feat(machine): allow to send 0 amount (#482)

pkg/core/funding.go

@@ -53,6 +53,12 @@ func (f Funding) Take(amount *MonetaryInt) (Funding, Funding, error) {
 	remainder := Funding{
 		Asset: f.Asset,
 	}
+	if amount.Eq(NewMonetaryInt(0)) && len(f.Parts) > 0 {
+		result.Parts = append(result.Parts, FundingPart{
+			Account: f.Parts[0].Account,
+			Amount:  amount,
+		})
+	}
 	remainingToWithdraw := amount
 	i := 0
 	for remainingToWithdraw.Gt(NewMonetaryInt(0)) && i < len(f.Parts) {

pkg/ledger/execute_script_test.go

@@ -107,10 +107,10 @@ func TestSend(t *testing.T) {
 					)`,
 				},
 			}
-			_, err := l.ExecuteScript(context.Background(), false, script)
-			require.Error(t, err)
-			require.True(t, ledger.IsValidationError(err))
-			require.ErrorContains(t, err, "transaction has no postings")
+			res, err := l.ExecuteScript(context.Background(), false, script)
+			require.NoError(t, err)
+
+			require.Equal(t, 1, len(res.Postings))
 		})
 
 		t.Run("one send with monetary all should fail", func(t *testing.T) {
@@ -123,10 +123,10 @@ func TestSend(t *testing.T) {
 					)`,
 				},
 			}
-			_, err := l.ExecuteScript(context.Background(), false, script)
-			require.Error(t, err)
-			require.True(t, ledger.IsValidationError(err))
-			require.ErrorContains(t, err, "transaction has no postings")
+			res, err := l.ExecuteScript(context.Background(), false, script)
+			require.NoError(t, err)
+
+			require.Equal(t, 1, len(res.Postings))
 		})
 
 		t.Run("one send with zero amount and another with positive amount should succeed", func(t *testing.T) {
@@ -145,7 +145,7 @@ func TestSend(t *testing.T) {
 			}
 			res, err := l.ExecuteScript(context.Background(), false, script)
 			require.NoError(t, err)
-			require.Equal(t, 1, len(res.Postings))
+			require.Equal(t, 2, len(res.Postings))
 
 			assertBalance(t, l, "user:001",
 				"USD/2", core.NewMonetaryInt(100))
@@ -167,7 +167,7 @@ func TestSend(t *testing.T) {
 			}
 			res, err := l.ExecuteScript(context.Background(), false, script)
 			require.NoError(t, err)
-			require.Equal(t, 1, len(res.Postings))
+			require.Equal(t, 2, len(res.Postings))
 
 			assertBalance(t, l, "user:001",
 				"USD/2", core.NewMonetaryInt(101))

pkg/machine/vm/machine.go

@@ -416,9 +416,6 @@ func (m *Machine) tick() (bool, byte, error) {
 		for _, part := range funding.Parts {
 			src := part.Account
 			amt := part.Amount
-			if amt.Eq(core.NewMonetaryInt(0)) {
-				continue
-			}
 			m.Postings = append(m.Postings, Posting{
 				Source:      string(src),
 				Destination: string(dest),

pkg/machine/vm/machine_test.go

@@ -207,6 +207,28 @@ func TestSend(t *testing.T) {
 	test(t, tc)
 }
 
+func TestSend0Amount(t *testing.T) {
+	tc := NewTestCase()
+	tc.compile(t, `send [EUR/2 0] (
+		source=@alice
+		destination=@bob
+	)`)
+	tc.setBalance("alice", "EUR/2", 100)
+	tc.expected = CaseResult{
+		Printed: []core.Value{},
+		Postings: []Posting{
+			{
+				Asset:       "EUR/2",
+				Amount:      core.NewMonetaryInt(0),
+				Source:      "alice",
+				Destination: "bob",
+			},
+		},
+		ExitCode: EXIT_OK,
+	}
+	test(t, tc)
+}
+
 func TestVariables(t *testing.T) {
 	tc := NewTestCase()
 	tc.compile(t, `vars {
@@ -555,16 +577,23 @@ func TestNoEmptyPostings(t *testing.T) {
 	test(t, tc)
 }
 
-func TestNoEmptyPostings2(t *testing.T) {
+func TestEmptyPostings(t *testing.T) {
 	tc := NewTestCase()
 	tc.compile(t, `send [GEM *] (
 		source = @foo
 		destination = @bar
 	)`)
 	tc.setBalance("foo", "GEM", 0)
 	tc.expected = CaseResult{
-		Printed:  []core.Value{},
-		Postings: []Posting{},
+		Printed: []core.Value{},
+		Postings: []Posting{
+			{
+				Source:      "foo",
+				Destination: "bar",
+				Amount:      core.NewMonetaryInt(0),
+				Asset:       "GEM",
+			},
+		},
 		ExitCode: EXIT_OK,
 	}
 	test(t, tc)