chore(lint): relinted code base according to strengthened rules.

Following the refactoring of error switch statements, added tests
cases to cover all new code branches.

NOTE: remember not to apply the auto fix for errlint, as it
embarks into ambitious code rewrites that are broken.

Signed-off-by: Frederic BIDON <fredbi@yahoo.com>

Author: fredbi

api.go

@@ -5,16 +5,19 @@ package errors
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"reflect"
 	"strings"
 )
 
 // DefaultHTTPCode is used when the error Code cannot be used as an HTTP code.
+//
+//nolint:gochecknoglobals // it should have been a constant in the first place, but now it is mutable so we have to leave it here or introduce a breaking change.
 var DefaultHTTPCode = http.StatusUnprocessableEntity
 
-// Error represents a error interface all swagger framework errors implement
+// Error represents a error interface all swagger framework errors implement.
 type Error interface {
 	error
 	Code() int32
@@ -33,15 +36,15 @@ func (a *apiError) Code() int32 {
 	return a.code
 }
 
-// MarshalJSON implements the JSON encoding interface
+// MarshalJSON implements the JSON encoding interface.
 func (a apiError) MarshalJSON() ([]byte, error) {
 	return json.Marshal(map[string]any{
 		"code":    a.code,
 		"message": a.message,
 	})
 }
 
-// New creates a new API error with a code and a message
+// New creates a new API error with a code and a message.
 func New(code int32, message string, args ...any) Error {
 	if len(args) > 0 {
 		return &apiError{
@@ -55,20 +58,20 @@ func New(code int32, message string, args ...any) Error {
 	}
 }
 
-// NotFound creates a new not found error
+// NotFound creates a new not found error.
 func NotFound(message string, args ...any) Error {
 	if message == "" {
 		message = "Not found"
 	}
 	return New(http.StatusNotFound, message, args...)
 }
 
-// NotImplemented creates a new not implemented error
+// NotImplemented creates a new not implemented error.
 func NotImplemented(message string) Error {
 	return New(http.StatusNotImplemented, "%s", message)
 }
 
-// MethodNotAllowedError represents an error for when the path matches but the method doesn't
+// MethodNotAllowedError represents an error for when the path matches but the method doesn't.
 type MethodNotAllowedError struct {
 	code    int32
 	Allowed []string
@@ -79,12 +82,12 @@ func (m *MethodNotAllowedError) Error() string {
 	return m.message
 }
 
-// Code the error code
+// Code the error code.
 func (m *MethodNotAllowedError) Code() int32 {
 	return m.code
 }
 
-// MarshalJSON implements the JSON encoding interface
+// MarshalJSON implements the JSON encoding interface.
 func (m MethodNotAllowedError) MarshalJSON() ([]byte, error) {
 	return json.Marshal(map[string]any{
 		"code":    m.code,
@@ -104,25 +107,33 @@ func errorAsJSON(err Error) []byte {
 
 func flattenComposite(errs *CompositeError) *CompositeError {
 	var res []error
-	for _, er := range errs.Errors {
-		switch e := er.(type) {
-		case *CompositeError:
-			if e != nil && len(e.Errors) > 0 {
-				flat := flattenComposite(e)
-				if len(flat.Errors) > 0 {
-					res = append(res, flat.Errors...)
-				}
-			}
-		default:
-			if e != nil {
-				res = append(res, e)
-			}
+
+	for _, err := range errs.Errors {
+		if err == nil {
+			continue
+		}
+
+		e := &CompositeError{}
+		if !errors.As(err, &e) {
+			res = append(res, err)
+
+			continue
+		}
+
+		if len(e.Errors) == 0 {
+			res = append(res, e)
+
+			continue
 		}
+
+		flat := flattenComposite(e)
+		res = append(res, flat.Errors...)
 	}
+
 	return CompositeValidationError(res...)
 }
 
-// MethodNotAllowed creates a new method not allowed error
+// MethodNotAllowed creates a new method not allowed error.
 func MethodNotAllowed(requested string, allow []string) Error {
 	msg := fmt.Sprintf("method %s is not allowed, but [%s] are", requested, strings.Join(allow, ","))
 	return &MethodNotAllowedError{
@@ -132,39 +143,55 @@ func MethodNotAllowed(requested string, allow []string) Error {
 	}
 }
 
-// ServeError implements the http error handler interface
+// ServeError implements the http error handler interface.
 func ServeError(rw http.ResponseWriter, r *http.Request, err error) {
 	rw.Header().Set("Content-Type", "application/json")
-	switch e := err.(type) {
-	case *CompositeError:
-		er := flattenComposite(e)
+
+	if err == nil {
+		rw.WriteHeader(http.StatusInternalServerError)
+		_, _ = rw.Write(errorAsJSON(New(http.StatusInternalServerError, "Unknown error")))
+
+		return
+	}
+
+	errComposite := &CompositeError{}
+	errMethodNotAllowed := &MethodNotAllowedError{}
+	var errError Error
+
+	switch {
+	case errors.As(err, &errComposite):
+		er := flattenComposite(errComposite)
 		// strips composite errors to first element only
 		if len(er.Errors) > 0 {
 			ServeError(rw, r, er.Errors[0])
-		} else {
-			// guard against empty CompositeError (invalid construct)
-			ServeError(rw, r, nil)
+
+			return
 		}
-	case *MethodNotAllowedError:
-		rw.Header().Add("Allow", strings.Join(e.Allowed, ","))
-		rw.WriteHeader(asHTTPCode(int(e.Code())))
+
+		// guard against empty CompositeError (invalid construct)
+		ServeError(rw, r, nil)
+
+	case errors.As(err, &errMethodNotAllowed):
+		rw.Header().Add("Allow", strings.Join(errMethodNotAllowed.Allowed, ","))
+		rw.WriteHeader(asHTTPCode(int(errMethodNotAllowed.Code())))
 		if r == nil || r.Method != http.MethodHead {
-			_, _ = rw.Write(errorAsJSON(e))
+			_, _ = rw.Write(errorAsJSON(errMethodNotAllowed))
 		}
-	case Error:
-		value := reflect.ValueOf(e)
+
+	case errors.As(err, &errError):
+		value := reflect.ValueOf(errError)
 		if value.Kind() == reflect.Ptr && value.IsNil() {
 			rw.WriteHeader(http.StatusInternalServerError)
 			_, _ = rw.Write(errorAsJSON(New(http.StatusInternalServerError, "Unknown error")))
+
 			return
 		}
-		rw.WriteHeader(asHTTPCode(int(e.Code())))
+
+		rw.WriteHeader(asHTTPCode(int(errError.Code())))
 		if r == nil || r.Method != http.MethodHead {
-			_, _ = rw.Write(errorAsJSON(e))
+			_, _ = rw.Write(errorAsJSON(errError))
 		}
-	case nil:
-		rw.WriteHeader(http.StatusInternalServerError)
-		_, _ = rw.Write(errorAsJSON(New(http.StatusInternalServerError, "Unknown error")))
+
 	default:
 		rw.WriteHeader(http.StatusInternalServerError)
 		if r == nil || r.Method != http.MethodHead {

api_test.go

@@ -98,7 +98,7 @@ func TestServeError(t *testing.T) {
 		)
 	})
 
-	t.Run("with composite erors", func(t *testing.T) {
+	t.Run("with composite errors", func(t *testing.T) {
 		t.Run("unrecognized - return internal error with first error only - the second error is ignored", func(t *testing.T) {
 			compositeErr := &CompositeError{
 				Errors: []error{
@@ -169,6 +169,28 @@ func TestServeError(t *testing.T) {
 			)
 		})
 
+		t.Run("check guard against nil members in a CompositeError", func(t *testing.T) {
+			compositeErr := &CompositeError{
+				Errors: []error{
+					New(600, "myApiError"),
+					nil,
+					New(601, "myOtherApiError"),
+				},
+			}
+			t.Run("flatten CompositeError should strip nil members", func(t *testing.T) {
+				flat := flattenComposite(compositeErr)
+				require.Len(t, flat.Errors, 2)
+			})
+
+			recorder := httptest.NewRecorder()
+			ServeError(recorder, nil, compositeErr)
+			assert.Equal(t, CompositeErrorCode, recorder.Code)
+			assert.JSONEq(t,
+				`{"code":600,"message":"myApiError"}`,
+				recorder.Body.String(),
+			)
+		})
+
 		t.Run("check guard against nil type", func(t *testing.T) {
 			recorder := httptest.NewRecorder()
 			ServeError(recorder, nil, nil)

auth.go

@@ -5,7 +5,7 @@ package errors
 
 import "net/http"
 
-// Unauthenticated returns an unauthenticated error
+// Unauthenticated returns an unauthenticated error.
 func Unauthenticated(scheme string) Error {
 	return New(http.StatusUnauthorized, "unauthenticated for %s", scheme)
 }

headers.go

@@ -9,8 +9,8 @@ import (
 	"net/http"
 )
 
-// Validation represents a failure of a precondition
-type Validation struct { //nolint: errname
+// Validation represents a failure of a precondition.
+type Validation struct { //nolint: errname // changing the name to abide by the naming rule would bring a breaking change.
 	code    int32
 	Name    string
 	In      string
@@ -23,12 +23,12 @@ func (e *Validation) Error() string {
 	return e.message
 }
 
-// Code the error code
+// Code the error code.
 func (e *Validation) Code() int32 {
 	return e.code
 }
 
-// MarshalJSON implements the JSON encoding interface
+// MarshalJSON implements the JSON encoding interface.
 func (e Validation) MarshalJSON() ([]byte, error) {
 	return json.Marshal(map[string]any{
 		"code":    e.code,
@@ -40,7 +40,7 @@ func (e Validation) MarshalJSON() ([]byte, error) {
 	})
 }
 
-// ValidateName sets the name for a validation or updates it for a nested property
+// ValidateName sets the name for a validation or updates it for a nested property.
 func (e *Validation) ValidateName(name string) *Validation {
 	if name != "" {
 		if e.Name == "" {
@@ -59,7 +59,7 @@ const (
 	responseFormatFail = `unsupported media type requested, only %v are available`
 )
 
-// InvalidContentType error for an invalid content type
+// InvalidContentType error for an invalid content type.
 func InvalidContentType(value string, allowed []string) *Validation {
 	values := make([]any, 0, len(allowed))
 	for _, v := range allowed {
@@ -75,7 +75,7 @@ func InvalidContentType(value string, allowed []string) *Validation {
 	}
 }
 
-// InvalidResponseFormat error for an unacceptable response format request
+// InvalidResponseFormat error for an unacceptable response format request.
 func InvalidResponseFormat(value string, allowed []string) *Validation {
 	values := make([]any, 0, len(allowed))
 	for _, v := range allowed {

middleware.go

@@ -10,7 +10,7 @@ import (
 )
 
 // APIVerificationFailed is an error that contains all the missing info for a mismatched section
-// between the api registrations and the api spec
+// between the api registrations and the api spec.
 type APIVerificationFailed struct { //nolint: errname
 	Section              string   `json:"section,omitempty"`
 	MissingSpecification []string `json:"missingSpecification,omitempty"`

parsing.go

@@ -9,7 +9,7 @@ import (
 	"net/http"
 )
 
-// ParseError represents a parsing error
+// ParseError represents a parsing error.
 type ParseError struct {
 	code    int32
 	Name    string
@@ -19,7 +19,7 @@ type ParseError struct {
 	message string
 }
 
-// NewParseError creates a new parse error
+// NewParseError creates a new parse error.
 func NewParseError(name, in, value string, reason error) *ParseError {
 	var msg string
 	if in == "" {
@@ -41,12 +41,12 @@ func (e *ParseError) Error() string {
 	return e.message
 }
 
-// Code returns the http status code for this error
+// Code returns the http status code for this error.
 func (e *ParseError) Code() int32 {
 	return e.code
 }
 
-// MarshalJSON implements the JSON encoding interface
+// MarshalJSON implements the JSON encoding interface.
 func (e ParseError) MarshalJSON() ([]byte, error) {
 	var reason string
 	if e.Reason != nil {