gdb: Add an error when 'list -' reaches the start of a file.

When a a user uses 'list +' to list forward through a source file they
eventually reach the end of the source file.  Subsequent uses of 'list
+' result in an error message like this, that let the user know they are
at the end of the source file:

  Line number XXX out of range; FILENAME has YYY lines.

Compare this to the current behaviour of 'list -' which lists backwards
through a source file.  When the user reaches the beginning of the
source file, subsequent uses of 'list -' result in the command silently
returning.  This can be confusing if the previous uses of 'list -' have
scrolled off the users display, the user receives no reminder that the
have already seen the start of the file.

After this commit a use of 'list -' when the user has already seen the
start of a file will receive the following error:

   Already at the start of FILENAME.

gdb/ChangeLog:

	* cli/cli-cmds.c (list_command): Add an error when trying to use
	'-' to scan read off the start of the source file.

gdb/testsuite/ChangeLog:

	* gdb.base/list.exp (test_list_forward): Add end of file error
	test.
	(test_repeat_list_command): Add end of file error test.
	(test_list_backwards): Add beginning of file error test.

4 files changed, 33 insertions, 4 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 970bea2..960a304 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2015-12-11  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* cli/cli-cmds.c (list_command): Add an error when trying to use
+	'-' to scan read off the start of the source file.
+
+2015-12-11  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* cli/cli-cmds.c (list_command): Check that the argument string is
 	a single character, either '+' or '-'.
 
diff --git a/gdb/cli/cli-cmds.c b/gdb/cli/cli-cmds.c
index 4557bfd..a6935bf 100644
--- a/gdb/cli/cli-cmds.c
+++ b/gdb/cli/cli-cmds.c
@@ -940,10 +940,15 @@ list_command (char *arg, int from_tty)
       /* "l -" lists previous ten lines, the ones before the ten just
 	 listed.  */
       else if (arg[0] == '-')
-	print_source_lines (cursal.symtab,
-			    max (get_first_line_listed ()
-				 - get_lines_to_list (), 1),
-			    get_first_line_listed (), 0);
+	{
+	  if (get_first_line_listed () == 1)
+	    error (_("Already at the start of %s."),
+		   symtab_to_filename_for_display (cursal.symtab));
+	  print_source_lines (cursal.symtab,
+			      max (get_first_line_listed ()
+				   - get_lines_to_list (), 1),
+			      get_first_line_listed (), 0);
+	}
 
       return;
     }
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 8c7af55..df8c768 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,12 @@
 2015-12-11  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* gdb.base/list.exp (test_list_forward): Add end of file error
+	test.
+	(test_repeat_list_command): Add end of file error test.
+	(test_list_backwards): Add beginning of file error test.
+
+2015-12-11  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* gdb.base/list.exp (test_list_invalid_args): New function,
 	defined, and called.
 
diff --git a/gdb/testsuite/gdb.base/list.exp b/gdb/testsuite/gdb.base/list.exp
index cac3a62..18b7d4f 100644
--- a/gdb/testsuite/gdb.base/list.exp
+++ b/gdb/testsuite/gdb.base/list.exp
@@ -244,6 +244,10 @@ proc test_list_forward {} {
     }
 
     pass "successive list commands to page forward ($testcnt tests)"
+
+    gdb_test "list" "Line number 44 out of range; \[^\r\n\]+ has 43 lines\." \
+	"end of file error after \"list\" command"
+
     gdb_stop_suppressing_tests
 }
 
@@ -287,6 +291,10 @@ proc test_repeat_list_command {} {
     }
 
     pass "repeat list commands to page forward using 'return' ($testcnt tests)"
+
+    gdb_test "list" "Line number 44 out of range; \[^\r\n\]+ has 43 lines\." \
+	"end of file error after using 'return' to repeat the list command"
+
     gdb_stop_suppressing_tests
 }
 
@@ -324,6 +332,10 @@ proc test_list_backwards {} {
     }
 
     pass "$testcnt successive \"list -\" commands to page backwards"
+
+    gdb_test "list -" "Already at the start of .*\." \
+	"beginning of file error after \"list -\" command"
+
     gdb_stop_suppressing_tests
 }