Support custom error type semantics (#7442)

Allow instrumentation to provide domain-specific error type values (i.e.
HTTP or gRPC status codes) for the "error.type" semantic attribute. This
is accomplished by passing an error value that implements the
`interface{ ErrorType string }` interface.

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

CHANGELOG.md

@@ -42,6 +42,8 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - `WithInstrumentationAttributes` in `go.opentelemetry.io/otel/log` synchronously de-duplicates the passed attributes instead of delegating it to the returned `LoggerOption`. (#7266)
 - `Distinct` in `go.opentelemetry.io/otel/attribute` is no longer guaranteed to uniquely identify an attribute set. Collisions between `Distinct` values for different Sets are possible with extremely high cardinality (billions of series per instrument), but are highly unlikely. (#7175)
 - The default `TranslationStrategy` in `go.opentelemetry.io/exporters/prometheus` is changed from `otlptranslator.NoUTF8EscapingWithSuffixes` to `otlptranslator.UnderscoreEscapingWithSuffixes`. (#7421)
+- The `ErrorType` function in `go.opentelemetry.io/otel/semconv/v1.37.0` now handles custom error types.
+  If an error implements an `ErrorType() string` method, the return value of that method will be used as the error type. (#7442)
 
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->

internal/tools/semconvkit/templates/error_type.go.tmpl

@@ -4,28 +4,54 @@
 package semconv // import "go.opentelemetry.io/otel/semconv/{{.TagVer}}"
 
 import (
-	"fmt"
 	"reflect"
 
 	"go.opentelemetry.io/otel/attribute"
 )
 
 // ErrorType returns an [attribute.KeyValue] identifying the error type of err.
+//
+// If err is nil, the returned attribute has the default value
+// [ErrorTypeOther].
+//
+// If err's type has the method
+//
+//	ErrorType() string
+//
+//
+// then the returned attribute has the value of err.ErrorType(). Otherwise, the
+// returned attribute has a value derived from the concrete type of err.
+//
+// The key of the returned attribute is [ErrorTypeKey].
 func ErrorType(err error) attribute.KeyValue {
 	if err == nil {
 		return ErrorTypeOther
 	}
-	t := reflect.TypeOf(err)
-	var value string
-	if t.PkgPath() == "" && t.Name() == "" {
-		// Likely a builtin type.
-		value = t.String()
-	} else {
-		value = fmt.Sprintf("%s.%s", t.PkgPath(), t.Name())
-	}
 
-	if value == "" {
+	return ErrorTypeKey.String(errorType(err))
-		return ErrorTypeOther
+}
-	}
+
-	return ErrorTypeKey.String(value)
+func errorType(err error) string {
+	var s string
+	if et, ok := err.(interface{ ErrorType() string }); ok {
+		// Prioritize the ErrorType method if available.
+		s = et.ErrorType()
+	}
+	if s == "" {
+		// Fallback to reflection if the ErrorType method is not supported or
+		// returns an empty value.
+
+		t := reflect.TypeOf(err)
+		pkg, name := t.PkgPath(), t.Name()
+		if pkg != "" && name != "" {
+			s = pkg + "." + name
+		} else {
+			// The type has no package path or name (predeclared, not-defined,
+			// or alias for a not-defined type).
+			//
+			// This is not guaranteed to be unique, but is a best effort.
+			s = t.String()
+		}
+	}
+	return s
 }

internal/tools/semconvkit/templates/error_type_test.go.tmpl

@@ -5,55 +5,41 @@ package semconv // import "go.opentelemetry.io/otel/semconv/{{.TagVer}}"
 
 import (
 	"errors"
-	"fmt"
-	"reflect"
 	"testing"
-
-	"go.opentelemetry.io/otel/attribute"
 )
 
-type CustomError struct{}
+const pkg = "go.opentelemetry.io/otel/semconv/{{.TagVer}}"
-
-func (CustomError) Error() string {
-	return "custom error"
-}
 
 func TestErrorType(t *testing.T) {
-	customErr := CustomError{}
+	check(t, nil, ErrorTypeOther.Value.AsString())
-	builtinErr := errors.New("something went wrong")
+	check(t, errors.New("msg"), "*errors.errorString")
-	var nilErr error
+	check(t, custom("aborted"), "aborted")
+	check(t, custom(""), pkg+".ErrCustomType") // empty ErrorType, use concrete type.
+}
 
-	wantCustomType := reflect.TypeOf(customErr)
+func check(t *testing.T, err error, want string) {
-	wantCustomStr := fmt.Sprintf("%s.%s", wantCustomType.PkgPath(), wantCustomType.Name())
+	t.Helper()
-
+	got := ErrorType(err)
-	tests := []struct {
+	if got.Key != ErrorTypeKey {
-		name string
+		t.Errorf("ErrorType(%v) key = %v, want %v", err, got.Key, ErrorTypeKey)
-		err  error
-		want attribute.KeyValue
-	}{
-		{
-			name: "BuiltinError",
-			err:  builtinErr,
-			want: attribute.String("error.type", "*errors.errorString"),
-		},
-		{
-			name: "CustomError",
-			err:  customErr,
-			want: attribute.String("error.type", wantCustomStr),
-		},
-		{
-			name: "NilError",
-			err:  nilErr,
-			want: ErrorTypeOther,
-		},
 	}
-
+	if got.Value.AsString() != want {
-	for _, tt := range tests {
+		t.Errorf("ErrorType(%v) value = %v, want %v", err, got.Value.AsString(), want)
-		t.Run(tt.name, func(t *testing.T) {
-			got := ErrorType(tt.err)
-			if got != tt.want {
-				t.Errorf("ErrorType(%v) = %v, want %v", tt.err, got, tt.want)
-			}
-		})
 	}
 }
+
+func custom(typ string) error {
+	return ErrCustomType{Type: typ}
+}
+
+type ErrCustomType struct {
+	Type string
+}
+
+func (e ErrCustomType) Error() string {
+	return "custom: " + e.Type
+}
+
+func (e ErrCustomType) ErrorType() string {
+	return e.Type
+}

semconv/v1.37.0/error_type.go

@@ -4,28 +4,57 @@
 package semconv // import "go.opentelemetry.io/otel/semconv/v1.37.0"
 
 import (
-	"fmt"
 	"reflect"
 
 	"go.opentelemetry.io/otel/attribute"
 )
 
 // ErrorType returns an [attribute.KeyValue] identifying the error type of err.
+//
+// If err is nil, the returned attribute has the default value
+// [ErrorTypeOther].
+//
+// If err implements the interface
+//
+//	// ErrorTyper is an error that provides a specific type definition for the
+//	// error it represents.
+//	type ErrorTyper interface {
+//	    ErrorType() string
+//	}
+//
+// then the returned attribute has the value of err.ErrorType(). Otherwise, the
+// returned attribute has a value derived from the concrete type of err.
+//
+// The key of the returned attribute is [ErrorTypeKey].
 func ErrorType(err error) attribute.KeyValue {
 	if err == nil {
 		return ErrorTypeOther
 	}
-	t := reflect.TypeOf(err)
-	var value string
-	if t.PkgPath() == "" && t.Name() == "" {
-		// Likely a builtin type.
-		value = t.String()
-	} else {
-		value = fmt.Sprintf("%s.%s", t.PkgPath(), t.Name())
-	}
 
-	if value == "" {
+	return ErrorTypeKey.String(errorType(err))
-		return ErrorTypeOther
+}
-	}
+
-	return ErrorTypeKey.String(value)
+func errorType(err error) string {
+	var s string
+	if et, ok := err.(interface{ ErrorType() string }); ok {
+		// Prioritize the ErrorType method if available.
+		s = et.ErrorType()
+	}
+	if s == "" {
+		// Fallback to reflection if the ErrorType method is not supported or
+		// returns an empty value.
+
+		t := reflect.TypeOf(err)
+		pkg, name := t.PkgPath(), t.Name()
+		if pkg != "" && name != "" {
+			s = pkg + "." + name
+		} else {
+			// The type has no package path or name (predeclared, not-defined,
+			// or alias for a not-defined type).
+			//
+			// This is not guaranteed to be unique, but is a best effort.
+			s = t.String()
+		}
+	}
+	return s
 }

semconv/v1.37.0/error_type_test.go

@@ -5,55 +5,41 @@ package semconv // import "go.opentelemetry.io/otel/semconv/v1.37.0"
 
 import (
 	"errors"
-	"fmt"
-	"reflect"
 	"testing"
-
-	"go.opentelemetry.io/otel/attribute"
 )
 
-type CustomError struct{}
+const pkg = "go.opentelemetry.io/otel/semconv/v1.37.0"
-
-func (CustomError) Error() string {
-	return "custom error"
-}
 
 func TestErrorType(t *testing.T) {
-	customErr := CustomError{}
+	check(t, nil, ErrorTypeOther.Value.AsString())
-	builtinErr := errors.New("something went wrong")
+	check(t, errors.New("msg"), "*errors.errorString")
-	var nilErr error
+	check(t, custom("aborted"), "aborted")
+	check(t, custom(""), pkg+".ErrCustomType") // empty ErrorType, use concrete type.
+}
 
-	wantCustomType := reflect.TypeOf(customErr)
+func check(t *testing.T, err error, want string) {
-	wantCustomStr := fmt.Sprintf("%s.%s", wantCustomType.PkgPath(), wantCustomType.Name())
+	t.Helper()
-
+	got := ErrorType(err)
-	tests := []struct {
+	if got.Key != ErrorTypeKey {
-		name string
+		t.Errorf("ErrorType(%v) key = %v, want %v", err, got.Key, ErrorTypeKey)
-		err  error
-		want attribute.KeyValue
-	}{
-		{
-			name: "BuiltinError",
-			err:  builtinErr,
-			want: attribute.String("error.type", "*errors.errorString"),
-		},
-		{
-			name: "CustomError",
-			err:  customErr,
-			want: attribute.String("error.type", wantCustomStr),
-		},
-		{
-			name: "NilError",
-			err:  nilErr,
-			want: ErrorTypeOther,
-		},
 	}
-
+	if got.Value.AsString() != want {
-	for _, tt := range tests {
+		t.Errorf("ErrorType(%v) value = %v, want %v", err, got.Value.AsString(), want)
-		t.Run(tt.name, func(t *testing.T) {
-			got := ErrorType(tt.err)
-			if got != tt.want {
-				t.Errorf("ErrorType(%v) = %v, want %v", tt.err, got, tt.want)
-			}
-		})
 	}
 }
+
+func custom(typ string) error {
+	return ErrCustomType{Type: typ}
+}
+
+type ErrCustomType struct {
+	Type string
+}
+
+func (e ErrCustomType) Error() string {
+	return "custom: " + e.Type
+}
+
+func (e ErrCustomType) ErrorType() string {
+	return e.Type
+}