panic: slice index out of range

[mvberg]

Describe the bug

When attempting to access a go struct that contains a slice, the engine will panic on Execute when index is out of range and will not emit the error back to caller.

To Reproduce

Example Rule

rule SliceOORRule {
  when
    PriceSlice.Prices[4] > 10 // will cause panic if slice is empty
  then
    Log("Price number 4 is greater than 10");
    Retract("SliceOORRule");
}

Code

package examples

import (
	"testing"

	"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"
	"github.com/stretchr/testify/assert"
)

const (
	SliceOORRule = `
		rule SliceOORRule {
			when
				PriceSlice.Prices[4] > 10 // will cause panic
			then
				Log("Price number 4 is greater than 10");
				Retract("SliceOORRule");
		}`
)

type AUserSliceIssue struct {
	Prices []int
}

func TestMethodCall_SliceOOR(t *testing.T) {
	ps := &AUserSliceIssue{
		Prices: []int{1, 2, 3},
	}

	dataContext := ast.NewDataContext()
	err := dataContext.Add("PriceSlice", ps)
	assert.NoError(t, err)

	// Prepare knowledgebase library and load it with our rule.
	lib := ast.NewKnowledgeLibrary()
	rb := builder.NewRuleBuilder(lib)
	err = rb.BuildRuleFromResource("Test", "0.1.1", pkg.NewBytesResource([]byte(SliceOORRule)))
	assert.NoError(t, err)
	eng1 := &engine.GruleEngine{MaxCycle: 5}
	kb := lib.NewKnowledgeBaseInstance("Test", "0.1.1")
	err = eng1.Execute(dataContext, kb)
	assert.NoError(t, err)
}

Expected behavior

Would expect the engine to recover() from the panic and return the error back to the Execute caller.

Additional context

I will take a stab at a PR this week.

Stack Trace from Example Code

=== RUN   TestMethodCall_SliceOOR
--- FAIL: TestMethodCall_SliceOOR (0.01s)
panic: reflect: slice index out of range [recovered]
	panic: reflect: slice index out of range

goroutine 19 [running]:
testing.tRunner.func1.2({0x14ad1e0, 0x1688110})
	C:/Program Files/Go/src/testing/testing.go:1396 +0x24e
testing.tRunner.func1()
	C:/Program Files/Go/src/testing/testing.go:1399 +0x39f
panic({0x14ad1e0, 0x1688110})
	C:/Program Files/Go/src/runtime/panic.go:884 +0x212
reflect.Value.Index({0x14a2760?, 0xc0000a4ac8?, 0xc000207650?}, 0xebe767?)
	C:/Program Files/Go/src/reflect/value.go:1412 +0x16d
github.com/hyperjumptech/grule-rule-engine/model.(*GoValueNode).GetArrayValueAt(0xc0001562c0?, 0xc00034c240?)
	c:/Users/Mike/git/grule-rule-engine/model/GoDataAccessLayer.go:101 +0x45
github.com/hyperjumptech/grule-rule-engine/model.(*GoValueNode).GetChildNodeByIndex(0xc0002e1c40, 0x1693c60?)
	c:/Users/Mike/git/grule-rule-engine/model/GoDataAccessLayer.go:109 +0x54
github.com/hyperjumptech/grule-rule-engine/ast.(*Variable).Evaluate(0xc000331180, {0x1693c60, 0xc00011f860}, 0x100?)
	c:/Users/Mike/git/grule-rule-engine/ast/Variable.go:242 +0x272
github.com/hyperjumptech/grule-rule-engine/ast.(*ExpressionAtom).Evaluate(0xc000127560, {0x1693c60?, 0xc00011f860?}, 0xc000357180?)
	c:/Users/Mike/git/grule-rule-engine/ast/ExpressionAtom.go:269 +0xd5d
github.com/hyperjumptech/grule-rule-engine/ast.(*Expression).Evaluate(0xc000331110, {0x1693c60?, 0xc00011f860?}, 0xc0002e1c00?)
	c:/Users/Mike/git/grule-rule-engine/ast/Expression.go:279 +0x9dc
github.com/hyperjumptech/grule-rule-engine/ast.(*Expression).Evaluate(0xc0003310a0, {0x1693c60, 0xc00011f860}, 0x14d7460?)
	c:/Users/Mike/git/grule-rule-engine/ast/Expression.go:305 +0xa6
github.com/hyperjumptech/grule-rule-engine/ast.(*WhenScope).Evaluate(...)
	c:/Users/Mike/git/grule-rule-engine/ast/WhenScope.go:122
github.com/hyperjumptech/grule-rule-engine/ast.(*RuleEntry).Evaluate(0xc0000e0e40, {0x1693c60?, 0xc00011f860?}, 0x0?)
	c:/Users/Mike/git/grule-rule-engine/ast/RuleEntry.go:167 +0x45
github.com/hyperjumptech/grule-rule-engine/engine.(*GruleEngine).ExecuteWithContext(0xc000207e38, {0x168e270, 0xc0000a60f8}, {0x1693c60?, 0xc00011f860}, 0xc000347770)
	c:/Users/Mike/git/grule-rule-engine/engine/GruleEngine.go:157 +0x7f9
github.com/hyperjumptech/grule-rule-engine/engine.(*GruleEngine).Execute(...)
	c:/Users/Mike/git/grule-rule-engine/engine/GruleEngine.go:80
github.com/hyperjumptech/grule-rule-engine/examples.TestMethodCall_SliceOOR(0x0?)
	c:/Users/Mike/git/grule-rule-engine/examples/SliceIndexOutOfRangePanic_test.go:58 +0x310
testing.tRunner(0xc00008da00, 0x15d5338)
	C:/Program Files/Go/src/testing/testing.go:1446 +0x10b
created by testing.(*T).Run
	C:/Program Files/Go/src/testing/testing.go:1493 +0x35f
FAIL	github.com/hyperjumptech/grule-rule-engine/examples	0.067s