Added panic recovery mechanism (#158)

pkg/compiler/compiler.go

@@ -59,9 +59,6 @@ func (c *FqlCompiler) Compile(query string) (program *runtime.Program, err error
 		return nil, ErrEmptyQuery
 	}
 
-	p := parser.New(query)
-	p.AddErrorListener(&errorListener{})
-
 	defer func() {
 		if r := recover(); r != nil {
 			// find out exactly what the error was and set err
@@ -78,6 +75,9 @@ func (c *FqlCompiler) Compile(query string) (program *runtime.Program, err error
 		}
 	}()
 
+	p := parser.New(query)
+	p.AddErrorListener(&errorListener{})
+
 	l := newVisitor(query, c.funcs)
 
 	res := p.Visit(l).(*result)

pkg/runtime/program.go

@@ -5,6 +5,7 @@ import (
 	"github.com/MontFerret/ferret/pkg/html"
 	"github.com/MontFerret/ferret/pkg/runtime/core"
 	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"github.com/pkg/errors"
 )
 
 type Program struct {
@@ -28,7 +29,23 @@ func (p *Program) Source() string {
 	return p.src
 }
 
-func (p *Program) Run(ctx context.Context, setters ...Option) ([]byte, error) {
+func (p *Program) Run(ctx context.Context, setters ...Option) (result []byte, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			// find out exactly what the error was and set err
+			switch x := r.(type) {
+			case string:
+				err = errors.New(x)
+			case error:
+				err = x
+			default:
+				err = errors.New("unknown panic")
+			}
+
+			result = nil
+		}
+	}()
+
 	scope, closeFn := core.NewRootScope()
 
 	defer closeFn()

pkg/runtime/program_test.go

@@ -0,0 +1,25 @@
+package runtime_test
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/compiler"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	. "github.com/smartystreets/goconvey/convey"
+	"testing"
+)
+
+func TestProgram(t *testing.T) {
+	Convey("Should recover from panic", t, func() {
+		c := compiler.New()
+		c.RegisterFunction("panic", func(ctx context.Context, args ...core.Value) (core.Value, error) {
+			panic("test")
+		})
+
+		p := c.MustCompile(`RETURN PANIC()`)
+
+		_, err := p.Run(context.Background())
+
+		So(err, ShouldBeError)
+		So(err.Error(), ShouldEqual, "test")
+	})
+}