Support xfail

Sources/_StringProcessing/Algorithms/Consumers/RegexConsumer.swift

@@ -6,8 +6,17 @@ public struct RegexConsumer<Consumed: BidirectionalCollection>
   // TODO: consider let, for now lets us toggle tracing
     var vm: Executor
 
+  // FIXME: Possibility of fatal error isn't user friendly
   public init<Capture>(_ regex: Regex<Capture>) {
-    self.vm = .init(program: try! Compiler(ast: regex.ast).emit())
+    do {
+      self.vm = .init(program: try Compiler(ast: regex.ast).emit())
+    } catch {
+      fatalError("error: \(error)")
+    }
+  }
+
+  public init(parsing regex: String) throws {
+    self.vm = try _compileRegex(regex)
   }
 
   func _consuming(

Sources/_StringProcessing/Compiler.swift

@@ -202,7 +202,7 @@ class Compiler {
       (.upToN, _),
       (.range, _),
       (_, .possessive):
-      fatalError("Not yet supported")
+      throw unsupported("\(quant._dumpBase)")
     }
   }
 }

Tests/RegexTests/MatchTests.swift

@@ -11,18 +11,22 @@ func matchTest(
   dumpAST: Bool = false,
   xfail: Bool = false
 ) {
-  guard !xfail else {
-//    XCTExpectFailure {
-//      XCTFail()
-//    }
+  do {
+    var consumer = try RegexConsumer<String>(parsing: regex)
+    consumer.vm.engine.enableTracing = enableTracing
+    guard let range = input.firstRange(of: consumer) else {
+      throw "expect xfail"
+    }
+
+    if xfail {
+      XCTAssertNotEqual(String(input[range]), match)
+    } else {
+      XCTAssertEqual(String(input[range]), match)
+    }
+  } catch {
+    XCTAssert(xfail)
     return
   }
-
-  let pattern = try! Regex(regex)
-  var consumer = RegexConsumer<String>(pattern)
-  consumer.vm.engine.enableTracing = enableTracing
-  let range = input.firstRange(of: consumer)!
-  XCTAssertEqual(String(input[range]), match)
 }
 
 extension RegexTests {
@@ -120,7 +124,7 @@ extension RegexTests {
     matchTest(
       #"a{2,}"#, input: "123aaaxyz", match: "aaa", xfail: true)
     matchTest(
-      #"a{1}"#, input: "123aaaxyz", match: "a", xfail: true)
+      #"a{1}"#, input: "123aaaxyz", match: "a")
     matchTest(
       #"a{1,2}?"#, input: "123aaaxyz", match: "a", xfail: true)
     matchTest(