Walk the own-family fence through a repeat and a draw group, and record that tables with token cells stay small

README.md

@@ -444,9 +444,10 @@ table another path in the group selects a row of, `{/city.name}` beside
 `{/country[SE].name}`, which the first token rendered would otherwise decide. `New`
 also refuses a link cell that is no key of the parent, a parent row no child links
 to, a chain of parents that closes, a table named like a column of any table above
-it, and a cell or format of a table that references a table of its own family, since
+it, and a cell or format of a table that references a table of its own family, through
-a row rendered whole would draw the family apart from itself: read the family from a
+any template, a `repeat` or a `drawGroup` included, since a row rendered whole would
-template beside it, or add the value as a column.
+draw the family apart from itself: read the family from a template beside it, or add
+the value as a column.
 
 ### Options and fields
 
@@ -969,6 +970,16 @@ renamed or retyped line is a major.
   they sit in two rows of one table, or in a row outside a selected ancestor's. A
   choice's items get no such treatment yet: two items selecting different rows
   are still refused.
+- **A table never reaches its own family, by any route.** A `repeat` iteration and a
+  `drawGroup` each draw apart on purpose, but a row that lists three localities from
+  other regions is the output the family exists to prevent, so the own-family fence
+  walks through both rather than stopping where the draw fences do.
+- **Tables carrying token cells stay small.** The family fence compares the reads of
+  every pair of rows that can render together, so a table whose every row's cell
+  selects a row of another table loads in time quadratic in its rows: about a
+  second at four thousand rows. No shipped table carries such cells, and a register
+  is a column set rather than a set of references, so the fence is left as it is
+  until a real data set needs the indexed form.
 - **A path is walked once without drawing before it is walked for real.** A path
   that fails below its first level then moves no seeded stream, at the cost of one
   draw-free walk per call, which allocates nothing.

draw.go

@@ -137,16 +137,19 @@ func (c *drawCheck) checkDrawGroup(path string, n node) error {
 
 func (c *drawCheck) checkDraws(path string, n node) error {
 	t, ok := n.(*template)
-	if !ok || !c.readsPath(t) {
+	if !ok {
+		return nil
+	}
+	if err := checkOwnFamily(t); err != nil {
+		return fmt.Errorf("%s: %w", path, err)
+	}
+	if !c.readsPath(t) {
 		return nil
 	}
 	w := newDrawWalk()
 	for _, e := range renderEdges(t) {
 		w.edge(t, e, drawAt{group: t.drawGroupKey, route: drawRoute{e.reached(), e.label}})
 	}
-	if err := w.checkOwnFamily(t); err != nil {
-		return fmt.Errorf("%s: %w", path, err)
-	}
 	if err := w.check(); err != nil {
 		return fmt.Errorf("%s: %w", path, err)
 	}
@@ -154,9 +157,10 @@ func (c *drawCheck) checkDraws(path string, n node) error {
 }
 
 // checkOwnFamily refuses a table's format or cell that reads, however many templates
-// away, a table of its own family: a row rendered whole draws its row without
+// away and through a repeat or a draw group too, a table of its own family: a row
-// pinning it, so the family would draw apart from the row being rendered.
+// rendered whole draws its row without pinning it, so the family would draw apart
-func (w *drawWalk) checkOwnFamily(t *template) error {
+// from the row being rendered, whichever draws the reaching template holds.
+func checkOwnFamily(t *template) error {
 	own := t.table
 	if own == nil {
 		own = t.cellOf
@@ -164,10 +168,27 @@ func (w *drawWalk) checkOwnFamily(t *template) error {
 	if own == nil {
 		return nil
 	}
-	for _, r := range w.reads {
+	seen := map[node]bool{}
-		if r.tr != nil && r.tr.head.family() == own.family() {
+	var find func(n node) (renderEdge, *table, bool)
-			return fmt.Errorf("%s reads %s, a table of its own family, which a row of %s rendered whole would draw apart from; read the family from a template beside it, or add the value as a column", r.at.route.spelled(r.a.name), r.tr.head.category, own.category)
+	find = func(n node) (renderEdge, *table, bool) {
+		if seen[n] {
+			return renderEdge{}, nil, false
 		}
+		seen[n] = true
+		for _, e := range renderEdges(n) {
+			if a, isRef := refRead(n, e.label); isRef {
+				if head, isTable := n.(*template).fields[a.key].(*table); isTable && head.family() == own.family() {
+					return e, head, true
+				}
+			}
+			if e, head, found := find(e.to); found {
+				return e, head, true
+			}
+		}
+		return renderEdge{}, nil, false
+	}
+	if e, head, found := find(t); found {
+		return fmt.Errorf("%s reads %s, a table of its own family, which a row of %s rendered whole would draw apart from; read the family from a template beside it, or add the value as a column", e.reached(), head.category, own.category)
 	}
 	return nil
 }