Subject: bug#23917: Please consider making Bug #23917 a blocker for 25.1 (was Re: org-capture: Capture template ‘g’: Match data clobbered by buffer modification hooks)

From: [email-masked]
Date: Thu, 21 Jul 2016 21:08:43 -0400

Eli Zaretskii <[email-masked]> writes:

>> From: [email-masked]
>> Cc: [email-masked],  [email-masked],  [email-masked],  [email-masked],  [email-masked],  [email-masked]
>> Date: Wed, 20 Jul 2016 23:00:59 -0400
>> 
>> > Please also make sure bug#23869 is still fixed after this.
>> 
>> Following the recipe in
>> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=23869#11 gives me 'Lisp
>> error: (error "Match data clobbered by buffer modification hooks")',
>> that indicates it's still fixed, right?
>
> Yes, but I thought we want to remove the error-out code.  Since we now
> protect ourselves from clobbered data, we don't need that extra
> protection, and I think leaving it in place will cause false positives
> (as a few people already reported).  That's because the adjustment of
> the search registers in the new function you introduce will itself
> trigger the error message, won't it?

I made the same adjustments to the saved sub_start and sub_end
variables, but I had a mistake in that adjustment which caused the false
positives.  Fixed in the attached v2 patch.  We could just drop the
check, though I've already found it useful to catch bugs
(https://github.com/joaotavora/yasnippet/issues/720).

If I drop the checks (see attached v3 patch), then after following the
bug#23869 recipe, I get:

    ## -*- Octave -*-
    -module(bug).
    -export([identity/1, is_even/1, size/1, reverse/1]).

>From 3e8f9b9f89108bcebf04e06e41a5ce2c719c6ad2 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <[email-masked]>
Date: Wed, 20 Jul 2016 20:15:14 -0400
Subject: [PATCH v2] Adjust match data before calling after-change-funs

* src/insdel.c (replace_range): Add new parameter ADJUST_MATCH_DATA, if
true call update_search_regs.  Update all callers (except
Freplace_match) to pass 0 for the new parameter.
* src/search.c (update_search_regs): New function, extracted from
Freplace_match.
(Freplace_match): Remove match data adjustment code, pass 1 for
ADJUST_MATCH_DATA to replace_range instead.
---
 src/cmds.c    |  2 +-
 src/editfns.c |  6 +++---
 src/insdel.c  | 10 ++++++++--
 src/lisp.h    |  4 +++-
 src/search.c  | 52 ++++++++++++++++++++++++++++++----------------------
 5 files changed, 45 insertions(+), 29 deletions(-)

diff --git a/src/cmds.c b/src/cmds.c
index 1e44ddd..4003d8b 100644
--- a/src/cmds.c
+++ b/src/cmds.c
@@ -447,7 +447,7 @@ internal_self_insert (int c, EMACS_INT n)
 	  string = concat2 (string, tem);
 	}
 
-      replace_range (PT, PT + chars_to_delete, string, 1, 1, 1);
+      replace_range (PT, PT + chars_to_delete, string, 1, 1, 1, 0);
       Fforward_char (make_number (n));
     }
   else if (n > 1)
diff --git a/src/editfns.c b/src/editfns.c
index 412745d..32c8bec 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3192,7 +3192,7 @@ DEFUN ("subst-char-in-region", Fsubst_char_in_region,
 	      /* replace_range is less efficient, because it moves the gap,
 		 but it handles combining correctly.  */
 	      replace_range (pos, pos + 1, string,
-			     0, 0, 1);
+			     0, 0, 1, 0);
 	      pos_byte_next = CHAR_TO_BYTE (pos);
 	      if (pos_byte_next > pos_byte)
 		/* Before combining happened.  We should not increment
@@ -3405,7 +3405,7 @@ DEFUN ("translate-region-internal", Ftranslate_region_internal,
 		  /* This is less efficient, because it moves the gap,
 		     but it should handle multibyte characters correctly.  */
 		  string = make_multibyte_string ((char *) str, 1, str_len);
-		  replace_range (pos, pos + 1, string, 1, 0, 1);
+		  replace_range (pos, pos + 1, string, 1, 0, 1, 0);
 		  len = str_len;
 		}
 	      else
@@ -3446,7 +3446,7 @@ DEFUN ("translate-region-internal", Ftranslate_region_internal,
 		{
 		  string = Fmake_string (make_number (1), val);
 		}
-	      replace_range (pos, pos + len, string, 1, 0, 1);
+	      replace_range (pos, pos + len, string, 1, 0, 1, 0);
 	      pos_byte += SBYTES (string);
 	      pos += SCHARS (string);
 	      cnt += SCHARS (string);
diff --git a/src/insdel.c b/src/insdel.c
index 4ad1074..fc3f19f 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -1268,7 +1268,9 @@ adjust_after_insert (ptrdiff_t from, ptrdiff_t from_byte,
 /* Replace the text from character positions FROM to TO with NEW,
    If PREPARE, call prepare_to_modify_buffer.
    If INHERIT, the newly inserted text should inherit text properties
-   from the surrounding non-deleted text.  */
+   from the surrounding non-deleted text.
+   If ADJUST_MATCH_DATA, then adjust the match data before calling
+   signal_after_change.  */
 
 /* Note that this does not yet handle markers quite right.
    Also it needs to record a single undo-entry that does a replacement
@@ -1279,7 +1281,8 @@ adjust_after_insert (ptrdiff_t from, ptrdiff_t from_byte,
 
 void
 replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
-	       bool prepare, bool inherit, bool markers)
+               bool prepare, bool inherit, bool markers,
+               bool adjust_match_data)
 {
   ptrdiff_t inschars = SCHARS (new);
   ptrdiff_t insbytes = SBYTES (new);
@@ -1426,6 +1429,9 @@ replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
   MODIFF++;
   CHARS_MODIFF = MODIFF;
 
+  if (adjust_match_data)
+    update_search_regs (from, to, from + SCHARS (new));
+
   signal_after_change (from, nchars_del, GPT - from);
   update_compositions (from, GPT, CHECK_BORDER);
 }
diff --git a/src/lisp.h b/src/lisp.h
index 6a98adb..25f811e 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3516,7 +3516,7 @@ extern void adjust_after_insert (ptrdiff_t, ptrdiff_t, ptrdiff_t,
 				 ptrdiff_t, ptrdiff_t);
 extern void adjust_markers_for_delete (ptrdiff_t, ptrdiff_t,
 				       ptrdiff_t, ptrdiff_t);
-extern void replace_range (ptrdiff_t, ptrdiff_t, Lisp_Object, bool, bool, bool);
+extern void replace_range (ptrdiff_t, ptrdiff_t, Lisp_Object, bool, bool, bool, bool);
 extern void replace_range_2 (ptrdiff_t, ptrdiff_t, ptrdiff_t, ptrdiff_t,
 			     const char *, ptrdiff_t, ptrdiff_t, bool);
 extern void syms_of_insdel (void);
@@ -3994,6 +3994,8 @@ extern Lisp_Object make_temp_name (Lisp_Object, bool);
 /* Defined in search.c.  */
 extern void shrink_regexp_cache (void);
 extern void restore_search_regs (void);
+extern void update_search_regs (ptrdiff_t oldstart,
+                                ptrdiff_t oldend, ptrdiff_t newend);
 extern void record_unwind_save_match_data (void);
 struct re_registers;
 extern struct re_pattern_buffer *compile_pattern (Lisp_Object,
diff --git a/src/search.c b/src/search.c
index 5c949ad..4bd6a46 100644
--- a/src/search.c
+++ b/src/search.c
@@ -2724,11 +2724,18 @@ DEFUN ("replace-match", Freplace_match, Sreplace_match, 1, 5, 0,
   ptrdiff_t sub_start = search_regs.start[sub];
   ptrdiff_t sub_end = search_regs.end[sub];
   unsigned  num_regs = search_regs.num_regs;
+  newpoint = search_regs.start[sub] + SCHARS (newtext);
 
   /* Replace the old text with the new in the cleanest possible way.  */
   replace_range (search_regs.start[sub], search_regs.end[sub],
-		 newtext, 1, 0, 1);
-  newpoint = search_regs.start[sub] + SCHARS (newtext);
+                 newtext, 1, 0, 1, 1);
+  /* Update saved data to match adjustment made by replace_range.  */
+  {
+    ptrdiff_t change = newpoint - sub_end;
+    if (sub_start >= sub_end)
+      sub_start += change;
+    sub_end += change;
+  }
 
   if (case_action == all_caps)
     Fupcase_region (make_number (search_regs.start[sub]),
@@ -2742,26 +2749,6 @@ DEFUN ("replace-match", Freplace_match, Sreplace_match, 1, 5, 0,
       || search_regs.num_regs != num_regs)
     error ("Match data clobbered by buffer modification hooks");
 
-  /* Adjust search data for this change.  */
-  {
-    ptrdiff_t oldend = search_regs.end[sub];
-    ptrdiff_t oldstart = search_regs.start[sub];
-    ptrdiff_t change = newpoint - search_regs.end[sub];
-    ptrdiff_t i;
-
-    for (i = 0; i < search_regs.num_regs; i++)
-      {
-	if (search_regs.start[i] >= oldend)
-	  search_regs.start[i] += change;
-	else if (search_regs.start[i] > oldstart)
-	  search_regs.start[i] = oldstart;
-	if (search_regs.end[i] >= oldend)
-	  search_regs.end[i] += change;
-	else if (search_regs.end[i] > oldstart)
-	  search_regs.end[i] = oldstart;
-      }
-  }
-
   /* Put point back where it was in the text.  */
   if (opoint <= 0)
     TEMP_SET_PT (opoint + ZV);
@@ -3102,6 +3089,27 @@ restore_search_regs (void)
     }
 }
 
+/* Called from replace-match via replace_range.  */
+void
+update_search_regs (ptrdiff_t oldstart, ptrdiff_t oldend, ptrdiff_t newend)
+{
+  /* Adjust search data for this change.  */
+  ptrdiff_t change = newend - oldend;
+  ptrdiff_t i;
+
+  for (i = 0; i < search_regs.num_regs; i++)
+    {
+      if (search_regs.start[i] >= oldend)
+        search_regs.start[i] += change;
+      else if (search_regs.start[i] > oldstart)
+        search_regs.start[i] = oldstart;
+      if (search_regs.end[i] >= oldend)
+        search_regs.end[i] += change;
+      else if (search_regs.end[i] > oldstart)
+        search_regs.end[i] = oldstart;
+    }
+}
+
 static void
 unwind_set_match_data (Lisp_Object list)
 {
-- 
2.8.0

>From bb533ffd333a28d2ea8bdb6c81b79eb4eda89fcc Mon Sep 17 00:00:00 2001
From: Noam Postavsky <[email-masked]>
Date: Wed, 20 Jul 2016 20:15:14 -0400
Subject: [PATCH v3] Adjust match data before calling after-change-funs

* src/insdel.c (replace_range): Add new parameter ADJUST_MATCH_DATA, if
true call update_search_regs.  Update all callers (except
Freplace_match) to pass 0 for the new parameter.
* src/search.c (update_search_regs): New function, extracted from
Freplace_match.
(Freplace_match): Remove match data adjustment code, pass 1 for
ADJUST_MATCH_DATA to replace_range instead.  Remove checks for match
data modification.
---
 src/cmds.c    |  2 +-
 src/editfns.c |  6 +++---
 src/insdel.c  | 10 ++++++++--
 src/lisp.h    |  4 +++-
 src/search.c  | 57 +++++++++++++++++++++++----------------------------------
 5 files changed, 38 insertions(+), 41 deletions(-)

diff --git a/src/cmds.c b/src/cmds.c
index 1e44ddd..4003d8b 100644
--- a/src/cmds.c
+++ b/src/cmds.c
@@ -447,7 +447,7 @@ internal_self_insert (int c, EMACS_INT n)
 	  string = concat2 (string, tem);
 	}
 
-      replace_range (PT, PT + chars_to_delete, string, 1, 1, 1);
+      replace_range (PT, PT + chars_to_delete, string, 1, 1, 1, 0);
       Fforward_char (make_number (n));
     }
   else if (n > 1)
diff --git a/src/editfns.c b/src/editfns.c
index 412745d..32c8bec 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -3192,7 +3192,7 @@ DEFUN ("subst-char-in-region", Fsubst_char_in_region,
 	      /* replace_range is less efficient, because it moves the gap,
 		 but it handles combining correctly.  */
 	      replace_range (pos, pos + 1, string,
-			     0, 0, 1);
+			     0, 0, 1, 0);
 	      pos_byte_next = CHAR_TO_BYTE (pos);
 	      if (pos_byte_next > pos_byte)
 		/* Before combining happened.  We should not increment
@@ -3405,7 +3405,7 @@ DEFUN ("translate-region-internal", Ftranslate_region_internal,
 		  /* This is less efficient, because it moves the gap,
 		     but it should handle multibyte characters correctly.  */
 		  string = make_multibyte_string ((char *) str, 1, str_len);
-		  replace_range (pos, pos + 1, string, 1, 0, 1);
+		  replace_range (pos, pos + 1, string, 1, 0, 1, 0);
 		  len = str_len;
 		}
 	      else
@@ -3446,7 +3446,7 @@ DEFUN ("translate-region-internal", Ftranslate_region_internal,
 		{
 		  string = Fmake_string (make_number (1), val);
 		}
-	      replace_range (pos, pos + len, string, 1, 0, 1);
+	      replace_range (pos, pos + len, string, 1, 0, 1, 0);
 	      pos_byte += SBYTES (string);
 	      pos += SCHARS (string);
 	      cnt += SCHARS (string);
diff --git a/src/insdel.c b/src/insdel.c
index 4ad1074..fc3f19f 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -1268,7 +1268,9 @@ adjust_after_insert (ptrdiff_t from, ptrdiff_t from_byte,
 /* Replace the text from character positions FROM to TO with NEW,
    If PREPARE, call prepare_to_modify_buffer.
    If INHERIT, the newly inserted text should inherit text properties
-   from the surrounding non-deleted text.  */
+   from the surrounding non-deleted text.
+   If ADJUST_MATCH_DATA, then adjust the match data before calling
+   signal_after_change.  */
 
 /* Note that this does not yet handle markers quite right.
    Also it needs to record a single undo-entry that does a replacement
@@ -1279,7 +1281,8 @@ adjust_after_insert (ptrdiff_t from, ptrdiff_t from_byte,
 
 void
 replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
-	       bool prepare, bool inherit, bool markers)
+               bool prepare, bool inherit, bool markers,
+               bool adjust_match_data)
 {
   ptrdiff_t inschars = SCHARS (new);
   ptrdiff_t insbytes = SBYTES (new);
@@ -1426,6 +1429,9 @@ replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
   MODIFF++;
   CHARS_MODIFF = MODIFF;
 
+  if (adjust_match_data)
+    update_search_regs (from, to, from + SCHARS (new));
+
   signal_after_change (from, nchars_del, GPT - from);
   update_compositions (from, GPT, CHECK_BORDER);
 }
diff --git a/src/lisp.h b/src/lisp.h
index 6a98adb..25f811e 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3516,7 +3516,7 @@ extern void adjust_after_insert (ptrdiff_t, ptrdiff_t, ptrdiff_t,
 				 ptrdiff_t, ptrdiff_t);
 extern void adjust_markers_for_delete (ptrdiff_t, ptrdiff_t,
 				       ptrdiff_t, ptrdiff_t);
-extern void replace_range (ptrdiff_t, ptrdiff_t, Lisp_Object, bool, bool, bool);
+extern void replace_range (ptrdiff_t, ptrdiff_t, Lisp_Object, bool, bool, bool, bool);
 extern void replace_range_2 (ptrdiff_t, ptrdiff_t, ptrdiff_t, ptrdiff_t,
 			     const char *, ptrdiff_t, ptrdiff_t, bool);
 extern void syms_of_insdel (void);
@@ -3994,6 +3994,8 @@ extern Lisp_Object make_temp_name (Lisp_Object, bool);
 /* Defined in search.c.  */
 extern void shrink_regexp_cache (void);
 extern void restore_search_regs (void);
+extern void update_search_regs (ptrdiff_t oldstart,
+                                ptrdiff_t oldend, ptrdiff_t newend);
 extern void record_unwind_save_match_data (void);
 struct re_registers;
 extern struct re_pattern_buffer *compile_pattern (Lisp_Object,
diff --git a/src/search.c b/src/search.c
index 5c949ad..7da1d86 100644
--- a/src/search.c
+++ b/src/search.c
@@ -2717,18 +2717,11 @@ DEFUN ("replace-match", Freplace_match, Sreplace_match, 1, 5, 0,
       xfree (substed);
     }
 
-  /* The functions below modify the buffer, so they could trigger
-     various modification hooks (see signal_before_change and
-     signal_after_change), which might clobber the match data we need
-     to adjust after the replacement.  If that happens, we error out.  */
-  ptrdiff_t sub_start = search_regs.start[sub];
-  ptrdiff_t sub_end = search_regs.end[sub];
-  unsigned  num_regs = search_regs.num_regs;
+  newpoint = search_regs.start[sub] + SCHARS (newtext);
 
   /* Replace the old text with the new in the cleanest possible way.  */
   replace_range (search_regs.start[sub], search_regs.end[sub],
-		 newtext, 1, 0, 1);
-  newpoint = search_regs.start[sub] + SCHARS (newtext);
+                 newtext, 1, 0, 1, 1);
 
   if (case_action == all_caps)
     Fupcase_region (make_number (search_regs.start[sub]),
@@ -2737,31 +2730,6 @@ DEFUN ("replace-match", Freplace_match, Sreplace_match, 1, 5, 0,
     Fupcase_initials_region (make_number (search_regs.start[sub]),
 			     make_number (newpoint));
 
-  if (search_regs.start[sub] != sub_start
-      || search_regs.end[sub] != sub_end
-      || search_regs.num_regs != num_regs)
-    error ("Match data clobbered by buffer modification hooks");
-
-  /* Adjust search data for this change.  */
-  {
-    ptrdiff_t oldend = search_regs.end[sub];
-    ptrdiff_t oldstart = search_regs.start[sub];
-    ptrdiff_t change = newpoint - search_regs.end[sub];
-    ptrdiff_t i;
-
-    for (i = 0; i < search_regs.num_regs; i++)
-      {
-	if (search_regs.start[i] >= oldend)
-	  search_regs.start[i] += change;
-	else if (search_regs.start[i] > oldstart)
-	  search_regs.start[i] = oldstart;
-	if (search_regs.end[i] >= oldend)
-	  search_regs.end[i] += change;
-	else if (search_regs.end[i] > oldstart)
-	  search_regs.end[i] = oldstart;
-      }
-  }
-
   /* Put point back where it was in the text.  */
   if (opoint <= 0)
     TEMP_SET_PT (opoint + ZV);
@@ -3102,6 +3070,27 @@ restore_search_regs (void)
     }
 }
 
+/* Called from replace-match via replace_range.  */
+void
+update_search_regs (ptrdiff_t oldstart, ptrdiff_t oldend, ptrdiff_t newend)
+{
+  /* Adjust search data for this change.  */
+  ptrdiff_t change = newend - oldend;
+  ptrdiff_t i;
+
+  for (i = 0; i < search_regs.num_regs; i++)
+    {
+      if (search_regs.start[i] >= oldend)
+        search_regs.start[i] += change;
+      else if (search_regs.start[i] > oldstart)
+        search_regs.start[i] = oldstart;
+      if (search_regs.end[i] >= oldend)
+        search_regs.end[i] += change;
+      else if (search_regs.end[i] > oldstart)
+        search_regs.end[i] = oldstart;
+    }
+}
+
 static void
 unwind_set_match_data (Lisp_Object list)
 {
-- 
2.8.0