os: add `signal_opt` and deprecate `signal` (#10005)

vlib/builtin/cfns.c.v

@@ -132,8 +132,6 @@ fn C.sigemptyset() int
 
 fn C.getcwd(buf &char, size size_t) &char
 
-fn C.signal(signal int, handlercb voidptr) voidptr
-
 [trusted]
 fn C.mktime() int
 

vlib/os/os_c.v

@@ -828,12 +828,6 @@ fn normalize_drive_letter(path string) string {
 	return path
 }
 
-// signal will assign `handler` callback to be called when `signum` signal is received.
-pub fn signal(signum int, handler voidptr) voidptr {
-	res := unsafe { C.signal(signum, handler) }
-	return res
-}
-
 // fork will fork the current system process and return the pid of the fork.
 pub fn fork() int {
 	mut pid := -1

vlib/os/signal.c.v

@@ -0,0 +1,58 @@
+module os
+
+#include <signal.h>
+
+pub enum Signal {
+	hup = 1
+	int
+	quit
+	ill
+	trap
+	abrt
+	bus
+	fpe
+	kill
+	usr1
+	segv
+	usr2
+	pipe
+	alrm
+	term
+	stkflt
+	chld
+	cont
+	stop
+	tstp
+	ttin
+	ttou
+	urg
+	xcpu
+	xfsz
+	vtalrm
+	prof
+	winch
+	poll
+	pwr
+	sys
+}
+
+type SignalHandler = fn (Signal)
+
+fn C.signal(signal int, handlercb SignalHandler) voidptr
+
+[deprecated: 'use os.signal_opt() instead']
+[deprecated_after: '2021-05-18']
+pub fn signal(signum int, handler voidptr) voidptr {
+	return voidptr(signal_opt(Signal(signum), handler) or { C.SIG_ERR })
+}
+
+// signal will assign `handler` callback to be called when `signum` signal is received.
+pub fn signal_opt(signum Signal, handler SignalHandler) ?SignalHandler {
+	C.errno = 0
+	prev_handler := C.signal(int(signum), handler)
+	if prev_handler == C.SIG_ERR {
+		// errno isn't correctly set on Windows, but EINVAL is this only possible value it can take anyway
+		return error_with_code(posix_get_error_msg(C.EINVAL), C.EINVAL)
+	}
+	return SignalHandler(prev_handler)
+}

vlib/os/signal_test.v

@@ -0,0 +1,35 @@
+import os
+
+fn former_handler(signal os.Signal) {
+	println('former_handler')
+	exit(0)
+}
+
+fn default_handler(signal os.Signal) {
+	println('default_handler')
+	exit(0)
+}
+
+fn test_signal_opt() {
+	os.signal_opt(.int, default_handler) or { assert false }
+}
+
+fn test_signal_opt_invalid_argument() {
+	// Can't register a signal on SIGKILL
+	if _ := os.signal_opt(.kill, default_handler) {
+		assert false
+	}
+	os.signal_opt(.kill, default_handler) or {
+		assert err.msg == 'Invalid argument'
+		assert err.code == 22
+	}
+}
+
+fn test_signal_opt_return_former_handler() {
+	func1 := os.signal_opt(.term, former_handler) or { panic('unexpected error') }
+	assert isnil(func1)
+	func2 := os.signal_opt(.term, default_handler) or { panic('unexpected error') }
+	assert !isnil(func2)
+	// this should work, but makes the CI fail because of a bug in clang -fsanitize=memory
+	// assert func2 == former_handler
+}

vlib/v/gen/c/cheaders.v

@@ -515,8 +515,6 @@ typedef int (*qsort_callback_func)(const void*, const void*);
 	#endif
 #endif
 
-//#include "fns.h"
-#include <signal.h>
 #include <stdarg.h> // for va_list
 
 //================================== GLOBALS =================================*/