[PATCH] Don't truncate the history file when history size is unlimited

[Patrick Palka <patrick@parcs.ath.cx>]

We still do not handle "set history size unlimited" correctly.  In
particular, after writing to the history file, we truncate the history
even if it is unlimited.

This patch makes sure that we do not call history_truncate_file() if the
history is not stifled (i.e. if it's unlimited).  This bug causes the
history file to be truncated to zero on exit when one has "set history
size unlimited" in their gdbinit file.  Although this code exists in GDB
7.8 it is masked by a pre-existing bug that's been only fixed in GDB 7.9
(PR gdb/17820).

I tried to make a test to check that the history does not get truncated
on exit when the history size is unlimited, but I could not get the test
to work properly.  Also I could not figure out a good way to create a
temporary file (to act as the history file) in tcl versions earlier than
8.6.  I am not sure if it's worth the effort to add a test.

(Apparently I did not test my changes to history file handling
extensively enough.  Sorry..)

gdb/ChangeLog:

	* top.c (gdb_safe_append_history): Do not call
	history_truncate_file if the history is not stifled.
---
 gdb/top.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gdb/top.c b/gdb/top.c
index 837bf16..f5a0819 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -981,7 +981,8 @@ gdb_safe_append_history (void)
       else
 	{
 	  append_history (command_count, local_history_filename);
-	  history_truncate_file (local_history_filename, history_max_entries);
+	  if (history_is_stifled ())
+	    history_truncate_file (local_history_filename, history_max_entries);
 	}
 
       ret = rename (local_history_filename, history_filename);
-- 
2.4.3.368.g7974889.dirty