Rename grammar's NameRead to PathRead and CheckName to CheckIdentifier, so a name in the engine is only a bound name

internal/grammar/identifier.go

@@ -0,0 +1,48 @@
+package grammar
+
+import (
+	"fmt"
+	"strings"
+)
+
+// reservedInIdentifier is what an identifier may not contain: a dot
+// separates the segments of a path, '|' the arms of a token, '(' opens a function
+// call, braces delimit the token, '/' starts a reference, and brackets and a quote
+// open a JSON value. An identifier carrying one is rejected where it is authored rather
+// than where it would be unreachable.
+const reservedInIdentifier = ".|({}/[]\""
+
+var reservedList = strings.Join(strings.Split(reservedInIdentifier, ""), " ")
+
+// CheckIdentifier rejects an identifier, the name of a folder, category, field or column, that the
+// dot path, {token} and JSON grammars cannot spell, or a struct tag cannot read.
+func CheckIdentifier(name string) error {
+	if name == "" {
+		return fmt.Errorf("%q is empty, which is not a path segment, so List never offers it", name)
+	}
+	if name == "-" {
+		return fmt.Errorf(`%q is reserved: the struct tag fake:"-" leaves a field unfilled, so no tag could read it; rename it`, name)
+	}
+	if strings.Contains(name, AsWord) {
+		return fmt.Errorf("%q contains %q, which a token reads as binding a name; rename it", name, AsWord)
+	}
+	if i := strings.IndexAny(name, reservedInIdentifier); i >= 0 {
+		return fmt.Errorf("%q contains %q; a name may not use %s, which the dot path, {token} and JSON grammars reserve",
+			name, name[i:i+1], reservedList)
+	}
+	return nil
+}
+
+// CheckPathIdentifiers rejects a dotted path with a segment no identifier may be.
+func CheckPathIdentifiers(path string) error {
+	segs, err := SplitPath(path)
+	if err != nil {
+		return err
+	}
+	for _, seg := range IdentifierSegments(segs) {
+		if err := CheckIdentifier(seg); err != nil {
+			return fmt.Errorf("path %w", err)
+		}
+	}
+	return nil
+}