[NFC] [ASTGen] Beef up Nullable/Optional bridging

Adds a failable `init(_:)` to `BridgedHasNullable` types which can convert the Nullable variant into an Optional of the non-Nullable variant. Also added a member to `BridgedSourceLoc` to support a new requirement for this feature.

Author: beccadax

include/swift/Basic/BasicBridging.h

@@ -322,6 +322,11 @@ class BridgedSourceLoc {
 SWIFT_NAME("getter:BridgedSourceLoc.isValid(self:)")
 BRIDGED_INLINE bool BridgedSourceLoc_isValid(BridgedSourceLoc loc);
 
+SWIFT_NAME("getter:BridgedSourceLoc.raw(self:)")
+inline const void * _Nullable BridgedSourceLoc_getRaw(BridgedSourceLoc bridged) {
+  return bridged.getOpaquePointerValue();
+}
+
 //===----------------------------------------------------------------------===//
 // MARK: SourceRange
 //===----------------------------------------------------------------------===//

lib/ASTGen/Sources/ASTGen/Bridge.swift

@@ -17,6 +17,7 @@ import BasicBridging
 public protocol BridgedNullable: ExpressibleByNilLiteral {
   associatedtype RawPtr
   init(raw: RawPtr?)
+  var raw: RawPtr? { get }
 }
 extension BridgedNullable {
   public init(nilLiteral: ()) {
@@ -35,6 +36,8 @@ extension BridgedNullableTrailingWhereClause: /*@retroactive*/ swiftASTGen.Bridg
 extension BridgedNullableParameterList: /*@retroactive*/ swiftASTGen.BridgedNullable {}
 extension BridgedNullablePatternBindingInitializer: /*@retroactive*/ swiftASTGen.BridgedNullable {}
 extension BridgedNullableArgumentList: /*@retroactive*/ swiftASTGen.BridgedNullable {}
+extension BridgedNullablePatternBindingDecl: /*@retroactive*/ swiftASTGen.BridgedNullable {}
+extension BridgedNullableVarDecl: /*@retroactive*/ swiftASTGen.BridgedNullable {}
 
 extension BridgedIdentifier: /*@retroactive*/ Swift.Equatable {
   public static func == (lhs: Self, rhs: Self) -> Bool {
@@ -47,6 +50,7 @@ extension BridgedIdentifier: /*@retroactive*/ Swift.Equatable {
 /// E.g. BridgedExpr vs BridgedNullableExpr.
 protocol BridgedHasNullable {
   associatedtype Nullable: BridgedNullable
+  init(raw: Nullable.RawPtr)
   var raw: Nullable.RawPtr { get }
 }
 extension Optional where Wrapped: BridgedHasNullable {
@@ -55,6 +59,14 @@ extension Optional where Wrapped: BridgedHasNullable {
     Wrapped.Nullable(raw: self?.raw)
   }
 }
+extension BridgedHasNullable {
+  init?(_ nullable: Nullable) {
+    guard let newRaw = nullable.raw else {
+      return nil
+    }
+    self.init(raw: newRaw)
+  }
+}
 
 extension BridgedStmt: BridgedHasNullable {
   typealias Nullable = BridgedNullableStmt
@@ -83,6 +95,12 @@ extension BridgedPatternBindingInitializer: BridgedHasNullable {
 extension BridgedArgumentList: BridgedHasNullable {
   typealias Nullable = BridgedNullableArgumentList
 }
+extension BridgedPatternBindingDecl: BridgedHasNullable {
+  typealias Nullable = BridgedNullablePatternBindingDecl
+}
+extension BridgedVarDecl: BridgedHasNullable {
+  typealias Nullable = BridgedNullableVarDecl
+}
 
 public extension BridgedSourceLoc {
   /// Form a source location at the given absolute position in `buffer`.

lib/ASTGen/Sources/ASTGen/Decls.swift

@@ -481,7 +481,7 @@ extension ASTGenVisitor {
     if let accessors = binding.accessorBlock {
       // FIXME: We ought to have a better way of converting from the Nullable
       // wrapper back to Optional.
-      if let primaryVar = pattern.singleVar.raw.map(BridgedVarDecl.init) {
+      if let primaryVar = BridgedVarDecl(pattern.singleVar) {
         let storage = primaryVar.asAbstractStorageDecl
         storage.setAccessors(generate(accessorBlock: accessors, for: storage))
       } else {