Repair reversed D&D evidence ranges

internal/modules/dnd/shared/source_ref_order.go

@@ -63,6 +63,29 @@ func (o SourceRefOrder) EarliestValid(refs []source.SourceRef) (int, bool) {
 	return earliest, found
 }
 
+// OrderEndpoints returns an owned copy of refs with each resolvable range
+// ordered by document position. References outside the indexed source, or
+// whose endpoints cannot both be resolved, remain unchanged so validators can
+// diagnose them.
+func (o SourceRefOrder) OrderEndpoints(refs []source.SourceRef) []source.SourceRef {
+	if refs == nil {
+		return nil
+	}
+	ordered := append([]source.SourceRef{}, refs...)
+	for index := range ordered {
+		ref := &ordered[index]
+		if ref.SourceID != o.sourceID || ref.StartUnitID <= 0 || ref.EndUnitID <= 0 {
+			continue
+		}
+		start, startOK := o.index.Position(ref.StartUnitID)
+		end, endOK := o.index.Position(ref.EndUnitID)
+		if startOK && endOK && start > end {
+			ref.StartUnitID, ref.EndUnitID = ref.EndUnitID, ref.StartUnitID
+		}
+	}
+	return ordered
+}
+
 // Canonicalize returns an owned, stable-sorted, exactly de-duplicated copy of
 // refs. It deliberately preserves invalid references for diagnostics.
 func (o SourceRefOrder) Canonicalize(refs []source.SourceRef) []source.SourceRef {

internal/modules/dnd/shared/source_ref_order_test.go

@@ -58,6 +58,38 @@ func TestSourceRefOrderCanonicalizePreservesRepresentationAndOwnership(t *testin
 	}
 }
 
+func TestSourceRefOrderOrdersOnlyResolvableCurrentSourceEndpoints(t *testing.T) {
+	doc := unitRefSourceDocument(30, 10, 20)
+	order := NewSourceRefOrder(doc)
+	input := []source.SourceRef{
+		{SourceID: doc.ID, StartUnitID: 30, EndUnitID: 10},
+		{SourceID: doc.ID, StartUnitID: 20, EndUnitID: 30},
+		{SourceID: doc.ID, StartUnitID: 10, EndUnitID: 10},
+		{SourceID: "other", StartUnitID: 20, EndUnitID: 30},
+		{SourceID: doc.ID, StartUnitID: 999, EndUnitID: 30},
+		{SourceID: doc.ID, StartUnitID: 20, EndUnitID: 0},
+	}
+	want := []source.SourceRef{
+		{SourceID: doc.ID, StartUnitID: 30, EndUnitID: 10},
+		{SourceID: doc.ID, StartUnitID: 30, EndUnitID: 20},
+		{SourceID: doc.ID, StartUnitID: 10, EndUnitID: 10},
+		{SourceID: "other", StartUnitID: 20, EndUnitID: 30},
+		{SourceID: doc.ID, StartUnitID: 999, EndUnitID: 30},
+		{SourceID: doc.ID, StartUnitID: 20, EndUnitID: 0},
+	}
+	got := order.OrderEndpoints(input)
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("OrderEndpoints() = %#v, want %#v", got, want)
+	}
+	got[0].StartUnitID = 999
+	if input[0].StartUnitID != 30 {
+		t.Fatal("OrderEndpoints() output aliases input")
+	}
+	if got := order.OrderEndpoints(nil); got != nil {
+		t.Fatalf("OrderEndpoints(nil) = %#v, want nil", got)
+	}
+}
+
 func TestSourceRefOrderSnapshotAndEarliestValid(t *testing.T) {
 	doc := unitRefSourceDocument(30, 10, 20)
 	sourceID := doc.ID