diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index 54e397cda9a..7bec3f10599 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -18,6 +18,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc
index 16dfeafc07a..ae899ec9f77 100644
--- a/gcc/cp/error.cc
+++ b/gcc/cp/error.cc
@@ -17,6 +17,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 /* For use with name_hint.  */
 #include "system.h"
diff --git a/gcc/diagnostic-global-context.cc b/gcc/diagnostic-global-context.cc
index 30fc1906790..94be0fed81e 100644
--- a/gcc/diagnostic-global-context.cc
+++ b/gcc/diagnostic-global-context.cc
@@ -22,6 +22,7 @@ along with GCC; see the file COPYING3.  If not see
 /* This file implements the parts of the language independent aspect
    of diagnostic messages that implicitly use global_dc.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/diagnostics/buffering.cc b/gcc/diagnostics/buffering.cc
index 019c9927c6d..420a9cfbeea 100644
--- a/gcc/diagnostics/buffering.cc
+++ b/gcc/diagnostics/buffering.cc
@@ -18,6 +18,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/diagnostics/context.cc b/gcc/diagnostics/context.cc
index cd14977d542..dd6bbdb29cd 100644
--- a/gcc/diagnostics/context.cc
+++ b/gcc/diagnostics/context.cc
@@ -361,6 +361,9 @@ context::finish ()
       dump (m_logger->get_stream (), m_logger->get_indent ());
     }
 
+  for (auto iter : m_sinks)
+    iter->finalize_extensions ();
+
   /* We might be handling a fatal error.
      Close any active diagnostic groups, which may trigger flushing
      sinks.  */
@@ -1860,6 +1863,20 @@ sink::dump (FILE *out, int indent) const
 {
   dumping::emit_heading (out, indent, "printer");
   m_printer->dump (out, indent + 2);
+
+  dumping::emit_heading (out, indent, "extensions");
+  if (m_extensions.empty ())
+    dumping::emit_none (out, indent + 2);
+  else
+    for (auto &ext : m_extensions)
+      ext->dump (out, indent + 2);
+}
+
+void
+sink::finalize_extensions ()
+{
+  for (auto &ext : m_extensions)
+    ext->finalize ();
 }
 
 void
diff --git a/gcc/diagnostics/macro-unwinding.cc b/gcc/diagnostics/macro-unwinding.cc
index fb4ee65f424..4d7133963ad 100644
--- a/gcc/diagnostics/macro-unwinding.cc
+++ b/gcc/diagnostics/macro-unwinding.cc
@@ -17,6 +17,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/diagnostics/selftest-context.cc b/gcc/diagnostics/selftest-context.cc
index 2eced4d3cd8..aafa90ac457 100644
--- a/gcc/diagnostics/selftest-context.cc
+++ b/gcc/diagnostics/selftest-context.cc
@@ -17,6 +17,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/diagnostics/sink.h b/gcc/diagnostics/sink.h
index aaa6c50ab21..a2094e9f5a5 100644
--- a/gcc/diagnostics/sink.h
+++ b/gcc/diagnostics/sink.h
@@ -34,6 +34,27 @@ class per_sink_buffer;
 class sink
 {
 public:
+  /* Abstract base class for adding additional functionality to a sink
+     (e.g. via a plugin).  */
+  class extension
+  {
+  public:
+    virtual ~extension () {}
+    virtual void dump (FILE *out, int indent) const = 0;
+    virtual void finalize () {}
+
+    sink &get_sink () const { return m_sink; }
+
+  protected:
+    extension (sink &sink_)
+    : m_sink (sink_)
+    {
+    }
+
+  private:
+    sink &m_sink;
+  };
+
   virtual ~sink () {}
 
   virtual text_sink *dyn_cast_text_sink () { return nullptr; }
@@ -92,6 +113,15 @@ public:
 
   logging::logger *get_logger () { return m_context.get_logger (); }
 
+  void
+  add_extension (std::unique_ptr<extension> sink_ext)
+  {
+    m_extensions.push_back (std::move (sink_ext));
+  }
+
+  void
+  finalize_extensions ();
+
 protected:
   sink (context &dc)
   : m_context (dc),
@@ -101,6 +131,9 @@ protected:
 protected:
   context &m_context;
   std::unique_ptr<pretty_printer> m_printer;
+
+private:
+  std::vector<std::unique_ptr<extension>> m_extensions;
 };
 
 extern void
diff --git a/gcc/fortran/error.cc b/gcc/fortran/error.cc
index ebf9e6197d2..8fde46ed6af 100644
--- a/gcc/fortran/error.cc
+++ b/gcc/fortran/error.cc
@@ -24,6 +24,7 @@ along with GCC; see the file COPYING3.  If not see
    for possible use later.  If a line does not match a legal
    construction, then the saved error message is reported.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index 5dd33c2dfcb..eae7f07d962 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -28,6 +28,7 @@ Once it knows which kind of compilation to perform, the procedure for
 compilation is specified by a string called a "spec".  */
 
 #define INCLUDE_STRING
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #ifdef HOST_HAS_PERSONALITY_ADDR_NO_RANDOMIZE
diff --git a/gcc/langhooks.cc b/gcc/langhooks.cc
index 20d27a6d7fd..6431d40af04 100644
--- a/gcc/langhooks.cc
+++ b/gcc/langhooks.cc
@@ -18,6 +18,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/opts.cc b/gcc/opts.cc
index 10ce2c3de33..21ac6b566e0 100644
--- a/gcc/opts.cc
+++ b/gcc/opts.cc
@@ -18,6 +18,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "intl.h"
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic_group_plugin.cc b/gcc/testsuite/gcc.dg/plugin/diagnostic_group_plugin.cc
index 48f832579ad..2bead63eede 100644
--- a/gcc/testsuite/gcc.dg/plugin/diagnostic_group_plugin.cc
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic_group_plugin.cc
@@ -1,5 +1,6 @@
 /* { dg-options "-O" } */
 
+#define INCLUDE_VECTOR
 #include "gcc-plugin.h"
 #include "config.h"
 #include "system.h"
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.cc b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.cc
index 92839cd35b7..9ee3219370c 100644
--- a/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.cc
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.cc
@@ -32,6 +32,7 @@
    to ensure that further very long lines don't start a new linemap.
    This also means that we can't use macros in the test files.  */
 
+#define INCLUDE_VECTOR
 #include "gcc-plugin.h"
 #include "config.h"
 #include "system.h"
diff --git a/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.cc b/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.cc
index 00ad8704477..2c40b311165 100644
--- a/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.cc
+++ b/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.cc
@@ -1,6 +1,7 @@
 /* Plugin for testing how gracefully we degrade in the face of very
    large source files.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "gcc-plugin.h"
 #include "system.h"
diff --git a/gcc/tree-diagnostic-client-data-hooks.cc b/gcc/tree-diagnostic-client-data-hooks.cc
index 77eb292f787..9ad608d17e0 100644
--- a/gcc/tree-diagnostic-client-data-hooks.cc
+++ b/gcc/tree-diagnostic-client-data-hooks.cc
@@ -19,6 +19,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/gcc/tree-diagnostic.cc b/gcc/tree-diagnostic.cc
index 20183c8bced..4cf742d047d 100644
--- a/gcc/tree-diagnostic.cc
+++ b/gcc/tree-diagnostic.cc
@@ -19,6 +19,7 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+#define INCLUDE_VECTOR
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
diff --git a/libcc1/context.cc b/libcc1/context.cc
index 38343a7c29e..b392f774c72 100644
--- a/libcc1/context.cc
+++ b/libcc1/context.cc
@@ -31,6 +31,7 @@ along with GCC; see the file COPYING3.  If not see
 #undef PACKAGE_TARNAME
 #undef PACKAGE_VERSION
 
+#define INCLUDE_VECTOR
 #include "gcc-plugin.h"
 #include "system.h"
 #include "coretypes.h"