Don't truncate the history file when history size is unlimited

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, the bug is masked by a pre-existing bug that's been only fixed in
GDB 7.9 (PR gdb/17820).

gdb/ChangeLog:

	* top.c (gdb_safe_append_history): Do not call
	history_truncate_file if the history is not stifled.

gdb/testsuite/ChangeLog:

	* gdb.base/gdbinit-history.exp: Add test case to check that
	an unlimited history file does not get truncated on exit.

4 files changed, 70 insertions, 1 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 00ecb60..e84bd28 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2015-06-17  Patrick Palka  <patrick@parcs.ath.cx>
+
+	* top.c (gdb_safe_append_history): Do not call
+	history_truncate_file if the history is not stifled.
+
 2015-06-17  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
 	* syscalls/s390-linux.xml: Add syscalls 344 through 354.
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 0e96862..e526cb3 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2015-06-17  Patrick Palka  <patrick@parcs.ath.cx>
+
+	* gdb.base/gdbinit-history.exp: Add test case to check that
+	an unlimited history file does not get truncated on exit.
+
 2015-06-17  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
 	* gdb.base/gnu_vector.c: Include stdarg.h and stdio.h.
diff --git a/gdb/testsuite/gdb.base/gdbinit-history.exp b/gdb/testsuite/gdb.base/gdbinit-history.exp
index 8adfd68..8c4f4ca 100644
--- a/gdb/testsuite/gdb.base/gdbinit-history.exp
+++ b/gdb/testsuite/gdb.base/gdbinit-history.exp
@@ -57,5 +57,63 @@ proc test_gdbinit_history_setting { home size } {
     array set env [array get old_env]
 }
 
+# Check that the history file does not get truncated to zero when a gdbinit
+# file sets the history size to unlimited.
+
+proc test_no_truncation_of_unlimited_history_file { } {
+    global env
+    global INTERNAL_GDBFLAGS
+
+    array set old_env [array get env]
+
+    # The HISTSIZE environment variable takes precedence over whatever
+    # history size is set in .gdbinit.  Make sure the former is not
+    # set.
+    unset -nocomplain env(HISTSIZE)
+
+    set saved_internal_gdbflags $INTERNAL_GDBFLAGS
+
+    set temp_gdbinit [standard_output_file "gdbinit-history.gdbinit"]
+    set temp_histfile [standard_output_file "gdbinit-history.gdb_history"]
+    file delete $temp_gdbinit
+    file delete $temp_histfile
+
+    set fd [open $temp_gdbinit "w"]
+    puts $fd "set history size unlimited\n"
+    puts $fd "set history filename $temp_histfile\n"
+    puts $fd "set history save\n"
+    close $fd
+
+    append INTERNAL_GDBFLAGS " -x $temp_gdbinit"
+
+    # We have to start then exit GDB twice: the first time to test the creation
+    # of the initial history file, and the second time to test appending to it.
+    # In either case the initial "print 1" command should persist through the
+    # history file.
+    with_test_prefix "truncation" {
+	gdb_exit
+	gdb_start
+	gdb_test "print 1"
+
+	with_test_prefix "creating" {
+		gdb_exit
+		gdb_start
+		gdb_test "server show commands" "    .  print 1.*"
+	}
+
+	with_test_prefix "appending" {
+		gdb_exit
+		gdb_start
+		gdb_test "server show commands" "    .  print 1.*"
+	}
+    }
+
+    set INTERNAL_GDBFLAGS $saved_internal_gdbflags
+
+    array set env [array get old_env]
+}
+
 test_gdbinit_history_setting "gdbinit-history/unlimited" "unlimited"
 test_gdbinit_history_setting "gdbinit-history/zero" "0"
+
+test_no_truncation_of_unlimited_history_file
diff --git a/gdb/top.c b/gdb/top.c
index 74e1e07..f8f926b 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -941,7 +941,8 @@ 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);