[AST] DoStmt always contains a BraceStmt

Author: DougGregor

include/swift/AST/Stmt.h

@@ -539,11 +539,11 @@ class LabeledStmt : public Stmt {
 /// DoStmt - do statement, without any trailing clauses.
 class DoStmt : public LabeledStmt {
   SourceLoc DoLoc;
-  Stmt *Body;
+  BraceStmt *Body;
 
 public:
   DoStmt(LabeledStmtInfo labelInfo, SourceLoc doLoc,
-         Stmt *body, Optional<bool> implicit = None)
+         BraceStmt *body, Optional<bool> implicit = None)
     : LabeledStmt(StmtKind::Do, getDefaultImplicitFlag(implicit, doLoc),
                   labelInfo),
       DoLoc(doLoc), Body(body) {}
@@ -553,8 +553,8 @@ class DoStmt : public LabeledStmt {
   SourceLoc getStartLoc() const { return getLabelLocOrKeywordLoc(DoLoc); }
   SourceLoc getEndLoc() const { return Body->getEndLoc(); }
 
-  Stmt *getBody() const { return Body; }
-  void setBody(Stmt *s) { Body = s; }
+  BraceStmt *getBody() const { return Body; }
+  void setBody(BraceStmt *s) { Body = s; }
 
   static bool classof(const Stmt *S) { return S->getKind() == StmtKind::Do; }
 };

lib/AST/ASTWalker.cpp

@@ -1493,7 +1493,7 @@ Stmt *Traversal::visitGuardStmt(GuardStmt *US) {
 }
 
 Stmt *Traversal::visitDoStmt(DoStmt *DS) {
-  if (Stmt *S2 = doIt(DS->getBody()))
+  if (BraceStmt *S2 = cast_or_null<BraceStmt>(doIt(DS->getBody())))
     DS->setBody(S2);
   else
     return nullptr;

lib/Sema/TypeCheckStmt.cpp

@@ -658,7 +658,7 @@ class StmtChecker : public StmtVisitor<StmtChecker, Stmt*> {
 
   Stmt *visitDoStmt(DoStmt *DS) {
     AddLabeledStmt loopNest(*this, DS);
-    Stmt *S = DS->getBody();
+    BraceStmt *S = DS->getBody();
     typeCheckStmt(S);
     DS->setBody(S);
     return DS;