Using constant maxFieldIndex to clean up bounds checking

parser.go

@@ -158,8 +158,8 @@ func (p *parser) parseField() (*Field, error) {
 	if err != nil {
 		return nil, err
 	}
-	index := 65536 + 1
-	if len(sIndex) <= len("65536") {
+	index := maxFieldIndex + 1
+	if len(sIndex) <= len(strconv.Itoa(maxFieldIndex)) {
 		index, err = strconv.Atoi(sIndex)
 		if err != nil {
 			// unexpected since sIndex should conform to pIndex

tree.go

@@ -14,8 +14,11 @@ package worksheets
 
 import (
 	"fmt"
+	"math"
 )
 
+const maxFieldIndex = math.MaxUint16
+
 type Definition struct {
 	name          string
 	fieldsByName  map[string]*Field
@@ -32,8 +35,8 @@ func (def *Definition) addField(field *Field) error {
 
 	if _, ok := def.fieldsByIndex[field.index]; ok {
 		return fmt.Errorf("%s.%s: index %d cannot be reused", def.name, field.name, field.index)
-	} else if field.index > 65536 {
-		return fmt.Errorf("%s.%s: index cannot be greater than 65536", def.name, field.name)
+	} else if field.index > maxFieldIndex {
+		return fmt.Errorf("%s.%s: index cannot be greater than %d", def.name, field.name, maxFieldIndex)
 	}
 	def.fieldsByIndex[field.index] = field
 

worksheets_test.go

@@ -49,6 +49,18 @@ func (s *Zuite) TestExample() {
 	require.False(s.T(), isSet)
 }
 
+func (s *Zuite) TestNewDefinitionsGood() {
+	cases := []string{
+		`worksheet simple {
+			65535:index_at_max bool
+		}`,
+	}
+	for _, ex := range cases {
+		_, err := NewDefinitions(strings.NewReader(ex))
+		assert.NoError(s.T(), err, ex)
+	}
+}
+
 func (s *Zuite) TestNewDefinitionsErrors() {
 	cases := map[string]string{
 		// crap input
@@ -60,12 +72,12 @@ func (s *Zuite) TestNewDefinitionsErrors() {
 
 		// worksheet semantics
 		`worksheet simple {
-			65537:index_too_large bool
-		}`: `simple.index_too_large: index cannot be greater than 65536`,
+			65536:index_too_large bool
+		}`: `simple.index_too_large: index cannot be greater than 65535`,
 
 		`worksheet simple {
 			9999999999999999999999999999999999999999999999999:index_too_large bool
-		}`: `simple.index_too_large: index cannot be greater than 65536`,
+		}`: `simple.index_too_large: index cannot be greater than 65535`,
 
 		`worksheet simple {
 			0:no_can_do_with_zero bool