compiler: support panic in source

In situations where VM's FAULT state needs to be reached,
panic function can be used. It compiles to THROW instruction.

pkg/compiler/panic_test.go

@@ -0,0 +1,71 @@
+package compiler_test
+
+import (
+	"fmt"
+	"math/big"
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/vm"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPanic(t *testing.T) {
+	t.Run("no panic", func(t *testing.T) {
+		src := getPanicSource(false, `"execution fault"`)
+		eval(t, src, big.NewInt(7))
+	})
+
+	t.Run("panic with message", func(t *testing.T) {
+		var logs []string
+		src := getPanicSource(true, `"execution fault"`)
+		v := vmAndCompile(t, src)
+		v.RegisterInteropGetter(logGetter(&logs))
+
+		require.Error(t, v.Run())
+		require.True(t, v.HasFailed())
+		require.Equal(t, 1, len(logs))
+		require.Equal(t, "execution fault", logs[0])
+	})
+
+	t.Run("panic with nil", func(t *testing.T) {
+		var logs []string
+		src := getPanicSource(true, `nil`)
+		v := vmAndCompile(t, src)
+		v.RegisterInteropGetter(logGetter(&logs))
+
+		require.Error(t, v.Run())
+		require.True(t, v.HasFailed())
+		require.Equal(t, 0, len(logs))
+	})
+}
+
+func getPanicSource(need bool, message string) string {
+	return fmt.Sprintf(`
+	package main
+	func Main() int {
+		needPanic := %#v
+		if needPanic {
+			panic(%s)
+			return 5
+		}
+		return 7
+	}
+	`, need, message)
+}
+
+func logGetter(logs *[]string) vm.InteropGetterFunc {
+	logID := vm.InteropNameToID([]byte("Neo.Runtime.Log"))
+	return func(id uint32) *vm.InteropFuncPrice {
+		if id != logID {
+			return nil
+		}
+
+		return &vm.InteropFuncPrice{
+			Func: func(v *vm.VM) error {
+				msg := string(v.Estack().Pop().Bytes())
+				*logs = append(*logs, msg)
+				return nil
+			},
+		}
+	}
+}