fix: a splice making room leaves the flow's parameters where they are (#1547)

.claude/skills/fix-issue/findings/mdl-backend/2026-10-21-splice-shift-moves-parameters.json

@@ -0,0 +1 @@
+{"area": "mdl/backend", "date": "2026-10-21", "symptom": "A splice that makes room for an inserted fragment (create or modify / alter … insert) moved the flow's parameters along with the row: one if/else inserted into NF_Do moved $Flag from its derived (200, 53) to (539, 53), a longer replace then to (699, 53), and from then on describe printed a parameter @position no script stated. Inserting before the first statement of a two-parameter microflow moved $Count from (300, 53) to (410, 53).", "cause": "mfmutator shift (splice.go) moves every top-level node past the cut, and a Microflows$MicroflowParameter is a top-level object of the unit's object collection (the decoded model keeps parameters apart, so nothing in the executor sees them as nodes). mxcli's derived parameter row is absolute (200 + idx*pitch, 53), right of the start event, so almost every insert's cut falls left of it.", "file": "mdl/backend/mfmutator/splice.go (shifted)", "insight": "Measure the authored convention before deciding what 'the row' is: 63 of 71 Studio Pro-authored parameters (PedApp 19/20, JTSBootLogboek 44/51) sit exactly at the start event's x, all above every other node, none within 60px of the flow line — a parameter belongs to the flow, not to the stretch of line past an insert, and Studio Pro moves nothing on insert. The decoded model hides this: microflows.Microflow carries Parameters apart from ObjectCollection, so a probe that type-switches the collection for *MicroflowParameter does not compile, while the BSON the mutator walks has them inline. Excluding them in shifted also keeps them out of pinnedPast, so a stated parameter position can no longer block a splice it is not in the way of.", "refs": ["ako/mxcli#1547", "ako/mxcli#1508"]}

mdl-examples/bug-tests/flow-geometry-1547-splice-leaves-parameters.mdl

@@ -0,0 +1,35 @@
+mdl 1;
+-- ============================================================================
+-- Bug: a splice making room moved the flow's parameters along with the row
+-- (ako/mxcli#1547)
+-- ============================================================================
+--
+-- The second statement inserts a log before the first one, so the splice
+-- makes room by moving everything after the start event along. Before the fix
+-- that included the two parameters, which mxcli draws on a row above the flow
+-- (x 200 and 300, y 53): both moved right, and from then on describe printed a
+-- @position on each that no script ever stated, the row drifting further with
+-- every insert.
+--
+-- Fixed: a parameter is not on the line the room is made on, so it stays
+-- where it is. Studio Pro authors draw a parameter above the start event, and
+-- inserting an activity in Studio Pro moves nothing.
+--
+-- Verify: exec, then
+--   mxcli -p app.mpr -c "describe microflow MyFirstModule.ACT_ParamRow"
+-- Expected: the parameters carry no @position (they are still on the derived
+-- row), and the new log is first.
+-- ============================================================================
+
+create or modify microflow MyFirstModule.ACT_ParamRow ($Name: String, $Count: Integer)
+begin
+  log info node 'Probe' 'first ' + $Name;
+  log info node 'Probe' 'second ' + toString($Count);
+end;
+
+create or modify microflow MyFirstModule.ACT_ParamRow ($Name: String, $Count: Integer)
+begin
+  log info node 'Probe' 'inserted';
+  log info node 'Probe' 'first ' + $Name;
+  log info node 'Probe' 'second ' + toString($Count);
+end;

mdl/backend/mfmutator/splice.go

@@ -881,10 +881,11 @@ func (m *Mutator) markRemoved(v any) {
 }
 
 // shift moves every top-level node past the cut (along axis ax, in the
-// direction of s) by delta. The sweep keeps everything on either side of the
-// cut exactly as it was relative to its neighbours, so only the flows that
-// cross the cut get longer; a flow's control vectors are relative to its ends,
-// so no curve changes. skip is a node that is about to be removed.
+// direction of s) by delta, but the parameters (shifted). The sweep keeps
+// everything on either side of the cut exactly as it was relative to its
+// neighbours, so only the flows that cross the cut get longer; a flow's
+// control vectors are relative to its ends, so no curve changes. skip is a
+// node that is about to be removed.
 func (m *Mutator) shift(g *graph, ax axis, s int, cut float64, delta int, skip string) {
 	for _, n := range g.order {
 		if !shifted(n, ax, s, cut, skip) {
@@ -895,9 +896,15 @@ func (m *Mutator) shift(g *graph, ax axis, s int, cut float64, delta int, skip s
 	}
 }
 
-// shifted reports whether shift moves n: a top-level node past the cut.
+// shifted reports whether shift moves n: a top-level node past the cut that
+// is not a parameter. A parameter is not on the line the room is made on: it
+// belongs to the flow as a whole, and Studio Pro authors draw it above the
+// start event (63 of 71 in PedApp and JTSBootLogboek at the start's x, none
+// within 60px of the line). Moved, it drifted right with every insert and
+// describe printed a @position the script never stated (ako/mxcli#1547).
 func shifted(n *node, ax axis, s int, cut float64, skip string) bool {
-	return n.loop == "" && n.id != skip && float64(s)*(float64(n.pos.get(ax))-cut) > 0
+	return n.loop == "" && n.id != skip && n.typ != "Microflows$MicroflowParameter" &&
+		float64(s)*(float64(n.pos.get(ax))-cut) > 0
 }
 
 // pinnedPast returns the first node shift would move that is drawn at a point

mdl/backend/mfmutator/splice_parameters_test.go

@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package mfmutator
+
+import (
+	"testing"
+
+	"github.com/mendixlabs/mxcli/model"
+)
+
+// A parameter is not on the line a fragment is spliced into, so making room
+// does not move it (ako/mxcli#1547). shift moved every top-level node past the
+// cut, parameters included: one inserted if/else moved a nanoflow's `$Flag`
+// from its derived (200, 53) to (539, 53), and from then on describe printed a
+// @position the script never stated, the row drifting right with every insert.
+// Studio Pro authors draw a parameter above the start event — 63 of 71 in
+// PedApp and JTSBootLogboek sit at the start's x, none within 60px of the line
+// — and an insert in Studio Pro moves nothing. The control is the activity
+// after the gap, which does move.
+func TestSplice_MakingRoomLeavesTheParameters(t *testing.T) {
+	positions := func(m *Mutator) map[string]point {
+		out := map[string]point{}
+		for _, n := range m.graph().order {
+			out[n.id] = n.pos
+		}
+		return out
+	}
+	objs := append(line(), obj("param", "Microflows$MicroflowParameter", 500, 53))
+	for _, c := range []struct {
+		name   string
+		splice func(m *Mutator) error
+	}{
+		{"an insert", func(m *Mutator) error { return m.InsertAfter(model.ID(uid("a")), oneActivity()) }},
+		{"a replace longer than what it replaces", func(m *Mutator) error { return m.Replace(model.ID(uid("a")), twoActivities()) }},
+	} {
+		t.Run(c.name, func(t *testing.T) {
+			m, _ := newMutator(t, unit(objs, lineFlows()))
+			if err := c.splice(m); err != nil {
+				t.Fatal(err)
+			}
+			got := positions(m)
+			if p := got[uid("b")]; p.X <= 420 {
+				t.Fatalf("control: b is at x=%d, want it moved along past 420 to make room", p.X)
+			}
+			if p := got[uid("param")]; p != (point{500, 53}) {
+				t.Errorf("the parameter moved to (%d, %d), want it left at (500, 53)", p.X, p.Y)
+			}
+		})
+	}
+}

mdl/executor/flow_modify_stated_positions_1508_test.go

@@ -160,6 +160,15 @@ func TestCreateOrModify_InsertDoesNotMoveStatedNodes1508(t *testing.T) {
 		if v.objectAt(t, -500, 200, "Microflows$ActionActivity") == "" {
 			t.Errorf("the declare the script draws at (-500, 200) moved:\n%s", describe())
 		}
+		// The parameter is not on the line the room was made on: it stays on
+		// its derived row (ako/mxcli#1547), where it moved to (539, 53).
+		for _, id := range v.order {
+			if o := v.objs[id]; afGet(o, "$Type") == "Microflows$MicroflowParameter" {
+				if x, y := afPoint(o); x != 200 || y != 53 {
+					t.Errorf("$Flag moved to (%d, %d), want it left at (200, 53):\n%s", x, y, describe())
+				}
+			}
+		}
 		split, merge, branch := nf1508Branch(t, v, "$Flag")
 		if len(branch) != 2 {
 			t.Fatalf("`if $Flag` has %d activities in its branch, want 2:\n%s", len(branch), describe())