checker: require unsafe for free()

examples/sokol/particles/particles.v

@@ -47,8 +47,10 @@ fn (mut a App) init() {
 }
 
 fn (mut a App) cleanup() {
+	unsafe {
 		a.ps.free()
 	}
+}
 
 fn (mut a App) run() {
 	title := 'V Particle Example'

examples/tcp_echo_server.v

@@ -26,8 +26,10 @@ fn handle_client(mut socket net.TcpConn) {
 	eprintln('> new client: $client_addr')
 	mut reader := io.new_buffered_reader(reader: socket)
 	defer {
+		unsafe {
 			reader.free()
 		}
+	}
 	socket.write_string('server: hello\n') or { return }
 	for {
 		received_line := reader.read_line() or { return }

examples/term.ui/pong.v

@@ -470,8 +470,10 @@ fn frame(x voidptr) {
 
 fn cleanup(x voidptr) {
 	mut app := &App(x)
+	unsafe {
 		app.free()
 	}
+}
 
 fn fail(error string) {
 	eprintln(error)

vlib/clipboard/clipboard.v

@@ -23,8 +23,10 @@ pub fn (mut cb Clipboard) clear_all() {
 
 // destroy destroys the clipboard and frees its resources.
 pub fn (mut cb Clipboard) destroy() {
+	unsafe {
 		cb.free()
 	}
+}
 
 // check_ownership returns `true` if the `Clipboard` has the content ownership.
 pub fn (cb Clipboard) check_ownership() bool {

vlib/net/http/server.v

@@ -88,8 +88,10 @@ fn (mut s Server) parse_and_respond(mut conn net.TcpConn) {
 
 	mut reader := io.new_buffered_reader(reader: conn)
 	defer {
+		unsafe {
 			reader.free()
 		}
+	}
 	req := parse_request(mut reader) or {
 		$if debug {
 			// only show in debug mode to prevent abuse

vlib/v/checker/fn.v

@@ -1164,6 +1164,10 @@ pub fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 			return ast.int_type
 		}
 	}
+	if !c.is_builtin_mod && !c.inside_unsafe && method_name == 'free' {
+		c.warn('manual memory management with `free()` is only allowed in unsafe code',
+			node.pos)
+	}
 	if left_type == ast.void_type {
 		// No need to print this error, since this means that the variable is unknown,
 		// and there already was an error before.

vlib/v/preludes/test_runner.v

@@ -100,8 +100,8 @@ mut:
 pub fn change_test_runner(x &TestRunner) {
 	pobj := unsafe { &C.main__TestRunner(&test_runner)._object }
 	if pobj != 0 {
-		test_runner.free()
 		unsafe {
+			test_runner.free()
 			(&C.main__TestRunner(&test_runner))._object = nil
 		}
 	}

vlib/vweb/vweb.v

@@ -442,8 +442,10 @@ fn handle_conn<T>(mut conn net.TcpConn, mut app T, routes map[string]Route) {
 
 	mut reader := io.new_buffered_reader(reader: conn)
 	defer {
+		unsafe {
 			reader.free()
 		}
+	}
 
 	page_gen_start := time.ticks()