From 603cbd6906ee3a92ba8789d4c3c61ef86aae2a90 Mon Sep 17 00:00:00 2001
From: Maxence Maireaux <maxence@maireaux.fr>
Date: Thu, 4 Jun 2026 13:29:32 +0200
Subject: [PATCH] fix: reject duplicate remaining allotments

---
 internal/interpreter/interpreter.go       |  6 +++++-
 internal/interpreter/interpreter_error.go |  8 ++++++++
 internal/interpreter/interpreter_test.go  | 18 ++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/internal/interpreter/interpreter.go b/internal/interpreter/interpreter.go
index 94b634af..2203cd8a 100644
--- a/internal/interpreter/interpreter.go
+++ b/internal/interpreter/interpreter.go
@@ -1029,9 +1029,13 @@ func (s *programState) makeAllotment(monetary *big.Int, items []parser.Allotment
 			allotments = append(allotments, rat)
 
 		case *parser.RemainingAllotment:
+			if remainingAllotmentIndex != -1 {
+				return nil, InvalidRemainingAllotment{
+					Range: allotment.Range,
+				}
+			}
 			remainingAllotmentIndex = i
 			allotments = append(allotments, new(big.Rat))
-			// TODO check there are not duplicate remaining clause
 		}
 	}
 
diff --git a/internal/interpreter/interpreter_error.go b/internal/interpreter/interpreter_error.go
index 3d8527c3..258c6766 100644
--- a/internal/interpreter/interpreter_error.go
+++ b/internal/interpreter/interpreter_error.go
@@ -153,6 +153,14 @@ func (e InvalidAllotmentInSendAll) Error() string {
 	return "cannot take all balance of an allotment source"
 }
 
+type InvalidRemainingAllotment struct {
+	parser.Range
+}
+
+func (e InvalidRemainingAllotment) Error() string {
+	return "Only one 'remaining' clause is allowed in an allotment expression"
+}
+
 type DivideByZero struct {
 	parser.Range
 	Numerator *big.Int
diff --git a/internal/interpreter/interpreter_test.go b/internal/interpreter/interpreter_test.go
index 651d17b7..fa4a944d 100644
--- a/internal/interpreter/interpreter_test.go
+++ b/internal/interpreter/interpreter_test.go
@@ -419,6 +419,24 @@ func TestInvalidDestinationAllotmentSum(t *testing.T) {
 	test(t, tc)
 }
 
+func TestRejectsDuplicateRemainingAllotments(t *testing.T) {
+	tc := NewTestCase()
+	src := tc.compile(t, `send [COIN 100] (
+		source = {
+			remaining from @a
+			remaining from @b
+		}
+		destination = @dest
+	)`)
+
+	tc.expected = CaseResult{
+		Error: machine.InvalidRemainingAllotment{
+			Range: parser.RangeOfIndexed(src, "remaining", 1),
+		},
+	}
+	test(t, tc)
+}
+
 func TestSourceAllotmentInvalidAmt(t *testing.T) {
 	tc := NewTestCase()
 	tc.compile(t, `send [COIN 100] (