[ASTGen] Wrap optional binding pattern with type annotation

lib/ASTGen/Sources/ASTGen/Stmts.swift

@@ -161,6 +161,14 @@ extension ASTGenVisitor {
       // I'm not sure this should really be implicit.
       pat.setImplicit()
 
+      if let typeAnnotation = node.typeAnnotation {
+        pat = BridgedTypedPattern.createParsed(
+          self.ctx,
+          pattern: pat,
+          type: self.generate(type: typeAnnotation.type)
+        ).asPattern
+      }
+
       let initializer: BridgedExpr
       if let initNode = node.initializer {
         initializer = self.generate(expr: initNode.value)

test/ASTGen/stmts.swift

@@ -116,6 +116,17 @@ func testThen() {
   }
 }
 
+func intOrString() -> Int? { 1 }
+func intOrString() -> String? { "" }
+func testIf() {
+  if
+    let i: Int = intOrString(),
+    case let str? = intOrString() as String?
+  {
+    _ = (i, str)
+  }
+}
+
 struct GenericTypeWithYields<T> {
   var storedProperty: T?