Error while using time.Parse when timezone and offset are together - date

Question

I have the following code :
package main
import (
"fmt"
"time"
"log"
)
func main() {
date, err := time.Parse("Monday, 2 January 2006 15:04:05 PM MST-07:00" ,"Thursday, 17 August 2020 13:20:00 PM GMT+08:00")
if err != nil {
log.Fatal(err.Error())
}
fmt.Println(date)
}
And it fails with the following error :
2009/11/10 23:00:00 parsing time "Thursday, 17 August 2020 13:20:00 PM
GMT+08:00" as "Monday, 2 January 2006 15:04:05 PM MST-07:00": cannot
parse ":00" as "-07:00"
But it succeeds if I separate MST-07:00 with a space as : "MST -07:00" in both layout sample and actual string.
What am I doing wrong?

Answer 1

GMT times undergo special handling by time.Parse. The signed offset for GMT in the value must be in the range -23 through +23 excluding zero, and may not include a colon. The layout should just specify MST without an offset.
For example:
package main
import (
"fmt"
"log"
"time"
)
func main() {
for _, ts := range []string{
"Thursday, 17 August 2020 13:20:00 PM GMT",
"Thursday, 17 August 2020 13:20:00 PM GMT+2",
"Thursday, 17 August 2020 13:20:00 PM GMT-2",
} {
date, err := time.Parse("Monday, 2 January 2006 15:04:05 PM MST", ts)
if err != nil {
log.Fatal(err.Error())
}
fmt.Println(date)
}
}
yields the output:
crow#mac:tp$ ./example
2020-08-17 13:20:00 +0000 GMT
2020-08-17 15:20:00 +0200 GMT+2
2020-08-17 11:20:00 -0200 GMT-2
An issue was raised for this a while back, and the outcome was (with reference to an example time string containing GMT+10:00):
The special handling of GMT, which is needed for other things, makes
it very difficult to know whether the +10:00 should be considered part
of the time zone or left alone to match the layout.
and so the issue was closed without proposed changes.