Allow overwriting media files of dependencies (#10752)

doc/lua_api.txt

@@ -256,6 +256,9 @@ Subfolders with names starting with `_` or `.` are ignored.
 If a subfolder contains a media file with the same name as a media file
 in one of its parents, the parent's file is used.
 
+Although it is discouraged, a mod can overwrite a media file of any mod that it
+depends on by supplying a file with an equal name.
+
 Naming conventions
 ------------------
 

games/devtest/mods/basenodes/textures/info.txt

@@ -0,0 +1,7 @@
+
+The dirt_with_grass folder is for testing loading textures from subfolders.
+If it works correctly, the default_grass_side.png file in the folder is used but
+default_grass.png is not overwritten by the file in the folder.
+
+default_dirt.png should be overwritten by the default_dirt.png in the unittests
+mod which depends on basenodes.

games/devtest/mods/unittests/mod.conf

@@ -1,2 +1,3 @@
 name = unittests
 description = Adds automated unit tests for the engine
+depends = basenodes

src/server/mods.cpp

@@ -98,7 +98,8 @@ void ServerModManager::getModNames(std::vector<std::string> &modlist) const
 
 void ServerModManager::getModsMediaPaths(std::vector<std::string> &paths) const
 {
-	for (const ModSpec &spec : m_sorted_mods) {
+	for (auto it = m_sorted_mods.crbegin(); it != m_sorted_mods.crend(); it++) {
+		const ModSpec &spec = *it;
 		fs::GetRecursiveDirs(paths, spec.path + DIR_DELIM + "textures");
 		fs::GetRecursiveDirs(paths, spec.path + DIR_DELIM + "sounds");
 		fs::GetRecursiveDirs(paths, spec.path + DIR_DELIM + "media");

src/server/mods.h

@@ -42,5 +42,13 @@ class ServerModManager : public ModConfiguration
 	void loadMods(ServerScripting *script);
 	const ModSpec *getModSpec(const std::string &modname) const;
 	void getModNames(std::vector<std::string> &modlist) const;
+	/**
+	 * Recursively gets all paths of mod folders that can contain media files.
+	 *
+	 * Result is ordered in descending priority, ie. files from an earlier path
+	 * should not be replaced by files from a latter one.
+	 *
+	 * @param paths result vector
+	 */
 	void getModsMediaPaths(std::vector<std::string> &paths) const;
 };