Destroy the diagnostic client first in ~DiagnosticEngine

Add a comment and a test to ~DiagnosticEngine about the ordering
requirements on the teardown of DiagnosticConsumer. This could also be
accomplished by rearranging the fields of ~DiagnosticEngine, but I felt
that this was a better, more explicit solution.

This fixes PR21911, an issue that occurred after the unique_ptr
migration in r222193.

llvm-svn: 224454

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/lib/Basic/Diagnostic.cpp b/clang/lib/Basic/Diagnostic.cpp
index 5c066efa108..a8929466084 100644
--- a/clang/lib/Basic/Diagnostic.cpp
+++ b/clang/lib/Basic/Diagnostic.cpp
@@ -61,6 +61,12 @@ DiagnosticsEngine::DiagnosticsEngine(
   Reset();
 }
 
+DiagnosticsEngine::~DiagnosticsEngine() {
+  // If we own the diagnostic client, destroy it first so that it can access the
+  // engine from its destructor.
+  setClient(nullptr);
+}
+
 void DiagnosticsEngine::setClient(DiagnosticConsumer *client,
                                   bool ShouldOwnClient) {
   Owner.reset(ShouldOwnClient ? client : nullptr);