Sema: Add a pretty stack trace entry when checking error handling

Author: slavapestov

lib/Sema/TypeCheckError.cpp

@@ -20,6 +20,7 @@
 #include "swift/AST/DiagnosticsSema.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/Pattern.h"
+#include "swift/AST/PrettyStackTrace.h"
 
 using namespace swift;
 
@@ -1648,6 +1649,10 @@ void TypeChecker::checkFunctionErrorHandling(AbstractFunctionDecl *fn) {
   // by the time we got here.
   if (!fn->hasInterfaceType()) return;
 
+#ifndef NDEBUG
+  PrettyStackTraceDecl debugStack("checking error handling for", fn);
+#endif
+
   CheckErrorCoverage checker(*this, Context::forFunction(fn));
 
   // If this is a debugger function, suppress 'try' marking at the top level.