Fix character class trivia matching

Rather than matching and not advancing the input,
we should always return `nil` to never match
against the trivia.

Author: hamishknight

Sources/_StringProcessing/ConsumerInterface.swift

@@ -287,11 +287,8 @@ extension DSLTree.CustomCharacterClass.Member {
       }
     case .trivia:
       // TODO: Should probably strip this earlier...
-      return { _, bounds in
-        return bounds.lowerBound
-      }
+      return { _, _ in nil }
     }
-
   }
 }
 

Tests/RegexTests/MatchTests.swift

@@ -1208,6 +1208,16 @@ extension RegexTests {
       ("CaFe", true),
       ("EfAc", true))
   }
+
+  func testNonSemanticWhitespace() {
+    firstMatchTest(#" \t "#, input: " \t ", match: " \t ")
+    firstMatchTest(#"(?xx) \t "#, input: " \t ", match: "\t")
+
+    firstMatchTest(#"[ \t]+"#, input: " \t ", match: " \t ")
+    firstMatchTest(#"(?xx)[ \t]+"#, input: " \t ", match: "\t")
+    firstMatchTest(#"(?xx)[ \t]+"#, input: " \t\t ", match: "\t\t")
+    firstMatchTest(#"(?xx)[ \t]+"#, input: " \t \t", match: "\t")
+  }
 
   func testASCIIClasses() {
     // 'D' ASCII-only digits