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

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

When GDB reads a nonsensical value for the HISTSIZE 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 HISTSIZE mostly match that of bash.
When we encounter an invalid or null HISTSIZE we now set the history
size to unlimited instead of 0.  Whereas bash ignores a non-numeric
HISTSIZE, we set the history to unlimited in that case so that an
accidental typo will not potentially truncate the user's history.

gdb/ChangeLog:

	PR gdb/16999
	* top.c (init_history): For invalid HISTSIZE, set history size
	to unlimited.

gdb/testsuite/ChangeLog:

	PR gdb/16999
	* gdb.base/histsize-history.exp: New test.
---
 gdb/testsuite/gdb.base/histsize-history.exp | 60 +++++++++++++++++++++++++++++
 gdb/top.c                                   | 22 ++++++-----
 2 files changed, 73 insertions(+), 9 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/histsize-history.exp

diff --git a/gdb/testsuite/gdb.base/histsize-history.exp b/gdb/testsuite/gdb.base/histsize-history.exp
new file mode 100644
index 0000000..10fc453
--- /dev/null
+++ b/gdb/testsuite/gdb.base/histsize-history.exp
@@ -0,0 +1,60 @@
+# 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 HISTSIZE environment variable
+
+
+# Check that the history size is properly set to SIZE when env(HISTSIZE) is set
+# to HISTSIZE.
+
+proc test_histsize_history_setting { histsize size } {
+    global env
+
+    set have_old_histsize 0
+    if [info exists env(HISTSIZE)] {
+        set have_old_histsize 1
+        set old_histsize $env(HISTSIZE)
+    }
+    set env(HISTSIZE) $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_histsize } {
+	    set env(HISTSIZE) $old_histsize
+	} else {
+	    unset env(HISTSIZE)
+	}
+    }
+}
+
+test_histsize_history_setting "" "unlimited"
+test_histsize_history_setting "0" "0"
+test_histsize_history_setting "20" "20"
+test_histsize_history_setting "-5" "unlimited"
+test_histsize_history_setting "not_an_integer" "unlimited"
+test_histsize_history_setting "10zab" "unlimited"
diff --git a/gdb/top.c b/gdb/top.c
index 74e1e07..38b4e5d 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1684,17 +1684,21 @@ init_history (void)
   if (tmpenv)
     {
       int var;
+      char *endptr;
 
-      var = atoi (tmpenv);
-      if (var < 0)
-	{
-	  /* Prefer ending up with no history rather than overflowing
-	     readline's history interface, which uses signed 'int'
-	     everywhere.  */
-	  var = 0;
-	}
+      var = strtol (tmpenv, &endptr, 10);
 
-      history_size_setshow_var = var;
+      /* If HISTSIZE is the empty string, negative, or non-numeric then set the
+	 history size to unlimited.  This behavior is mostly consistent with
+	 that of bash.  Whereas bash ignores a non-numeric HISTSIZE, we set the
+	 history to unlimited in that case to avoid potentially truncating the
+	 user's history.  */
+      if (strlen (tmpenv) == 0
+	  || var < 0
+	  || *endptr != '\0')
+	history_size_setshow_var = -1;
+      else
+	history_size_setshow_var = var;
     }
   /* If the init file hasn't set a size yet, pick the default.  */
   else if (history_size_setshow_var == -2)
-- 
2.4.1.217.g6c1249c