Merge pull request #17529 from rudkx/rdar41305565

[Stmt] Do not crash if we have a switch after a fallthrough.

Author: rudkx

lib/Sema/TypeCheckStmt.cpp

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2018 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
@@ -948,7 +948,7 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
 
       // If the previous case fellthrough, similarly check that that case's bindings
       // includes our first label item's pattern bindings and types.
-      if (PreviousFallthrough) {
+      if (PreviousFallthrough && previousBlock) {
         auto firstPattern = caseBlock->getCaseLabelItems()[0].getPattern();
         SmallVector<VarDecl *, 4> Vars;
         firstPattern->collectVariables(Vars);

test/stmt/switch_stmt2.swift

@@ -136,3 +136,17 @@ func non_fully_covered_switch(x: Int) -> Int {
   }
   return x
 }
+
+// Do not crash if another switch statement follows a fallthrough.
+func fallthrough_not_last(i: Int) {
+  switch i {
+  case 1:
+    fallthrough
+    switch i {
+    case 1: break
+    default: break
+    }
+  default:
+    break
+  }
+}