[gdb/testsuite] Fix linefeed scrolling in tuiterm

I came across a bug in the implementation of line feed in tuiterm, and added a
unit test that exposes it.

Before sending the line feed we have:
...
Screen Dump (size 8 columns x 4 rows, cursor at column 0, row 3):
    0 abcdefgh
    1 ijklmnop
    2 qrstuvwx
    3 yz01234
...
and after it we have:
...
Screen Dump (size 8 columns x 4 rows, cursor at column 0, row 1):
    0 ijklmnop
    1 qrstuvwx
    2 yz01234
    3 yz01234
...

Note how the cursor started at row 3 and after the line feed ended up at
row 1, while it should have stayed in row 3.

Fix this by moving "incr _cur_row -1" one level up in the loop nest in
proc _ctl_0x0a.

Tested on x86_64-linux.

2 files changed, 15 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.tui/tuiterm.exp b/gdb/testsuite/gdb.tui/tuiterm.exp
index c175141..74800d9 100644
--- a/gdb/testsuite/gdb.tui/tuiterm.exp
+++ b/gdb/testsuite/gdb.tui/tuiterm.exp
@@ -131,6 +131,18 @@ proc test_linefeed { } {
     } 1 3
 }
 
+proc test_linefeed_scroll { } {
+    Term::_move_cursor 0 3
+    Term::_ctl_0x0a
+    check "linefeed_scroll" {
+	"ijklmnop"
+	"qrstuvwx"
+	"yz01234 "
+	"yz01234 "
+    } 0 3
+    Term::dump_screen
+}
+
 proc test_carriage_return { } {
     Term::_move_cursor 1 2
     Term::_ctl_0x0d
@@ -761,6 +773,7 @@ proc run_one_test_large { test_proc_name } {
 foreach_with_prefix test {
     test_backspace
     test_linefeed
+    test_linefeed_scroll
     test_carriage_return
     test_insert_characters
     test_cursor_up
diff --git a/gdb/testsuite/lib/tuiterm.exp b/gdb/testsuite/lib/tuiterm.exp
index b7c8775..96f9b9d 100644
--- a/gdb/testsuite/lib/tuiterm.exp
+++ b/gdb/testsuite/lib/tuiterm.exp
@@ -115,8 +115,9 @@ namespace eval Term {
 		    for {set x 0} {$x < $_cols} {incr x} {
 			set _chars($x,$y) $_chars($x,$next_y)
 		    }
-		    incr _cur_row -1
 		}
+
+		incr _cur_row -1
 	    }
 	}
     }