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

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 }