sys/error: handle errors.Is for common context use-cases (#1313)

Signed-off-by: Alan Braithwaite <alan@runreveal.com>

sys/error.go

@@ -73,5 +73,11 @@ func (e *ExitError) Is(err error) bool {
 	if target, ok := err.(*ExitError); ok {
 		return e.exitCode == target.exitCode
 	}
+	if e.exitCode == ExitCodeContextCanceled && err == context.Canceled {
+		return true
+	}
+	if e.exitCode == ExitCodeDeadlineExceeded && err == context.DeadlineExceeded {
+		return true
+	}
 	return false
 }

sys/error_test.go

@@ -1,6 +1,7 @@
 package sys
 
 import (
+	"context"
 	"errors"
 	"testing"
 
@@ -55,11 +56,13 @@ func TestExitError_Error(t *testing.T) {
 		err := NewExitError(ExitCodeDeadlineExceeded)
 		require.Equal(t, ExitCodeDeadlineExceeded, err.ExitCode())
 		require.EqualError(t, err, "module closed with context deadline exceeded")
+		require.ErrorIs(t, err, context.DeadlineExceeded, "exit code context deadline exceeded should work")
 	})
 	t.Run("cancel", func(t *testing.T) {
 		err := NewExitError(ExitCodeContextCanceled)
 		require.Equal(t, ExitCodeContextCanceled, err.ExitCode())
 		require.EqualError(t, err, "module closed with context canceled")
+		require.ErrorIs(t, err, context.Canceled, "exit code context canceled should work")
 	})
 	t.Run("normal", func(t *testing.T) {
 		err := NewExitError(123)