From ea45295200abb6b9b498e97fbef37567315dddbe Mon Sep 17 00:00:00 2001
From: Ed Catmur <edward.catmur@mavensecurities.com>
Date: Tue, 18 Jan 2022 14:02:11 +0000
Subject: [PATCH 1/2] Check that lazy_ostream argument is printable

The operator() is not instantiated till later, which makes it
difficult to locate an erroneous usage of <<.  Place a
static_assert in the ctor (copied from print_helper.hpp) to check
at construction time, which will point back to the << site.
---
 include/boost/test/utils/lazy_ostream.hpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/boost/test/utils/lazy_ostream.hpp b/include/boost/test/utils/lazy_ostream.hpp
index 2d1edbed8e..7d62fd46b1 100644
--- a/include/boost/test/utils/lazy_ostream.hpp
+++ b/include/boost/test/utils/lazy_ostream.hpp
@@ -15,6 +15,10 @@
 #include <boost/test/detail/config.hpp>
 #include <boost/test/tools/detail/print_helper.hpp>
 
+// Boost
+#include <boost/static_assert.hpp>
+#include <boost/type_traits/has_left_shift.hpp>
+
 // STL
 #include <iosfwd>
 
@@ -75,6 +79,8 @@ class lazy_ostream_impl : public lazy_ostream {
     , m_prev( prev )
     , m_value( value )
     {
+        BOOST_STATIC_ASSERT_MSG( (boost::has_left_shift<std::ostream,T>::value),
+                                "Type has to implement operator<< to be printable");
     }
 
     std::ostream&   operator()( std::ostream& ostr ) const BOOST_OVERRIDE

From d3a47fe0b1e3812289a1bc92a0f09f128b44e1f3 Mon Sep 17 00:00:00 2001
From: Raffi Enficiaud <raffi.enficiaud@mines-paris.org>
Date: Mon, 7 Mar 2022 21:19:05 +0100
Subject: [PATCH 2/2] Change log

---
 doc/closing_chapters/change_log.qbk | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/closing_chapters/change_log.qbk b/doc/closing_chapters/change_log.qbk
index 90c4fc4d30..64eeb2c0de 100644
--- a/doc/closing_chapters/change_log.qbk
+++ b/doc/closing_chapters/change_log.qbk
@@ -43,6 +43,7 @@ Boost.Test releases:
 # [pull_request 275] Replace anonymous `enum` arity with `static constexpr`
 # [pull_request 278] Use `boost_test_print_type` customization point in `lazy_ostream`
 # [pull_request 281] Export `execution_aborted` exception to allow catching it from outside the DLL
+# [pull_request 323] Check that `lazy_ostream` argument is printable
 
 [#ref_CHANGE_LOG_3_14][h4 Boost.Test v3.14 / boost 1.74]