enum value change detector

stringer.go

@@ -445,6 +445,7 @@ func (g *Generator) generate(typeName string, includeJSON, includeYAML, includeS
 	default:
 		g.buildMap(runs, typeName)
 	}
+	g.buildNoOpOrderChangeDetect(runs, typeName)
 
 	g.buildBasicExtras(runs, typeName, runsThreshold)
 	if includeJSON {
@@ -819,6 +820,24 @@ func (g *Generator) buildMap(runs [][]Value, typeName string) {
 	g.Printf(stringMap, typeName)
 }
 
+// buildNoOpOrderChangeDetect try to let the compiler and the user know if the order/value of the ENUMS have changed.
+func (g *Generator) buildNoOpOrderChangeDetect(runs [][]Value, typeName string) {
+	g.Printf("\n")
+
+	g.Printf(`
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	`)
+	g.Printf("func _%sNoOp (){ ", typeName)
+	g.Printf("\n var x [1]struct{}\n")
+	for _, values := range runs {
+		for _, value := range values {
+			g.Printf("\t_ = x[%s-(%s)]\n", value.originalName, value.str)
+		}
+	}
+	g.Printf("}\n\n")
+}
+
 // Argument to format is the type name.
 const stringMap = `func (i %[1]s) String() string {
 	if str, ok := _%[1]sMap[i]; ok {

util_test.go

@@ -54,7 +54,7 @@ Outer:
 	for n, test := range splitTests {
 		values := make([]Value, len(test.input))
 		for i, v := range test.input {
-			values[i] = Value{"", v, test.signed, fmt.Sprint(v)}
+			values[i] = Value{"", "", v, test.signed, fmt.Sprint(v)}
 		}
 		runs := splitIntoRuns(values)
 		if len(runs) != len(test.output) {