The Go Programming Language

5.9 Panic

Go’s type system catches many mistakes at compile time, but others, like an out-of-bounds array access or nil pointer dereference, require checks at run time. When the Go runtime detects these mistakes, it panics.

During a typical panic, normal execution stops, all deferred function calls in that goroutine are executed, and the program crashes with a log message. This log message includes the panic value, which is usually an error message of some sort, and, for each goroutine, a stack trace showing the stack of function calls that were active at the time of the panic. This log message often has enough information to diagnose the root cause of the problem without running the program again, so it should always be included in a bug ...