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.

1 files changed, 12 insertions, 0 deletions

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
 }