Make gdb.base/corefile.exp work on terminals with few rows

  When creating a pty to spawn a subprocess (such as gdb), Expect
copies the settings of its own controlling terminal, including the
number of rows and columns.  If you "make check" on a terminal with just
a few rows (e.g. 4), GDB will paginate before reaching the initial
prompt.  In default_gdb_start, used by most tests, this is already
handled: if we see the pagination prompt, we sent \n to continue.

Philippe reported that gdb.base/corefile.exp didn't work in terminals
with just a few rows.  This test spawns GDB by hand, because it needs to
check things before the initial prompt, which it couldn't do if it used
default_gdb_start.

In this case I think it's not safe to use the same technique as in
default_gdb_start.  Even if we could send a \n if we see a pagination
prompt, we match some multiline regexes in there.  So if a pagination
slips in there, it might make the regexes not match and fail the test.

It's also not possible to use -ex "set height 0" or -iex "set height 0",
it is handled after the introduction text is shown.

The simplest way I found to avoid showing the pagination completely is
to set stty_init (documented in expect's man page) to initialize gdb's
pty with a fixed number of rows.

gdb/testsuite/ChangeLog:

	* gdb.base/corefile.exp: Set stty_init.
---
 gdb/testsuite/gdb.base/corefile.exp | 4 ++++
 1 file changed, 4 insertions(+)
  

On 02/06/2019 03:48 AM, Simon Marchi wrote:
> When creating a pty to spawn a subprocess (such as gdb), Expect
> copies the settings of its own controlling terminal, including the
> number of rows and columns.  If you "make check" on a terminal with just
> a few rows (e.g. 4), GDB will paginate before reaching the initial
> prompt.  In default_gdb_start, used by most tests, this is already
> handled: if we see the pagination prompt, we sent \n to continue.
> 
> Philippe reported that gdb.base/corefile.exp didn't work in terminals
> with just a few rows.  This test spawns GDB by hand, because it needs to
> check things before the initial prompt, which it couldn't do if it used
> default_gdb_start.
> 
> In this case I think it's not safe to use the same technique as in
> default_gdb_start.  Even if we could send a \n if we see a pagination
> prompt, we match some multiline regexes in there.  So if a pagination
> slips in there, it might make the regexes not match and fail the test.
> 
> It's also not possible to use -ex "set height 0" or -iex "set height 0",
> it is handled after the introduction text is shown.
> 
> The simplest way I found to avoid showing the pagination completely is
> to set stty_init (documented in expect's man page) to initialize gdb's
> pty with a fixed number of rows.

Hmm, good idea.  But, if you have a small terminal with just a few
columns (as opposed to rows), then the testsuite all breaks, AFAICT.

E.g., I just tried running gdb.base/break.exp with a small window and
the test hangs starting GDB.

But with:

 --- c/gdb/testsuite/lib/gdb.exp
 +++ w/gdb/testsuite/lib/gdb.exp
 @@ -4752,6 +4752,9 @@ proc gdb_init { test_file_name } {
      # tests.
      setenv TERM "dumb"
  
 +    global stty_init
 +    set stty_init "rows 25 cols 80"
 +
      # Some tests (for example gdb.base/maint.exp) shell out from gdb to use
      # grep.  Clear GREP_OPTIONS to make the behavior predictable,
      # especially having color output turned on can cause tests to fail.

... it passes.  And so does gdb.base/corefile.exp.

Is there any reason we'd ever want GDB's terminal size to match
whatever the user's term size was?  I'd think that sanitizing / forcing
the same sizes everywhere would just lead to more stable testing,
and thus be a good thing.

Thanks,
Pedro Alves