Refuse a calc over digits(0) or a repeat of 0, name an option's wrong kind as JSON does, type the name scope kinds, and compile only from a jsonvalue.Value

README.md

@@ -996,6 +996,7 @@ internal/datatype/ the datatype a record column holds; the root's DataType is an
 internal/drawstate/ the seeded randomness and the {seq()} counters a generator draws through
 internal/grammar/ how the template language is written: format tokens, paths and selectors, reference sigils, identifiers, calc syntax, and whether a string is a template or a path
 internal/invariant/ the one phrase every package panics with when an invariant breaks
+internal/jsonvalue/ a decoded JSON value, its numbers kept as written, the one input a template compiles from
 internal/proven/ what a proof knows of a value, and the bounds a calc takes from its operands
 internal/rows/  a table's rows: the TSV, the options proved over it, the links between tables, row selection and draws, and the pin set one path or one named pick fixes
 data/           shipped data (JSON, and a TSV per table), embedded at build: locale folders, geo, misc

calc.go

@@ -114,14 +114,17 @@ func constantValue(n grammar.CalcNode, operand func(string) []node) (float64, bo
 	return 0, false
 }
 
-// neverNumeric reports a node no render of which is a number: a null, fixed text that
-// does not parse, or a choice of only such items. text is one such render.
+// neverNumeric reports a node no render of which is a number: a null, a repeat of 0, fixed
+// text that does not parse, or a choice of only such items. text is one such render.
 func neverNumeric(n node) (text string, never bool) {
 	switch n := n.(type) {
 	case *nullItem:
 		return "", true
 	case *template:
 		lit, fixed := n.fixedText()
+		if n.repeat == 0 {
+			return "", true
+		}
 		if !fixed || n.repeat != 1 {
 			return "", false
 		}

datatype.go

@@ -29,7 +29,7 @@ func datatypeOf(m map[string]any, pos position) (*DataType, error) {
 	}
 	name, ok := v.(string)
 	if !ok {
-		return nil, fmt.Errorf("datatype must be a string, got %T", v)
+		return nil, fmt.Errorf("datatype must be a string, not %s", jsonKind(v))
 	}
 	for d := DataTypeString; d < datatype.Count; d++ {
 		if name != d.String() {

fejkdata_test.go

@@ -7,8 +7,8 @@ import (
 	"testing"
 	"testing/fstest"
 
-	"github.com/larvit/fejkdata/internal/datafiles"
 	"github.com/larvit/fejkdata/internal/drawstate"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 )
 
 // newGenerator creates a generator over a single data directory, failing on
@@ -102,9 +102,9 @@ func engine(seed uint64) *Generator {
 }
 
 // parse unmarshals a JSON template fragment into its dynamic form.
-func parse(t *testing.T, s string) any {
+func parse(t *testing.T, s string) jsonvalue.Value {
 	t.Helper()
-	v, err := datafiles.DecodeJSON([]byte(s))
+	v, err := jsonvalue.Decode([]byte(s))
 	if err != nil {
 		t.Fatalf("parse %q: %v", s, err)
 	}

inline.go

@@ -3,8 +3,8 @@ package fejkdata
 import (
 	"fmt"
 
-	"github.com/larvit/fejkdata/internal/datafiles"
 	"github.com/larvit/fejkdata/internal/grammar"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 )
 
 // Template is an inline template compiled, referenced and validated against a
@@ -70,10 +70,10 @@ func compileInput(input string) (node, error) {
 
 // inputValue reads an inline template as the value compile takes: the JSON value it holds, the
 // whitespace around it dropped, or the input itself as a format string when it is not JSON.
-func inputValue(input string) any {
-	raw, err := datafiles.DecodeJSON([]byte(input))
+func inputValue(input string) jsonvalue.Value {
+	raw, err := jsonvalue.Decode([]byte(input))
 	if err != nil {
-		return input
+		return jsonvalue.String(input)
 	}
 	return raw
 }

internal/builtinfunc/builtins.go

@@ -36,6 +36,9 @@ var builtins = withTransforms(map[string]builtin{
 	"nanoid": {arity: 1, checkArgs: countArg, prep: chars(nanoidAlphabet)},
 	"hex":    {arity: 1, checkArgs: countArg, prep: chars(hexDigits)},
 	"digits": {arity: 1, checkArgs: countArg, prep: chars("0123456789"), prints: datatype.String, proveNumber: func(token string, prints datatype.DataType, a []string) proven.Facts {
+		if atoi(a[0]) == 0 {
+			return proven.Unproven("{" + token + "} prints nothing, which is no number")
+		}
 		return proven.Printing(token, prints, proven.Bounded(0, math.Pow(10, float64(atoi(a[0])))-1, true))
 	}},
 	"upper": {arity: 1, checkArgs: countArg, prep: chars("ABCDEFGHIJKLMNOPQRSTUVWXYZ")},

internal/datafiles/datafiles.go

@@ -2,8 +2,6 @@
 package datafiles
 
 import (
-	"bytes"
-	"encoding/json"
 	"fmt"
 	"io/fs"
 	"os"
@@ -11,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/larvit/fejkdata/internal/grammar"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 )
 
 // Source is one tree to load: an fs.FS and the directory in it to start from. label
@@ -35,7 +34,7 @@ func FS(fsys fs.FS, base string) Source { return Source{fsys: fsys, base: base}
 type Category struct {
 	Folders []string
 	Name    string
-	JSON    any
+	JSON    jsonvalue.Value
 	rows    *rowsFiles
 }
 
@@ -142,7 +141,7 @@ func (s Source) compileFile(dir []string, file string, rows *rowsFiles, compile
 	if err != nil {
 		return false, fmt.Errorf("%s: %w", s.labelled(full), err)
 	}
-	raw, err := DecodeJSON(b)
+	raw, err := jsonvalue.Decode(b)
 	if err != nil {
 		return false, fmt.Errorf("%s: %w", s.labelled(full), err)
 	}
@@ -179,14 +178,3 @@ func (r *rowsFiles) read(name string) (string, error) {
 	}
 	return string(b), nil
 }
-
-// DecodeJSON decodes one JSON value, keeping each number as the json.Number it is written as.
-func DecodeJSON(b []byte) (any, error) {
-	var v any
-	if !json.Valid(b) {
-		return nil, json.Unmarshal(b, &v)
-	}
-	dec := json.NewDecoder(bytes.NewReader(b))
-	dec.UseNumber()
-	return v, dec.Decode(&v)
-}

internal/datafiles/datafiles_test.go

@@ -20,7 +20,7 @@ func walk(t *testing.T, src Source) ([]handed, error) {
 	t.Helper()
 	var got []handed
 	err := src.Walk(func(c Category) error {
-		got = append(got, handed{c.Folders, c.Name, c.JSON})
+		got = append(got, handed{c.Folders, c.Name, c.JSON.Any()})
 		return nil
 	})
 	return got, err
@@ -133,7 +133,7 @@ func TestLoadHandsOneCategoryAndItsRows(t *testing.T) {
 	var got handed
 	var rows string
 	err := src.Load([]string{"sub"}, "t", func(c Category) error {
-		got = handed{c.Folders, c.Name, c.JSON}
+		got = handed{c.Folders, c.Name, c.JSON.Any()}
 		var err error
 		rows, err = c.ReadRows("t.tsv")
 		return err

internal/jsonvalue/jsonvalue.go

@@ -0,0 +1,39 @@
+// Package jsonvalue holds a decoded JSON value whose numbers keep the text they are written in.
+package jsonvalue
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+// Value is a JSON value that only Decode, String and Object make, so a template never compiles
+// from a value encoding/json decoded with its numbers as float64.
+type Value struct{ v any }
+
+// Decode decodes one JSON value, keeping each number as the json.Number it is written as.
+func Decode(b []byte) (Value, error) {
+	var v any
+	if !json.Valid(b) {
+		return Value{}, json.Unmarshal(b, &v)
+	}
+	dec := json.NewDecoder(bytes.NewReader(b))
+	dec.UseNumber()
+	err := dec.Decode(&v)
+	return Value{v}, err
+}
+
+// String is the JSON string s.
+func String(s string) Value { return Value{s} }
+
+// Object is the JSON object holding fields.
+func Object(fields map[string]Value) Value {
+	m := make(map[string]any, len(fields))
+	for k, f := range fields {
+		m[k] = f.v
+	}
+	return Value{m}
+}
+
+// Any is the value as encoding/json decodes it: a map[string]any, []any, string, json.Number,
+// bool or nil.
+func (v Value) Any() any { return v.v }

name.go

@@ -111,22 +111,37 @@ func (sc *nameScope) bindAll(t *template, where string) error {
 
 // spelled names the scope in an error.
 func (sc *nameScope) spelled() string {
-	if sc.up == nil && sc.kind() != "repeat" {
-		return "outside any repeat"
+	if k := sc.kind(); k != scopeCategory {
+		return "in one " + k.String()
 	}
-	return "in one " + sc.kind()
+	return "outside any repeat"
 }
 
-// kind names what a scope inside the category's is: a repeat, or a choice's item.
-func (sc *nameScope) kind() string {
-	if t, isTemplate := sc.owner.(*template); isTemplate && t.repeat > 1 {
-		return "repeat"
-	}
-	return "choice item"
+// scopeKind is what a name scope is: the category's own, a repeat's, or a choice's item's.
+type scopeKind uint8
+
+const (
+	scopeCategory scopeKind = iota
+	scopeRepeat
+	scopeChoiceItem
+)
+
+func (k scopeKind) String() string {
+	return [...]string{scopeCategory: "category", scopeRepeat: "repeat", scopeChoiceItem: "choice item"}[k]
 }
 
-// ownScope is the scope t renders a frame of: a category's, once per render of its root, or a
-// repeat's, once per iteration. It is nil where t owns no scope, or its scope binds no name.
+func (sc *nameScope) kind() scopeKind {
+	switch t, isTemplate := sc.owner.(*template); {
+	case isTemplate && t.repeat > 1:
+		return scopeRepeat
+	case sc.up == nil:
+		return scopeCategory
+	}
+	return scopeChoiceItem
+}
+
+// ownScope is the scope t renders a frame of: a category's, once per render of its root, a
+// repeat's, once per iteration, or a choice item's, once per draw of the item. It is nil where t owns no scope, or its scope binds no name.
 func (t *template) ownScope() *nameScope {
 	if sc := t.nameScope; sc != nil && sc.owner == node(t) && len(sc.order) > 0 {
 		return sc
@@ -190,7 +205,7 @@ func unanswered(where string, u unboundRead, seen *nameScope, scopes []*nameScop
 			if at == "" {
 				at = "an item of the root choice"
 			}
-			if sc.kind() == "choice item" {
+			if sc.kind() == scopeChoiceItem {
 				return fmt.Errorf("%s%w; name %q is bound at %s, inside an item of a choice, which a read outside that item cannot see; bind it outside the choice", where, u.err, u.head, at)
 			}
 			return fmt.Errorf("%s%w; name %q is bound at %s, inside a repeat, which a read outside the repeat cannot see; bind it outside the repeat to read one pick on every line", where, u.err, u.head, at)

node.go

@@ -9,6 +9,7 @@ import (
 	"github.com/larvit/fejkdata/internal/datafiles"
 	"github.com/larvit/fejkdata/internal/grammar"
 	"github.com/larvit/fejkdata/internal/invariant"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 )
 
 // node is a compiled element of the namespace tree: a folder, choice, null,
@@ -89,8 +90,8 @@ func (t *template) startOf(name string) node {
 
 // compile converts parsed JSON — a category or an inline template — into a node tree,
 // validating structure up front.
-func compile(v any) (node, error) {
-	n, err := compileItem(v, atTop)
+func compile(v jsonvalue.Value) (node, error) {
+	n, err := compileItem(v.Any(), atTop)
 	if err != nil {
 		return nil, err
 	}
@@ -100,7 +101,7 @@ func compile(v any) (node, error) {
 // compileCategory compiles a data file's value, which may be a table over a rows
 // file beside it.
 func compileCategory(c datafiles.Category) (node, error) {
-	if m, ok := c.JSON.(map[string]any); ok {
+	if m, ok := c.JSON.Any().(map[string]any); ok {
 		if _, isTable := m["rows"]; isTable {
 			return compileTable(m, c.Folders, c.Name, c.ReadRows)
 		}
@@ -276,7 +277,7 @@ func readOptions(m map[string]any, pos position) (templateOptions, error) {
 	}
 	if sv, ok := m["separator"]; ok {
 		if o.separator, ok = sv.(string); !ok {
-			return o, fmt.Errorf("separator must be a string, got %T", sv)
+			return o, fmt.Errorf("separator must be a string, not %s", jsonKind(sv))
 		}
 	}
 	return o, nil

struct.go

@@ -12,6 +12,7 @@ import (
 	"github.com/larvit/fejkdata/internal/drawstate"
 	"github.com/larvit/fejkdata/internal/grammar"
 	"github.com/larvit/fejkdata/internal/invariant"
+	"github.com/larvit/fejkdata/internal/jsonvalue"
 	"github.com/larvit/fejkdata/internal/proven"
 )
 
@@ -95,7 +96,7 @@ type structFields struct {
 	*structCompile
 	typ   reflect.Type
 	label string
-	tags  map[string]any
+	tags  map[string]jsonvalue.Value
 	shape *structShape
 }
 
@@ -105,7 +106,7 @@ func (sc *structCompile) compileShape(t reflect.Type, label string) (*structShap
 	}
 	sc.visiting[t] = true
 	defer delete(sc.visiting, t)
-	c := &structFields{structCompile: sc, typ: t, label: label, tags: map[string]any{}, shape: &structShape{}}
+	c := &structFields{structCompile: sc, typ: t, label: label, tags: map[string]jsonvalue.Value{}, shape: &structShape{}}
 	if err := c.gatherFields(t, nil); err != nil {
 		return nil, err
 	}
@@ -214,25 +215,25 @@ func (c *structFields) nest(sf reflect.StructField, elem reflect.Type) error {
 
 // tagValue reads a field's fake tag as the value its column compiles from: an inline template
 // as written, or a path as the reference {/path}.
-func tagValue(sf reflect.StructField, tag string) (any, error) {
+func tagValue(sf reflect.StructField, tag string) (jsonvalue.Value, error) {
 	if err := checkTaggedType(sf); err != nil {
-		return nil, err
+		return jsonvalue.Value{}, err
 	}
 	inline, err := grammar.IsTemplate(tag)
 	switch {
 	case err != nil:
-		return nil, err
+		return jsonvalue.Value{}, err
 	case inline:
 		return inputValue(tag), nil
 	}
 	path, err := grammar.CallerPath(tag)
 	if err != nil {
-		return nil, err
+		return jsonvalue.Value{}, err
 	}
 	if err := grammar.CheckPathIdentifiers(path); err != nil {
-		return nil, err
+		return jsonvalue.Value{}, err
 	}
-	return "{/" + path + "}", nil
+	return jsonvalue.String("{/" + path + "}"), nil
 }
 
 // checkTaggedType rejects a tagged field no column can fill.
@@ -254,9 +255,9 @@ func checkTaggedType(sf reflect.StructField) error {
 
 // compileRecord compiles the tagged fields of t as one record, and proves each column holds
 // only what its field's Go type can.
-func (s *structShape) compileRecord(root *folder, t reflect.Type, label string, tags map[string]any) error {
-	tags["format"] = ""
-	n, err := compile(tags)
+func (s *structShape) compileRecord(root *folder, t reflect.Type, label string, tags map[string]jsonvalue.Value) error {
+	tags["format"] = jsonvalue.String("")
+	n, err := compile(jsonvalue.Object(tags))
 	if err != nil {
 		return fmt.Errorf("%s: %w", label, err)
 	}

table.go

@@ -102,7 +102,7 @@ func readTableOptions(m map[string]any) (tableOptionValues, error) {
 		}
 		s, isString := v.(string)
 		if !isString {
-			return o, fmt.Errorf("%s must be a string, got %T", k, v)
+			return o, fmt.Errorf("%s must be a string, not %s", k, jsonKind(v))
 		}
 		if k != "format" && s == "" {
 			return o, fmt.Errorf("%s names a column, so it cannot be empty; drop it", k)