signals/utils: always handle received signals

The changes in
https://github.com/docker/compose/commit/dcbf005fe4fa2b360b8dd013d6dedc4796c37602
fixed the "cancellable context" detection, and made it so that Compose
would conditionally set up signal handling when the context was already
not cancellable/when the plugin was running through the CLI, as we'd
introduced a mechanism into the CLI to signal plugins to exit through a
socket instead of handling signals themselves.

This had some (not noticed at the time) issues when running through the
CLI as, due to sharing a process group id with the parent CLI process,
when a user CTRL-Cs the CLI will notify the plugin via the socket but
the plugin process itself will also be signalled if attached to the TTY.
This impacted some Compose commands that don't set up signal handling -
so not `compose up`, but other commands would immediately quit instead
of getting some "graceful" cancelled output.

We initially attempted to address this "double notification" issue in
the CLI by executing plugins under a new pgid so that they wouldn't be
signalled, but that posed an issue with Buildx reading from the TTY,
(see: https://github.com/moby/moby/issues/47073) so we reverted the
process group id changes and ended at a temporary solution in
https://github.com/docker/cli/pull/4792 where the CLI will only notify
plugins via the socket when they are not already going to be signalled
(when attached to a TTY).

Due to this, plugins should always set up some signal handling, which
this commit implements.

Signed-off-by: Laura Brehm <[email protected]>

cmd/compose/compose.go

@@ -42,7 +42,6 @@ import (
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 
-	"github.com/docker/cli/cli-plugins/plugin"
 	"github.com/docker/compose/v2/cmd/formatter"
 	"github.com/docker/compose/v2/pkg/api"
 	"github.com/docker/compose/v2/pkg/compose"
@@ -74,20 +73,17 @@ type CobraCommand func(context.Context, *cobra.Command, []string) error
 // AdaptCmd adapt a CobraCommand func to cobra library
 func AdaptCmd(fn CobraCommand) func(cmd *cobra.Command, args []string) error {
 	return func(cmd *cobra.Command, args []string) error {
-		ctx := cmd.Context()
-		contextString := fmt.Sprintf("%s", ctx)
-		if !strings.Contains(contextString, ".WithCancel") || plugin.RunningStandalone() { // need to handle cancel
-			cancellableCtx, cancel := context.WithCancel(cmd.Context())
-			ctx = cancellableCtx
-			s := make(chan os.Signal, 1)
-			signal.Notify(s, syscall.SIGTERM, syscall.SIGINT)
-			go func() {
-				<-s
-				cancel()
-				signal.Stop(s)
-				close(s)
-			}()
-		}
+		ctx, cancel := context.WithCancel(cmd.Context())
+
+		s := make(chan os.Signal, 1)
+		signal.Notify(s, syscall.SIGTERM, syscall.SIGINT)
+		go func() {
+			<-s
+			cancel()
+			signal.Stop(s)
+			close(s)
+		}()
+
 		err := fn(ctx, cmd, args)
 		var composeErr compose.Error
 		if api.IsErrCanceled(err) || errors.Is(ctx.Err(), context.Canceled) {