time: fix repetitive time.now().local().local().local() offsetting the time further and further (#13861)

vlib/time/time.c.v

@@ -117,5 +117,9 @@ fn convert_ctime(t C.tm, microsecond int) Time {
 		second: t.tm_sec
 		microsecond: microsecond
 		unix: make_unix_time(t)
+		// for the actual code base when we
+		// call convert_ctime, it is always
+		// when we manage the local time.
+		is_local: true
 	}
 }

vlib/time/time.v

@@ -45,6 +45,7 @@ pub:
 	second      int
 	microsecond int
 	unix        i64
+	is_local    bool // used to make time.now().local().local() == time.now().local()
 }
 
 // FormatDelimiter contains different time formats.
@@ -348,7 +349,7 @@ pub fn (d Duration) str() string {
 
 // offset returns time zone UTC offset in seconds.
 pub fn offset() int {
-	t := now()
+	t := utc()
 	local := t.local()
 	return int(local.unix - t.unix)
 }

vlib/time/time_nix.c.v

@@ -20,7 +20,8 @@ struct C.tm {
 
 fn C.timegm(&C.tm) C.time_t
 
-// fn C.gmtime_r(&tm, &gbuf)
+// prefering localtime_r over the localtime because
+// from docs localtime_r is thread safe,
 fn C.localtime_r(t &C.time_t, tm &C.tm)
 
 fn make_unix_time(t C.tm) i64 {
@@ -29,6 +30,9 @@ fn make_unix_time(t C.tm) i64 {
 
 // local returns t with the location set to local time.
 pub fn (t Time) local() Time {
+	if t.is_local {
+		return t
+	}
 	loc_tm := C.tm{}
 	C.localtime_r(voidptr(&t.unix), &loc_tm)
 	return convert_ctime(loc_tm, t.microsecond)

vlib/time/time_test.v

@@ -254,3 +254,12 @@ fn test_since() {
 	d2 := time.since(t1)
 	assert d2 >= 40_000_000
 }
+
+// issue relate https://github.com/vlang/v/issues/13828
+// problem: the local method add 2h on the time in a Linux machine
+// the other machine are not tested in a local env
+fn test_recursive_local_call() {
+	now_tm := time.now()
+	assert now_tm.str() == now_tm.local().str()
+	assert now_tm.local().str() == now_tm.local().local().str()
+}

vlib/time/time_windows.c.v

@@ -104,6 +104,7 @@ pub fn (t Time) local() Time {
 		hour: u16(t.hour)
 		minute: u16(t.minute)
 		second: u16(t.second)
+		millisecond: u16(t.microsecond / 1000)
 	}
 	st_local := SystemTime{}
 	C.SystemTimeToTzSpecificLocalTime(voidptr(0), &st_utc, &st_local)