE_VALUE)
+	return FAIL;
+
+    ok = DeviceIoControl(h, FSCTL_GET_REPARSE_POINT, NULL, 0, buf, *buf_len,
+	    buf_len, NULL);
+    CloseHandle(h);
+
+    return ok ? OK : FAIL;
+}
+
     static int
 wstat_symlink_aware(const WCHAR *name, stat_T *stp)
 {
@@ -491,6 +512,61 @@ wstat_symlink_aware(const WCHAR *name, stat_T *stp)
     return _wstat(name, (struct _stat *)stp);
 }
 
+    char_u *
+resolve_appexeclink(char_u *fname)
+{
+    DWORD	        attr = 0;
+    int	                idx;
+    WCHAR	        *p, *end, *wname;
+    // The buffer size is arbitrarily chosen to be "big enough" (TM), the
+    // ceiling should be around 16k.
+    char_u	        buf[4096];
+    DWORD	        buf_len = sizeof(buf);
+    REPARSE_DATA_BUFFER *rb = (REPARSE_DATA_BUFFER *)buf;
+
+    wname = enc_to_utf16(fname, NULL);
+    if (wname == NULL)
+	return NULL;
+
+    attr = GetFileAttributesW(wname);
+    if (attr == INVALID_FILE_ATTRIBUTES ||
+	    (attr & FILE_ATTRIBUTE_REPARSE_POINT) == 0)
+    {
+	vim_free(wname);
+	return NULL;
+    }
+
+    // The applinks are similar to symlinks but with a huge difference: they can
+    // only be executed, any other I/O operation on them is bound to fail with
+    // ERROR_FILE_NOT_FOUND even though the file exists.
+    if (read_reparse_point(wname, buf, &buf_len) == FAIL)
+    {
+	vim_free(wname);
+	return NULL;
+    }
+    vim_free(wname);
+
+    if (rb->ReparseTag != IO_REPARSE_TAG_APPEXECLINK)
+	return NULL;
+
+    // The (undocumented) reparse buffer contains a set of N null-terminated
+    // Unicode strings, the application path is stored in the third one.
+    if (rb->AppExecLinkReparseBuffer.StringCount < 3)
+	return NULL;
+
+    p = rb->AppExecLinkReparseBuffer.StringList;
+    end = p + rb->ReparseDataLength / sizeof(WCHAR);
+    for (idx = 0; p < end
+	    && idx < (int)rb->AppExecLinkReparseBuffer.StringCount
+	    && idx != 2; )
+    {
+	if ((*p++ == L'\0'))
+	    ++idx;
+    }
+
+    return utf16_to_enc(p, NULL);
+}
+
 /*
  * stat() can't handle a trailing '/' or '\', remove it first.
  */