fix: support encoding.TextMarshaler in StyleParamWithLocation (#634)

Co-authored-by: Marcin Romaszewicz <47459980+deepmap-marcinr@users.noreply.github.com>

pkg/runtime/styleparam.go

@@ -14,6 +14,7 @@
 package runtime
 
 import (
+	"encoding"
 	"errors"
 	"fmt"
 	"net/url"
@@ -62,6 +63,25 @@ func StyleParamWithLocation(style string, explode bool, paramName string, paramL
 		t = v.Type()
 	}
 
+	// If the value implements encoding.TextMarshaler we use it for marshaling
+	// https://github.com/deepmap/oapi-codegen/issues/504
+	if tu, ok := value.(encoding.TextMarshaler); ok {
+		t := reflect.Indirect(reflect.ValueOf(value)).Type()
+		convertableToTime := t.ConvertibleTo(reflect.TypeOf(time.Time{}))
+		convertableToDate := t.ConvertibleTo(reflect.TypeOf(types.Date{}))
+
+		// Since both time.Time and types.Date implement encoding.TextMarshaler
+		// we should avoid calling theirs MarshalText()
+		if !convertableToTime && !convertableToDate {
+			b, err := tu.MarshalText()
+			if err != nil {
+				return "", fmt.Errorf("error marshaling '%s' as text: %s", value, err)
+			}
+
+			return stylePrimitive(style, explode, paramName, paramLocation, string(b))
+		}
+	}
+
 	switch t.Kind() {
 	case reflect.Slice:
 		n := v.Len()

pkg/runtime/styleparam_test.go

@@ -14,6 +14,7 @@
 package runtime
 
 import (
+	"github.com/google/uuid"
 	"testing"
 	"time"
 
@@ -676,4 +677,18 @@ func TestStyleParam(t *testing.T) {
 	result, err = StyleParamWithLocation("simple", false, "id", ParamLocationQuery, object3)
 	assert.NoError(t, err)
 	assert.EqualValues(t, "date_field,1996-03-19,time_field,1996-03-19T00%3A00%3A00Z,uuid_field,baa07328-452e-40bd-aa2e-fa823ec13605", result)
+
+	// Test handling of struct that implement encoding.TextMarshaler
+  timeVal = time.Date(1996, time.March, 19, 0, 0, 0, 0, time.UTC)
+
+	result, err = StyleParamWithLocation("simple", false, "id", ParamLocationQuery, timeVal)
+	assert.NoError(t, err)
+	assert.EqualValues(t, "1996-03-19T00%3A00%3A00Z", result)
+
+	uuidD := uuid.MustParse("972beb41-e5ea-4b31-a79a-96f4999d8769")
+
+	result, err = StyleParamWithLocation("simple", false, "id", ParamLocationQuery, uuidD)
+	assert.NoError(t, err)
+	assert.EqualValues(t, "972beb41-e5ea-4b31-a79a-96f4999d8769", result)
+
 }