Record each selector's table and spelling in pathProbe.readRow

path.go

@@ -289,10 +289,13 @@ func (w *pathCover) walk(n node, tail []string) (node, error) {
 
 // pathProbe proves a path resolves without drawing. Where pathCheck walks every
 // variant of a choice, it walks the first, which carriedByAll lets stand for all; at a
-// table it selects as pathCheck does and marks in drawn the tables a draw would pin.
+// table it selects as pathCheck does. Probing an arm, it records what the read takes:
+// in drawn the tables a draw would pin, and in sels each selector's table and spelling.
 type pathProbe struct {
 	pins  pinSet
+	a     *arm
 	drawn map[*table]bool
+	sels  []tableSel
 }
 
 func (w *pathProbe) walk(n node, tail []string) (node, error) {
@@ -310,7 +313,7 @@ func (w *pathProbe) walk(n node, tail []string) (node, error) {
 			if r, err = x.route(tail, descended); err != nil {
 				return nil, err
 			}
-			if err := w.readRow(x, r); err != nil {
+			if err := w.readRow(x, tail, r); err != nil {
 				return nil, err
 			}
 			n, tail, descended = r.next, r.rest, r.descends
@@ -324,15 +327,22 @@ func (w *pathProbe) walk(n node, tail []string) (node, error) {
 	return n, nil
 }
 
-func (w *pathProbe) readRow(t *table, r tableRoute) error {
+func (w *pathProbe) readRow(t *table, tail []string, r tableRoute) error {
-	if r.sel != "" {
+	switch {
+	case r.sel != "":
+		if w.a != nil {
+			walked := len(w.a.tail) - len(tail) + 1
+			written := w.a.spelling[:len(w.a.spelling)-len(joinSegments(w.a.tail))]
+			w.sels = append(w.sels, tableSel{t, written + joinSegments(w.a.tail[:walked])})
+		}
 		return w.pins.selectRow(t, r.sel)
-	}
+	case r.draw && w.a != nil:
-	if !r.draw {
+		if w.drawn == nil {
-		return nil
+			w.drawn = map[*table]bool{}
-	}
+		}
-	for stop := w.pins.nearestPinned(t); t != stop; t = t.parentT {
+		for stop := w.pins.nearestPinned(t); t != stop; t = t.parentT {
-		w.drawn[t] = true
+			w.drawn[t] = true
+		}
 	}
 	return nil
 }

readsurvey.go

@@ -191,21 +191,10 @@ func tableReadOf(head node, a arm, leaf node) *tableRead {
 	if !isTable {
 		return nil
 	}
-	probe := &pathProbe{drawn: map[*table]bool{}}
+	probe := &pathProbe{a: &a}
 	_, _ = probe.walk(t, a.tail)
-	tr := &tableRead{headTable: t, pins: probe.pins, drawn: probe.drawn}
+	_, landsRow := leaf.(*tableRow)
-	written := a.spelling[:len(a.spelling)-len(joinSegments(a.tail))]
+	return &tableRead{headTable: t, pins: probe.pins, drawn: probe.drawn, sels: probe.sels, landsRow: landsRow}
-	cur := t
-	for i, seg := range a.tail {
-		switch d := cur.descendant(seg); {
-		case isSelector(seg):
-			tr.sels = append(tr.sels, tableSel{cur, written + joinSegments(a.tail[:i+1])})
-		case d != nil:
-			cur = d
-		}
-	}
-	_, tr.landsRow = leaf.(*tableRow)
-	return tr
 }
 
 // selected is the selector in r on t, or on the nearest ancestor of t it selects.

render.go

@@ -39,7 +39,7 @@ func (f *Generator) Fake(path string) (string, error) {
 // selects or draws.
 func descend(s *session, root node, segments []string, sc renderScope) (node, error) {
 	// docs/decisions.md#a-path-is-walked-once-without-drawing-before-it-is-walked-for-real
-	if _, err := (&pathProbe{drawn: map[*table]bool{}}).walk(root, segments); err != nil {
+	if _, err := (&pathProbe{}).walk(root, segments); err != nil {
 		return nil, err
 	}
 	return drawPath(root, segments, "", &pathDraw{s: s, pins: &sc.groupHold().pins}), nil

todo.md

@@ -28,9 +28,6 @@ ranking `readSurvey.walk` hardest and all seven the unit they would least modify
 
 This round, in order:
 
-- Record each selector's table and spelling in `pathProbe.readRow`, and delete
-  `tableReadOf`'s second walk over the tail: it steps by `descendant` apart from
-  `route`, so a route that steps up to a parent row credits a selector to the wrong table.
 - Move the render's read path — `readField`, `readReference`, `readHeld`, `traceRead`,
   `renderLeaf`, `resolveChoice`, `renderOnce` and `expandAnew` — into `render.go`, and
   merge what `hold.go` and `holdset.go` keep into one file: both architects followed one read