[PATCH] Append to input history file instead of overwriting it

[Patrick Palka]

This patch makes readline append new history lines to the GDB history
file on exit instead of overwriting the entire history file on exit.
This change allows us to run multiple simultaneous GDB sessions without
having each session overwrite the added history of each other session on
exit.  It is particularly helpful when debugging GDB with GDB.

Does this look OK to commit?  Tested on x86_64-unknown-linux-gnu.

gdb/ChangeLog:

	* top.h (gdb_add_history): Declare.
	* top.c (command_count): New variable.
	(gdb_add_history): New function.
	(quit_force): Append to history file instead of overwriting it.
	(command_line_input): Use gdb_add_history instead of
	add_history.
	* event-top.c (command_line_handler): Likewise.
---
 gdb/event-top.c |  2 +-
 gdb/top.c       | 19 ++++++++++++++++---
 gdb/top.h       |  2 ++
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/gdb/event-top.c b/gdb/event-top.c
index cb438ac..490bca6 100644
--- a/gdb/event-top.c
+++ b/gdb/event-top.c
@@ -667,7 +667,7 @@ command_line_handler (char *rl)
 
   /* Add line to history if appropriate.  */
   if (*linebuffer && input_from_terminal_p ())
-    add_history (linebuffer);
+    gdb_add_history (linebuffer);
 
   /* Note: lines consisting solely of comments are added to the command
      history.  This is useful when you type a command, and then
diff --git a/gdb/top.c b/gdb/top.c
index c4b5c2c..6ec3acc 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -895,7 +895,20 @@ gdb_rl_operate_and_get_next (int count, int key)
 
   return rl_newline (1, key);
 }
-
+
+/* Number of user commands executed during this session.  */
+
+static int command_count;
+
+/* Add the user command COMMAND to the input history list.  */
+
+void
+gdb_add_history (const char *command)
+{
+  add_history (command);
+  command_count++;
+}
+
 /* Read one line from the command input stream `instream'
    into the local static buffer `linebuffer' (whose current length
    is `linelength').
@@ -1090,7 +1103,7 @@ command_line_input (char *prompt_arg, int repeat, char *annotation_suffix)
 
   /* Add line to history if appropriate.  */
   if (*linebuffer && input_from_terminal_p ())
-    add_history (linebuffer);
+    gdb_add_history (linebuffer);
 
   /* Save into global buffer if appropriate.  */
   if (repeat)
@@ -1441,7 +1454,7 @@ quit_force (char *args, int from_tty)
     {
       if (write_history_p && history_filename
 	  && input_from_terminal_p ())
-	write_history (history_filename);
+	append_history (command_count, history_filename);
     }
   DO_PRINT_EX;
 
diff --git a/gdb/top.h b/gdb/top.h
index 94f6c48..d8baea8 100644
--- a/gdb/top.h
+++ b/gdb/top.h
@@ -79,6 +79,8 @@ extern int history_expansion_p;
 extern int server_command;
 extern char *lim_at_start;
 
+extern void gdb_add_history (const char *);
+
 extern void show_commands (char *args, int from_tty);
 
 extern void set_history (char *, int);
-- 
2.2.0.rc1.23.gf570943