Give prove, stepInto and columnItems a case per node kind, panicking on the rest

datatype.go

@@ -138,6 +138,9 @@ func columnItems(n node) (items []*template, nullable bool) {
 			items = append(items, n)
 		case *nullItem:
 			nullable = true
+		case *tableColumn:
+		default:
+			panic(internalError("columnItems has no case for node %T", n))
 		}
 	}
 	collect(n)

node.go

@@ -11,8 +11,9 @@ import (
 
 // node is a compiled element of the namespace tree: a folder, choice, null,
 // template, table, column or row. Compiling JSON into these once (see compile)
-// means rendering never re-inspects the raw JSON. A new kind needs a
+// means rendering never re-inspects the raw JSON. A new kind needs a case in
-// case in contained, paths, render and renderEdges; each panics on a kind it does not list.
+// columnItems, contained, paths, prove, render, renderEdges and stepInto; each
+// panics on a kind it does not list.
 type node interface{ isNode() }
 
 // folder is a namespace of named children, built from a directory of JSON files

path.go

@@ -142,6 +142,9 @@ func stepInto(n node, seg string) (node, error) {
 		}
 	case *tableColumn:
 		return nil, fmt.Errorf("no field %q: %q is a column, and a cell holds no fields", seg, n.t.header[n.i])
+	case *nullItem:
+	default:
+		panic(internalError("stepInto has no case for node %T", n))
 	}
 	return nil, fmt.Errorf("no field %q", seg)
 }

todo.md

@@ -28,10 +28,6 @@ ranking `readSurvey.walk` hardest and all seven the unit they would least modify
 
 This round, in order:
 
-- Give `prove`, `stepInto` and `columnItems` a case per node kind and panic through
-  `internalError` on the rest, and list every such switch in `node`'s doc: `prove`'s
-  default tells a typed column reading a bare table that it reads a null, and six seats
-  found `node` naming four of them.
 - Replace `disagreements`' ten keys with the rule they encode: a declared fix holds one
   datatype, a read one is `readTyped` where proven and `readAsText` otherwise, a text one
   is `otherAsText` beside an unproven read and `declare` otherwise. Six seats could not
@@ -222,8 +218,6 @@ by a `data-import/` script, as README goal 12 asks.
   first in Go's map order.
 - Report a CRLF rows file holding only its header as having no rows: `parseRows`
   answers "line 2 is empty".
-- Refuse a bare table read in a typed column with a reason naming the table, once
-  `prove` has a case per node kind.
 - Keep one copy of the selector characters in `data-import/`: `httpmethod.py` and
   `protocol.py` each copy `inSelector`, and `tsv.py`'s `write` enforces neither.
 - Refuse two whole reads of one table family in one render, which goal 5 promises is a

value.go

@@ -89,10 +89,14 @@ func (p *valueProof) prove(n node) proven {
 		v = p.proveTemplate(n)
 	case *tableColumn:
 		v = p.proveCells(n)
+	case *table:
+		v = p.prove(n.rowNode)
 	case *tableRow:
 		v = unproven(fmt.Sprintf("%q renders a row of %s, which is composed text", n.t.formatTemplate.format, n.t.segment))
-	default:
+	case *nullItem:
 		v = unproven(`it reads a null, which renders "" outside its own column`)
+	default:
+		panic(internalError("prove has no case for node %T", n))
 	}
 	p.memo[n] = v
 	return v