Expose file.Error type for better error handling

Author: antonmedv

checker/checker.go

@@ -38,7 +38,7 @@ func Check(tree *parser.Tree, config *conf.Config) (reflect.Type, error) {
 	}
 
 	if v.err != nil {
-		return t, fmt.Errorf("%v", v.err.Format(tree.Source))
+		return t, v.err.Bind(tree.Source)
 	}
 
 	return t, nil

expr.go

@@ -167,7 +167,7 @@ func Compile(input string, ops ...Option) (*vm.Program, error) {
 		err = optimizer.Optimize(&tree.Node, config)
 		if err != nil {
 			if fileError, ok := err.(*file.Error); ok {
-				return nil, fmt.Errorf("%v", fileError.Format(tree.Source))
+				return nil, fileError.Bind(tree.Source)
 			}
 			return nil, err
 		}

expr_test.go

@@ -1,8 +1,10 @@
 package expr_test
 
 import (
+	"encoding/json"
 	"fmt"
 	"github.com/antonmedv/expr/ast"
+	"github.com/antonmedv/expr/file"
 	"reflect"
 	"strings"
 	"testing"
@@ -1017,6 +1019,41 @@ func TestPatch_length(t *testing.T) {
 	require.Equal(t, true, output)
 }
 
+func TestCompile_exposed_error(t *testing.T) {
+	_, err := expr.Compile(`1 == true`)
+	require.Error(t, err)
+
+	fileError, ok := err.(*file.Error)
+	require.True(t, ok, "error should be of type *file.Error")
+	require.Equal(t, "invalid operation: == (mismatched types int and bool) (1:3)\n | 1 == true\n | ..^", fileError.Error())
+	require.Equal(t, 2, fileError.Column)
+	require.Equal(t, 1, fileError.Line)
+
+	b, err := json.Marshal(err)
+	require.NoError(t, err)
+	require.Equal(t, `{"Line":1,"Column":2,"Message":"invalid operation: == (mismatched types int and bool)","Snippet":"\n | 1 == true\n | ..^"}`, string(b))
+}
+
+func TestAsBool_exposed_error_(t *testing.T) {
+	_, err := expr.Compile(`42`, expr.AsBool())
+	require.Error(t, err)
+
+	_, ok := err.(*file.Error)
+	require.False(t, ok, "error must not be of type *file.Error")
+	require.Equal(t, "expected bool, but got int", err.Error())
+}
+
+func TestEval_exposed_error(t *testing.T) {
+	_, err := expr.Eval(`1/0`, nil)
+	require.Error(t, err)
+
+	fileError, ok := err.(*file.Error)
+	require.True(t, ok, "error should be of type *file.Error")
+	require.Equal(t, "runtime error: integer divide by zero (1:2)\n | 1/0\n | .^", fileError.Error())
+	require.Equal(t, 1, fileError.Column)
+	require.Equal(t, 1, fileError.Line)
+}
+
 //
 // Mock types
 //

file/error.go

@@ -9,27 +9,14 @@ import (
 type Error struct {
 	Location
 	Message string
+	Snippet string
 }
 
-const (
-	dot = "."
-	ind = "^"
-)
-
 func (e *Error) Error() string {
-	return e.Message
+	return e.format()
 }
 
-func (e *Error) Format(source *Source) string {
-	if e.Location.Empty() {
-		return e.Message
-	}
-	var result = fmt.Sprintf(
-		"%s (%d:%d)",
-		e.Message,
-		e.Location.Line,
-		e.Location.Column+1, // add one to the 0-based column for display
-	)
+func (e *Error) Bind(source *Source) *Error {
 	if snippet, found := source.Snippet(e.Location.Line); found {
 		snippet := strings.Replace(snippet, "\t", " ", -1)
 		srcLine := "\n | " + snippet
@@ -41,18 +28,31 @@ func (e *Error) Format(source *Source) string {
 			if sz > 1 {
 				goto noind
 			} else {
-				indLine += dot
+				indLine += "."
 			}
 		}
 		if _, sz := utf8.DecodeRune(bytes); sz > 1 {
 			goto noind
 		} else {
-			indLine += ind
+			indLine += "^"
 		}
 		srcLine += indLine
 
 	noind:
-		result += srcLine
+		e.Snippet = srcLine
 	}
-	return result
+	return e
+}
+
+func (e *Error) format() string {
+	if e.Location.Empty() {
+		return e.Message
+	}
+	return fmt.Sprintf(
+		"%s (%d:%d)%s",
+		e.Message,
+		e.Line,
+		e.Column+1, // add one to the 0-based column for display
+		e.Snippet,
+	)
 }

parser/lexer/lexer.go

@@ -23,7 +23,7 @@ func Lex(source *file.Source) ([]Token, error) {
 	}
 
 	if l.err != nil {
-		return nil, fmt.Errorf("%v", l.err.Format(source))
+		return nil, l.err.Bind(source)
 	}
 
 	return l.tokens, nil

parser/parser.go

@@ -105,7 +105,7 @@ func Parse(input string) (*Tree, error) {
 	}
 
 	if p.err != nil {
-		return nil, fmt.Errorf("%v", p.err.Format(source))
+		return nil, p.err.Bind(source)
 	}
 
 	return &Tree{

vm/vm.go

@@ -22,11 +22,11 @@ func Run(program *Program, env interface{}) (out interface{}, err error) {
 
 	defer func() {
 		if r := recover(); r != nil {
-			h := file.Error{
+			f := &file.Error{
 				Location: program.Locations[vm.pp],
 				Message:  fmt.Sprintf("%v", r),
 			}
-			err = fmt.Errorf("%v", h.Format(program.Source))
+			err = f.Bind(program.Source)
 		}
 	}()