Tweak the handling of $GDBHISTSIZE edge cases [PR gdb/16999]

When GDB reads a nonsensical value for the GDBHISTSIZE environment
variable, i.e. one that is non-numeric or negative, GDB then sets its
history size to 0.  This behavior is annoying and also inconsistent
with the behavior of bash.

This patch makes the behavior of invalid GDBHISTSIZE consistent with how
bash handles HISTSIZE.  When we encounter a null or out-of-range
GDBHISTSIZE (outside of [0, INT_MAX]) we now set the history size to
unlimited instead of 0.  When we encounter a non-numeric GDBHISTSIZE we
do nothing.

gdb/ChangeLog:

	PR gdb/16999
	* NEWS: Mention new GDBHISTSIZE behavior.
	* top.c (init_history): For null or out-of-range GDBHISTSIZE,
	set history size to unlimited.  Ignore non-numeric GDBHISTSIZE.

gdb/doc/ChangeLog:

	PR gdb/16999
	* gdb.texinfo (Command History): Mention new GDBHISTSIZE
	behavior.

gdb/testsuite/ChangeLog:

	PR gdb/16999
	* gdb.base/gdbhistsize-history.exp: New test.

2 files changed, 75 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index abb067764c6..0f3749e8350 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2015-06-17  Patrick Palka  <patrick@parcs.ath.cx>
 
+	PR gdb/16999
+	* gdb.base/gdbhistsize-history.exp: New test.
+
+2015-06-17  Patrick Palka  <patrick@parcs.ath.cx>
+
 	* gdb.base/gdbinit-history.exp: Replace occurrences of HISTSIZE
 	with GDBHISTSIZE.
 	* gdb.base/readline.exp: Likewise.
diff --git a/gdb/testsuite/gdb.base/gdbhistsize-history.exp b/gdb/testsuite/gdb.base/gdbhistsize-history.exp
new file mode 100644
index 00000000000..0c3f93ff213
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gdbhistsize-history.exp
@@ -0,0 +1,70 @@
+# Copyright 2015 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite.
+
+# Test the setting of "history size" via the GDBHISTSIZE environment variable
+
+
+# Check that the history size is properly set to SIZE when the environment
+# variable ENV_VAR is set to GDBHISTSIZE.
+
+proc test_histsize_history_setting { histsize size { env_var "GDBHISTSIZE" } } {
+    global env
+
+    set have_old_gdbhistsize 0
+    if [info exists env($env_var)] {
+        set have_old_gdbhistsize 1
+        set old_gdbhistsize $env($env_var)
+    }
+    set env($env_var) $histsize
+
+    with_test_prefix "histsize=$histsize" {
+	gdb_exit
+	gdb_start
+
+	gdb_test "show history size" "The size of the command history is $size."
+
+	if { $size == "0" } {
+	    gdb_test_no_output "show commands"
+	} elseif { $size != "1" } {
+	    gdb_test "show commands" \
+		     "    .  show history size\r\n    .  show commands"
+	}
+
+	if { $have_old_gdbhistsize } {
+	    set env($env_var) $old_gdbhistsize
+	} else {
+	    unset env($env_var)
+	}
+    }
+}
+
+test_histsize_history_setting "" "unlimited"
+test_histsize_history_setting "0" "0"
+test_histsize_history_setting "20" "20"
+test_histsize_history_setting " 20 " "20"
+test_histsize_history_setting "-5" "unlimited"
+
+# Test defaulting to 256 upon encountering a non-numeric GDBHISTSIZE.
+test_histsize_history_setting "not_an_integer" "256"
+test_histsize_history_setting "10zab" "256"
+test_histsize_history_setting "-5ab" "256"
+
+# A huge number (hopefully larger than INT_MAX)
+test_histsize_history_setting "99999999999999999999999999999999999" "unlimited"
+
+# We no longer read HISTSIZE
+test_histsize_history_setting "50" "256" "HISTSIZE"