record all plugin panics, and print on main exit

Create a logger that will record any apparent crash output for later
processing.

If the cli command returns with a non-zero exit status, check for any
recorded crashes and add those to the output.

internal/logging/panic_test.go

@@ -0,0 +1,51 @@
+package logging
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestPanicRecorder(t *testing.T) {
+	rec := panics.registerPlugin("test")
+
+	output := []string{
+		"panic: test",
+		"  stack info",
+	}
+
+	for _, line := range output {
+		rec(line)
+	}
+
+	expected := fmt.Sprintf(pluginPanicOutput, "test", strings.Join(output, "\n"))
+
+	res := PluginPanics()
+	if len(res) == 0 {
+		t.Fatal("no output")
+	}
+
+	if res[0] != expected {
+		t.Fatalf("expected: %q\ngot: %q", expected, res[0])
+	}
+}
+
+func TestPanicLimit(t *testing.T) {
+	rec := panics.registerPlugin("test")
+
+	rec("panic: test")
+
+	for i := 0; i < 200; i++ {
+		rec(fmt.Sprintf("LINE: %d", i))
+	}
+
+	res := PluginPanics()
+	// take the extra content into account
+	max := strings.Count(pluginPanicOutput, "\n") + panics.maxLines
+	for _, out := range res {
+		found := strings.Count(out, "\n")
+		if found > max {
+			t.Fatalf("expected no more than %d lines, got: %d", max, found)
+		}
+	}
+}