feat: support flags with array types

Basic array types are supported:
- strings
- ints
- floats
- bools

Author: arikkfir

flag_def.go

@@ -2,10 +2,12 @@ package command
 
 import (
 	"cmp"
+	"encoding/csv"
 	"errors"
 	"fmt"
 	"reflect"
 	"strconv"
+	"strings"
 )
 
 type ErrInvalidValue struct {
@@ -104,6 +106,47 @@ func (fd *flagDef) setValue(sv string) error {
 			}
 		case reflect.String:
 			fv.SetString(sv)
+		case reflect.Slice:
+			r := csv.NewReader(strings.NewReader(sv))
+			r.LazyQuotes = true
+			r.TrimLeadingSpace = true
+			rec, err := r.Read()
+			if err != nil {
+				return &ErrInvalidValue{Cause: err, Value: sv, Flag: fd.Name}
+			}
+
+			inValue := reflect.ValueOf(rec)
+
+			targetType := fv.Type().Elem()
+			outSlice := reflect.MakeSlice(reflect.SliceOf(targetType), inValue.Len(), inValue.Len())
+			for i, inElem := range rec {
+				var outElem interface{}
+				var err error
+				switch targetType.Kind() {
+				case reflect.String:
+					outElem = inElem
+				case reflect.Int:
+					outElem, err = strconv.Atoi(inElem)
+				case reflect.Float32:
+					if f64, parseErr := strconv.ParseFloat(inElem, 32); parseErr == nil {
+						outElem = float32(f64)
+					} else {
+						outElem = nil
+						err = parseErr
+					}
+				case reflect.Float64:
+					outElem, err = strconv.ParseFloat(inElem, 64)
+				case reflect.Bool:
+					outElem, err = strconv.ParseBool(inElem)
+				default:
+					return fmt.Errorf("%w: field kind is '%s'", errors.ErrUnsupported, fv.Kind())
+				}
+				if err != nil {
+					return &ErrInvalidValue{Cause: err, Value: inElem, Flag: fd.Name}
+				}
+				outSlice.Index(i).Set(reflect.ValueOf(outElem).Convert(outSlice.Type().Elem()))
+			}
+			fv.Set(outSlice)
 		default:
 			return fmt.Errorf("%w: field kind is '%s'", errors.ErrUnsupported, fv.Kind())
 		}

flag_set.go

@@ -253,6 +253,17 @@ func (fs *flagSet) readFlagFromField(fieldValue reflect.Value, structField refle
 	case reflect.String:
 		fd.HasValue = true
 		fd.DefaultValue = fieldValue.String()
+	case reflect.Slice:
+		fd.HasValue = true
+		var defaultValues []string
+		for i := 0; i < fieldValue.Len(); i++ {
+			defaultValues = append(defaultValues, fieldValue.Index(i).String())
+		}
+		if defaultValues != nil {
+			fd.DefaultValue = strings.Join(defaultValues, ",")
+		} else {
+			fd.DefaultValue = ""
+		}
 	default:
 		// Unsupported flag field type
 		return fmt.Errorf("unsupported field type: %s", fieldValue.Kind())

flag_set_test.go

@@ -609,6 +609,30 @@ func TestNewFlagSet(t *testing.T) {
 	}
 }
 
+func TestFlagSetWithArrays(t *testing.T) {
+	t.Parallel()
+
+	config := &struct {
+		MyArray []string `flag:"true" `
+	}{MyArray: []string{"v1", "v2"}}
+
+	valueOfConfig := reflect.ValueOf(config)
+	fs, err := newFlagSet(nil, valueOfConfig)
+	With(t).Verify(err).Will(BeNil()).OrFail()
+	if len(fs.flags) != 1 {
+		t.Fatalf("Expected 1 flag, got %d", len(fs.flags))
+	}
+
+	f := fs.flags[0]
+	With(t).Verify(f.Name).Will(EqualTo("my-array")).OrFail()
+	With(t).Verify(f.EnvVarName).Will(BeNil()).OrFail()
+	With(t).Verify(f.HasValue).Will(EqualTo(true)).OrFail()
+	With(t).Verify(f.ValueName).Will(BeNil()).OrFail()
+	With(t).Verify(f.Description).Will(BeNil()).OrFail()
+	With(t).Verify(f.Required).Will(BeNil()).OrFail()
+	With(t).Verify(f.DefaultValue).Will(EqualTo("v1,v2")).OrFail()
+}
+
 func TestFlagSetGetMergedFlagDefs(t *testing.T) {
 	t.Parallel()
 	type testCase struct {
@@ -891,6 +915,51 @@ func TestFlagSetApply(t *testing.T) {
 		expectedError        string
 	}
 	testCases := map[string]testCase{
+		"all types are supported from CLI": {
+			config: &struct {
+				String       string    `flag:"true"`
+				Int          int       `flag:"true"`
+				Float32      float32   `flag:"true"`
+				Float64      float64   `flag:"true"`
+				Bool         bool      `flag:"true"`
+				StringArray  []string  `flag:"true"`
+				IntArray     []int     `flag:"true"`
+				Float32Array []float32 `flag:"true"`
+				Float64Array []float64 `flag:"true"`
+			}{},
+			args: []string{
+				"--string", "s1",
+				"--int", "9",
+				"--float32", "1.2",
+				"--float64", "123.456",
+				"--bool",
+				"--string-array", `sa1,"s with space",sa3,,,"`,
+				"--int-array", `1,2,3,5,8`,
+				"--float32array", `1.2,3.4,5.6`,
+				"--float64array", `11.22,33.44,55.66`,
+			},
+			expectedConfig: &struct {
+				String       string    `flag:"true"`
+				Int          int       `flag:"true"`
+				Float32      float32   `flag:"true"`
+				Float64      float64   `flag:"true"`
+				Bool         bool      `flag:"true"`
+				StringArray  []string  `flag:"true"`
+				IntArray     []int     `flag:"true"`
+				Float32Array []float32 `flag:"true"`
+				Float64Array []float64 `flag:"true"`
+			}{
+				String:       "s1",
+				Int:          9,
+				Float32:      1.2,
+				Float64:      123.456,
+				Bool:         true,
+				StringArray:  []string{"sa1", "s with space", "sa3", "", "", ""},
+				IntArray:     []int{1, 2, 3, 5, 8},
+				Float32Array: []float32{1.2, 3.4, 5.6},
+				Float64Array: []float64{11.22, 33.44, 55.66},
+			},
+		},
 		"CLI overrides environment variables": {
 			config: &struct {
 				F1 string `name:"my-field1"`