From 054f85423bf4b83b39deaab7e096b615dffd491f Mon Sep 17 00:00:00 2001
From: ccamel <camel.christophe@gmail.com>
Date: Sat, 24 Jun 2023 18:34:02 +0200
Subject: [PATCH] fix(logic): fix empty array management in json predicate

---
 x/logic/predicate/atom.go | 9 +++++++++
 x/logic/predicate/json.go | 6 ++++++
 2 files changed, 15 insertions(+)

diff --git a/x/logic/predicate/atom.go b/x/logic/predicate/atom.go
index 88048e0e..14e343f0 100644
--- a/x/logic/predicate/atom.go
+++ b/x/logic/predicate/atom.go
@@ -22,6 +22,9 @@ var AtomTrue = engine.NewAtom("true")
 // AtomFalse is the term false.
 var AtomFalse = engine.NewAtom("false")
 
+// AtomEmptyArray is the term [].
+var AtomEmptyArray = engine.NewAtom("[]")
+
 // AtomNull is the term null.
 var AtomNull = engine.NewAtom("null")
 
@@ -39,3 +42,9 @@ func MakeBool(b bool) engine.Term {
 
 	return AtomAt.Apply(AtomFalse)
 }
+
+// MakeEmptyArray returns is the compound term @([]).
+// It is used to represent the empty array in json objects.
+func MakeEmptyArray() engine.Term {
+	return AtomAt.Apply(AtomEmptyArray)
+}
diff --git a/x/logic/predicate/json.go b/x/logic/predicate/json.go
index 19e1e94a..de00066c 100644
--- a/x/logic/predicate/json.go
+++ b/x/logic/predicate/json.go
@@ -126,6 +126,8 @@ func termsToJSON(term engine.Term, env *engine.Env) ([]byte, error) {
 			return json.Marshal(true)
 		case MakeBool(false).Compare(t, env) == 0:
 			return json.Marshal(false)
+		case MakeEmptyArray().Compare(t, env) == 0:
+			return json.Marshal([]json.RawMessage{})
 		case MakeNull().Compare(t, env) == 0:
 			return json.Marshal(nil)
 		}
@@ -168,6 +170,10 @@ func jsonToTerms(value any) (engine.Term, error) {
 		return AtomJSON.Apply(engine.List(attributes...)), nil
 	case []any:
 		elements := make([]engine.Term, 0, len(v))
+		if len(v) == 0 {
+			return MakeEmptyArray(), nil
+		}
+
 		for _, element := range v {
 			term, err := jsonToTerms(element)
 			if err != nil {