misc: Add two scripts to help debug things

This adds two new helper scripts that are good for debugging mgmt. Just
build and add `sigtee` to your ~/bin/ along with filter-golang-stack.py
and mgmt_debug.sh and use the later to call mgmt as you would normally.

For example, I might do:

$ mgmt_debug.sh ./mgmt run --tmp-prefix lang examples/lang/hello0.mcl

And if I kill it with ^\ then I'll get a filtered trace at the end in my
$PAGER (which is assumed to be `less`) and this should make my life
easier.

As a cool bonus, this means we use bash, python, and golang all
together!

misc/mgmt_debug.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+# This is a helper script to run mgmt and capture and filter stack traces. Any
+# time mgmt crashes with a trace, it will first be filtered, and then displayed
+# with `less`.
+
+f1=`mktemp /tmp/tmp.X'X'X`
+f2=`mktemp /tmp/tmp.X'X'X`
+
+# run the program until it ends
+# XXX: we need an --ignore-exit signal blocker too so we can ^\
+#$@ 2>&1 | tee --ignore-interrupts --ignore-exit "$f1"
+$@ 2>&1 | sigtee "$f1"
+
+# clean up when we're done
+function cleanup {
+	filter-golang-stack.py "$f1" > "$f2"
+	if [ $? -eq 0 ]; then
+		less "$f2"
+	fi
+	if [ "$1" = "--preserve" ]; then
+		echo "logged:"
+		echo "$f1"
+		echo "$f2"
+	else
+		rm "$f2"
+		rm "$f1"
+	fi
+
+}
+trap cleanup EXIT

misc/sigtee.go

@@ -0,0 +1,63 @@
+// Signal tee
+// Copyright (C) 2013-2020+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// This program works exactly like the `tee` program, if it was invoked with an
+// implicit --ignore-interrupts argument, and if it also had an --ignore-quit
+// argument. These are needed so that it doesn't exit prematurely when called as
+// a receiving member of a shell pipeline. This is needed so that a ^C or ^\ can
+// cause the sending process to shutdown and relay its data into the tee. Sadly,
+// the venerable `tee` program can't currently ignore the QUIT signal.
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"os/signal"
+	"syscall"
+)
+
+func main() {
+	// TODO: Add better argv parsing and implement explicit flags for
+	// --ignore-interrupts argument, and --ignore-quit so that it's cleaner.
+	if len(os.Args) != 2 {
+		fmt.Fprintf(os.Stderr, "usage: <STDIN> | %s <FILE>\n", os.Args[0])
+		os.Exit(1)
+		return
+	}
+	filename := os.Args[1]
+
+	// Make sure we ignore ^C and ^\ when run in a shell pipe.
+	signal.Ignore(os.Interrupt, syscall.SIGQUIT) // TODO: add os.Kill ?
+
+	f, err := os.Create(filename)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "can't write to: %s\n", filename)
+		os.Exit(1)
+		return
+	}
+	defer f.Close()
+
+	writer := io.MultiWriter(os.Stdout, f) // tee !
+
+	_, err = io.Copy(writer, os.Stdin)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "copy error: %w\n", err)
+		os.Exit(1)
+		return
+	}
+}