fix: propagate validator errors from empty bool sources

flag_empty_bool_validator_test.go

@@ -0,0 +1,95 @@
+package cli_test
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	cli "github.com/urfave/cli/v3"
+)
+
+func TestBoolFlagEmptySourceRunsValidator(t *testing.T) {
+	tests := []struct {
+		name        string
+		sourceKind  string
+		sourceValue string
+		override    bool
+		wantError   bool
+	}{
+		{name: "env/empty", sourceKind: "env", sourceValue: "", wantError: true},
+		{name: "env/empty/override", sourceKind: "env", sourceValue: "", override: true},
+		{name: "env/false", sourceKind: "env", sourceValue: "false", wantError: true},
+		{name: "env/false/override", sourceKind: "env", sourceValue: "false", override: true},
+		{name: "env/true", sourceKind: "env", sourceValue: "true"},
+		{name: "env/true/override", sourceKind: "env", sourceValue: "true", override: true},
+		{name: "file/empty", sourceKind: "file", sourceValue: "", wantError: true},
+		{name: "file/empty/override", sourceKind: "file", sourceValue: "", override: true},
+		{name: "file/false", sourceKind: "file", sourceValue: "false", wantError: true},
+		{name: "file/false/override", sourceKind: "file", sourceValue: "false", override: true},
+		{name: "file/true", sourceKind: "file", sourceValue: "true"},
+		{name: "file/true/override", sourceKind: "file", sourceValue: "true", override: true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var sources cli.ValueSourceChain
+			if tt.sourceKind == "env" {
+				t.Setenv("CLI_BOOL_VALIDATOR_TEST", tt.sourceValue)
+				sources = cli.EnvVars("CLI_BOOL_VALIDATOR_TEST")
+			} else {
+				path := filepath.Join(t.TempDir(), "enabled")
+				if err := os.WriteFile(path, []byte(tt.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 tt.override {
+				args = append(args, "--enabled=true")
+			}
+			err := cmd.Run(context.Background(), args)
+			if tt.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