Wire up ctx through system() (#119)

This wires up ctx (for when using ExecuteContext) through `system()` and
simplifies the error handling in the `system()` implementation a bit.

interp/io.go

@@ -187,8 +187,11 @@ func (p *interp) execShell(code string) *exec.Cmd {
 	executable := p.shellCommand[0]
 	args := p.shellCommand[1:]
 	args = append(args, code)
-	cmd := exec.Command(executable, args...)
-	return cmd
+	if p.checkCtx {
+		return exec.CommandContext(p.ctx, executable, args...)
+	} else {
+		return exec.Command(executable, args...)
+	}
 }
 
 // Get input Scanner to use for "getline" based on file name

interp/newexecute.go

@@ -144,7 +144,7 @@ func (p *Interpreter) ResetRand() {
 // system() won't be interrupted.
 func (p *Interpreter) ExecuteContext(ctx context.Context, config *Config) (int, error) {
 	p.interp.resetCore()
-	p.interp.checkCtx = ctx != context.Background()
+	p.interp.checkCtx = ctx != context.Background() && ctx != context.TODO()
 	p.interp.ctx = ctx
 	p.interp.ctxDone = ctx.Done()
 	p.interp.ctxOps = 0

interp/newexecute_test.go

@@ -138,6 +138,16 @@ func TestExecuteContextCancel(t *testing.T) {
 	}
 }
 
+func TestExecuteContextSystemTimeout(t *testing.T) {
+	interpreter := newInterp(t, `BEGIN { print system("sleep 4") }`)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Millisecond)
+	defer cancel()
+	_, err := interpreter.ExecuteContext(ctx, nil)
+	if !errors.Is(err, context.DeadlineExceeded) {
+		t.Fatalf("expected DeadlineExceeded error, got: %v", err)
+	}
+}
+
 func newInterp(t *testing.T, src string) *interp.Interpreter {
 	t.Helper()
 	prog, err := parser.ParseProgram([]byte(src), nil)

interp/vm.go

@@ -1071,22 +1071,17 @@ func (p *interp) callBuiltin(builtinOp compiler.BuiltinOp) error {
 		cmd.Stdout = p.output
 		cmd.Stderr = p.errorOutput
 		_ = p.flushAll() // ensure synchronization
-		err := cmd.Start()
-		var ret float64
+		err := cmd.Run()
+		ret := 0.0
 		if err != nil {
-			p.printErrorf("%s\n", err)
-			ret = -1
-		} else {
-			err = cmd.Wait()
-			if err != nil {
-				if exitErr, ok := err.(*exec.ExitError); ok {
-					ret = float64(exitErr.ProcessState.ExitCode())
-				} else {
-					p.printErrorf("unexpected error running command %q: %v\n", cmdline, err)
-					ret = -1
-				}
+			if p.checkCtx && p.ctx.Err() != nil {
+				return p.ctx.Err()
+			}
+			if exitErr, ok := err.(*exec.ExitError); ok {
+				ret = float64(exitErr.ProcessState.ExitCode())
 			} else {
-				ret = 0
+				p.printErrorf("%v\n", err)
+				ret = -1
 			}
 		}
 		p.replaceTop(num(ret))