Resolves symlinks against <dir prefix="relative">

When a config file is symlinked and obtaining an relative path from it for <dir>,
it behaved like:

$ realpath /path/to/foo.conf
/path/to/realpath/foo.conf
$ FONTCONFIG_FILE=/path/to/foo.conf fc-cache -v
Font directories:
        /path/to/fonts
/path/to/fonts: skipping, existing cache is valid: 1 fonts, 0 dirs
/path/to/cachedir: cleaning cache directory
fc-cache: succeeded

And after this change:

$ FONTCONFIG_FILE=/path/to/foo.conf fc-cache -v
Font directories:
        /path/to/relpath/fonts
/path/to/realpath/fonts: skipping, existing cache is valid: 1 fonts, 0 dirs
/path/to/cachedir: cleaning cache directory
fc-cache: succeeded

Fixes https://gitlab.freedesktop.org/fontconfig/fontconfig/-/issues/290

src/fccfg.c

@@ -131,30 +131,6 @@ FcConfigFini (void)
     free_lock ();
 }
 
-static FcChar8 *
-FcConfigRealPath(const FcChar8 *path)
-{
-    char	resolved_name[FC_PATH_MAX+1];
-    char	*resolved_ret;
-
-    if (!path)
-	return NULL;
-
-#ifndef _WIN32
-    resolved_ret = realpath((const char *) path, resolved_name);
-#else
-    if (GetFullPathNameA ((LPCSTR) path, FC_PATH_MAX, resolved_name, NULL) == 0)
-    {
-        fprintf (stderr, "Fontconfig warning: GetFullPathNameA failed.\n");
-        return NULL;
-    }
-    resolved_ret = resolved_name;
-#endif
-    if (resolved_ret)
-	path = (FcChar8 *) resolved_ret;
-    return FcStrCopyFilename(path);
-}
-
 FcConfig *
 FcConfigCreate (void)
 {
@@ -221,7 +197,7 @@ FcConfigCreate (void)
 
     config->expr_pool = NULL;
 
-    config->sysRoot = FcConfigRealPath((const FcChar8 *) getenv("FONTCONFIG_SYSROOT"));
+    config->sysRoot = FcStrRealPath ((const FcChar8 *) getenv("FONTCONFIG_SYSROOT"));
 
     config->rulesetList = FcPtrListCreate (FcDestroyAsRuleSet);
     if (!config->rulesetList)
@@ -3048,7 +3024,7 @@ retry:
 
     if (sysroot)
     {
-	s = FcConfigRealPath(sysroot);
+	s = FcStrRealPath (sysroot);
 	if (!s)
 	    return;
     }

src/fcint.h

@@ -1345,6 +1345,9 @@ FcStrHashIgnoreCase (const FcChar8 *s);
 FcPrivate FcChar32
 FcStrHashIgnoreBlanksAndCase (const FcChar8 *s);
 
+FcPrivate FcChar8 *
+FcStrRealPath (const FcChar8 *path);
+
 FcPrivate FcChar8 *
 FcStrCanonFilename (const FcChar8 *s);
 

src/fcstr.c

@@ -1091,6 +1091,30 @@ FcStrBasename (const FcChar8 *file)
     return FcStrCopy (slash + 1);
 }
 
+FcChar8 *
+FcStrRealPath (const FcChar8 *path)
+{
+    char	resolved_name[FC_PATH_MAX+1];
+    char	*resolved_ret;
+
+    if (!path)
+	return NULL;
+
+#ifndef _WIN32
+    resolved_ret = realpath((const char *) path, resolved_name);
+#else
+    if (GetFullPathNameA ((LPCSTR) path, FC_PATH_MAX, resolved_name, NULL) == 0)
+    {
+        fprintf (stderr, "Fontconfig warning: GetFullPathNameA failed.\n");
+        return NULL;
+    }
+    resolved_ret = resolved_name;
+#endif
+    if (resolved_ret)
+	path = (FcChar8 *) resolved_ret;
+    return FcStrCopyFilename(path);
+}
+
 static FcChar8 *
 FcStrCanonAbsoluteFilename (const FcChar8 *s)
 {

src/fcxml.c

@@ -1318,9 +1318,16 @@ _get_real_paths_from_prefix(FcConfigParse *parse, const FcChar8 *path, const FcC
 	}
 	else if (FcStrCmp (prefix, (const FcChar8 *) "relative") == 0)
 	{
-	    parent = FcStrDirname (parse->name);
+	    FcChar8 *p = FcStrRealPath (parse->name);
-	    if (!parent)
+
+	    if (!p)
 		return NULL;
+	    parent = FcStrDirname (p);
+	    if (!parent)
+	    {
+		free (p);
+		return NULL;
+	    }
 	}
     }
 #ifndef _WIN32