Trace the reads a render makes, gather a render's draws in renderDraws and columnDraws, and drop the done item

drawfence.go

@@ -69,14 +69,19 @@ func (c *drawCheck) checkDraws(path string, n node) error {
 	if !c.readsPath(t) {
 		return nil
 	}
+	if err := renderDraws(t).check(); err != nil {
+		return fmt.Errorf("%s: %w", path, err)
+	}
+	return nil
+}
+
+// renderDraws gathers the reads one render of t makes.
+func renderDraws(t *template) *drawWalk {
 	w := newDrawWalk()
 	for _, e := range renderEdges(t) {
 		w.edge(t, e, drawAt{group: t.drawGroupKey, route: drawRoute{e.reached(), e.label}})
 	}
-	if err := w.check(); err != nil {
-		return fmt.Errorf("%s: %w", path, err)
-	}
-	return nil
+	return w
 }
 
 // checkRecordDraws fences the columns of a record — a template compiled at the top without a
@@ -172,12 +177,15 @@ func refRead(n node, label string) (arm, bool) {
 }
 
 // checkColumnDraws fences a record's columns as one render.
-func checkColumnDraws(t *template, columns []string) error {
+func checkColumnDraws(t *template, columns []string) error { return columnDraws(t, columns).check() }
+
+// columnDraws gathers the reads one record render of t's columns makes.
+func columnDraws(t *template, columns []string) *drawWalk {
 	w := newDrawWalk()
 	for _, name := range columns {
 		w.walk(t.fields[name], drawAt{group: t.drawGroupKey, route: drawRoute{spelling: fmt.Sprintf("column %q", name)}})
 	}
-	return w.check()
+	return w
 }
 
 // drawWalk gathers the references one render reads, by draw group, for check to compare.

drawfence_test.go

@@ -10,7 +10,7 @@ import (
 func fenceCorpus(t *testing.T) *Generator {
 	t.Helper()
 	dir := writeFiles(t, with(geo(), map[string]string{
-		"addr.json":  `{"format":"{a} {b} {c}","a":{"format":"{/locality.name}, {/municipality.name}"},"b":{"format":"{/region[12].name} {/place}","drawGroup":"g"},"c":{"format":"{/place.zip} ","repeat":2}}`,
+		"addr.json":  `{"format":"{a} {b} {c}","a":"{/locality.name}, {/municipality.name}","b":{"format":"{/region[12].name} {/place}","drawGroup":"g"},"c":{"format":"{/place.zip} ","repeat":2}}`,
 		"place.json": `{"format":"{zip} {name} {tag}","rows":"place.tsv","key":"name"}`,
 		"place.tsv":  "name\tzip\ttag\nStockholm\t1{digits(2)} {digits(2)}\t{/w}\nTranås\t573 {digits(2)}\t{/region[12].name}\n",
 		"rec.json":   `{"format":"","l":"{/locality.name}","m":"{/municipality.name}","t":"{/place[Stockholm].tag}"}`,
@@ -67,13 +67,23 @@ func TestEveryReadARenderMakesIsGathered(t *testing.T) {
 }
 
 // wantGathered renders a root five times over the seeded stream and fails where a reference the
-// render read is not among gathered: same draw group and path, under rows that can render together.
+// render read is not among gathered: same draw group and path, and where the read sits in a cell,
+// gathered from that row or from no row of its table.
 func wantGathered(t *testing.T, s *session, label string, gathered []pathRead, renderOnce func()) {
 	t.Helper()
 	var reads []pathRead
-	s.trace = &renderTrace{read: func(_ *template, group string, pins pinSet, a arm) {
-		if s.trace.depth == 0 && isRef(a.key) {
-			reads = append(reads, pathRead{at: drawAt{group: group, pins: pins}, a: a})
+	seen := map[readKey]bool{}
+	s.trace = &renderTrace{read: func(from *template, group string, a arm) {
+		if s.trace.depth != 0 || !isRef(a.key) {
+			return
+		}
+		r := pathRead{at: drawAt{group: group}, a: a}
+		if from.cellOf != nil {
+			r.at.pins.add(from.cellOf, from.cellRow)
+		}
+		if k := (readKey{group, a.path, r.at.rowsKey()}); !seen[k] {
+			seen[k] = true
+			reads = append(reads, r)
 		}
 	}}
 	defer func() { s.trace = nil }()
@@ -82,27 +92,27 @@ func wantGathered(t *testing.T, s *session, label string, gathered []pathRead, r
 	}
 	for _, r := range reads {
 		if !gathers(gathered, r) {
-			t.Errorf("%s: the render read {%s} in draw group %q with %s pinned, and drawWalk gathered no such read", label, r.a.spelling, r.at.group, pinned(&r.at.pins))
+			t.Errorf("%s: the render read {%s} in draw group %q from %s, and drawWalk gathered no such read", label, r.a.spelling, r.at.group, spellPins(&r.at.pins))
 		}
 	}
 }
 
 func gathers(gathered []pathRead, r pathRead) bool {
 	for _, g := range gathered {
-		if g.at.group == r.at.group && g.a.path == r.a.path && !g.at.pins.differs(&r.at.pins) {
+		if g.at.group == r.at.group && g.a.path == r.a.path && !g.at.pins.differs(&r.at.pins) && !g.at.wholePins.differs(&r.at.pins) {
 			return true
 		}
 	}
 	return false
 }
 
-func pinned(p *pinSet) string {
+func spellPins(p *pinSet) string {
 	var rows []string
 	p.each(func(t *table, r int) { rows = append(rows, t.selectorSpelling(r)) })
 	if len(rows) == 0 {
-		return "no row"
+		return "no cell"
 	}
-	return strings.Join(rows, ", ")
+	return "the cell of " + strings.Join(rows, ", ")
 }
 
 // renderRoot renders t the way the render reaches it: a table's format through its table, a cell in

fejkdata.go

@@ -45,6 +45,7 @@ type Generator struct {
 type session struct {
 	*rand.Rand
 	counters map[string]uint64
+	trace    *renderTrace
 }
 
 func (s *session) next(key string) uint64 {

hold.go

@@ -2,6 +2,7 @@ package fejkdata
 
 import (
 	"fmt"
+	"strings"
 )
 
 // hold is what has already been drawn for held names: the variant each was drawn as, so every
@@ -27,6 +28,9 @@ type draw struct {
 // drawn afresh, so {word} {word} still draws twice. checkTokens, checkPath and
 // linkRefs prove every step, so the walk cannot fail.
 func readField(s *session, t *template, held *hold, sc renderScope, a arm) draw {
+	if s.trace != nil {
+		s.trace.read(t, strings.Clone(sc.group), a)
+	}
 	if !t.held[a.key] {
 		if len(a.tail) > 0 {
 			panic(fmt.Sprintf("fejkdata: %q reads a path into %q, which the expansion does not hold", a.spelling, a.key))
@@ -45,6 +49,13 @@ func readField(s *session, t *template, held *hold, sc renderScope, a arm) draw
 	return r
 }
 
+// renderTrace is a test's view of a render: each field a format reads, and how many repeat
+// iterations, each a render of its own, the read sits inside. nil outside a test.
+type renderTrace struct {
+	read  func(from *template, group string, a arm)
+	depth int
+}
+
 // readHold is the hold a held read keeps its draw in: for a reference that reads a path,
 // the render's hold for its group, so its draw spans the render; for a sibling, or a
 // reference read whole, held.

holdset.go

@@ -35,6 +35,10 @@ func renderOnce(s *session, n node) string {
 //go:noinline
 func expandAnew(s *session, t *template) string {
 	var set holdSet
+	if s.trace != nil {
+		s.trace.depth++
+		defer func() { s.trace.depth-- }()
+	}
 	return expand(s, t, renderScope{set: &set})
 }
 

todo.md

@@ -21,9 +21,6 @@ Self-sufficiency 5.6), every seat capped by Locality, and all nine naming
 
 This round, in order:
 
-- Hold the draw fences to what render does: a test rendering seeded draws that fails
-  where a read the render makes falls outside what `drawWalk` gathered. Today the two
-  models agree by a comment on `renderEdges`, and a new render route drifts silently.
 - Give "whole" one meaning: `doc.go` defines it as a read landing on a `tableRow`,
   while `drawAt.wholeTable`, `checkFamilyPair` and `checkOwnFamily`'s comment use it for
   a bare read landing on a `*table`, the one that draws without pinning.