Create CACHEDIR.TAG in path_cache (#14458)

src/porting.cpp

@@ -553,7 +553,8 @@ bool setSystemPaths()
 
 #endif
 
-void migrateCachePath()
+// Move cache folder from path_user to system cache location if possible.
+[[maybe_unused]] static void migrateCachePath()
 {
 	const std::string local_cache_path = path_user + DIR_DELIM + "cache";
 
@@ -573,6 +574,24 @@ void migrateCachePath()
 	}
 }
 
+// Create tag in cache folder according to <https://bford.info/cachedir/> spec
+static void createCacheDirTag()
+{
+	const auto path = path_cache + DIR_DELIM + "CACHEDIR.TAG";
+
+	if (fs::PathExists(path))
+		return;
+	fs::CreateAllDirs(path_cache);
+	std::ofstream ofs(path, std::ios::out | std::ios::binary);
+	if (!ofs.good())
+		return;
+	ofs << "Signature: 8a477f597d28d172789f06886806bc55\n"
+		"# This file is a cache directory tag automatically created by "
+		PROJECT_NAME_C ".\n"
+		"# For information about cache directory tags, see: "
+		"https://bford.info/cachedir/\n";
+}
+
 void initializePaths()
 {
 #if RUN_IN_PLACE
@@ -652,6 +671,8 @@ void initializePaths()
 	infostream << "Detected user path: " << path_user << std::endl;
 	infostream << "Detected cache path: " << path_cache << std::endl;
 
+	createCacheDirTag();
+
 #if USE_GETTEXT
 	bool found_localedir = false;
 #  ifdef STATIC_LOCALEDIR

src/porting.h

@@ -129,12 +129,6 @@ bool getCurrentExecPath(char *buf, size_t len);
 */
 std::string getDataPath(const char *subpath);
 
-/*
-	Move cache folder from path_user to the
-	system cache location if possible.
-*/
-void migrateCachePath();
-
 /*
 	Initialize path_*.
 */