Add optional Validate() error method

enumer.go

@@ -59,6 +59,16 @@ const altStringValuesMethod = `func (%[1]s) Values() []string {
 }
 `
 
+// Arguments to format are: [1]: type name
+const validateMethod = `// Validate returns an error if the value is not listed in the enum definition.
+func (i %[1]s) Validate() error {
+	if !i.IsA%[1]s() {
+		return fmt.Errorf("%%v is not a valid value for %[1]s values", i)
+	}
+	return nil
+}
+`
+
 func (g *Generator) buildAltStringValuesMethod(typeName string) {
 	g.Printf("\n")
 	g.Printf(altStringValuesMethod, typeName)
@@ -215,3 +225,7 @@ func (g *Generator) buildYAMLMethods(runs [][]Value, typeName string, runsThresh
 	// We rely on the %[1]sString method to provide typed errors when enabled
 	g.Printf(yamlMethods, typeName)
 }
+
+func (g *Generator) buildValidateMethod(typeName string) {
+	g.Printf(validateMethod, typeName)
+}

golden_test.go

@@ -10,7 +10,7 @@
 package main
 
 import (
-	"io/ioutil"
+	"io"
 	"os"
 	"path/filepath"
 	"strings"
@@ -76,6 +76,10 @@ var goldenLinecomment = []Golden{
 	{"dayWithLinecomment", linecommentIn},
 }
 
+var goldenValidateMethod = []Golden{
+	{name: "validate", input: dayIn},
+}
+
 var goldenTypedErrors = []Golden{
 	{"typedErrors", typedErrorsIn},
 }
@@ -327,48 +331,51 @@ const (
 
 func TestGolden(t *testing.T) {
 	for _, test := range golden {
-		runGoldenTest(t, test, false, false, false, false, false, false, true, "", "", false)
+		runGoldenTest(t, test, false, false, false, false, false, false, true, false, "", "", false)
 	}
 	for _, test := range goldenJSON {
-		runGoldenTest(t, test, true, false, false, false, false, false, false, "", "", false)
+		runGoldenTest(t, test, true, false, false, false, false, false, false, false, "", "", false)
 	}
 	for _, test := range goldenText {
-		runGoldenTest(t, test, false, false, false, true, false, false, false, "", "", false)
+		runGoldenTest(t, test, false, false, false, true, false, false, false, false, "", "", false)
 	}
 	for _, test := range goldenYAML {
-		runGoldenTest(t, test, false, true, false, false, false, false, false, "", "", false)
+		runGoldenTest(t, test, false, true, false, false, false, false, false, false, "", "", false)
 	}
 	for _, test := range goldenSQL {
-		runGoldenTest(t, test, false, false, true, false, false, false, false, "", "", false)
+		runGoldenTest(t, test, false, false, true, false, false, false, false, false, "", "", false)
 	}
 	for _, test := range goldenJSONAndSQL {
-		runGoldenTest(t, test, true, false, true, false, false, false, false, "", "", false)
+		runGoldenTest(t, test, true, false, true, false, false, false, false, false, "", "", false)
 	}
 	for _, test := range goldenGQLGen {
-		runGoldenTest(t, test, false, false, false, false, false, true, false, "", "", false)
+		runGoldenTest(t, test, false, false, false, false, false, true, false, false, "", "", false)
 	}
 	for _, test := range goldenTrimPrefix {
-		runGoldenTest(t, test, false, false, false, false, false, false, false, "Day", "", false)
+		runGoldenTest(t, test, false, false, false, false, false, false, false, false, "Day", "", false)
 	}
 	for _, test := range goldenTrimPrefixMultiple {
-		runGoldenTest(t, test, false, false, false, false, false, false, false, "Day,Night", "", false)
+		runGoldenTest(t, test, false, false, false, false, false, false, false, false, "Day,Night", "", false)
 	}
 	for _, test := range goldenWithPrefix {
-		runGoldenTest(t, test, false, false, false, false, false, false, false, "", "Day", false)
+		runGoldenTest(t, test, false, false, false, false, false, false, false, false, "", "Day", false)
 	}
 	for _, test := range goldenTrimAndAddPrefix {
-		runGoldenTest(t, test, false, false, false, false, false, false, false, "Day", "Night", false)
+		runGoldenTest(t, test, false, false, false, false, false, false, false, false, "Day", "Night", false)
 	}
 	for _, test := range goldenLinecomment {
-		runGoldenTest(t, test, false, false, false, false, true, false, false, "", "", false)
+		runGoldenTest(t, test, false, false, false, false, true, false, false, false, "", "", false)
+	}
+	for _, test := range goldenValidateMethod {
+		runGoldenTest(t, test, false, false, false, false, false, false, false, true, "", "", false)
 	}
 	for _, test := range goldenTypedErrors {
-		runGoldenTest(t, test, false, false, false, false, false, false, false, "", "", true)
+		runGoldenTest(t, test, false, false, false, false, false, false, false, false, "", "", true)
 	}
 }
 
 func runGoldenTest(t *testing.T, test Golden,
-	generateJSON, generateYAML, generateSQL, generateText, linecomment, generateGQLGen, generateValuesMethod bool,
+	generateJSON, generateYAML, generateSQL, generateText, linecomment, generateGQLGen, generateValuesMethod, generateIsValidMethod bool,
 	trimPrefix string, prefix string, useTypedErrors bool) {
 
 	var g Generator
@@ -397,7 +404,7 @@ func runGoldenTest(t *testing.T, test Golden,
 	if len(tokens) != 3 {
 		t.Fatalf("%s: need type declaration on first line", test.name)
 	}
-	g.generate(tokens[1], generateJSON, generateYAML, generateSQL, generateText, generateGQLGen, "noop", trimPrefix, prefix, linecomment, generateValuesMethod, useTypedErrors)
+	g.generate(tokens[1], generateJSON, generateYAML, generateSQL, generateText, generateGQLGen, "noop", trimPrefix, prefix, linecomment, generateValuesMethod, generateIsValidMethod, useTypedErrors)
 	got := string(g.format())
 	if got != loadGolden(test.name) {
 		// Use this to help build a golden text when changes are needed
@@ -416,7 +423,7 @@ func loadGolden(name string) string {
 		return ""
 	}
 	defer fh.Close()
-	b, err := ioutil.ReadAll(fh)
+	b, err := io.ReadAll(fh)
 	if err != nil {
 		return ""
 	}

stringer.go

@@ -51,6 +51,7 @@ var (
 	text            = flag.Bool("text", false, "if true, text marshaling methods will be generated. Default: false")
 	gqlgen          = flag.Bool("gqlgen", false, "if true, GraphQL marshaling methods for gqlgen will be generated. Default: false")
 	altValuesFunc   = flag.Bool("values", false, "if true, alternative string values method will be generated. Default: false")
+	validateFunc    = flag.Bool("validate", false, "if true, a `Validate() error` method will be generated. Default: false")
 	output          = flag.String("output", "", "output file name; default srcdir/<type>_string.go")
 	transformMethod = flag.String("transform", "noop", "enum item name transformation method. Default: noop")
 	trimPrefix      = flag.String("trimprefix", "", "transform each item name by removing a prefix or comma separated list of prefixes. Default: \"\"")
@@ -140,7 +141,7 @@ func main() {
 
 	// Run generate for each type.
 	for _, typeName := range typs {
-		g.generate(typeName, *json, *yaml, *sql, *text, *gqlgen, *transformMethod, *trimPrefix, *addPrefix, *linecomment, *altValuesFunc, *typedErrors)
+		g.generate(typeName, *json, *yaml, *sql, *text, *gqlgen, *transformMethod, *trimPrefix, *addPrefix, *linecomment, *altValuesFunc, *validateFunc, *typedErrors)
 	}
 
 	// Format the output.
@@ -420,7 +421,9 @@ func (g *Generator) prefixValueNames(values []Value, prefix string) {
 // generate produces the String method for the named type.
 func (g *Generator) generate(typeName string,
 	includeJSON, includeYAML, includeSQL, includeText, includeGQLGen bool,
-	transformMethod string, trimPrefix string, addPrefix string, lineComment bool, includeValuesMethod bool, useTypedErrors bool) {
+	transformMethod string, trimPrefix string, addPrefix string,
+	lineComment, includeValuesMethod, includeValidateFunc, useTypedErrors bool,
+) {
 	values := make([]Value, 0, 100)
 	for _, file := range g.pkg.files {
 		file.lineComment = lineComment
@@ -470,6 +473,9 @@ func (g *Generator) generate(typeName string,
 	if includeValuesMethod {
 		g.buildAltStringValuesMethod(typeName)
 	}
+	if includeValidateFunc {
+		g.buildValidateMethod(typeName)
+	}
 
 	g.buildNoOpOrderChangeDetect(runs, typeName)
 

testdata/validate.golden

@@ -0,0 +1,98 @@
+
+const _DayName = "MondayTuesdayWednesdayThursdayFridaySaturdaySunday"
+
+var _DayIndex = [...]uint8{0, 6, 13, 22, 30, 36, 44, 50}
+
+const _DayLowerName = "mondaytuesdaywednesdaythursdayfridaysaturdaysunday"
+
+func (i Day) String() string {
+	if i < 0 || i >= Day(len(_DayIndex)-1) {
+		return fmt.Sprintf("Day(%d)", i)
+	}
+	return _DayName[_DayIndex[i]:_DayIndex[i+1]]
+}
+
+// Validate returns an error if the value is not listed in the enum definition.
+func (i Day) Validate() error {
+	if !i.IsADay() {
+		return fmt.Errorf("%v is not a valid value for Day values", i)
+	}
+	return nil
+}
+
+// An "invalid array index" compiler error signifies that the constant values have changed.
+// Re-run the stringer command to generate them again.
+func _DayNoOp() {
+	var x [1]struct{}
+	_ = x[Monday-(0)]
+	_ = x[Tuesday-(1)]
+	_ = x[Wednesday-(2)]
+	_ = x[Thursday-(3)]
+	_ = x[Friday-(4)]
+	_ = x[Saturday-(5)]
+	_ = x[Sunday-(6)]
+}
+
+var _DayValues = []Day{Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}
+
+var _DayNameToValueMap = map[string]Day{
+	_DayName[0:6]:        Monday,
+	_DayLowerName[0:6]:   Monday,
+	_DayName[6:13]:       Tuesday,
+	_DayLowerName[6:13]:  Tuesday,
+	_DayName[13:22]:      Wednesday,
+	_DayLowerName[13:22]: Wednesday,
+	_DayName[22:30]:      Thursday,
+	_DayLowerName[22:30]: Thursday,
+	_DayName[30:36]:      Friday,
+	_DayLowerName[30:36]: Friday,
+	_DayName[36:44]:      Saturday,
+	_DayLowerName[36:44]: Saturday,
+	_DayName[44:50]:      Sunday,
+	_DayLowerName[44:50]: Sunday,
+}
+
+var _DayNames = []string{
+	_DayName[0:6],
+	_DayName[6:13],
+	_DayName[13:22],
+	_DayName[22:30],
+	_DayName[30:36],
+	_DayName[36:44],
+	_DayName[44:50],
+}
+
+// DayString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func DayString(s string) (Day, error) {
+	if val, ok := _DayNameToValueMap[s]; ok {
+		return val, nil
+	}
+
+	if val, ok := _DayNameToValueMap[strings.ToLower(s)]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to Day values", s)
+}
+
+// DayValues returns all values of the enum
+func DayValues() []Day {
+	return _DayValues
+}
+
+// DayStrings returns a slice of all String values of the enum
+func DayStrings() []string {
+	strs := make([]string, len(_DayNames))
+	copy(strs, _DayNames)
+	return strs
+}
+
+// IsADay returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i Day) IsADay() bool {
+	for _, v := range _DayValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}