Adding a fix-it to diagnosting to replace 'defer' with a 'do' statement.

Author: vguerra

include/swift/AST/DiagnosticsCommon.def

@@ -55,7 +55,8 @@ NOTE(brace_stmt_suggest_do,none,
      "did you mean to use a 'do' statement?", ())
 
 NOTE(defer_stmt_at_block_end,none,
-     "'defer' at the end of its scope is redundant and will execute immediately", ())
+     "'defer' at the end of its scope is redundant and will execute immediately; "
+     "replace it with 'do'", ())
 
 // Generic disambiguation
 NOTE(while_parsing_as_left_angle_bracket,none,

lib/Sema/TypeCheckStmt.cpp

@@ -1412,7 +1412,8 @@ Stmt *StmtChecker::visitBraceStmt(BraceStmt *BS) {
     if (auto stmt =
             BS->getElement(BS->getNumElements() - 1).dyn_cast<Stmt *>()) {
       if (auto deferStmt = dyn_cast<DeferStmt>(stmt)) {
-        TC.diagnose(deferStmt->getStartLoc(), diag::defer_stmt_at_block_end);
+        TC.diagnose(deferStmt->getStartLoc(), diag::defer_stmt_at_block_end)
+            .fixItReplace(deferStmt->getStartLoc(), "do");
       }
     }
   }