Fix interoperability bug

examples/exceptions/main.go

@@ -29,8 +29,8 @@ type applicationForm struct {
 	Country          string `smname:"Country"`
 	Location         string `smname:"Location (City)"`
 	CanTravel        bool   `smname:"Travel" smdes:"Can you travel for work?"`
-	BlacklistedField string `bl:""` //
-	BlacklistMe      int
+	BlacklistedField string `bl:""` // field blacklisted at the type level
+	BlacklistMe      int    // field to be blacklisted with an exception list
 }
 
 func main() {

menu/idx.go

@@ -20,7 +20,9 @@ import (
 // If the first non-blacklisted field is found to have an `idx` tag,
 // all others will be expected to have one as well. Likewise, if it
 // does not have the tag, all others will be expected not to have the tag.
-// When no `idx` tags are used, the map keys and values will match.
+// When no `idx` tags are used, the map keys and values will match, unless
+// offset by 1 after and for each instance where a field is found to be
+// blacklisted with the `bl` tag.
 //
 // Where validation fails, a nil map and error are returned.
 func getOrderedFields(t reflect.Type) (map[int]int, error) {
@@ -30,6 +32,7 @@ func getOrderedFields(t reflect.Type) (map[int]int, error) {
 	}{val: false, isSet: false}
 
 	idxTagVals := map[int]int{}
+	blacklistCount := 0
 	for i := 0; i < t.NumField(); i++ {
 		field := t.Field(i)
 
@@ -40,6 +43,7 @@ func getOrderedFields(t reflect.Type) (map[int]int, error) {
 			if isIndexed {
 				return nil, fmt.Errorf("incompatible struct tags; unexpected `idx` tag found on `bl`-tagged field %s", field.Name)
 			}
+			blacklistCount++
 			continue
 		}
 
@@ -57,19 +61,26 @@ func getOrderedFields(t reflect.Type) (map[int]int, error) {
 			if err != nil || idx < 0 {
 				return nil, fmt.Errorf("value for `idx` tag on field %s must be an integer >= 0", field.Name)
 			}
-			if val, ok := idxTagVals[idx]; ok {
-				return nil, fmt.Errorf("value %d for `idx` tag on field %s already assigned to another field", val, field.Name)
+			if _, ok := idxTagVals[idx]; ok {
+				return nil, fmt.Errorf("value %d for `idx` tag on field %s already assigned to another field", idx, field.Name)
 			}
 			idxTagVals[idx] = i
+
 		} else if isIndexed {
 			return nil, fmt.Errorf("unexpected `idx` tag found on field %s", field.Name)
+		} else {
+			idxTagVals[i-blacklistCount] = i
 		}
 
 	}
 
 	for i := 0; i < len(idxTagVals); i++ {
 		if _, ok := idxTagVals[i]; !ok {
-			return nil, fmt.Errorf("expected to find idx value of %d on some field, but found none", i)
+			if wantIdx.val {
+				return nil, fmt.Errorf("expected to find idx value of %d on some field, but found none", i)
+			}
+			return nil, fmt.Errorf("expected sequential indeces for map, but index %d is missing", i)
+
 		}
 	}
 

menu/idx_test.go

@@ -16,14 +16,18 @@ func TestGetOrderedFields(t *testing.T) {
 
 	idxTestsIsolated := []idxTest{
 		{
-			name: "no idx validation returns empty with no error",
+			name: "no idx validation returns matching key-value pairs",
 			input: struct {
 				s string
 				i int
 				b bool
 			}{},
-			expected: map[int]int{},
-			wantErr:  false,
+			expected: map[int]int{
+				0: 0,
+				1: 1,
+				2: 2,
+			},
+			wantErr: false,
 		},
 		{
 			name: "idx validation returns indeces as specified per field",
@@ -81,6 +85,19 @@ func TestGetOrderedFields(t *testing.T) {
 		},
 	}
 	idxTestsWithBlacklistTag := []idxTest{
+		{
+			name: "no idx validation returns only bl-offset key-value pairs",
+			input: struct {
+				s string
+				i int `bl:""`
+				b bool
+			}{},
+			expected: map[int]int{
+				0: 0,
+				1: 2,
+			},
+			wantErr: false,
+		},
 		{
 			name: "idx validation skips bl-tagged field (first)",
 			input: struct {