From 646ff7d9933b550b65b8377b3fa1b9bd85056cb3 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 28 Jun 2019 13:07:21 +0200
Subject: Add ability to specify custom diag_record writer

---
 libbutl/diagnostics.cxx | 27 +++++++++++++++++++--------
 libbutl/diagnostics.mxx |  5 +++++
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/libbutl/diagnostics.cxx b/libbutl/diagnostics.cxx
index 43d931f..d9a979e 100644
--- a/libbutl/diagnostics.cxx
+++ b/libbutl/diagnostics.cxx
@@ -155,6 +155,23 @@ namespace butl
     diag_mutex.unlock ();
   }
 
+  static void
+  default_writer (const diag_record& r)
+  {
+    r.os.put ('\n');
+    diag_stream_lock () << r.os.str ();
+
+    // We can endup flushing the result of several writes. The last one may
+    // possibly be incomplete, but that's not a problem as it will also be
+    // followed by the flush() call.
+    //
+    // @@ Strange: why not just hold the lock for both write and flush?
+    //
+    diag_stream->flush ();
+  }
+
+  void (*diag_record::writer) (const diag_record&) = &default_writer;
+
   void diag_record::
   flush () const
   {
@@ -162,14 +179,8 @@ namespace butl
     {
       if (epilogue_ == nullptr)
       {
-        os.put ('\n');
-        diag_stream_lock () << os.str ();
-
-        // We can endup flushing the result of several writes. The last one may
-        // possibly be incomplete, but that's not a problem as it will also be
-        // followed by the flush() call.
-        //
-        diag_stream->flush ();
+        if (writer != nullptr)
+          writer (*this);
 
         empty_ = true;
       }
diff --git a/libbutl/diagnostics.mxx b/libbutl/diagnostics.mxx
index 43f13ad..c9ade44 100644
--- a/libbutl/diagnostics.mxx
+++ b/libbutl/diagnostics.mxx
@@ -179,6 +179,11 @@ LIBBUTL_MODEXPORT namespace butl
     diag_record (const diag_record&) = delete;
     diag_record& operator= (const diag_record&) = delete;
 
+    // Diagnostics writer. The default implementation writes the record text
+    // to diag_stream. If it is NULL, then the record text is ignored.
+    //
+    static void (*writer) (const diag_record&);
+
   protected:
 #ifdef __cpp_lib_uncaught_exceptions
     const int uncaught_;
-- 
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