fix: handle string pointer in fromJSON builtin

Support *string input in fromJSON builtin function by
dereferencing pointer before JSON unmarshaling.

Added tests covering both direct string and pointer string
use cases, including toJSON, which already supports this.

Signed-off-by: Ville Vesilehto <[email protected]>

builtin/builtin.go

@@ -443,7 +443,11 @@ var Builtins = []*Function{
 		Name: "fromJSON",
 		Func: func(args ...any) (any, error) {
 			var v any
-			err := json.Unmarshal([]byte(args[0].(string)), &v)
+			jsonStr := args[0]
+			if strPtr, ok := jsonStr.(*string); ok {
+				jsonStr = *strPtr
+			}
+			err := json.Unmarshal([]byte(jsonStr.(string)), &v)
 			if err != nil {
 				return nil, err
 			}

builtin/builtin_test.go

@@ -638,3 +638,55 @@ func Test_int_unwraps_underlying_value(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, true, out)
 }
+
+func TestBuiltin_json(t *testing.T) {
+	t.Run("fromJSON/string", func(t *testing.T) {
+		env := map[string]any{
+			"json": `{"foo": "bar"}`,
+		}
+		program, err := expr.Compile(`fromJSON(json)`, expr.Env(env))
+		require.NoError(t, err)
+
+		out, err := expr.Run(program, env)
+		require.NoError(t, err)
+		assert.Equal(t, map[string]any{"foo": "bar"}, out)
+	})
+
+	t.Run("fromJSON/string pointer", func(t *testing.T) {
+		jsonString := `{"foo": "bar"}`
+		env := map[string]any{
+			"json": &jsonString,
+		}
+		program, err := expr.Compile(`fromJSON(json)`, expr.Env(env))
+		require.NoError(t, err)
+
+		out, err := expr.Run(program, env)
+		require.NoError(t, err)
+		assert.Equal(t, map[string]any{"foo": "bar"}, out)
+	})
+
+	t.Run("toJSON/object", func(t *testing.T) {
+		env := map[string]any{
+			"obj": map[string]any{"foo": "bar"},
+		}
+		program, err := expr.Compile(`toJSON(obj)`, expr.Env(env))
+		require.NoError(t, err)
+
+		out, err := expr.Run(program, env)
+		require.NoError(t, err)
+		assert.Equal(t, "{\n  \"foo\": \"bar\"\n}", out)
+	})
+
+	t.Run("toJSON/object pointer", func(t *testing.T) {
+		obj := map[string]any{"foo": "bar"}
+		env := map[string]any{
+			"obj": &obj,
+		}
+		program, err := expr.Compile(`toJSON(obj)`, expr.Env(env))
+		require.NoError(t, err)
+
+		out, err := expr.Run(program, env)
+		require.NoError(t, err)
+		assert.Equal(t, "{\n  \"foo\": \"bar\"\n}", out)
+	})
+}