Enable resilience for _MatchingEngine and _StringProcessing.

_MatchingEngine and _StringProcessing are built with resilience enabled in Swift core libs. Currently the compiler build produces lots of warnings of missing `@unknown default`. We enable resilience in this package so that we can catch these issues early.

Author: rxwei

Package.swift

@@ -31,13 +31,19 @@ let package = Package(
         // Targets can depend on other targets in this package, and on products in packages which this package depends on.
         .target(
             name: "_MatchingEngine",
-            dependencies: [/*"_Unicode"*/]),
+            dependencies: [/*"_Unicode"*/],
+            swiftSettings: [
+                .unsafeFlags(["-enable-library-evolution"])
+            ]),
         .testTarget(
             name: "MatchingEngineTests",
             dependencies: ["_MatchingEngine"]),
         .target(
             name: "_StringProcessing",
-            dependencies: ["_MatchingEngine"]),
+            dependencies: ["_MatchingEngine"],
+            swiftSettings: [
+                .unsafeFlags(["-enable-library-evolution"])
+            ]),
         .target(
             name: "_Unicode",
             dependencies: []),

Sources/_StringProcessing/CharacterClass.swift

@@ -56,6 +56,8 @@ public struct CharacterClass: Hashable {
         return lhs.matches(c) && !rhs.matches(c)
       case .symmetricDifference:
         return lhs.matches(c) != rhs.matches(c)
+      @unknown default:
+        fatalError("unhandled")
       }
     }
   }
@@ -410,6 +412,8 @@ extension AST.CustomCharacterClass {
             lhs: .characterClass(.custom(lhs)),
             op: op.value,
             rhs: .characterClass(.custom(rhs)))))
+        @unknown default:
+          fatalError("unhandled")
         }
       }
       return result

Sources/_StringProcessing/Compiler.swift

@@ -113,6 +113,9 @@ class Compiler {
 
     case .customCharacterClass, .atom:
       throw unsupported(node._dumpBase)
+
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 
@@ -185,6 +188,9 @@ class Compiler {
         !CharacterClass.word.isBoundary(
           input, at: pos, bounds: bounds)
       }
+
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 
@@ -408,6 +414,8 @@ class Compiler {
       // quantification break if trying to restore to a prior
       // iteration because the register got overwritten?
       //
+    @unknown default:
+      fatalError("unhandled")
     }
 
     builder.label(exit)

Sources/_StringProcessing/ConsumerInterface.swift

@@ -39,10 +39,11 @@ extension AST {
       return try a.generateConsumer(opts)
     case .customCharacterClass(let ccc):
       return try ccc.generateConsumer(opts)
-
     case .alternation, .concatenation, .group,
         .quantification, .quote, .trivia, .empty,
         .groupTransform: return nil
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 }
@@ -105,6 +106,9 @@ extension AST.Atom {
         .backreference, .subpattern, .condition:
       // FIXME: implement
       return nil
+
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 }
@@ -180,8 +184,14 @@ extension AST.CustomCharacterClass.Member {
             return rhsIdxOpt == nil ? idx : nil
           }
           return rhsIdxOpt
+
+        @unknown default:
+          fatalError("unhandled")
         }
       }
+
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 }
@@ -300,6 +310,9 @@ extension AST.Atom.CharacterProperty {
 
       case let .other(key, value):
         throw unsupported("TODO: map other \(key ?? "")=\(value)")
+
+      @unknown default:
+        fatalError("unhandled")
       }
     }()
 
@@ -466,6 +479,8 @@ extension Unicode.BinaryProperty {
     case .expandsOnNFC, .expandsOnNFD, .expandsOnNFKD,
         .expandsOnNFKC:
       throw unsupported("Unicode-deprecated: \(self)")
+    @unknown default:
+      fatalError("unhandled")
     }
 
     throw unsupported("TODO: map prop \(self)")
@@ -513,6 +528,9 @@ extension Unicode.POSIXProperty {
 
     case .xdigit:
       return consumeScalarProp(\.isHexDigit) // or number
+
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 
@@ -628,6 +646,8 @@ extension Unicode.ExtendedGeneralCategory {
       return consumeScalarGC(.paragraphSeparator)
     case .spaceSeparator:
       return consumeScalarGC(.spaceSeparator)
+    @unknown default:
+      fatalError("unhandled")
     }
   }
 }

Sources/_StringProcessing/Legacy/LegacyCompile.swift

@@ -251,8 +251,10 @@ func compile(
 
     case .atom(let a) where a.characterClass != nil:
       fatalError("unreachable")
-    }
 
+    @unknown default:
+      fatalError("unhandled")
+    }
   }
 
   try compileNode(ast)