fix: propagate validator errors from empty bool sources

flag_empty_bool_validator_test.go

@@ -0,0 +1,80 @@
+package cli_test
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	cli "github.com/urfave/cli/v3"
+)
+
+func TestBoolFlagEmptySourceRunsValidator(t *testing.T) {
+	for _, sourceKind := range []string{"env", "file"} {
+		for _, sourceValue := range []string{"", "false", "true"} {
+			for _, override := range []bool{false, true} {
+				t.Run(sourceKind+"/"+sourceValue+"/override="+map[bool]string{false: "no", true: "yes"}[override], func(t *testing.T) {
+					var sources cli.ValueSourceChain
+					if sourceKind == "env" {
+						t.Setenv("CLI_BOOL_VALIDATOR_TEST", sourceValue)
+						sources = cli.EnvVars("CLI_BOOL_VALIDATOR_TEST")
+					} else {
+						path := filepath.Join(t.TempDir(), "enabled")
+						if err := os.WriteFile(path, []byte(sourceValue), 0o600); err != nil {
+							t.Fatal(err)
+						}
+						sources = cli.Files(path)
+					}
+					calls := 0
+					actionRan := false
+					flagActionRan := false
+					destination := true
+					rejected := errors.New("enabled must be true")
+					flag := &cli.BoolFlag{
+						Name: "enabled", Value: true, Destination: &destination, Sources: sources,
+						Validator: func(value bool) error {
+							calls++
+							if !value {
+								return rejected
+							}
+							return nil
+						},
+						Action: func(context.Context, *cli.Command, bool) error { flagActionRan = true; return nil },
+					}
+					cmd := &cli.Command{
+						Name: "test", Writer: io.Discard, ErrWriter: io.Discard,
+						Flags:  []cli.Flag{flag},
+						Action: func(context.Context, *cli.Command) error { actionRan = true; return nil },
+					}
+					args := []string{"test"}
+					if override {
+						args = append(args, "--enabled=true")
+					}
+					err := cmd.Run(context.Background(), args)
+					wantError := sourceValue != "true" && !override
+					if wantError {
+						if err == nil || !strings.Contains(err.Error(), rejected.Error()) {
+							t.Errorf("Run() error = %v, want validation error", err)
+						}
+						if actionRan || flagActionRan {
+							t.Errorf("actions ran after rejected source: command=%v flag=%v", actionRan, flagActionRan)
+						}
+					} else {
+						if err != nil {
+							t.Fatal(err)
+						}
+						if !actionRan || !flagActionRan || !destination || !flag.IsSet() {
+							t.Errorf("accepted source: action=%v flagAction=%v destination=%v IsSet=%v", actionRan, flagActionRan, destination, flag.IsSet())
+						}
+					}
+					if calls != 1 {
+						t.Errorf("validator calls = %d, want 1", calls)
+					}
+				})
+			}
+		}
+	}
+}

flag_impl.go

@@ -155,15 +155,14 @@ func (f *FlagBase[T, C, V]) PostParse() error {
 				continue
 			}
 
-			if val != "" || kind == reflect.String {
-				if err := f.Set(f.Name, val); err != nil {
-					return fmt.Errorf(
-						"could not parse %[1]q as %[2]T value from %[3]s for flag %[4]s: %[5]s",
-						val, f.Value, source, f.Name, err,
-					)
-				}
-			} else {
-				_ = f.Set(f.Name, "false")
+			if val == "" && kind == reflect.Bool {
+				val = "false"
+			}
+			if err := f.Set(f.Name, val); err != nil {
+				return fmt.Errorf(
+					"could not parse %[1]q as %[2]T value from %[3]s for flag %[4]s: %[5]s",
+					val, f.Value, source, f.Name, err,
+				)
 			}
 
 			f.hasBeenSet = true