Fix incorrect path conversion (trailing slash)

The problem with the original approach is not that it is completely
bogus. After all, when you pass the option --prefix=/tmp/ to Git, you do
want to end up with a trailing slash.

The real problem with the original approach is that it simply changed
path_conv, completely oblivious and careless about other users of
path_conv.

That was really wrong, of course, and cost us time, sweat and tears. The
appropriate approach is to *not* affect other users, but instead
introduce a flag that we use in *our* caller, so that everybody gets
what they want:

- emulation of inodes on FAT by calculating the hash on the normalized
  path: works.

- MSYS2's conversion of "POSIX" paths to Windows paths: works.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/cygwin/msys2_path_conv.cc

@@ -624,7 +624,7 @@ void posix_to_win32_path(const char* from, const char* to, char** dst, const cha
         strncpy(one_path, from, to-from);
         one_path[to-from] = '\0';
 
-        path_conv conv (one_path, 0);
+        path_conv conv (one_path, PC_KEEP_FINAL_SLASH);
         if (conv.error)
         {
           set_errno(conv.error);

winsup/cygwin/path.cc

@@ -1254,9 +1254,22 @@ path_conv::check (const char *src, unsigned opt,
 		cfree (wide_path);
 	      wide_path = NULL;
 	    }
+
+	  if (need_directory)
+	    {
+	      size_t n = strlen (this->path);
+	      /* Do not add trailing \ to UNC device names like \\.\a: */
+	      if (this->path[n - 1] != '\\' &&
+		  (strncmp (this->path, "\\\\.\\", 4) != 0))
+		{
+		  this->modifiable_path ()[n] = '\\';
+		  this->modifiable_path ()[n + 1] = '\0';
+		}
+	      need_directory = 0;
+	    }
 	}
 
-      if (need_directory)
+      if ((opt & PC_KEEP_FINAL_SLASH) && need_directory)
 	{
 	  size_t n = strlen (this->path);
 	  /* Do not add trailing \ to UNC device names like \\.\a: */
@@ -1266,6 +1279,7 @@ path_conv::check (const char *src, unsigned opt,
 	      this->modifiable_path ()[n] = '\\';
 	      this->modifiable_path ()[n + 1] = '\0';
 	    }
+	  need_directory = 0;
 	}
 
       if (opt & PC_OPEN)

winsup/cygwin/path.h

@@ -59,6 +59,7 @@ enum pathconv_arg
   PC_KEEP_HANDLE	 = _BIT (12),	/* keep handle for later stat calls */
   PC_NO_ACCESS_CHECK	 = _BIT (13),	/* helper flag for error check */
   PC_SYM_NOFOLLOW_DIR	 = _BIT (14),	/* don't follow a trailing slash */
+  PC_KEEP_FINAL_SLASH	 = _BIT (15),   /* do not remove a trailing slash */
   PC_DONT_USE		 = _BIT (31)	/* conversion to signed happens. */
 };