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diff --git a/gcc/diagnostics/buffering.h b/gcc/diagnostics/buffering.h
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+/* Support for buffering diagnostics before flushing them to output sinks.
+   Copyright (C) 2024-2025 Free Software Foundation, Inc.
+   Contributed by David Malcolm <dmalcolm@redhat.com>.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+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/>.  */
+
+#ifndef GCC_DIAGNOSTICS_BUFFERING_H
+#define GCC_DIAGNOSTICS_BUFFERING_H
+
+#include "diagnostic.h"
+
+namespace diagnostics {
+
+class per_sink_buffer;
+class sink;
+  class text_sink;
+
+/* Class representing a buffer of zero or more diagnostics that
+   have been reported to a diagnostics::context, but which haven't
+   yet been flushed.
+
+   A diagnostics::buffer can be:
+
+   * flushed to the diagnostics::context, which issues
+   the diagnostics within the buffer to the output format
+   and checks for limits such as -fmax-errors=, or
+
+   * moved to another diagnostics::buffer, which moves the diagnostics
+   within the first buffer to the other buffer, appending them after any
+   existing diagnostics within the destination buffer, emptying the
+   source buffer, or
+
+   * cleared, which discards any diagnostics within the buffer
+   without issuing them to the output format.
+
+   Since a buffer needs to contain output-format-specific data,
+   it's not possible to change the output format of the
+   diagnostics::context once any buffers are non-empty.
+
+   To simplify implementing output formats, it's not possible
+   to change buffering on a diagnostics::context whilst within a
+   diagnostic group.  */
+
+class buffer
+{
+ public:
+  friend class context;
+
+  buffer (context &ctxt);
+  ~buffer ();
+
+  void dump (FILE *out, int indent) const;
+  void DEBUG_FUNCTION dump () const { dump (stderr, 0); }
+
+  int diagnostic_count (enum kind kind) const
+  {
+    return m_diagnostic_counters.get_count (kind);
+  }
+
+  bool empty_p () const;
+
+  void move_to (buffer &dest);
+
+ private:
+  void ensure_per_sink_buffers ();
+
+  context &m_ctxt;
+  auto_vec<per_sink_buffer *> *m_per_sink_buffers;
+
+  /* The number of buffered diagnostics of each kind.  */
+  counters m_diagnostic_counters;
+};
+
+/* Implementation detail of diagnostics::buffer.
+
+   Abstract base class describing how to represent zero of more
+   buffered diagnostics for a particular diagnostics::sink
+   (e.g. text vs SARIF).
+
+   Each diagnostics::sink subclass should implement its own
+   subclass for handling diagnostics::buffer.  */
+
+class per_sink_buffer
+{
+public:
+  virtual ~per_sink_buffer () {}
+
+  virtual void dump (FILE *out, int indent) const = 0;
+  void DEBUG_FUNCTION dump () const { dump (stderr, 0); }
+
+  virtual bool empty_p () const = 0;
+  virtual void move_to (per_sink_buffer &dest) = 0;
+  virtual void clear () = 0;
+  virtual void flush () = 0;
+};
+
+} // namespace diagnostics
+
+#endif /* ! GCC_DIAGNOSTICS_BUFFERING_H */