logging: added a log on panic

Since panics still regularly "destroy" the terminal, it is hard to get a
stack trace for panics you do not anticipate. This commit adds a panic
handler that automatically creates a logfile inside the current working
directory.

It has to be added to every goroutine that is started and will repair
the terminal on a panic.

Signed-off-by: Moritz Poldrack <git@moritz.sh>
Acked-by: Robin Jarry <robin@jarry.cc>

logging/panic-logger.go

@@ -0,0 +1,56 @@
+package logging
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"runtime/debug"
+	"strings"
+	"time"
+)
+
+var UICleanup = func() {}
+
+// PanicHandler tries to restore the terminal. A stack trace is written to
+// aerc-crash.log and then passed on if a panic occurs.
+func PanicHandler() {
+	r := recover()
+
+	if r == nil {
+		return
+	}
+
+	UICleanup()
+
+	filename := time.Now().Format("/tmp/aerc-crash-20060102-150405.log")
+
+	panicLog, err := os.OpenFile(filename, os.O_SYNC|os.O_APPEND|os.O_CREATE|os.O_WRONLY|os.O_EXCL, 0o600)
+	if err != nil {
+		// we tried, not possible. bye
+		panic(r)
+	}
+	defer panicLog.Close()
+
+	outputs := io.MultiWriter(panicLog, os.Stderr)
+
+	// if any error happens here, we do not care.
+	fmt.Fprintln(panicLog, strings.Repeat("#", 80))
+	fmt.Fprint(panicLog, strings.Repeat(" ", 34))
+	fmt.Fprintln(panicLog, "PANIC CAUGHT!")
+	fmt.Fprint(panicLog, strings.Repeat(" ", 24))
+	fmt.Fprintln(panicLog, time.Now().Format("2006-01-02T15:04:05.000000-0700"))
+	fmt.Fprintln(panicLog, strings.Repeat("#", 80))
+	fmt.Fprintf(outputs, "%s\n", panicMessage)
+	fmt.Fprintf(panicLog, "Error: %v\n\n", r)
+	panicLog.Write(debug.Stack())
+	fmt.Fprintf(os.Stderr, "\nThis error was also written to: %s\n", filename)
+	panic(r)
+}
+
+const panicMessage = `
+aerc has encountered a critical error and has terminated. Please help us fixing
+this by sending this log and the steps to reproduce the crash to:
+~rjarry/aerc-devel@lists.sr.ht
+
+Thank you
+`