diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 1e8a311..ec79317 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -1395,7 +1395,6 @@ OBJS = \
 	ira-color.o \
 	ira-emit.o \
 	ira-lives.o \
-	json.o \
 	jump.o \
 	langhooks.o \
 	lcm.o \
@@ -1619,6 +1618,7 @@ OBJS = \
 # Objects in libcommon.a, potentially used by all host binaries and with
 # no target dependencies.
 OBJS-libcommon = diagnostic.o diagnostic-color.o diagnostic-show-locus.o \
+	diagnostic-format-json.o json.o \
 	edit-context.o \
 	pretty-print.o intl.o \
 	sbitmap.o \
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index 356bd4c..ce015bb 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -165,7 +165,8 @@ c_common_option_lang_mask (void)
 /* Diagnostic finalizer for C/C++/Objective-C/Objective-C++.  */
 static void
 c_diagnostic_finalizer (diagnostic_context *context,
-			diagnostic_info *diagnostic)
+			diagnostic_info *diagnostic,
+			diagnostic_t)
 {
   diagnostic_show_locus (context, diagnostic->richloc, diagnostic->kind);
   /* By default print macro expansion contexts in the diagnostic
diff --git a/gcc/common.opt b/gcc/common.opt
index 73065f5..72a7135 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1277,6 +1277,23 @@ Enum(diagnostic_color_rule) String(always) Value(DIAGNOSTICS_COLOR_YES)
 EnumValue
 Enum(diagnostic_color_rule) String(auto) Value(DIAGNOSTICS_COLOR_AUTO)
 
+fdiagnostics-format=
+Common Joined RejectNegative Enum(diagnostics_output_format)
+-fdiagnostics-format=[text|json] Select output format
+
+; Required for these enum values.
+SourceInclude
+diagnostic.h
+
+Enum
+Name(diagnostics_output_format) Type(int)
+
+EnumValue
+Enum(diagnostics_output_format) String(text) Value(DIAGNOSTICS_OUTPUT_FORMAT_TEXT)
+
+EnumValue
+Enum(diagnostics_output_format) String(json) Value(DIAGNOSTICS_OUTPUT_FORMAT_JSON)
+
 fdiagnostics-parseable-fixits
 Common Var(flag_diagnostics_parseable_fixits)
 Print fix-it hints in machine-readable form.
diff --git a/gcc/diagnostic-format-json.cc b/gcc/diagnostic-format-json.cc
new file mode 100644
index 0000000..8d56120
--- /dev/null
+++ b/gcc/diagnostic-format-json.cc
@@ -0,0 +1,264 @@
+/* JSON output for diagnostics
+   Copyright (C) 2018 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/>.  */
+
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "diagnostic.h"
+#include "json.h"
+
+/* The top-level JSON array of pending diagnostics.  */
+
+static json::array *toplevel_array;
+
+/* The JSON object for the current diagnostic group.  */
+
+static json::object *cur_group;
+
+/* The JSON array for the "children" array within the current diagnostic
+   group.  */
+
+static json::array *cur_children_array;
+
+/* Generate a JSON object for LOC.  */
+
+static json::object *
+json_from_expanded_location (location_t loc)
+{
+  expanded_location exploc = expand_location (loc);
+  json::object *result = new json::object ();
+  result->set ("file", new json::string (exploc.file));
+  result->set ("line", new json::number (exploc.line));
+  result->set ("column", new json::number (exploc.column));
+  return result;
+}
+
+/* Generate a JSON object for LOC_RANGE.  */
+
+static json::object *
+json_from_location_range (const location_range *loc_range, unsigned range_idx)
+{
+  location_t caret_loc = get_pure_location (loc_range->m_loc);
+
+  if (caret_loc == UNKNOWN_LOCATION)
+    return NULL;
+
+  location_t start_loc = get_start (loc_range->m_loc);
+  location_t finish_loc = get_finish (loc_range->m_loc);
+
+  json::object *result = new json::object ();
+  result->set ("caret", json_from_expanded_location (caret_loc));
+  if (start_loc != caret_loc)
+    result->set ("start", json_from_expanded_location (start_loc));
+  if (finish_loc != caret_loc)
+    result->set ("finish", json_from_expanded_location (finish_loc));
+
+  if (loc_range->m_label)
+    {
+      label_text text;
+      text = loc_range->m_label->get_text (range_idx);
+      if (text.m_buffer)
+	result->set ("label", new json::string (text.m_buffer));
+      text.maybe_free ();
+    }
+
+  return result;
+}
+
+/* Generate a JSON object for HINT.  */
+
+static json::object *
+json_from_fixit_hint (const fixit_hint *hint)
+{
+  json::object *fixit_obj = new json::object ();
+
+  location_t start_loc = hint->get_start_loc ();
+  fixit_obj->set ("start", json_from_expanded_location (start_loc));
+  location_t next_loc = hint->get_next_loc ();
+  fixit_obj->set ("next", json_from_expanded_location (next_loc));
+  fixit_obj->set ("string", new json::string (hint->get_string ()));
+
+  return fixit_obj;
+}
+
+/* No-op implementation of "begin_diagnostic" for JSON output.  */
+
+static void
+json_begin_diagnostic (diagnostic_context *, diagnostic_info *)
+{
+}
+
+/* Implementation of "end_diagnostic" for JSON output.
+   Generate a JSON object for DIAGNOSTIC, and store for output
+   within current diagnostic group.  */
+
+static void
+json_end_diagnostic (diagnostic_context *context, diagnostic_info *diagnostic,
+		     diagnostic_t orig_diag_kind)
+{
+  json::object *diag_obj = new json::object ();
+
+  /* Get "kind" of diagnostic.  */
+  {
+    static const char *const diagnostic_kind_text[] = {
+#define DEFINE_DIAGNOSTIC_KIND(K, T, C) (T),
+#include "diagnostic.def"
+#undef DEFINE_DIAGNOSTIC_KIND
+      "must-not-happen"
+    };
+    /* Lose the trailing ": ".  */
+    const char *kind_text = diagnostic_kind_text[diagnostic->kind];
+    size_t len = strlen (kind_text);
+    gcc_assert (len > 2);
+    gcc_assert (kind_text[len - 2] == ':');
+    gcc_assert (kind_text[len - 1] == ' ');
+    char *rstrip = xstrdup (kind_text);
+    rstrip[len - 2] = '\0';
+    diag_obj->set ("kind", new json::string (rstrip));
+    free (rstrip);
+  }
+
+  // FIXME: encoding of the message (json::string requires UTF-8)
+  diag_obj->set ("message",
+		 new json::string (pp_formatted_text (context->printer)));
+  pp_clear_output_area (context->printer);
+
+  char *option_text;
+  option_text = context->option_name (context, diagnostic->option_index,
+				      orig_diag_kind, diagnostic->kind);
+  if (option_text)
+    {
+      diag_obj->set ("option", new json::string (option_text));
+      free (option_text);
+    }
+
+  /* If we've already emitted a diagnostic within this auto_diagnostic_group,
+     then add diag_obj to its "children" array.  */
+  if (cur_group)
+    {
+      gcc_assert (cur_children_array);
+      cur_children_array->append (diag_obj);
+    }
+  else
+    {
+      /* Otherwise, make diag_obj be the top-level object within the group;
+	 add a "children" array.  */
+      toplevel_array->append (diag_obj);
+      cur_group = diag_obj;
+      cur_children_array = new json::array ();
+      diag_obj->set ("children", cur_children_array);
+    }
+
+  const rich_location *richloc = diagnostic->richloc;
+
+  json::array *loc_array = new json::array ();
+  diag_obj->set ("locations", loc_array);
+
+  for (unsigned int i = 0; i < richloc->get_num_locations (); i++)
+    {
+      const location_range *loc_range = richloc->get_range (i);
+      json::object *loc_obj = json_from_location_range (loc_range, i);
+      if (loc_obj)
+	loc_array->append (loc_obj);
+    }
+
+  if (richloc->get_num_fixit_hints ())
+    {
+      json::array *fixit_array = new json::array ();
+      diag_obj->set ("fixits", fixit_array);
+      for (unsigned int i = 0; i < richloc->get_num_fixit_hints (); i++)
+	{
+	  const fixit_hint *hint = richloc->get_fixit_hint (i);
+	  json::object *fixit_obj = json_from_fixit_hint (hint);
+	  fixit_array->append (fixit_obj);
+	}
+    }
+
+  /* TODO: tree-ish things:
+     TODO: functions
+     TODO: inlining information
+     TODO: macro expansion information.  */
+}
+
+/* No-op implementation of "begin_group_cb" for JSON output.  */
+
+static void
+json_begin_group (diagnostic_context *)
+{
+}
+
+/* Implementation of "end_group_cb" for JSON output.  */
+
+static void
+json_end_group (diagnostic_context *)
+{
+  cur_group = NULL;
+  cur_children_array = NULL;
+}
+
+/* Callback for final cleanup for JSON output.  */
+
+static void
+json_final_cb (diagnostic_context *)
+{
+  /* Flush the top-level array.  */
+  toplevel_array->dump (stderr);
+  fprintf (stderr, "\n");
+  delete toplevel_array;
+  toplevel_array = NULL;
+}
+
+/* Set the output format for CONTEXT to FORMAT.  */
+
+void
+diagnostic_output_format_init (diagnostic_context *context,
+			       enum diagnostics_output_format format)
+{
+  switch (format)
+    {
+    default:
+      gcc_unreachable ();
+    case DIAGNOSTICS_OUTPUT_FORMAT_TEXT:
+      /* The default; do nothing.  */
+      break;
+
+    case DIAGNOSTICS_OUTPUT_FORMAT_JSON:
+      {
+	/* Set up top-level JSON array.  */
+	if (toplevel_array == NULL)
+	  toplevel_array = new json::array ();
+
+	/* Override callbacks.  */
+	context->begin_diagnostic = json_begin_diagnostic;
+	context->end_diagnostic = json_end_diagnostic;
+	context->begin_group_cb = json_begin_group;
+	context->end_group_cb =  json_end_group;
+	context->final_cb =  json_final_cb;
+
+	/* The option is handled in JSON format, rather than as text.  */
+	context->show_option_requested = false;
+
+	/* Don't colorize the text.  */
+	pp_show_color (context->printer) = false;
+      }
+      break;
+    }
+}
diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c
index 3d86a21..27e98fa 100644
--- a/gcc/diagnostic.c
+++ b/gcc/diagnostic.c
@@ -131,6 +131,28 @@ diagnostic_set_caret_max_width (diagnostic_context *context, int value)
   context->caret_max_width = value;
 }
 
+/* Default implementation of final_cb.  */
+
+static void
+default_diagnostic_final_cb (diagnostic_context *context)
+{
+  /* Some of the errors may actually have been warnings.  */
+  if (diagnostic_kind_count (context, DK_WERROR))
+    {
+      /* -Werror was given.  */
+      if (context->warning_as_error_requested)
+	pp_verbatim (context->printer,
+		     _("%s: all warnings being treated as errors"),
+		     progname);
+      /* At least one -Werror= was given.  */
+      else
+	pp_verbatim (context->printer,
+		     _("%s: some warnings being treated as errors"),
+		     progname);
+      pp_newline_and_flush (context->printer);
+    }
+}
+
 /* Initialize the diagnostic message outputting machinery.  */
 void
 diagnostic_initialize (diagnostic_context *context, int n_opts)
@@ -185,6 +207,7 @@ diagnostic_initialize (diagnostic_context *context, int n_opts)
   context->diagnostic_group_emission_count = 0;
   context->begin_group_cb = NULL;
   context->end_group_cb = NULL;
+  context->final_cb = default_diagnostic_final_cb;
 }
 
 /* Maybe initialize the color support. We require clients to do this
@@ -220,21 +243,8 @@ diagnostic_color_init (diagnostic_context *context, int value /*= -1 */)
 void
 diagnostic_finish (diagnostic_context *context)
 {
-  /* Some of the errors may actually have been warnings.  */
-  if (diagnostic_kind_count (context, DK_WERROR))
-    {
-      /* -Werror was given.  */
-      if (context->warning_as_error_requested)
-	pp_verbatim (context->printer,
-		     _("%s: all warnings being treated as errors"),
-		     progname);
-      /* At least one -Werror= was given.  */
-      else
-	pp_verbatim (context->printer,
-		     _("%s: some warnings being treated as errors"),
-		     progname);
-      pp_newline_and_flush (context->printer);
-    }
+  if (context->final_cb)
+    context->final_cb (context);
 
   diagnostic_file_cache_fini ();
 
@@ -642,7 +652,8 @@ default_diagnostic_start_span_fn (diagnostic_context *context,
 
 void
 default_diagnostic_finalizer (diagnostic_context *context,
-			      diagnostic_info *diagnostic)
+			      diagnostic_info *diagnostic,
+			      diagnostic_t)
 {
   diagnostic_show_locus (context, diagnostic->richloc, diagnostic->kind);
   pp_destroy_prefix (context->printer);
@@ -1006,7 +1017,7 @@ diagnostic_report_diagnostic (diagnostic_context *context,
   pp_output_formatted_text (context->printer);
   if (context->show_option_requested)
     print_option_information (context, diagnostic, orig_diag_kind);
-  (*diagnostic_finalizer (context)) (context, diagnostic);
+  (*diagnostic_finalizer (context)) (context, diagnostic, orig_diag_kind);
   if (context->parseable_fixits_p)
     {
       print_parseable_fixits (context->printer, diagnostic->richloc);
diff --git a/gcc/diagnostic.h b/gcc/diagnostic.h
index 3498a9b..a926f9b 100644
--- a/gcc/diagnostic.h
+++ b/gcc/diagnostic.h
@@ -24,6 +24,17 @@ along with GCC; see the file COPYING3.  If not see
 #include "pretty-print.h"
 #include "diagnostic-core.h"
 
+/* Enum for overriding the standard output format.  */
+
+enum diagnostics_output_format
+{
+  /* The default: textual output.  */
+  DIAGNOSTICS_OUTPUT_FORMAT_TEXT,
+
+  /* JSON-based output.  */
+  DIAGNOSTICS_OUTPUT_FORMAT_JSON
+};
+
 /* A diagnostic is described by the MESSAGE to send, the FILE and LINE of
    its context and its KIND (ice, error, warning, note, ...)  See complete
    list in diagnostic.def.  */
@@ -60,7 +71,9 @@ typedef void (*diagnostic_starter_fn) (diagnostic_context *,
 typedef void (*diagnostic_start_span_fn) (diagnostic_context *,
 					  expanded_location);
 
-typedef diagnostic_starter_fn diagnostic_finalizer_fn;
+typedef void (*diagnostic_finalizer_fn) (diagnostic_context *,
+					 diagnostic_info *,
+					 diagnostic_t);
 
 class edit_context;
 
@@ -243,6 +256,9 @@ struct diagnostic_context
   /* If non-NULL, this will be called when a stack of groups is
      popped if any diagnostics were emitted within that group.  */
   void (*end_group_cb) (diagnostic_context * context);
+
+  /* Callback for final cleanup.  */
+  void (*final_cb) (diagnostic_context *context);
 };
 
 static inline void
@@ -341,7 +357,8 @@ extern char *diagnostic_build_prefix (diagnostic_context *, const diagnostic_inf
 void default_diagnostic_starter (diagnostic_context *, diagnostic_info *);
 void default_diagnostic_start_span_fn (diagnostic_context *,
 				       expanded_location);
-void default_diagnostic_finalizer (diagnostic_context *, diagnostic_info *);
+void default_diagnostic_finalizer (diagnostic_context *, diagnostic_info *,
+				   diagnostic_t);
 void diagnostic_set_caret_max_width (diagnostic_context *context, int value);
 void diagnostic_action_after_output (diagnostic_context *, diagnostic_t);
 void diagnostic_check_max_errors (diagnostic_context *, bool flush = false);
@@ -401,5 +418,7 @@ extern char *file_name_as_prefix (diagnostic_context *, const char *);
 
 extern char *build_message_string (const char *, ...) ATTRIBUTE_PRINTF_1;
 
+extern void diagnostic_output_format_init (diagnostic_context *,
+					   enum diagnostics_output_format);
 
 #endif /* ! GCC_DIAGNOSTIC_H */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 283d20f..5a41f46 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -268,6 +268,7 @@ Objective-C and Objective-C++ Dialects}.
 @gccoptlist{-fmessage-length=@var{n}  @gol
 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}  @gol
 -fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]}  @gol
+-fdiagnostics-format=@r{[}text@r{|}json@r{]}  @gol
 -fno-diagnostics-show-option  -fno-diagnostics-show-caret @gol
 -fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers @gol
 -fdiagnostics-minimum-margin-width=@var{width} @gol
@@ -3979,6 +3980,193 @@ Do not print column numbers in diagnostics.  This may be necessary if
 diagnostics are being scanned by a program that does not understand the
 column numbers, such as @command{dejagnu}.
 
+@item -fdiagnostics-format=@var{FORMAT}
+@opindex fdiagnostics-format
+Select a different format for printing diagnostics.
+@var{FORMAT} is @samp{text} or @samp{json}.
+The default is @samp{text}.
+
+The @samp{json} format consists of a top-level JSON array containing JSON
+objects representing the diagnostics.
+
+The JSON is emitted as one line, without formatting; the examples below
+have been formatted for clarity.
+
+Diagnostics can have child diagnostics.  For example, this error and note:
+
+@smallexample
+misleading-indentation.c:15:3: warning: this 'if' clause does not
+  guard... [-Wmisleading-indentation]
+   15 |   if (flag)
+      |   ^~
+misleading-indentation.c:17:5: note: ...this statement, but the latter
+  is misleadingly indented as if it were guarded by the 'if'
+   17 |     y = 2;
+      |     ^
+@end smallexample
+
+@noindent
+might be printed in JSON form (after formatting) like this:
+
+@smallexample
+[
+    @{
+        "kind": "warning",
+        "locations": [
+            @{
+                "caret": @{
+                    "column": 3,
+                    "file": "misleading-indentation.c",
+                    "line": 15
+                @},
+                "finish": @{
+                    "column": 4,
+                    "file": "misleading-indentation.c",
+                    "line": 15
+                @}
+            @}
+        ],
+        "message": "this \u2018if\u2019 clause does not guard...",
+        "option": "-Wmisleading-indentation",
+        "children": [
+            @{
+                "kind": "note",
+                "locations": [
+                    @{
+                        "caret": @{
+                            "column": 5,
+                            "file": "misleading-indentation.c",
+                            "line": 17
+                        @}
+                    @}
+                ],
+                "message": "...this statement, but the latter is @dots{}"
+            @}
+        ]
+    @},
+    @dots{}
+]
+@end smallexample
+
+@noindent
+where the @code{note} is a child of the @code{warning}.
+
+A diagnostic has a @code{kind}.  If this is @code{warning}, then there is
+an @code{option} key describing the command-line option controlling the
+warning.
+
+A diagnostic can contain zero or more locations.  Each location has up
+to three positions within it: a @code{caret} position and optional
+@code{start} and @code{finish} positions.  A location can also have
+an optional @code{label} string.  For example, this error:
+
+@smallexample
+bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' @{aka
+   'struct s'@} and 'T' @{aka 'struct t'@})
+   64 |   return callee_4a () + callee_4b ();
+      |          ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~
+      |          |              |
+      |          |              T @{aka struct t@}
+      |          S @{aka struct s@}
+@end smallexample
+
+@noindent
+has three locations.  Its primary location is at the ``+'' token at column
+23.  It has two secondary locations, describing the left and right-hand sides
+of the expression, which have labels.  It might be printed in JSON form as:
+
+@smallexample
+    @{
+        "children": [],
+        "kind": "error",
+        "locations": [
+            @{
+                "caret": @{
+                    "column": 23, "file": "bad-binary-ops.c", "line": 64
+                @}
+            @},
+            @{
+                "caret": @{
+                    "column": 10, "file": "bad-binary-ops.c", "line": 64
+                @},
+                "finish": @{
+                    "column": 21, "file": "bad-binary-ops.c", "line": 64
+                @},
+                "label": "S @{aka struct s@}"
+            @},
+            @{
+                "caret": @{
+                    "column": 25, "file": "bad-binary-ops.c", "line": 64
+                @},
+                "finish": @{
+                    "column": 36, "file": "bad-binary-ops.c", "line": 64
+                @},
+                "label": "T @{aka struct t@}"
+            @}
+        ],
+        "message": "invalid operands to binary + @dots{}"
+    @}
+@end smallexample
+
+If a diagnostic contains fix-it hints, it has a @code{fixits} array,
+consisting of half-open intervals, similar to the output of
+@option{-fdiagnostics-parseable-fixits}.  For example, this diagnostic
+with a replacement fix-it hint:
+
+@smallexample
+demo.c:8:15: error: 'struct s' has no member named 'colour'; did you
+  mean 'color'?
+    8 |   return ptr->colour;
+      |               ^~~~~~
+      |               color
+@end smallexample
+
+@noindent
+might be printed in JSON form as:
+
+@smallexample
+    @{
+        "children": [],
+        "fixits": [
+            @{
+                "next": @{
+                    "column": 21,
+                    "file": "demo.c",
+                    "line": 8
+                @},
+                "start": @{
+                    "column": 15,
+                    "file": "demo.c",
+                    "line": 8
+                @},
+                "string": "color"
+            @}
+        ],
+        "kind": "error",
+        "locations": [
+            @{
+                "caret": @{
+                    "column": 15,
+                    "file": "demo.c",
+                    "line": 8
+                @},
+                "finish": @{
+                    "column": 20,
+                    "file": "demo.c",
+                    "line": 8
+                @}
+            @}
+        ],
+        "message": "\u2018struct s\u2019 has no member named @dots{}"
+    @}
+@end smallexample
+
+@noindent
+where the fix-it hint suggests replacing the text from @code{start} up
+to but not including @code{next} with @code{string}'s value.  Deletions
+are expressed via an empty value for @code{string}, insertions by
+having @code{start} equal @code{next}.
+
 @end table
 
 @node Warning Options
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 8b478aa..4fb0527 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -24267,6 +24267,7 @@ gen_producer_string (void)
       case OPT_fdiagnostics_show_labels:
       case OPT_fdiagnostics_show_line_numbers:
       case OPT_fdiagnostics_color_:
+      case OPT_fdiagnostics_format_:
       case OPT_fverbose_asm:
       case OPT____:
       case OPT__sysroot_:
diff --git a/gcc/fortran/error.c b/gcc/fortran/error.c
index b3b0138..5b41fd3 100644
--- a/gcc/fortran/error.c
+++ b/gcc/fortran/error.c
@@ -1132,7 +1132,8 @@ gfc_diagnostic_start_span (diagnostic_context *context,
 
 static void
 gfc_diagnostic_finalizer (diagnostic_context *context,
-			  diagnostic_info *diagnostic ATTRIBUTE_UNUSED)
+			  diagnostic_info *diagnostic ATTRIBUTE_UNUSED,
+			  diagnostic_t orig_diag_kind ATTRIBUTE_UNUSED)
 {
   pp_destroy_prefix (context->printer);
   pp_newline_and_flush (context->printer);
diff --git a/gcc/gcc.c b/gcc/gcc.c
index c0d17eb..afc18b3 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -4001,6 +4001,11 @@ driver_handle_option (struct gcc_options *opts,
       diagnostic_color_init (dc, value);
       break;
 
+    case OPT_fdiagnostics_format_:
+      diagnostic_output_format_init (dc,
+				     (enum diagnostics_output_format)value);
+      break;
+
     case OPT_Wa_:
       {
 	int prev, j;
diff --git a/gcc/jit/dummy-frontend.c b/gcc/jit/dummy-frontend.c
index 4c7f960..ec91852 100644
--- a/gcc/jit/dummy-frontend.c
+++ b/gcc/jit/dummy-frontend.c
@@ -110,7 +110,8 @@ jit_begin_diagnostic (diagnostic_context */*context*/,
 
 static void
 jit_end_diagnostic (diagnostic_context *context,
-		    diagnostic_info *diagnostic)
+		    diagnostic_info *diagnostic,
+		    diagnostic_t)
 {
   gcc_assert (gcc::jit::active_playback_ctxt);
   JIT_LOG_SCOPE (gcc::jit::active_playback_ctxt->get_logger ());
diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
index 2b9d47e..90d8c1c 100644
--- a/gcc/lto-wrapper.c
+++ b/gcc/lto-wrapper.c
@@ -646,6 +646,7 @@ append_diag_options (obstack *argv_obstack, struct cl_decoded_option *opts,
       switch (option->opt_index)
 	{
 	case OPT_fdiagnostics_color_:
+	case OPT_fdiagnostics_format_:
 	case OPT_fdiagnostics_show_caret:
 	case OPT_fdiagnostics_show_labels:
 	case OPT_fdiagnostics_show_line_numbers:
diff --git a/gcc/opts.c b/gcc/opts.c
index e21967b..528da3f 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -2221,6 +2221,11 @@ common_handle_option (struct gcc_options *opts,
       diagnostic_color_init (dc, value);
       break;
 
+    case OPT_fdiagnostics_format_:
+      diagnostic_output_format_init (dc,
+				     (enum diagnostics_output_format)value);
+      break;
+
     case OPT_fdiagnostics_parseable_fixits:
       dc->parseable_fixits_p = value;
       break;
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c
new file mode 100644
index 0000000..9359db48
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c
@@ -0,0 +1,25 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-format=json" } */
+
+#error message
+
+/* Use dg-regexp to consume the JSON output starting with
+   the innermost values, and working outwards.
+   We can't rely on any ordering of the keys.  */
+
+/* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"message\": \"#error message\"" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 2" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 6" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+/* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
+/* { dg-regexp "\[\[\{\}, \]*\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c
new file mode 100644
index 0000000..239c75e
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-format=json" } */
+
+#warning message
+
+/* Use dg-regexp to consume the JSON output starting with
+   the innermost values, and working outwards.
+   We can't rely on any ordering of the keys.  */
+
+/* { dg-regexp "\"kind\": \"warning\"" } */
+/* { dg-regexp "\"message\": \"#warning message\"" } */
+/* { dg-regexp "\"option\": \"-Wcpp\"" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 2" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 8" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+/* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
+/* { dg-regexp "\[\[\{\}, \]*\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c
new file mode 100644
index 0000000..1c54eca
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-format=json -Werror" } */
+
+#warning message
+
+/* Use dg-regexp to consume the JSON output starting with
+   the innermost values, and working outwards.
+   We can't rely on any ordering of the keys.  */
+
+/* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"message\": \"#warning message\"" } */
+/* { dg-regexp "\"option\": \"-Werror=cpp\"" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 2" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.c\"" } */
+/* { dg-regexp "\"line\": 4" } */
+/* { dg-regexp "\"column\": 8" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+/* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
+/* { dg-regexp "\[\[\{\}, \]*\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c
new file mode 100644
index 0000000..1c3b034
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c
@@ -0,0 +1,55 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-format=json -Wmisleading-indentation" } */
+
+int test (void)
+{
+  if (1)
+    return 3;
+    return 4;
+  return 5;
+}
+
+/* Use dg-regexp to consume the JSON output starting with
+   the innermost values, and working outwards.
+   We can't rely on any ordering of the keys.  */
+
+/* Verify nested diagnostics.  */
+
+/* The nested diagnostic.  */
+
+/* { dg-regexp "\"kind\": \"note\"" } */
+/* { dg-regexp "\"message\": \"...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'\"" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 5" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 10" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+
+/* The outer diagnostic.  */
+
+/* { dg-regexp "\"kind\": \"warning\"" } */
+/* { dg-regexp "\"message\": \"this 'if' clause does not guard...\"" } */
+/* { dg-regexp "\"option\": \"-Wmisleading-indentation\"" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
+/* { dg-regexp "\"line\": 6" } */
+/* { dg-regexp "\"column\": 3" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
+/* { dg-regexp "\"line\": 6" } */
+/* { dg-regexp "\"column\": 4" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+
+/* { dg-regexp "\"children\": \[\[\{\}, \]*\]" } */
+/* { dg-regexp "\[\[\{\}, \]*\]" } */
+
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c
new file mode 100644
index 0000000..f36e896
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-options "-fdiagnostics-format=json" } */
+
+struct s { int color; };
+
+int test (struct s *ptr)
+{
+  return ptr->colour;
+}
+
+/* Use dg-regexp to consume the JSON output starting with
+   the innermost values, and working outwards.
+   We can't rely on any ordering of the keys.  */
+
+/* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"message\": \".*\"" } */
+
+/* Verify fix-it hints.  */
+
+/* { dg-regexp "\"string\": \"color\"" } */
+
+/* { dg-regexp "\"start\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 15" } */
+
+/* { dg-regexp "\"next\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 21" } */
+
+/* { dg-regexp "\"fixits\": \[\[\{\}, \]*\]" } */
+
+/* { dg-regexp "\"caret\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 15" } */
+
+/* { dg-regexp "\"finish\": \{" } */
+/* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
+/* { dg-regexp "\"line\": 8" } */
+/* { dg-regexp "\"column\": 20" } */
+
+/* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
+/* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
+/* { dg-regexp "\[\[\{\}, \]*\]" } */
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.c b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
index 7cc90de..fce68a1 100644
--- a/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_show_locus.c
@@ -129,7 +129,8 @@ static bool force_show_locus_color = false;
 
 static void
 custom_diagnostic_finalizer (diagnostic_context *context,
-			     diagnostic_info *diagnostic)
+			     diagnostic_info *diagnostic,
+			     diagnostic_t)
 {
   bool old_show_color = pp_show_color (context->printer);
   if (force_show_locus_color)
diff --git a/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.c b/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.c
index 3644d9f..5c9d5ba 100644
--- a/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.c
+++ b/gcc/testsuite/gcc.dg/plugin/location_overflow_plugin.c
@@ -39,7 +39,8 @@ static diagnostic_finalizer_fn original_finalizer = NULL;
 
 static void
 verify_unpacked_ranges  (diagnostic_context *context,
-			 diagnostic_info *diagnostic)
+			 diagnostic_info *diagnostic,
+			 diagnostic_t orig_diag_kind)
 {
   /* Verify that the locations are ad-hoc, not packed. */
   location_t loc = diagnostic_location (diagnostic);
@@ -47,12 +48,13 @@ verify_unpacked_ranges  (diagnostic_context *context,
 
   /* We're done testing; chain up to original finalizer.  */
   gcc_assert (original_finalizer);
-  original_finalizer (context, diagnostic);
+  original_finalizer (context, diagnostic, orig_diag_kind);
 }
 
 static void
 verify_no_columns  (diagnostic_context *context,
-		    diagnostic_info *diagnostic)
+		    diagnostic_info *diagnostic,
+		    diagnostic_t orig_diag_kind)
 {
   /* Verify that the locations have no columns. */
   location_t loc = diagnostic_location (diagnostic);
@@ -60,7 +62,7 @@ verify_no_columns  (diagnostic_context *context,
 
   /* We're done testing; chain up to original finalizer.  */
   gcc_assert (original_finalizer);
-  original_finalizer (context, diagnostic);
+  original_finalizer (context, diagnostic, orig_diag_kind);
 }
 
 int
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90
new file mode 100644
index 0000000..7fade1f
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90
@@ -0,0 +1,25 @@
+! { dg-do compile }
+! { dg-options "-fdiagnostics-format=json" }
+
+#error message
+
+! Use dg-regexp to consume the JSON output starting with
+! the innermost values, and working outwards.
+! We can't rely on any ordering of the keys.
+
+! { dg-regexp "\"kind\": \"error\"" }
+! { dg-regexp "\"message\": \"#error message\"" }
+
+! { dg-regexp "\"caret\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 2" }
+
+! { dg-regexp "\"finish\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 6" }
+
+! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
+! { dg-regexp "\"children\": \[\[\]\[\]\]" }
+! { dg-regexp "\[\[\{\}, \]*\]" }
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90
new file mode 100644
index 0000000..a6d27d9
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90
@@ -0,0 +1,26 @@
+! { dg-do compile }
+! { dg-options "-fdiagnostics-format=json" }
+
+#warning message
+
+! Use dg-regexp to consume the JSON output starting with
+! the innermost values, and working outwards.
+! We can't rely on any ordering of the keys. 
+
+! { dg-regexp "\"kind\": \"warning\"" }
+! { dg-regexp "\"message\": \"#warning message\"" }
+! { dg-regexp "\"option\": \"-Wcpp\"" }
+
+! { dg-regexp "\"caret\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 2" }
+
+! { dg-regexp "\"finish\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 8" }
+
+! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
+! { dg-regexp "\"children\": \[\[\]\[\]\]" }
+! { dg-regexp "\[\[\{\}, \]*\]" }
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90
new file mode 100644
index 0000000..702a937
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90
@@ -0,0 +1,26 @@
+! { dg-do compile }
+! { dg-options "-fdiagnostics-format=json -Werror" }
+
+#warning message
+
+! Use dg-regexp to consume the JSON output starting with
+! the innermost values, and working outwards.
+! We can't rely on any ordering of the keys.
+
+! { dg-regexp "\"kind\": \"error\"" }
+! { dg-regexp "\"message\": \"#warning message\"" }
+! { dg-regexp "\"option\": \"-Werror=cpp\"" }
+
+! { dg-regexp "\"caret\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 2" }
+
+! { dg-regexp "\"finish\": \{" }
+! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.F90\"" }
+! { dg-regexp "\"line\": 4" }
+! { dg-regexp "\"column\": 8" }
+
+! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
+! { dg-regexp "\"children\": \[\[\]\[\]\]" }
+! { dg-regexp "\[\[\{\}, \]*\]" }
