Re: [PATCH 3/7] Emit macro expansion related diagnostics

[Dodji Seketeli <dodji@redhat.com>]

Hello,

Below is an amended version of this patch after Jason's comments at
http://gcc.gnu.org/ml/gcc-patches/2011-08/msg00099.html.

From: Dodji Seketeli <dodji@redhat.com>
Date: Sat, 4 Dec 2010 16:31:35 +0100
Subject: [PATCH 3/7] Emit macro expansion related diagnostics

In this third instalment the diagnostic machinery -- when faced with
the virtual location of a token resulting from macro expansion -- uses
the new linemap APIs to unwind the stack of macro expansions that led
to that token and emits a [hopefully] more useful message than what we
have today.

diagnostic_report_current_module has been slightly changed to use the
location given by client code instead of the global input_location
variable. This results in more precise diagnostic locations in general
but then the patch adjusts some C++ tests which output changed as a
result of this.

Three new regression tests have been added.

The mandatory screenshot goes like this:

[dodji@adjoa gcc]$ cat -n test.c
     1    #define OPERATE(OPRD1, OPRT, OPRD2) \
     2      OPRD1 OPRT OPRD2;
     3
     4    #define SHIFTL(A,B) \
     5      OPERATE (A,<<,B)
     6
     7    #define MULT(A) \
     8      SHIFTL (A,1)
     9
    10    void
    11    g ()
    12    {
    13      MULT (1.0);/* 1.0 << 1; <-- so this is an error.  */
    14    }

[dodji@adjoa gcc]$ ./cc1 -quiet -ftrack-macro-expansion test.c
test.c: In function ‘g’:
test.c:5:14: erreur: invalid operands to binary << (have ‘double’ and ‘int’)
test.c:2:9: note: in expansion of macro 'OPERATE'
test.c:5:3: note: expanded from here
test.c:5:14: note: in expansion of macro 'SHIFTL'
test.c:8:3: note: expanded from here
test.c:8:3: note: in expansion of macro 'MULT2'
test.c:13:3: note: expanded from here

The combination of this patch and the previous ones boostrapped with
--enable-languages=all,ada and passed regression tests on
x86_64-unknown-linux-gnu.

gcc/
	* gcc/diagnostic.h (diagnostic_report_current_module): Add a
	location parameter.
	* diagnostic.c (diagnostic_report_current_module): Add a location
	parameter to the function definition.  Use it instead of
	input_location.  Resolve the virtual location rather than just
	looking up its map and risking to touch a resulting macro map.
	(default_diagnostic_starter): Pass the relevant diagnostic
	location to diagnostic_report_current_module.
	* tree-diagnostic.c (maybe_unwind_expanded_macro_loc): New.
	(virt_loc_aware_diagnostic_finalizer): Likewise.
	(diagnostic_report_current_function): Pass the
	relevant location to diagnostic_report_current_module.
	* tree-diagnostic.h (virt_loc_aware_diagnostic_finalizer): Declare
	new function.
	* toplev.c (general_init): By default, use the new
	virt_loc_aware_diagnostic_finalizer as diagnostic finalizer.

gcc/cp/

	* error.c (cp_diagnostic_starter): Pass the relevant location to
	diagnostic_report_current_module.
	(cp_diagnostic_finalizer): Call virt_loc_aware_diagnostic_finalizer.

gcc/testsuite/

	* gcc.dg/cpp/macro-exp-tracking-1.c: New test.
	* gcc.dg/cpp/macro-exp-tracking-2.c: Likewise.
	* gcc.dg/cpp/macro-exp-tracking-3.c: Likewise.
	* gcc.dg/cpp/pragma-diagnostic-2.c: Likewise.
	* g++.dg/cpp0x/initlist15.C: Discard errors pointing at multiple
	levels of included files.
	* g++.old-deja/g++.robertl/eb43.C: Likewise.
	* g++.old-deja/g++.robertl/eb79.C: Likewise.
	* gcc.target/i386/sse-vect-types.c: Likewise.
---
 gcc/Makefile.in                                 |    2 +-
 gcc/cp/error.c                                  |    5 +-
 gcc/diagnostic.c                                |   14 ++-
 gcc/diagnostic.h                                |    2 +-
 gcc/testsuite/g++.dg/cpp0x/initlist15.C         |    1 +
 gcc/testsuite/g++.old-deja/g++.robertl/eb43.C   |    4 +
 gcc/testsuite/g++.old-deja/g++.robertl/eb79.C   |    4 +
 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-1.c |   21 +++
 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-2.c |   21 +++
 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-3.c |   14 ++
 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-4.c |   14 ++
 gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-2.c  |   34 +++++
 gcc/testsuite/gcc.target/i386/sse-vect-types.c  |    6 +
 gcc/toplev.c                                    |    3 +
 gcc/tree-diagnostic.c                           |  176 ++++++++++++++++++++++-
 gcc/tree-diagnostic.h                           |    3 +-
 16 files changed, 313 insertions(+), 11 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-1.c
 create mode 100644 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-2.c
 create mode 100644 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-3.c
 create mode 100644 gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-4.c
 create mode 100644 gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-2.c

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 116a70b..2dae39d 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -2793,7 +2793,7 @@ fold-const.o : fold-const.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) \
    $(GGC_H) $(TM_P_H) langhooks.h $(MD5_H) intl.h $(TARGET_H) \
    $(GIMPLE_H) realmpfr.h $(TREE_FLOW_H)
 diagnostic.o : diagnostic.c $(CONFIG_H) $(SYSTEM_H) coretypes.h \
-   version.h $(INPUT_H) intl.h $(DIAGNOSTIC_H) diagnostic.def
+   version.h $(INPUT_H) intl.h $(DIAGNOSTIC_H) diagnostic.def $(VEC_H)
 opts.o : opts.c $(OPTS_H) $(OPTIONS_H) $(DIAGNOSTIC_CORE_H) $(CONFIG_H) $(SYSTEM_H) \
    coretypes.h $(TM_H) \
    $(DIAGNOSTIC_H) insn-attr-common.h intl.h $(COMMON_TARGET_H) \
diff --git a/gcc/cp/error.c b/gcc/cp/error.c
index d435bbe..4915315 100644
--- a/gcc/cp/error.c
+++ b/gcc/cp/error.c
@@ -2763,7 +2763,7 @@ static void
 cp_diagnostic_starter (diagnostic_context *context,
 		       diagnostic_info *diagnostic)
 {
-  diagnostic_report_current_module (context);
+  diagnostic_report_current_module (context, diagnostic->location);
   cp_print_error_function (context, diagnostic);
   maybe_print_instantiation_context (context);
   maybe_print_constexpr_context (context);
@@ -2773,8 +2773,9 @@ cp_diagnostic_starter (diagnostic_context *context,
 
 static void
 cp_diagnostic_finalizer (diagnostic_context *context,
-			 diagnostic_info *diagnostic ATTRIBUTE_UNUSED)
+			 diagnostic_info *diagnostic)
 {
+  virt_loc_aware_diagnostic_finalizer (context, diagnostic);
   pp_base_destroy_prefix (context->printer);
 }
 
diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c
index b46eb35..06e73a5 100644
--- a/gcc/diagnostic.c
+++ b/gcc/diagnostic.c
@@ -30,6 +30,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "input.h"
 #include "intl.h"
 #include "diagnostic.h"
+#include "vec.h"
 
 #define pedantic_warning_kind(DC)			\
   ((DC)->pedantic_errors ? DK_ERROR : DK_WARNING)
@@ -255,9 +256,9 @@ diagnostic_action_after_output (diagnostic_context *context,
 }
 
 void
-diagnostic_report_current_module (diagnostic_context *context)
+diagnostic_report_current_module (diagnostic_context *context, location_t where)
 {
-  const struct line_map *map;
+  const struct line_map *map = NULL;
 
   if (pp_needs_newline (context->printer))
     {
@@ -265,10 +266,13 @@ diagnostic_report_current_module (diagnostic_context *context)
       pp_needs_newline (context->printer) = false;
     }
 
-  if (input_location <= BUILTINS_LOCATION)
+  if (where <= BUILTINS_LOCATION)
     return;
 
-  map = linemap_lookup (line_table, input_location);
+  linemap_resolve_location (line_table, where,
+			    LRK_MACRO_PARM_REPLACEMENT_POINT,
+			    &map);
+
   if (map && diagnostic_last_module_changed (context, map))
     {
       diagnostic_set_last_module (context, map);
@@ -301,7 +305,7 @@ void
 default_diagnostic_starter (diagnostic_context *context,
 			    diagnostic_info *diagnostic)
 {
-  diagnostic_report_current_module (context);
+  diagnostic_report_current_module (context, diagnostic->location);
   pp_set_prefix (context->printer, diagnostic_build_prefix (context,
 							    diagnostic));
 }
diff --git a/gcc/diagnostic.h b/gcc/diagnostic.h
index 8074354..4b1265b 100644
--- a/gcc/diagnostic.h
+++ b/gcc/diagnostic.h
@@ -253,7 +253,7 @@ extern diagnostic_context *global_dc;
 /* Diagnostic related functions.  */
 extern void diagnostic_initialize (diagnostic_context *, int);
 extern void diagnostic_finish (diagnostic_context *);
-extern void diagnostic_report_current_module (diagnostic_context *);
+extern void diagnostic_report_current_module (diagnostic_context *, location_t);
 
 /* Force diagnostics controlled by OPTIDX to be kind KIND.  */
 extern diagnostic_t diagnostic_classify_diagnostic (diagnostic_context *,
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist15.C b/gcc/testsuite/g++.dg/cpp0x/initlist15.C
index b75cc81..cca56b1 100644
--- a/gcc/testsuite/g++.dg/cpp0x/initlist15.C
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist15.C
@@ -2,6 +2,7 @@
 
 // Just discard errors pointing at header files
 // { dg-prune-output "include" }
+// { dg-prune-output "        from" }
 
 #include <vector>
 #include <typeinfo>
diff --git a/gcc/testsuite/g++.old-deja/g++.robertl/eb43.C b/gcc/testsuite/g++.old-deja/g++.robertl/eb43.C
index 1dc4328..bd784b1 100644
--- a/gcc/testsuite/g++.old-deja/g++.robertl/eb43.C
+++ b/gcc/testsuite/g++.old-deja/g++.robertl/eb43.C
@@ -6,6 +6,10 @@
 
 // { dg-prune-output "note" }
 
+// Discard errors pointing at header files
+// { dg-prune-output "In file included from" }
+// { dg-prune-output "        from" }
+
 #include <vector>
 #include <algorithm>
 #include <functional>
diff --git a/gcc/testsuite/g++.old-deja/g++.robertl/eb79.C b/gcc/testsuite/g++.old-deja/g++.robertl/eb79.C
index 1c1ad3e..60cc713 100644
--- a/gcc/testsuite/g++.old-deja/g++.robertl/eb79.C
+++ b/gcc/testsuite/g++.old-deja/g++.robertl/eb79.C
@@ -1,5 +1,9 @@
 // { dg-do assemble  }
 // { dg-prune-output "note" }
+
+// Discard errors pointing at header files
+// { dg-prune-output "In file included from" }
+// { dg-prune-output "        from" }
 // Makes bogus x86 assembly code.
 #include <iostream>
 
diff --git a/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-1.c b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-1.c
new file mode 100644
index 0000000..d975c8c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-1.c
@@ -0,0 +1,21 @@
+/*
+   { dg-options "-ftrack-macro-expansion=1" }
+   { dg-do compile }
+*/
+
+#define OPERATE(OPRD1, OPRT, OPRD2) \
+do \
+{ \
+  OPRD1 OPRT OPRD2; /* { dg-message "expansion" }*/ 	   \
+} while (0)
+
+#define SHIFTL(A,B) \
+  OPERATE (A,<<,B) /* { dg-message "expanded|expansion" } */
+
+void
+foo ()
+{
+  SHIFTL (0.1,0.2); /* { dg-message "expanded" } */
+}
+
+/* { dg-error "invalid operands" "" { target *-*-* } 13 } */
diff --git a/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-2.c b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-2.c
new file mode 100644
index 0000000..684af4c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-2.c
@@ -0,0 +1,21 @@
+/* 
+   { dg-options "-ftrack-macro-expansion=1" }
+   { dg-do compile }
+*/
+
+#define OPERATE(OPRD1, OPRT, OPRD2) \
+ OPRD1 OPRT OPRD2;		/* { dg-message "expansion" } */
+
+#define SHIFTL(A,B) \
+  OPERATE (A,<<,B) /* { dg-message "expanded|expansion" } */
+
+#define MULT(A) \
+  SHIFTL (A,1)			/* { dg-message "expanded|expansion" } */
+
+void
+foo ()
+{
+  MULT (1.0);			/* { dg-message "expanded" } */
+}
+
+/* { dg-error "invalid operands to binary <<" "" { target *-*-* } { 10 } } */
diff --git a/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-3.c b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-3.c
new file mode 100644
index 0000000..119053e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-3.c
@@ -0,0 +1,14 @@
+/*
+  { dg-options "-fshow-column -ftrack-macro-expansion=1" }
+  { dg-do compile }
+ */
+
+#define SQUARE(A) A * A		/* { dg-message "expansion" } */
+
+void
+foo()
+{
+  SQUARE (1 << 0.1);		/* { dg-message "expanded" } */
+}
+
+/* { dg-error "16:invalid operands to binary <<" "" {target *-*-* } { 11 } } */
diff --git a/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-4.c b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-4.c
new file mode 100644
index 0000000..1f9fe6a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/macro-exp-tracking-4.c
@@ -0,0 +1,14 @@
+/*
+  { dg-options "-fshow-column -ftrack-macro-expansion=2" }
+  { dg-do compile }
+ */
+
+#define SQUARE(A) A * A		/* { dg-message "expansion" } */
+
+void
+foo()
+{
+  SQUARE (1 << 0.1);		/* { dg-message "expanded" } */
+}
+
+/* { dg-error "13:invalid operands to binary <<" "" { target *-*-* } { 11 } } */
diff --git a/gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-2.c b/gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-2.c
new file mode 100644
index 0000000..7ab95b0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/cpp/pragma-diagnostic-2.c
@@ -0,0 +1,34 @@
+/*
+  { dg-options "-Wuninitialized -ftrack-macro-expansion=2" }
+  { dg-do compile }
+*/
+
+void f (unsigned);
+
+#define CODE_WITH_WARNING \
+  int a; /* { dg-message "expansion|declared here" } */  \
+  f (a)	 /* { dg-message "expansion" } */
+
+#pragma GCC diagnostic ignored "-Wuninitialized"
+
+void
+g (void)
+{
+  CODE_WITH_WARNING;
+}
+
+#pragma GCC diagnostic push
+
+#pragma GCC diagnostic error "-Wuninitialized"
+
+void
+h (void)
+{
+  CODE_WITH_WARNING;		/* { dg-message "expanded" } */
+}
+
+/*
+  { dg-message "some warnings being treated as errors" "" {target *-*-*} 0 }
+*/
+
+/* { dg-error "uninitialized" "" { target *-*-* } { 10 } } */
diff --git a/gcc/testsuite/gcc.target/i386/sse-vect-types.c b/gcc/testsuite/gcc.target/i386/sse-vect-types.c
index 9cb6f3e..ce70125 100644
--- a/gcc/testsuite/gcc.target/i386/sse-vect-types.c
+++ b/gcc/testsuite/gcc.target/i386/sse-vect-types.c
@@ -1,6 +1,12 @@
 /* { dg-do compile } */
 /* { dg-options "-O0 -msse2" } */
 
+
+/*
+   Just discard diagnostic prolog about errors in include files
+   { dg-prune-output "In file included from" }
+*/
+
 #include <xmmintrin.h>
 
 __m128d foo1(__m128d z, __m128d  a, int N) { 
diff --git a/gcc/toplev.c b/gcc/toplev.c
index de0a58a..5f63b69 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1132,6 +1132,9 @@ general_init (const char *argv0)
      can give warnings and errors.  */
   diagnostic_initialize (global_dc, N_OPTS);
   diagnostic_starter (global_dc) = default_tree_diagnostic_starter;
+  /* By default print macro expansion contexts in the diagnostic
+     finalizer -- for tokens resulting from macro macro expansion.  */
+  diagnostic_finalizer (global_dc) = virt_loc_aware_diagnostic_finalizer;
   /* Set a default printer.  Language specific initializations will
      override it later.  */
   pp_format_decoder (global_dc->printer) = &default_tree_printer;
diff --git a/gcc/tree-diagnostic.c b/gcc/tree-diagnostic.c
index b456a2a..be4a4c2 100644
--- a/gcc/tree-diagnostic.c
+++ b/gcc/tree-diagnostic.c
@@ -35,7 +35,7 @@ void
 diagnostic_report_current_function (diagnostic_context *context,
 				    diagnostic_info *diagnostic)
 {
-  diagnostic_report_current_module (context);
+  diagnostic_report_current_module (context, diagnostic->location);
   lang_hooks.print_error_function (context, input_filename, diagnostic);
 }
 
@@ -47,3 +47,177 @@ default_tree_diagnostic_starter (diagnostic_context *context,
   pp_set_prefix (context->printer, diagnostic_build_prefix (context,
 							    diagnostic));
 }
+
+/* Unwind the different macro expansions that lead to the token which
+   location is WHERE and emit diagnostics showing the resulting
+   unwound macro expansion stack.  If TOPMOST_EXP_POINT_MAP is
+   non-null, *TOPMOST_EXP_POINT_MAP is set to the map of the expansion
+   point of the top most macro of the stack.  This must be an ordinary
+   map.  */
+
+static void
+maybe_unwind_expanded_macro_loc (diagnostic_context *context,
+				 diagnostic_info *diagnostic,
+				 source_location where,
+				 const struct line_map **topmost_exp_point_map)
+{
+  typedef struct
+  {
+    const struct line_map *map;
+    source_location where;
+  } loc_t;
+
+  const struct line_map *map, *resolved_map;
+  bool unwind = true;
+  source_location resolved_location;
+  unsigned loc_vec_capacity = 0, num_locs = 0;
+  loc_t *loc_vec = NULL;
+  unsigned ix;
+  loc_t loc, *iter;
+
+#define APPEND_LOC_TO_VEC(LOC)						\
+  if (num_locs >= loc_vec_capacity)					\
+    {									\
+      loc_vec_capacity += 4;						\
+      loc_vec = XRESIZEVEC (loc_t, loc_vec, loc_vec_capacity);		\
+    }									\
+  loc_vec[num_locs++] = LOC;
+
+  map = linemap_lookup (line_table, where);
+  if (!linemap_macro_expansion_map_p (map))
+    return;
+
+  /* Let's unwind the stack of macros that got expanded and that led
+     to the token which location is WHERE.  We are going to store the
+     stack into MAP_VEC, so that we can later walk MAP_VEC backward to
+     display a somewhat meaningful trace of the macro expansion
+     history to the user.  Note that the deepest macro expansion is
+     going to be stored at the beginning of MAP_VEC.  */
+  while (unwind)
+    {
+      loc.where = where;
+      loc.map = map;
+
+      APPEND_LOC_TO_VEC (loc);
+
+      /* WHERE is the location of a token inside the expansion of a
+	 macro. MAP is the map holding the locations of that macro
+	 expansion. Let's get the location of the token inside the
+	 *definition* of the macro of MAP, that got expanded at
+	 WHERE. This is basically how we go "up" in the stack of
+	 macro expansions that led to WHERE.  */
+      resolved_location =
+	linemap_macro_map_loc_to_def_point (map, where, false);
+      resolved_map = linemap_lookup (line_table, resolved_location);
+
+      /* If the token at RESOLVED_LOCATION [at macro definition point]
+	 is itself inside an expanded macro then we keep unwinding the
+	 expansion stack by tracing the "parent macro" that got expanded
+	 inside the definition of the macro of MAP...  */
+      if (linemap_macro_expansion_map_p (resolved_map))
+	{
+	  where = resolved_location;
+	  map = resolved_map;
+	}
+      else
+	{
+	  /* Otherwise, let's consider the location of the expansion
+	     point of the macro of MAP. Keep in mind that MAP is a
+	     macro expansion map. To get a "normal map" (i.e a non
+	     macro expansion map) and be done with the unwinding, we
+	     must either consider the location of the location
+	     expansion point of the macro or the location of the token
+	     inside the macro definition that got expanded to
+	     WHERE.  */
+	  where =
+	    linemap_macro_map_loc_to_exp_point (map, where);
+	  map = linemap_lookup (line_table, where);
+	}
+      if (!linemap_macro_expansion_map_p (map))
+	unwind = false;
+    }
+
+  if (topmost_exp_point_map)
+    *topmost_exp_point_map = map;
+
+  /* Walk the map_vec and print the macro expansion stack, unless the
+     topmost macro which expansion triggered this stack [assuming the
+     stack grows downwards] was expanded inside a system header.  */
+  if (!LINEMAP_SYSP (resolved_map))
+    for (ix = 0; num_locs && ix < num_locs; ++ix)
+      {
+	source_location resolved_def_loc = 0, resolved_exp_loc = 0;
+	diagnostic_t saved_kind;
+	const char *saved_prefix;
+	source_location saved_location;
+
+	iter = &loc_vec[ix];
+
+	/* Okay, now here is what we want.  For each token resulting
+	   from macro expansion we want to show: 1/ where in the
+	   definition of the macro the token comes from.  2/ where the
+	   macro got expanded.  */
+
+	/* Resolve the location iter->where into the locus 1/ of the
+	   comment above.  */
+	resolved_def_loc =
+	  linemap_resolve_location (line_table, iter->where,
+				    LRK_MACRO_PARM_REPLACEMENT_POINT, NULL);
+
+	/* Resolve the location of the expansion point of the macro
+	   which expansion gave the token at represented by def_loc.
+	   This is the locus 2/ of the earlier comment.  */
+	resolved_exp_loc =
+	  linemap_resolve_location (line_table, MACRO_MAP_EXPANSION_POINT_LOCATION (iter->map),
+				    LRK_MACRO_PARM_REPLACEMENT_POINT, NULL);
+
+	saved_kind = diagnostic->kind;
+	saved_prefix = context->printer->prefix;
+	saved_location = diagnostic->location;
+
+	diagnostic->kind = DK_NOTE;
+	diagnostic->location = resolved_def_loc;
+	pp_base_set_prefix (context->printer,
+			    diagnostic_build_prefix (context,
+						     diagnostic));
+	pp_newline (context->printer);
+	pp_printf (context->printer, "in expansion of macro '%s'",
+		   linemap_map_get_macro_name (iter->map));
+	pp_destroy_prefix (context->printer);
+	diagnostic->location = resolved_exp_loc;
+	pp_base_set_prefix (context->printer,
+			    diagnostic_build_prefix (context,
+						     diagnostic));
+	pp_newline (context->printer);
+	pp_printf (context->printer, "expanded from here");
+	pp_destroy_prefix (context->printer);
+
+	diagnostic->kind = saved_kind;
+	diagnostic->location = saved_location;
+	context->printer->prefix = saved_prefix;
+      }
+
+  free (loc_vec);
+}
+
+/*  This is a diagnostic finalizer implementation that is aware of
+    virtual locations produced by libcpp.
+
+    It has to be called by the diagnostic finalizer of front ends that
+    uses libcpp and wish to get diagnostics involving tokens resulting
+    from macro expansion.
+
+    For a given location, if said location belongs to a token
+    resulting from a macro expansion, this starter prints the context
+    of the token.  E.g, for a multiply nested macro expansions, it
+    unwinds the nested macro expansions and prints them in a manner
+    that is similar to what is done for function call stacks, or
+    template instantiation contexts.  */
+void
+virt_loc_aware_diagnostic_finalizer (diagnostic_context *context,
+				     diagnostic_info *diagnostic)
+{
+  maybe_unwind_expanded_macro_loc (context, diagnostic,
+				   diagnostic->location,
+				   NULL);
+}
diff --git a/gcc/tree-diagnostic.h b/gcc/tree-diagnostic.h
index 7d88089..6b8e8e6 100644
--- a/gcc/tree-diagnostic.h
+++ b/gcc/tree-diagnostic.h
@@ -52,5 +52,6 @@ along with GCC; see the file COPYING3.  If not see
 void default_tree_diagnostic_starter (diagnostic_context *, diagnostic_info *);
 extern void diagnostic_report_current_function (diagnostic_context *,
 						diagnostic_info *);
-
+void virt_loc_aware_diagnostic_finalizer (diagnostic_context *,
+					  diagnostic_info *);
 #endif /* ! GCC_TREE_DIAGNOSTIC_H */
-- 
		Dodji