Cleanups and refactorings

Sources/Exercises/Participants/PEGParticipant.swift

@@ -40,7 +40,7 @@ private func graphemeBreakPropertyData(forLine line: String) -> GraphemeBreakEnt
   let program = PEG.Program(start: "Entry", environment: ["Entry": entry])
 
   let vm = program.compile(for: String.self)
-  let engine = program.transpile(for: String.self)
+  let engine = try! program.transpile(for: String.self)
   _ = (vm, engine)
 
   fatalError("Unsupported")

Sources/Prototypes/PEG/PEGTranspile.swift

@@ -13,7 +13,7 @@ import _MatchingEngine
 
 extension PEG.VM {
   typealias MEProgram = _MatchingEngine.Program<Input>
-  func transpile() -> MEProgram {
+  func transpile() throws -> MEProgram {
     typealias Builder = MEProgram.Builder
     var builder = MEProgram.Builder()
 
@@ -106,14 +106,14 @@ extension PEG.VM {
       }
     }
 
-    return builder.assemble()
+    return try builder.assemble()
   }
 }
 
 extension PEG.Program {
   public func transpile<Input: Collection>(
     for input: Input.Type = Input.self
-  ) -> Engine<Input> where Input.Element == Element {
-    Engine(compile(for: input).vm.transpile())
+  ) throws -> Engine<Input> where Input.Element == Element {
+    try Engine(compile(for: input).vm.transpile())
   }
 }

Sources/_MatchingEngine/Engine/Builder.swift

@@ -230,7 +230,7 @@ extension Program.Builder {
 
   // TODO: Mutating because of fail address fixup, drop when
   // that's removed
-  public mutating func assemble() -> Program {
+  public mutating func assemble() throws -> Program {
     // TODO: This will add a fail instruction at the end every
     // time it's assembled. Better to do to the local instruction
     // list copy, but that complicates logic. It's possible we
@@ -262,12 +262,12 @@ extension Program.Builder {
 
       case .splitSaving:
         guard let fix2 = tok.second else {
-          fatalError("unreachable")
+          throw Unreachable("TODO: reason")
         }
         let saving = addressTokens[fix2.rawValue]!
         payload = .init(addr: addr, addr2: saving)
 
-      default: fatalError("unreachable")
+      default: throw Unreachable("TODO: reason")
 
       }
 

Sources/_MatchingEngine/Regex/Parse/LexicalAnalysis.swift

@@ -1785,7 +1785,7 @@ extension Source {
         if customCC {
           return .char(char)
         }
-        fatalError("unreachable")
+        throw Unreachable("TODO: reason")
 
       // (sometimes) special metacharacters
       case ".": return customCC ? .char(".") : .any

Sources/_MatchingEngine/Regex/Parse/Parse.swift

@@ -223,7 +223,7 @@ extension Parser {
         continue
       }
 
-      fatalError("unreachable?")
+      throw Unreachable("TODO: reason")
     }
     guard !result.isEmpty else {
       return .empty(.init(loc(_start)))

Sources/_MatchingEngine/Utility/Errors.swift

@@ -0,0 +1,54 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2021-2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+public struct Unsupported: Error, CustomStringConvertible {
+  var message: String
+  var file: String
+  var line: Int
+
+  public var description: String { """
+    Unsupported: '\(message)'
+      \(file):\(line)
+    """
+  }
+
+  public init(
+    _ s: String,
+    file: StaticString = #file,
+    line: UInt = #line
+  ) {
+    self.message = s
+    self.file = file.description
+    self.line = Int(asserting: line)
+  }
+}
+
+public struct Unreachable: Error, CustomStringConvertible {
+  var message: String
+  var file: String
+  var line: Int
+
+  public var description: String { """
+    Unreachable: '\(message)'
+      \(file):\(line)
+    """
+  }
+
+  public init(
+    _ s: String,
+    file: StaticString = #file,
+    line: UInt = #line
+  ) {
+    self.message = s
+    self.file = file.description
+    self.line = Int(asserting: line)
+  }
+}

Sources/_MatchingEngine/Utility/Misc.swift

@@ -15,16 +15,6 @@ extension FixedWidthInteger {
   }
 }
 
-// TODO: Replace all fatal error unreachables with these calls.
-// We will likely want to convert them to unhandleable throws
-// or something similar.
-func unreachable(_ s: @autoclosure () -> String) -> Never {
-  fatalError("unreachable \(s())")
-}
-func unreachable() -> Never {
-  fatalError("unreachable")
-}
-
 extension Substring {
   var string: String { String(self) }
 }

Sources/_StringProcessing/ByteCodeGen.swift

@@ -5,9 +5,10 @@ extension Compiler {
     var options: MatchingOptions
     var builder = _MatchingEngine.Program<String>.Builder()
 
-    mutating func finish() -> _MatchingEngine.Program<String> {
+    mutating func finish(
+    ) throws -> _MatchingEngine.Program<String> {
       builder.buildAccept()
-      return builder.assemble()
+      return try builder.assemble()
     }
   }
 }
@@ -90,7 +91,7 @@ extension Compiler.ByteCodeGen {
 
     case .resetStartOfMatch:
       // FIXME: Figure out how to communicate this out
-      throw unsupported(#"\K (reset/keep assertion)"#)
+      throw Unsupported(#"\K (reset/keep assertion)"#)
 
     case .firstMatchingPositionInSubject:
       // TODO: We can probably build a nice model with API here
@@ -100,11 +101,11 @@ extension Compiler.ByteCodeGen {
 
     case .textSegment:
       // This we should be able to do!
-      throw unsupported(#"\y (text segment)"#)
+      throw Unsupported(#"\y (text segment)"#)
 
     case .notTextSegment:
       // This we should be able to do!
-      throw unsupported(#"\Y (not text segment)"#)
+      throw Unsupported(#"\Y (not text segment)"#)
 
     case .startOfLine:
       builder.buildAssert { (input, pos, bounds) in
@@ -204,7 +205,7 @@ extension Compiler.ByteCodeGen {
     _ child: DSLTree.Node
   ) throws {
     guard kind.forwards else {
-      throw unsupported("backwards assertions")
+      throw Unsupported("backwards assertions")
     }
 
     let positive = kind.positive
@@ -259,7 +260,7 @@ extension Compiler.ByteCodeGen {
     switch kind {
     case .lookahead, .negativeLookahead,
         .lookbehind, .negativeLookbehind:
-      fatalError("unreachable")
+      throw Unreachable("TODO: reason")
 
     case .capture, .namedCapture:
       let cap = builder.makeCapture()
@@ -299,7 +300,7 @@ extension Compiler.ByteCodeGen {
       // Ok
       break
     default:
-      fatalError("unreachable?")
+      throw Unreachable("TODO: reason")
     }
 
     // Compiler and/or parser should enforce these invariants

Sources/_StringProcessing/Compiler.swift

@@ -34,7 +34,7 @@ class Compiler {
     // TODO: Handle global options
     var codegen = ByteCodeGen(options: options)
     try codegen.emitNode(tree.root)
-    let program = codegen.finish()
+    let program = try codegen.finish()
     return RegexProgram(program: program)
   }
 }