Feat/resiliency Fixing #270 (#271)

* Better make file

* Fixes issue #270, where in JSON DOM, evaluating non-existent field in map interface yield a zero value, thus caling val.elem() causes a panic. Now the zero is evaluated and returned a normal error

Makefile

@@ -10,7 +10,11 @@ build: fix-antlr4-bug
 	go build ./...
 
 lint: build
-	${GOBIN}/golint -set_exit_status builder/... engine/... examples/... ast/... pkg/... antlr/. model/...
+ifndef GOBIN
+	"${GOPATH}/bin/golint" -set_exit_status builder/... engine/... examples/... ast/... pkg/... antlr/. model/...
+else
+	"${GOBIN}/golint" -set_exit_status builder/... engine/... examples/... ast/... pkg/... antlr/. model/...
+endif
 
 test-short: build
 	go test ./... -v -covermode=count -coverprofile=coverage.out -short

examples/EvaluateMissingDataContext_test.go

@@ -0,0 +1,51 @@
+package examples
+
+import (
+	"fmt"
+	"github.com/hyperjumptech/grule-rule-engine/ast"
+	"github.com/hyperjumptech/grule-rule-engine/builder"
+	"github.com/hyperjumptech/grule-rule-engine/engine"
+	"github.com/hyperjumptech/grule-rule-engine/pkg"
+	"testing"
+)
+
+const (
+	input_rule = `
+	rule TestRule "" {
+		when
+			R.Result == 'NoResult' &&
+			inputs.i_am_missing == 'abc' &&
+                        inputs.name.first == 'john'
+		then
+			R.Result = "ok";
+	}
+	`
+)
+
+
+func TestDataContextMissingFact(t *testing.T) {
+
+	oresult := &ObjectResult{
+		Result: "NoResult",
+	}
+
+	// build rules
+	lib := ast.NewKnowledgeLibrary()
+	rb := builder.NewRuleBuilder(lib)
+	err := rb.BuildRuleFromResource("Test", "0.0.1", pkg.NewBytesResource([]byte(input_rule)))
+
+	// 	add JSON fact
+	json := []byte(`{"blabla":"bla","name":{"first":"john","last":"doe"}}`)
+	kb := lib.NewKnowledgeBaseInstance("Test", "0.0.1")
+	dcx := ast.NewDataContext()
+
+	err = dcx.Add("R", oresult)
+	err = dcx.AddJSON("inputs", json)
+	if err != nil {
+		fmt.Println(err.Error())
+	}
+
+	// results in panic
+	engine.NewGruleEngine().Execute(dcx, kb)
+
+}

model/JsonDataAccessLayer.go

@@ -191,6 +191,9 @@ func (vn *JSONValueNode) GetObjectValueByField(field string) (reflect.Value, err
 		return reflect.ValueOf(nil), fmt.Errorf("not an object or map")
 	}
 	tmap := vn.data.MapIndex(reflect.ValueOf(field))
+	if tmap == reflect.ValueOf(nil) {
+		return reflect.ValueOf(nil), fmt.Errorf("json field '%s' is undefined", field)
+	}
 	return tmap.Elem(), nil
 }