Rename LexError -> DelimiterLexError

To avoid confusion with more general regex lexical
analysis.

Author: hamishknight

Sources/_MatchingEngine/Regex/Parse/DelimiterLexing.swift

@@ -37,7 +37,7 @@ enum Delimiter: Hashable, CaseIterable {
   }
 }
 
-struct LexError: Error, CustomStringConvertible {
+struct DelimiterLexError: Error, CustomStringConvertible {
   enum Kind: Hashable {
     case endOfString
     case invalidUTF8 // TODO: better range reporting
@@ -97,14 +97,14 @@ func lexRegex(
   guard let delimiter = Delimiter.allCases.first(
     where: { tryEat($0.opening.utf8) }
   ) else {
-    throw LexError(.unknownDelimiter, resumeAt: current.successor())
+    throw DelimiterLexError(.unknownDelimiter, resumeAt: current.successor())
   }
 
   let contentsStart = current
   while true {
     switch load() {
     case nil, ascii("\n"), ascii("\r"):
-      throw LexError(.endOfString, resumeAt: current)
+      throw DelimiterLexError(.endOfString, resumeAt: current)
 
     case ascii("\\"):
       // Skip next byte.
@@ -125,7 +125,7 @@ func lexRegex(
       let s = String(decoding: contents, as: UTF8.self)
 
       guard s.utf8.elementsEqual(contents) else {
-        throw LexError(.invalidUTF8, resumeAt: current)
+        throw DelimiterLexError(.invalidUTF8, resumeAt: current)
       }
       return (contents: s, delimiter, end: current)
     }

Sources/_MatchingEngine/Regex/Parse/Mocking.swift

@@ -52,7 +52,7 @@ func libswiftLexRegexLiteral(
     let (_, _, endPtr) = try lexRegex(start: inputPtr, end: bufferEndPtr)
     curPtrPtr.pointee = endPtr.assumingMemoryBound(to: CChar.self)
     return false
-  } catch let error as LexError {
+  } catch let error as DelimiterLexError {
     if error.kind == .unknownDelimiter {
       // An unknown delimiter should be recovered from, as we may want to try
       // lex something else.
@@ -66,7 +66,7 @@ func libswiftLexRegexLiteral(
     // closing delimiters, which would help with code completion.
     return true
   } catch {
-    fatalError("Should be a LexError")
+    fatalError("Should be a DelimiterLexError")
   }
 }