Add precondition that the prefix of consumePrefix matches tokenKind.defaultText

Author: ahoppen

Sources/SwiftParser/Lookahead.swift

@@ -117,6 +117,10 @@ extension Parser.Lookahead {
   ///
   ///     <TOKEN> ... -> consumePrefix(<TOK>) -> [ <TOK> ] <EN> ...
   mutating func consumePrefix(_ prefix: SyntaxText, as tokenKind: RawTokenKind) {
+    precondition(
+      tokenKind.defaultText == nil || prefix == tokenKind.defaultText!,
+      "If tokenKind has a defaultText, the prefix needs to match it"
+    )
     let tokenText = self.currentToken.tokenText
 
     if tokenText == prefix {

Sources/SwiftParser/Parser.swift

@@ -605,6 +605,10 @@ extension Parser {
     _ prefix: SyntaxText,
     as tokenKind: RawTokenKind
   ) -> RawTokenSyntax {
+    precondition(
+      tokenKind.defaultText == nil || prefix == tokenKind.defaultText!,
+      "If tokenKind has a defaultText, the prefix needs to match it"
+    )
     let current = self.currentToken
     // Current token can be either one-character token we want to consume...
     let tokenText = current.tokenText