fix: respect Binder interface for primitive types in BindStringToObject (#86)

Previously, the Binder interface was only checked within the struct case
of the type switch, causing primitive types (strings, ints, etc.) that
implement Binder to bypass their custom binding logic. This fix moves
the Binder check to the beginning of BindStringToObject, ensuring all
types implementing Binder use their custom Bind method, regardless of
their underlying type. The redundant check in the struct case has been
removed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Viktor Stanchev <viktor@anchorlabs.com>

Author: 3 people

bindstring.go

@@ -49,6 +49,11 @@ type BindStringToObjectOptions struct {
 func BindStringToObjectWithOptions(src string, dst interface{}, opts BindStringToObjectOptions) error {
 	var err error
 
+	// Check if the destination implements Binder interface before any reflection
+	if binder, ok := dst.(Binder); ok {
+		return binder.Bind(src)
+	}
+
 	v := reflect.ValueOf(dst)
 	t := reflect.TypeOf(dst)
 
@@ -134,11 +139,6 @@ func BindStringToObjectWithOptions(src string, dst interface{}, opts BindStringT
 		}
 		fallthrough
 	case reflect.Struct:
-		// if this is not of type Time or of type Date look to see if this is of type Binder.
-		if dstType, ok := dst.(Binder); ok {
-			return dstType.Bind(src)
-		}
-
 		if t.ConvertibleTo(reflect.TypeOf(time.Time{})) {
 			// Don't fail on empty string.
 			if src == "" {

bindstring_test.go

@@ -26,6 +26,16 @@ import (
 	"github.com/oapi-codegen/runtime/types"
 )
 
+// CustomStringBinder is a string type that implements Binder but not TextUnmarshaler
+// This tests that Binder interface is checked for primitive types
+type CustomStringBinder string
+
+func (c *CustomStringBinder) Bind(src string) error {
+	// Custom binding logic: add a prefix to demonstrate the Bind method was called
+	*c = CustomStringBinder("CUSTOM:" + src)
+	return nil
+}
+
 func TestBindStringToObject(t *testing.T) {
 	var i int
 	assert.NoError(t, BindStringToObject("5", &i))
@@ -211,6 +221,12 @@ func TestBindStringToObject(t *testing.T) {
 	assert.NoError(t, BindStringToObject(uuidString, &dstUUID))
 	assert.Equal(t, dstUUID.String(), uuidString)
 
+	// Checks that primitive types implementing Binder are respected
+	// This tests the fix for ensuring Binder is checked before type reflection
+	var customString CustomStringBinder
+	assert.NoError(t, BindStringToObject("hello", &customString))
+	assert.Equal(t, CustomStringBinder("CUSTOM:hello"), customString)
+
 }
 
 // TestBindStringToObject_ByteSlice tests that BindStringToObject correctly handles