[2/2] Tweak the handling of $GDBHISTSIZE edge cases [PR gdb/16999]

diff --git a/gdb/NEWS b/gdb/NEWS
index 1be239f..f3cee13 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -50,7 +50,9 @@ 
 
 * The HISTSIZE environment variable is no longer read when determining
   the size of GDB's command history.  GDB now instead reads the dedicated
-  GDBHISTSIZE environment variable.
+  GDBHISTSIZE environment variable.  Setting GDBHISTSIZE to "-1" or to "" now
+  disables truncation of command history.  Non-numeric values of GDBHISTSIZE
+  are ignored.
 
 * Guile Scripting
 
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index c21a312..b0bd194 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -22603,10 +22603,11 @@  Stop recording command history in a file.
 @item set history size @var{size}
 @itemx set history size unlimited
 Set the number of commands which @value{GDBN} keeps in its history list.
-This defaults to the value of the environment variable
-@code{GDBHISTSIZE}, or to 256 if this variable is not set.  If @var{size}
-is @code{unlimited}, the number of commands @value{GDBN} keeps in the
-history list is unlimited.
+This defaults to the value of the environment variable @code{GDBHISTSIZE}, or
+to 256 if this variable is not set.  Non-numeric values of @code{GDBHISTSIZE}
+are ignored.  If @var{size} is @code{unlimited} or if @code{GDBHISTSIZE} is a
+negative number, the number of commands @value{GDBN} keeps in the history list
+is unlimited.
 @end table
 
 History expansion assigns special meaning to the character @kbd{!}.
diff --git a/gdb/testsuite/gdb.base/gdbhistsize-history.exp b/gdb/testsuite/gdb.base/gdbhistsize-history.exp
new file mode 100644
index 0000000..a7b70d1
--- /dev/null
+++ b/gdb/testsuite/gdb.base/gdbhistsize-history.exp
@@ -0,0 +1,69 @@ 
+# 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"
+
+# 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"
diff --git a/gdb/top.c b/gdb/top.c
index 6f0421d..efcb8d0 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -1683,21 +1683,35 @@  init_history (void)
   tmpenv = getenv ("GDBHISTSIZE");
   if (tmpenv)
     {
-      int var;
-
-      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;
-	}
-
-      history_size_setshow_var = var;
+      long var;
+      char *endptr;
+
+      while (isspace (*tmpenv))
+	tmpenv++;
+
+      var = strtol (tmpenv, &endptr, 10);
+
+      while (isspace (*endptr))
+	endptr++;
+
+      /* If GDBHISTSIZE is non-numeric then ignore it.  If GDBHISTSIZE is the
+	 empty string, a negative number or a huge positive number (larger than
+	 INT_MAX) then set the history size to unlimited.  Otherwise set our
+	 history size to the number we have read.  This behavior is consistent
+	 with how bash handles HISTSIZE.  */
+      if (*endptr != '\0')
+	;
+      else if (*tmpenv == '\0'
+	       || var < 0
+	       || var > INT_MAX)
+	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)
+
+  /* If neither the init file nor GDBHISTSIZE has set a size yet, pick the
+     default.  */
+  if (history_size_setshow_var == -2)
     history_size_setshow_var = 256;
 
   set_readline_history_size (history_size_setshow_var);