Add sample spec to catch external file reference issues in swagger-parser (#17773)

* add a sample that catches swagger-parser issues with external refs

* generate samples for new test spec

samples/client/echo_api/go-external-refs/model_bird.go

@@ -0,0 +1,163 @@
+/*
+Echo Server API
+
+Echo Server API
+
+API version: 0.1.0
+Contact: team@openapitools.org
+*/
+
+// Code generated by OpenAPI Generator (https://openapi-generator.tech); DO NOT EDIT.
+
+package openapi
+
+import (
+	"encoding/json"
+)
+
+// checks if the Bird type satisfies the MappedNullable interface at compile time
+var _ MappedNullable = &Bird{}
+
+// Bird struct for Bird
+type Bird struct {
+	Size *string `json:"size,omitempty"`
+	Color *string `json:"color,omitempty"`
+}
+
+// NewBird instantiates a new Bird object
+// This constructor will assign default values to properties that have it defined,
+// and makes sure properties required by API are set, but the set of arguments
+// will change when the set of required properties is changed
+func NewBird() *Bird {
+	this := Bird{}
+	return &this
+}
+
+// NewBirdWithDefaults instantiates a new Bird object
+// This constructor will only assign default values to properties that have it defined,
+// but it doesn't guarantee that properties required by API are set
+func NewBirdWithDefaults() *Bird {
+	this := Bird{}
+	return &this
+}
+
+// GetSize returns the Size field value if set, zero value otherwise.
+func (o *Bird) GetSize() string {
+	if o == nil || IsNil(o.Size) {
+		var ret string
+		return ret
+	}
+	return *o.Size
+}
+
+// GetSizeOk returns a tuple with the Size field value if set, nil otherwise
+// and a boolean to check if the value has been set.
+func (o *Bird) GetSizeOk() (*string, bool) {
+	if o == nil || IsNil(o.Size) {
+		return nil, false
+	}
+	return o.Size, true
+}
+
+// HasSize returns a boolean if a field has been set.
+func (o *Bird) HasSize() bool {
+	if o != nil && !IsNil(o.Size) {
+		return true
+	}
+
+	return false
+}
+
+// SetSize gets a reference to the given string and assigns it to the Size field.
+func (o *Bird) SetSize(v string) {
+	o.Size = &v
+}
+
+// GetColor returns the Color field value if set, zero value otherwise.
+func (o *Bird) GetColor() string {
+	if o == nil || IsNil(o.Color) {
+		var ret string
+		return ret
+	}
+	return *o.Color
+}
+
+// GetColorOk returns a tuple with the Color field value if set, nil otherwise
+// and a boolean to check if the value has been set.
+func (o *Bird) GetColorOk() (*string, bool) {
+	if o == nil || IsNil(o.Color) {
+		return nil, false
+	}
+	return o.Color, true
+}
+
+// HasColor returns a boolean if a field has been set.
+func (o *Bird) HasColor() bool {
+	if o != nil && !IsNil(o.Color) {
+		return true
+	}
+
+	return false
+}
+
+// SetColor gets a reference to the given string and assigns it to the Color field.
+func (o *Bird) SetColor(v string) {
+	o.Color = &v
+}
+
+func (o Bird) MarshalJSON() ([]byte, error) {
+	toSerialize,err := o.ToMap()
+	if err != nil {
+		return []byte{}, err
+	}
+	return json.Marshal(toSerialize)
+}
+
+func (o Bird) ToMap() (map[string]interface{}, error) {
+	toSerialize := map[string]interface{}{}
+	if !IsNil(o.Size) {
+		toSerialize["size"] = o.Size
+	}
+	if !IsNil(o.Color) {
+		toSerialize["color"] = o.Color
+	}
+	return toSerialize, nil
+}
+
+type NullableBird struct {
+	value *Bird
+	isSet bool
+}
+
+func (v NullableBird) Get() *Bird {
+	return v.value
+}
+
+func (v *NullableBird) Set(val *Bird) {
+	v.value = val
+	v.isSet = true
+}
+
+func (v NullableBird) IsSet() bool {
+	return v.isSet
+}
+
+func (v *NullableBird) Unset() {
+	v.value = nil
+	v.isSet = false
+}
+
+func NewNullableBird(val *Bird) *NullableBird {
+	return &NullableBird{value: val, isSet: true}
+}
+
+func (v NullableBird) MarshalJSON() ([]byte, error) {
+	return json.Marshal(v.value)
+}
+
+func (v *NullableBird) UnmarshalJSON(src []byte) error {
+	v.isSet = true
+	return json.Unmarshal(src, &v.value)
+}
+
+