Add oneofci validator (oneof case insensitive) (#1321)

## Fixes Or Enhances

- Adds oneofci, a case insensitive version of oneof
- resolves #840

**Make sure that you've checked the boxes below before you submit PR:**
- [ X] Tests exist or have been written that cover this particular
change.

@go-playground/validator-maintainers

Author: miscalibrated

baked_in.go

@@ -205,6 +205,7 @@ var (
 		"fqdn":                          isFQDN,
 		"unique":                        isUnique,
 		"oneof":                         isOneOf,
+		"oneofci":                       isOneOfCI,
 		"html":                          isHTML,
 		"html_encoded":                  isHTMLEncoded,
 		"url_encoded":                   isURLEncoded,
@@ -299,6 +300,23 @@ func isOneOf(fl FieldLevel) bool {
 	return false
 }
 
+// isOneOfCI is the validation function for validating if the current field's value is one of the provided string values (case insensitive).
+func isOneOfCI(fl FieldLevel) bool {
+	vals := parseOneOfParam2(fl.Param())
+	field := fl.Field()
+
+	if field.Kind() != reflect.String {
+		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
+	}
+	v := field.String()
+	for _, val := range vals {
+		if strings.EqualFold(val, v) {
+			return true
+		}
+	}
+	return false
+}
+
 // isUnique is the validation function for validating if each array|slice|map value is unique
 func isUnique(fl FieldLevel) bool {
 	field := fl.Field()

doc.go

@@ -495,6 +495,13 @@ the target string between single quotes. Kind of like an 'enum'.
 	       oneof='red green' 'blue yellow'
 	       oneof=5 7 9
 
+# One Of Case Insensitive
+
+Works the same as oneof but is case insensitive and therefore only accepts strings.
+
+	Usage: oneofci=red green
+	       oneofci='red green' 'blue yellow'
+
 # Greater Than
 
 For numbers, this will ensure that the value is greater than the

validator_test.go

@@ -5680,6 +5680,82 @@ func TestOneOfValidation(t *testing.T) {
 	}, "Bad field type float64")
 }
 
+func TestOneOfCIValidation(t *testing.T) {
+	validate := New()
+
+	passSpecs := []struct {
+		f interface{}
+		t string
+	}{
+		{f: "red", t: "oneofci=RED GREEN"},
+		{f: "RED", t: "oneofci=red green"},
+		{f: "red", t: "oneofci=red green"},
+		{f: "RED", t: "oneofci=RED GREEN"},
+		{f: "green", t: "oneofci=red green"},
+		{f: "red green", t: "oneofci='red green' blue"},
+		{f: "blue", t: "oneofci='red green' blue"},
+		{f: "GREEN", t: "oneofci=Red Green"},
+		{f: "ReD", t: "oneofci=RED GREEN"},
+		{f: "gReEn", t: "oneofci=rEd GrEeN"},
+		{f: "RED GREEN", t: "oneofci='red green' blue"},
+		{f: "red Green", t: "oneofci='RED GREEN' Blue"},
+		{f: "Red green", t: "oneofci='Red Green' BLUE"},
+		{f: "rEd GrEeN", t: "oneofci='ReD gReEn' BlUe"},
+		{f: "BLUE", t: "oneofci='Red Green' BLUE"},
+		{f: "BlUe", t: "oneofci='RED GREEN' Blue"},
+		{f: "bLuE", t: "oneofci='red green' BLUE"},
+	}
+
+	for _, spec := range passSpecs {
+		t.Logf("%#v", spec)
+		errs := validate.Var(spec.f, spec.t)
+		Equal(t, errs, nil)
+	}
+
+	failSpecs := []struct {
+		f interface{}
+		t string
+	}{
+		{f: "", t: "oneofci=red green"},
+		{f: "yellow", t: "oneofci=red green"},
+		{f: "green", t: "oneofci='red green' blue"},
+	}
+
+	for _, spec := range failSpecs {
+		t.Logf("%#v", spec)
+		errs := validate.Var(spec.f, spec.t)
+		AssertError(t, errs, "", "", "", "", "oneofci")
+	}
+
+	panicSpecs := []struct {
+		f interface{}
+		t string
+	}{
+		{f: 3.14, t: "oneofci=red green"},
+		{f: 5, t: "oneofci=red green"},
+		{f: uint(6), t: "oneofci=7"},
+		{f: int8(5), t: "oneofci=red green"},
+		{f: int16(5), t: "oneofci=red green"},
+		{f: int32(5), t: "oneofci=red green"},
+		{f: int64(5), t: "oneofci=red green"},
+		{f: uint(5), t: "oneofci=red green"},
+		{f: uint8(5), t: "oneofci=red green"},
+		{f: uint16(5), t: "oneofci=red green"},
+		{f: uint32(5), t: "oneofci=red green"},
+		{f: uint64(5), t: "oneofci=red green"},
+	}
+
+	panicCount := 0
+	for _, spec := range panicSpecs {
+		t.Logf("%#v", spec)
+		PanicMatches(t, func() {
+			_ = validate.Var(spec.f, spec.t)
+		}, fmt.Sprintf("Bad field type %T", spec.f))
+		panicCount++
+	}
+	Equal(t, panicCount, len(panicSpecs))
+}
+
 func TestBase32Validation(t *testing.T) {
 	validate := New()