From 478f413b80204ac4097b8db8a6ae5056d14adb54 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 1 Mar 2017 17:53:09 +0200
Subject: Support fancier epilogues in diagnostics

---
 butl/diagnostics     |  9 ++++-----
 butl/diagnostics.cxx | 25 +++++++++++++++++--------
 2 files changed, 21 insertions(+), 13 deletions(-)

diff --git a/butl/diagnostics b/butl/diagnostics
index 694fae7..56219ce 100644
--- a/butl/diagnostics
+++ b/butl/diagnostics
@@ -71,14 +71,13 @@ namespace butl
     void
     append (diag_epilogue* e) const
     {
-      if (e != nullptr)
+      // Ignore subsequent epilogues (e.g., from nested marks, etc).
+      //
+      if (empty_)
       {
-        assert (epilogue_ == nullptr); // No multiple epilogues support.
         epilogue_ = e;
-      }
-
-      if (empty_)
         empty_ = false;
+      }
       else
         os << "\n  ";
     }
diff --git a/butl/diagnostics.cxx b/butl/diagnostics.cxx
index 4cd8515..7dc8bd0 100644
--- a/butl/diagnostics.cxx
+++ b/butl/diagnostics.cxx
@@ -17,14 +17,23 @@ namespace butl
   {
     if (!empty_)
     {
-      os.put ('\n');
-      *diag_stream << os.str ();
-      diag_stream->flush ();
-
-      empty_ = true;
-
-      if (epilogue_ != nullptr)
-        epilogue_ (*this); // Can throw.
+      if (epilogue_ == nullptr)
+      {
+        os.put ('\n');
+        *diag_stream << os.str ();
+        diag_stream->flush ();
+
+        empty_ = true;
+      }
+      else
+      {
+        // Clear the epilogue in case it calls us back.
+        //
+        auto e (epilogue_);
+        epilogue_ = nullptr;
+        e (*this); // Can throw.
+        flush ();  // Call ourselves to write the data in case it returns.
+      }
     }
   }
 
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