Split the expansion's hold from the group's, and read a table's row from where the table is entered

doc.go

@@ -24,7 +24,7 @@ package fejkdata
 //     start one each, `FakeStruct` one per record, and `expandAnew` one per
 //     iteration of a `template.repeat`.
 //   - hold — keeping one draw of a name, so every route to it reads that value:
-//     `template.held`, `hold`, `readField`.
+//     `template.held`, `hold`, `groupHold`, `readField`.
 //   - draw group — reference draws held apart inside one render:
 //     `template.drawGroup` as the data spells it, `template.drawGroupKey` as a
 //     render reads it, `holdSet`, `renderScope`.

drawfence_test.go

@@ -134,7 +134,7 @@ func renderRoot(s *session, t *template) {
 			var set holdSet
 			sc := renderScope{set: &set}
 			sc.hold().pins.pin(t.table, r)
-			render(s, t.table.pinnedRow, sc)
+			render(s, t.table.pinnedRow, sc.at(t.table.pinnedRow, &sc.hold().pins))
 		}
 	case t.repeat > 1:
 		expand(s, t, sc)

hold.go

@@ -5,13 +5,18 @@ import (
 	"strings"
 )
 
-// hold is what has already been drawn for held names: the variant each was drawn as, so every
+// hold is what one expansion has drawn for the names it holds: the variant each was drawn as, so
-// path under it reads one row; the value each read produced, by its path, so the same read
+// every path under it reads one variant; and the value each read produced, by its path, so the
-// written twice reads one value; and the table rows those reads pinned. An expansion keeps one for
+// same read written twice reads one value.
-// its sibling names, and a render one per group for its reference paths.
 type hold struct {
 	variant map[string]node
 	value   map[string]readValue
+}
+
+// groupHold is what one render's draw group has drawn for its reference paths: a hold, and the
+// table rows those paths pinned.
+type groupHold struct {
+	hold
 	pins pinSet
 }
 
@@ -25,7 +30,9 @@ type readValue struct {
 // token addresses by dotted path, or a field an operand reads — is drawn once and
 // kept, so {place.postal-code} and {place.locality} read one row, either read twice
 // gives one value, and a shown operand is the operand computed. Every other name is
-// drawn afresh, so {word} {word} still draws twice.
+// drawn afresh, so {word} {word} still draws twice. A reference path is kept in the
+// render's hold for its group, so its draw spans the render; every other held name in
+// held, the expansion's.
 func readField(s *session, t *template, held *hold, sc renderScope, a arm) readValue {
 	if s.trace != nil {
 		traceRead(s.trace, t, sc, a)
@@ -36,18 +43,23 @@ func readField(s *session, t *template, held *hold, sc renderScope, a arm) readV
 		}
 		return readValue{text: render(s, t.head(a.key), sc)}
 	}
-	d := readHold(held, sc, a)
+	w := pathDraw{s: s, held: held, a: &a}
-	if r, done := d.value[a.path]; done {
+	if isRef(a.key) && len(a.tail) > 0 {
+		group := sc.hold()
+		w.held, w.pins = &group.hold, &group.pins
+	}
+	if r, done := w.held.value[a.path]; done {
 		return r
 	}
-	if len(a.tail) > 0 {
+	leaf := drawPath(t.head(a.key), a.tail, a.key, &w)
-		sc.pins = &d.pins
+	if w.pins != nil {
+		sc = sc.at(leaf, w.pins)
 	}
-	r := renderLeaf(s, drawPath(t.head(a.key), a.tail, a.key, &pathDraw{s: s, pins: &d.pins, held: d, a: &a}), sc)
+	r := renderLeaf(s, leaf, sc)
-	if d.value == nil {
+	if w.held.value == nil {
-		d.value = map[string]readValue{}
+		w.held.value = map[string]readValue{}
 	}
-	d.value[a.path] = r
+	w.held.value[a.path] = r
 	return r
 }
 
@@ -64,21 +76,11 @@ func traceRead(trace *renderTrace, t *template, sc renderScope, a arm) {
 	case t.cellOf != nil:
 		table, row = t.cellOf.path, t.cellRow
 	case t.table != nil:
-		table, row = t.table.path, sc.rows().mustRow(t.table)
+		table, row = t.table.path, sc.rowOf(t.table)
 	}
 	trace.read(strings.Clone(sc.group), strings.Clone(table), row, a)
 }
 
-// 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
-// bare reference, held.
-func readHold(held *hold, sc renderScope, a arm) *hold {
-	if isRef(a.key) && len(a.tail) > 0 {
-		return sc.hold()
-	}
-	return held
-}
-
 // renderLeaf draws and renders what a read lands on: null on a null item, or on a column of one
 // reference alone whose read drew null.
 func renderLeaf(s *session, n node, sc renderScope) readValue {

holdset.go

@@ -1,23 +1,23 @@
 package fejkdata
 
 import (
+	"fmt"
 	"strings"
 )
 
 // holdSet is one render's reference draws: the unnamed draw group's, and each named one's.
 type holdSet struct {
-	unnamed hold
+	unnamed groupHold
-	named   map[string]*hold
+	named   map[string]*groupHold
 }
 
 // renderScope is where a render reads its reference paths: a hold set, in the draw group of the
-// template rendering, and the pin set a table's columns read their row from: a whole read's own,
+// template rendering; and row, the row of the table rendering, which its columns read. It passes by value, and what is read from it reaches a map key, an interface or
-// else the hold's. It passes by value, and what is read from it reaches a map key, an interface or
 // a func value only as a copy; else sc, and with it every render's hold set, moves to the heap.
 type renderScope struct {
 	set   *holdSet
 	group string
-	pins  *pinSet
+	row   tablePin
 }
 
 // renderOnce renders n as one render, over a hold set of its own.
@@ -47,23 +47,36 @@ func (sc renderScope) in(t *template) renderScope {
 	return sc
 }
 
-func (sc renderScope) rows() *pinSet {
+// at is the scope n, the leaf of a path that pinned its rows in pins, renders in: where n is a
-	if sc.pins != nil {
+// table's row or column, at the row pins holds for that table.
-		return sc.pins
+func (sc renderScope) at(n node, pins *pinSet) renderScope {
+	switch n := n.(type) {
+	case *tableRow:
+		sc.row = tablePin{n.t, pins.mustRow(n.t)}
+	case *tableColumn:
+		sc.row = tablePin{n.t, pins.mustRow(n.t)}
 	}
-	return &sc.hold().pins
+	return sc
 }
 
-func (sc renderScope) hold() *hold {
+// rowOf is the row of t its columns render from.
+func (sc renderScope) rowOf(t *table) int {
+	if sc.row.t != t {
+		panic(fmt.Sprintf("fejkdata: a column of %s is rendered with no row pinned", t.category))
+	}
+	return sc.row.row
+}
+
+func (sc renderScope) hold() *groupHold {
 	if sc.group == "" {
 		return &sc.set.unnamed
 	}
 	d, drew := sc.set.named[sc.group]
 	if !drew {
 		if sc.set.named == nil {
-			sc.set.named = map[string]*hold{}
+			sc.set.named = map[string]*groupHold{}
 		}
-		d = &hold{}
+		d = &groupHold{}
 		sc.set.named[strings.Clone(sc.group)] = d
 	}
 	return d

path.go

@@ -332,9 +332,9 @@ func (w *pathProbe) readRow(t *table, r tableRoute) error {
 	return nil
 }
 
-// pathDraw draws the rows and variants a proved path reads, pinning them in pins.
+// pathDraw draws the rows and variants a proved path reads, pinning the rows in pins, which
-// For a held read, held keeps the variant drawn at each level of a, so paths
+// only a path from a reference needs: a table is a category. For a held read, held keeps the
-// sharing a prefix share it.
+// variant drawn at each level of a, so paths sharing a prefix share it.
 type pathDraw struct {
 	s    *session
 	pins *pinSet

record.go

@@ -263,6 +263,9 @@ func recordOf(n node) (*template, []Column, error) {
 // over sc's hold; a table's columns read the row pinned there.
 func renderRecord(s *session, t *template, columns []Column, sc renderScope) *Record {
 	sc = sc.in(t)
+	if t.table != nil {
+		sc = sc.at(t.table.pinnedRow, &sc.hold().pins)
+	}
 	r := &Record{columns: append([]Column(nil), columns...)}
 	for i := range r.columns {
 		column := renderLeaf(s, t.fields[r.columns[i].Name], sc)

render.go

@@ -33,7 +33,7 @@ func (f *Generator) Fake(path string) (string, error) {
 	if _, ok := n.(*folder); ok {
 		return "", fmt.Errorf("fejkdata: %s names a folder, not a value", path)
 	}
-	return render(f.rand, n, sc), nil
+	return render(f.rand, n, sc.at(n, &sc.hold().pins)), nil
 }
 
 // descend walks a caller's path to the node it names, pinning in sc the rows it
@@ -56,14 +56,12 @@ func render(s *session, n node, sc renderScope) string {
 	case *nullItem:
 		return ""
 	case *table:
-		var own pinSet
+		sc.row = tablePin{n, n.drawRow(s)}
-		own.add(n, n.drawRow(s))
-		sc.pins = &own
 		return expand(s, n.formatTemplate, sc)
 	case *tableRow:
 		return expand(s, n.t.formatTemplate, sc)
 	case *tableColumn:
-		row := sc.rows().mustRow(n.t)
+		row := sc.rowOf(n.t)
 		if cell := n.t.cellTemplate(row, n.i); cell != nil {
 			return render(s, cell, sc)
 		}