diff --git a/gcc/libdiagnostics.h b/gcc/libdiagnostics.h
new file mode 100644
index 000000000000..43138a911123
--- /dev/null
+++ b/gcc/libdiagnostics.h
@@ -0,0 +1,691 @@
+/* A pure C API for emitting diagnostics.
+   Copyright (C) 2023-2024 Free Software Foundation, Inc.
+
+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 LIBDIAGNOSTICS_H
+#define LIBDIAGNOSTICS_H
+
+#include <stdarg.h>
+#include <stdio.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/**********************************************************************
+ Compatibility macros.
+ **********************************************************************/
+
+/* This macro simplifies testing whether we are using gcc, and if it
+   is of a particular minimum version. (Both major & minor numbers are
+   significant.)  This macro will evaluate to 0 if we are not using
+   gcc at all.  */
+#define LIBDIAGNOSTICS_GCC_VERSION (__GNUC__ * 1000 + __GNUC_MINOR__)
+
+/**********************************************************************
+ Macros for attributes.
+ **********************************************************************/
+
+# if (LIBDIAGNOSTICS_GCC_VERSION >= 3003)
+#  define LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL(ARG_NUM) __attribute__ ((__nonnull__ (ARG_NUM)))
+# else
+#  define LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL(ARG_NUM)
+# endif /* GNUC >= 3.3 */
+
+#define LIBDIAGNOSTICS_PARAM_CAN_BE_NULL(ARG_NUM)
+  /* empty; for the human reader */
+
+#define LIBDIAGNOSTICS_PARAM_GCC_FORMAT_STRING(FMT_ARG_NUM, ARGS_ARG_NUM) \
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (FMT_ARG_NUM)
+  /* In theory we'd also add
+       __attribute__ ((__format__ (__gcc_diag__, FMT_ARG_NUM, ARGS_ARG_NUM)))
+     if LIBDIAGNOSTICS_GCC_VERSION >= 4001
+     However, doing so leads to warnings from -Wformat-diag, which is part
+     of -Wall but undocumented, and much fussier than I'd want to inflict
+     on users of libdiagnostics.  */
+
+/**********************************************************************
+ Data structures and types.
+ All structs within the API are opaque.
+ **********************************************************************/
+
+/* An opaque bundle of state for a client of the library.
+   Has zero of more "sinks" to which diagnostics are emitted.
+   Responsibilities:
+   - location-management
+   - caching of source file content
+   - patch generation.  */
+typedef struct diagnostic_manager diagnostic_manager;
+
+/* Types relating to diagnostic output sinks.  */
+
+typedef struct diagnostic_text_sink diagnostic_text_sink;
+
+/* An enum for determining if we should colorize a text output sink.  */
+enum diagnostic_colorize
+{
+  DIAGNOSTIC_COLORIZE_IF_TTY,
+  DIAGNOSTIC_COLORIZE_NO,
+  DIAGNOSTIC_COLORIZE_YES
+};
+
+/* An enum for choosing the SARIF version for a SARIF output sink.
+   Eventually the SARIF output may support multiple SARIF versions.  */
+
+enum diagnostic_sarif_version
+{
+  DIAGNOSTIC_SARIF_VERSION_2_1_0
+};
+
+/* Types relating to "physical" source locations i.e. locations within
+   specific files expressed via line/column.  */
+
+/* Opaque type describing a particular input file.  */
+typedef struct diagnostic_file diagnostic_file;
+
+/* Opaque type representing a key into a database of source locations within
+   a diagnostic_manager.  Locations are created by various API calls into
+   the diagnostic_manager expressing source code points and ranges.  They
+   persist until the diagnostic_manager is released, which cleans them
+   up.
+
+   NULL means "UNKNOWN", and can be returned by the manager as a
+   fallback when a problem occurs (e.g. too many locations).
+
+   A diagnostic_location can be a single point within the source code,
+   such as here (at the the '"' at the start of the string literal):
+
+   |  int i = "foo";
+   |          ^
+
+   or be a range with a start and finish, and a "caret" location.
+
+   |   a = (foo && bar)
+   |       ~~~~~^~~~~~~
+
+   where the caret here is at the first "&", and the start and finish
+   are at the parentheses.  */
+
+typedef struct diagnostic_physical_location diagnostic_physical_location;
+
+/* Types for storing line and column information in text files.
+
+   Both libdiagnostics and emacs number source *lines* starting at 1, but
+   they have differing conventions for *columns*.
+
+   libdiagnostics uses a 1-based convention for source columns,
+   whereas Emacs's M-x column-number-mode uses a 0-based convention.
+
+   For example, an error in the initial, left-hand
+   column of source line 3 is reported by libdiagnostics as:
+
+      some-file.c:3:1: error: ...etc...
+
+   On navigating to the location of that error in Emacs
+   (e.g. via "next-error"),
+   the locus is reported in the Mode Line
+   (assuming M-x column-number-mode) as:
+
+     some-file.c   10%   (3, 0)
+
+   i.e. "3:1:" in libdiagnostics corresponds to "(3, 0)" in Emacs.  */
+
+typedef unsigned int diagnostic_line_num_t;
+typedef unsigned int diagnostic_column_num_t;
+
+/* An opaque type describing a "logical" source location
+   e.g. "within function 'foo'".  */
+
+typedef struct diagnostic_logical_location diagnostic_logical_location;
+
+/* An enum for discriminating between different kinds of logical location
+   for a diagnostic.
+
+   Roughly corresponds to logicalLocation's "kind" property in SARIF v2.1.0
+   (section 3.33.7).  */
+
+enum diagnostic_logical_location_kind_t
+{
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_FUNCTION,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_MEMBER,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_MODULE,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_NAMESPACE,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_TYPE,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_RETURN_TYPE,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_PARAMETER,
+  DIAGNOSTIC_LOGICAL_LOCATION_KIND_VARIABLE
+};
+
+/* A "diagnostic" is an opaque bundle of state for a particular
+   diagnostic that is being constructed in memory.
+
+   A diagnostic has a primary location and zero or more secondary
+   locations.  For example:
+
+   |   a = (foo && bar)
+   |       ~~~~~^~~~~~~
+
+   This diagnostic has a single diagnostic_location, with the caret
+   at the first "&", and the start/finish at the parentheses.
+
+   Contrast with:
+
+   |   a = (foo && bar)
+   |        ~~~ ^~ ~~~
+
+   This diagnostic has three locations
+   - The primary location (at "&&") has its caret and start location at
+   the first "&" and end at the second "&.
+   - The secondary location for "foo" has its start and finish at the "f"
+   and "o" of "foo"; the caret is not flagged for display, but is perhaps at
+   the "f" of "foo".
+   - Similarly, the other secondary location (for "bar") has its start and
+   finish at the "b" and "r" of "bar"; the caret is not flagged for
+   display, but is perhaps at the"b" of "bar".  */
+typedef struct diagnostic diagnostic;
+
+enum diagnostic_level
+{
+  DIAGNOSTIC_LEVEL_ERROR,
+  DIAGNOSTIC_LEVEL_WARNING,
+  DIAGNOSTIC_LEVEL_NOTE,
+
+  /* A problem where the input is valid, but the tool isn't
+     able to handle it.  */
+  DIAGNOSTIC_LEVEL_SORRY
+};
+
+/* Types for working with execution paths.  */
+typedef struct diagnostic_execution_path diagnostic_execution_path;
+typedef int diagnostic_event_id;
+
+/**********************************************************************
+ API entrypoints.
+ **********************************************************************/
+
+/* Create a new diagnostic_manager.
+   The client needs to call diagnostic_release_manager on it at some
+   point.
+   Note that no output sinks are created by default.  */
+
+extern diagnostic_manager *
+diagnostic_manager_new (void);
+
+/* Release a diagnostic_manager.
+   This will flush output to all of the output sinks, and clean up. */
+
+extern void
+diagnostic_manager_release (diagnostic_manager *)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Optional metadata about the manager.  */
+
+/* Set a string suitable for use as the value of the SARIF "name" property
+   (SARIF v2.1.0 section 3.19.8).  */
+
+extern void
+diagnostic_manager_set_tool_name (diagnostic_manager *diag_mgr,
+				  const char *value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Set a string suitable for use as the value of the SARIF "fullName" property
+   (SARIF v2.1.0 section 3.19.9).  */
+
+extern void
+diagnostic_manager_set_full_name (diagnostic_manager *diag_mgr,
+				  const char *value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Set a string suitable for use as the value of the SARIF "version" property
+   (SARIF v2.1.0 section 3.19.13).  */
+
+extern void
+diagnostic_manager_set_version_string (diagnostic_manager *diag_mgr,
+				       const char *value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Set a string suitable for use as the value of the SARIF "informationUri"
+   property (SARIF v2.1.0 section 3.19.17).  */
+
+extern void
+diagnostic_manager_set_version_url (diagnostic_manager *diag_mgr,
+				    const char *value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Destinations for diagnostics.  */
+
+/* Add a new output sink to DIAG_MGR, which writes GCC-style diagnostics
+   to DST_STREAM.
+   Return a borrowed pointer to the sink, which is cleaned up when DIAG_MGR
+   is released.
+   DST_STREAM is borrowed, and must outlive DIAG_MGR.
+   The output for each diagnostic is written and flushed as each
+   diagnostic is finished.  */
+
+extern diagnostic_text_sink *
+diagnostic_manager_add_text_sink (diagnostic_manager *diag_mgr,
+				  FILE *dst_stream,
+				  enum diagnostic_colorize colorize)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Functions to manipulate text sinks.  */
+
+/* Enable/disable printing of source text in the text sink.
+   Default: enabled.  */
+
+extern void
+diagnostic_text_sink_set_source_printing_enabled (diagnostic_text_sink *text_sink,
+						  int value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Update colorization of text sink.  */
+
+extern void
+diagnostic_text_sink_set_colorize (diagnostic_text_sink *text_sink,
+				   enum diagnostic_colorize colorize)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Enable/disable colorization of the characters of source text
+   that are underlined.
+   This should be true for clients that generate range information
+   (so that the ranges of code are colorized),
+   and false for clients that merely specify points within the
+   source code (to avoid e.g. colorizing just the first character in
+   a token, which would look strange).
+   Default: enabled.  */
+
+extern void
+diagnostic_text_sink_set_labelled_source_colorization_enabled (diagnostic_text_sink *text_sink,
+							       int value)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Add a new output sink to DIAG_MGR, which writes SARIF of the given
+   version to DST_STREAM.
+
+   The output is not written until DIAG_MGR is released.
+
+   DST_STREAM is borrowed, and must outlive DIAG_MGR.
+
+   For the result to be a valid SARIF file according to the schema,
+   DIAG_MGR must have had diagnostic_manager_set_tool_name called on it.  */
+
+extern void
+diagnostic_manager_add_sarif_sink (diagnostic_manager *diag_mgr,
+				   FILE *dst_stream,
+				   const diagnostic_file *main_input_file,
+				   enum diagnostic_sarif_version version)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* Write a patch to DST_STREAM consisting of all fix-it hints
+   on all diagnostics that have been finished on DIAG_MGR.  */
+
+extern void
+diagnostic_manager_write_patch (diagnostic_manager *diag_mgr,
+				FILE *dst_stream)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Location management.  */
+
+/* Create a new diagnostic_file * for file NAME.
+
+   Repeated calls with matching NAMEs will return the
+   same object.
+
+   If SARIF_SOURCE_LANGUAGE is non-NULL, it specifies a "sourceLanguage"
+   value for the file when use when writing SARIF.
+   See SARIF v2.1.0 Appendix J for suggested values for various
+   programmming languages.  */
+
+extern const diagnostic_file *
+diagnostic_manager_new_file (diagnostic_manager *diag_mgr,
+			     const char *name,
+			     const char *sarif_source_language)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3);
+
+/* Write a representation of FILE to OUT, for debugging.  */
+
+extern void
+diagnostic_manager_debug_dump_file (diagnostic_manager *diag_mgr,
+				    const diagnostic_file *file,
+				    FILE *out)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* Attempt to create a diagnostic_location representing
+   FILENAME:LINE_NUM, with no column information
+   (thus "the whole line").  */
+
+extern const diagnostic_physical_location *
+diagnostic_manager_new_location_from_file_and_line (diagnostic_manager *diag_mgr,
+						    const diagnostic_file *file,
+						    diagnostic_line_num_t line_num)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Attempt to create a diagnostic_physical_location representing
+   FILENAME:LINE_NUM:COLUMN_NUM.  */
+
+extern const diagnostic_physical_location *
+diagnostic_manager_new_location_from_file_line_column (diagnostic_manager *diag_mgr,
+						       const diagnostic_file *file,
+						       diagnostic_line_num_t line_num,
+						       diagnostic_column_num_t column_num)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Attempt to create a diagnostic_physical_location representing a
+   range within a source file, with a highlighted "caret" location.
+
+   All must be within the same file, but they can be on different lines.
+
+   For example, consider the location of the binary expression below:
+
+     ...|__________1111111112222222
+     ...|12345678901234567890123456
+     ...|
+     521|int sum (int foo, int bar)
+     522|{
+     523|   return foo + bar;
+     ...|          ~~~~^~~~~
+     524|}
+
+   The location's caret is at the "+", line 523 column 15, but starts
+   earlier, at the "f" of "foo" at column 11.  The finish is at the "r"
+   of "bar" at column 19.  */
+
+extern const diagnostic_physical_location *
+diagnostic_manager_new_location_from_range (diagnostic_manager *diag_mgr,
+					    const diagnostic_physical_location *loc_caret,
+					    const diagnostic_physical_location *loc_start,
+					    const diagnostic_physical_location *loc_end)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (4);
+
+/* Write a representation of LOC to OUT, for debugging.  */
+
+extern void
+diagnostic_manager_debug_dump_location (const diagnostic_manager *diag_mgr,
+					const diagnostic_physical_location *loc,
+					FILE *out)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* A bundle of state describing a logical location in the user's source,
+   such as "in function 'foo'".
+
+   SHORT_NAME can be NULL, or else a string suitable for use by
+   the SARIF logicalLocation "name" property (SARIF v2.1.0 section 3.33.4).
+
+   FULLY_QUALIFIED_NAME can be NULL or else a string  suitable for use by
+   the SARIF logicalLocation "fullyQualifiedName" property
+   (SARIF v2.1.0 section 3.33.5).
+
+   DECORATED_NAME can be NULL or else a string  suitable for use by
+   the SARIF logicalLocation "decoratedName" property
+   (SARIF v2.1.0 section 3.33.6).  */
+
+extern const diagnostic_logical_location *
+diagnostic_manager_new_logical_location (diagnostic_manager *diag_mgr,
+					 enum diagnostic_logical_location_kind_t kind,
+					 const diagnostic_logical_location *parent,
+					 const char *short_name,
+					 const char *fully_qualified_name,
+					 const char *decorated_name)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (4)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (5)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (6);
+
+/* Write a representation of LOC to OUT, for debugging.  */
+
+extern void
+diagnostic_manager_debug_dump_logical_location (const diagnostic_manager *diag_mgr,
+						const diagnostic_logical_location *loc,
+						FILE *out)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* Diagnostic groups.  */
+
+/* Begin a diagnostic group.  All diagnostics emitted within
+   DIAG_MGR after the first one will be treated as notes about
+   the initial diagnostic.  */
+
+extern void
+diagnostic_manager_begin_group (diagnostic_manager *diag_mgr)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Finish a diagnostic group.  */
+
+extern void
+diagnostic_manager_end_group (diagnostic_manager *diag_mgr)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Step-by-step creation of a diagnostic.  */
+
+extern diagnostic *
+diagnostic_begin (diagnostic_manager *diag_mgr,
+		  enum diagnostic_level level)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Associate this diagnostic with the given ID within
+   the Common Weakness Enumeration.  */
+
+extern void
+diagnostic_set_cwe (diagnostic *diag,
+		    unsigned cwe_id)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Associate this diagnostic with a particular rule that has been violated
+   (such as in a coding standard, or within a specification).
+   The rule must have at least one of a title and a URL, but these
+   can be NULL.
+   A diagnostic can be associated with zero or more rules.  */
+
+extern void
+diagnostic_add_rule (diagnostic *diag,
+		     const char *title,
+		     const char *url)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3);
+
+/* Set the primary location of DIAG.  */
+
+extern void
+diagnostic_set_location (diagnostic *diag,
+			 const diagnostic_physical_location * loc)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2);
+
+/* Set the primary location of DIAG, with a label.  */
+
+extern void
+diagnostic_set_location_with_label (diagnostic *diag,
+				    const diagnostic_physical_location *loc,
+				    const char *fmt, ...)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* Add a secondary location to DIAG.  */
+
+extern void
+diagnostic_add_location (diagnostic *diag,
+			 const diagnostic_physical_location * loc)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Add a secondary location to DIAG, with a label.  */
+
+extern void
+diagnostic_add_location_with_label (diagnostic *diag,
+				    const diagnostic_physical_location *loc,
+				    const char *text)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+/* Set the logical location of DIAG.  */
+
+extern void
+diagnostic_set_logical_location (diagnostic *diag,
+				 const diagnostic_logical_location *logical_loc)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2);
+
+/* Fix-it hints.  */
+
+extern void
+diagnostic_add_fix_it_hint_insert_before (diagnostic *diag,
+					  const diagnostic_physical_location *loc,
+					  const char *addition)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+extern void
+diagnostic_add_fix_it_hint_insert_after (diagnostic *diag,
+					 const diagnostic_physical_location *loc,
+					 const char *addition)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+extern void
+diagnostic_add_fix_it_hint_replace (diagnostic *diag,
+				    const diagnostic_physical_location *loc,
+				    const char *replacement)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (3);
+
+extern void
+diagnostic_add_fix_it_hint_delete (diagnostic *diag,
+				   const diagnostic_physical_location *loc)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2);
+
+/* Create and borrow a pointer to an execution path for DIAG.
+   The path is automatically cleaned up when DIAG is finished.  */
+
+extern diagnostic_execution_path *
+diagnostic_add_execution_path (diagnostic *diag)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Create a new execution path.
+   This is owned by the called and must have either
+   diagnostic_take_execution_path or diagnostic_execution_path_release
+   called on it.  */
+
+extern diagnostic_execution_path *
+diagnostic_manager_new_execution_path (diagnostic_manager *manager)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1);
+
+/* Set DIAG to use PATH as its execution path, taking ownership of PATH.  */
+
+extern void
+diagnostic_take_execution_path (diagnostic *diag,
+				diagnostic_execution_path *path)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2);
+
+/* Release ownership of PATH, which must not have been taken
+   by a diagnostic.  */
+
+extern void
+diagnostic_execution_path_release (diagnostic_execution_path *path)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (1);
+
+/* Append an event to the end of PATH.  */
+
+extern diagnostic_event_id
+diagnostic_execution_path_add_event (diagnostic_execution_path *path,
+				     const diagnostic_physical_location *physical_loc,
+				     const diagnostic_logical_location *logical_loc,
+				     unsigned stack_depth,
+				     const char *fmt, ...)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (5)
+  LIBDIAGNOSTICS_PARAM_GCC_FORMAT_STRING (5, 6);
+
+/* Append an event to the end of PATH.  */
+
+extern diagnostic_event_id
+diagnostic_execution_path_add_event_va (diagnostic_execution_path *path,
+					const diagnostic_physical_location *physical_loc,
+					const diagnostic_logical_location *logical_loc,
+					unsigned stack_depth,
+					const char *fmt,
+					va_list *args)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (2)
+  LIBDIAGNOSTICS_PARAM_CAN_BE_NULL (3)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (5)
+  LIBDIAGNOSTICS_PARAM_GCC_FORMAT_STRING (5, 0);
+
+/* Emit DIAG to all sinks of its manager, and release DIAG.
+   Use FMT for the message.
+   Note that this uses gcc's pretty-print format, which is *not* printf.
+   TODO: who is responsible for putting FMT through gettext?  */
+
+extern void
+diagnostic_finish (diagnostic *diag, const char *fmt, ...)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2)
+  LIBDIAGNOSTICS_PARAM_GCC_FORMAT_STRING (2, 3);
+
+/* As diagnostic_finish, but with a va_list.  */
+
+extern void
+diagnostic_finish_va (diagnostic *diag, const char *fmt, va_list *args)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (1)
+  LIBDIAGNOSTICS_PARAM_MUST_BE_NON_NULL (2)
+  LIBDIAGNOSTICS_PARAM_GCC_FORMAT_STRING (2, 0);
+
+/* DEFERRED:
+   - thread-safety
+   - plural forms
+   - enum about what a "column number" means (bytes, unichars, etc)
+   - locations within binary files
+   - options and URLs for warnings
+   - enable/disable of warnings by kind
+   - plugin metadata.  */
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif  /* LIBDIAGNOSTICS_H  */
