lib,mito: add support for runtime error source location reporting

lib/errors.go

@@ -0,0 +1,55 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package lib
+
+import (
+	"fmt"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/common"
+)
+
+// DecoratedError implements error source location rendering.
+type DecoratedError struct {
+	AST *cel.Ast
+	Err error
+}
+
+func (e DecoratedError) Error() string {
+	if e.Err == nil {
+		return "<nil>"
+	}
+	type nodeIDer interface {
+		NodeID() int64
+	}
+	nodeErr, ok := e.Err.(nodeIDer)
+	if !ok {
+		return e.Err.Error()
+	}
+	id := nodeErr.NodeID()
+	if id == 0 {
+		return fmt.Sprintf("%v: unset node id", e.Err)
+	}
+	if e.AST == nil {
+		return fmt.Sprintf("%v: node %d", e.Err, id)
+	}
+	loc := e.AST.NativeRep().SourceInfo().GetStartLocation(id)
+	errs := common.NewErrors(e.AST.Source())
+	errs.ReportErrorAtID(id, loc, e.Err.Error())
+	return errs.ToDisplayString()
+}

mito.go

@@ -298,41 +298,41 @@ func debug(tag string, value any) {
 }
 
 func eval(src, root string, input interface{}, libs ...cel.EnvOption) (string, any, error) {
-	prg, err := compile(src, root, libs...)
+	prg, ast, err := compile(src, root, libs...)
 	if err != nil {
 		return "", nil, fmt.Errorf("failed program instantiation: %v", err)
 	}
-	return run(prg, false, input)
+	return run(prg, ast, false, input)
 }
 
-func compile(src, root string, libs ...cel.EnvOption) (cel.Program, error) {
+func compile(src, root string, libs ...cel.EnvOption) (cel.Program, *cel.Ast, error) {
 	opts := append([]cel.EnvOption{
 		cel.Declarations(decls.NewVar(root, decls.Dyn)),
 	}, libs...)
 	env, err := cel.NewEnv(opts...)
 	if err != nil {
-		return nil, fmt.Errorf("failed to create env: %v", err)
+		return nil, nil, fmt.Errorf("failed to create env: %v", err)
 	}
 
 	ast, iss := env.Compile(src)
 	if iss.Err() != nil {
-		return nil, fmt.Errorf("failed compilation: %v", iss.Err())
+		return nil, nil, fmt.Errorf("failed compilation: %v", iss.Err())
 	}
 
 	prg, err := env.Program(ast)
 	if err != nil {
-		return nil, fmt.Errorf("failed program instantiation: %v", err)
+		return nil, nil, fmt.Errorf("failed program instantiation: %v", err)
 	}
-	return prg, nil
+	return prg, ast, nil
 }
 
-func run(prg cel.Program, fast bool, input interface{}) (string, any, error) {
+func run(prg cel.Program, ast *cel.Ast, fast bool, input interface{}) (string, any, error) {
 	if input == nil {
 		input = interpreter.EmptyActivation()
 	}
 	out, _, err := prg.Eval(input)
 	if err != nil {
-		return "", nil, fmt.Errorf("failed eval: %v", err)
+		return "", nil, fmt.Errorf("failed eval: %v", lib.DecoratedError{AST: ast, Err: err})
 	}
 
 	v, err := out.ConvertToNative(reflect.TypeOf(&structpb.Value{}))