[Bug c/98892] FAIL: gcc.dg/plugin/diagnostic-test-expressions-1.c

["wilson at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98892

Jim Wilson <wilson at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |wilson at gcc dot gnu.org

--- Comment #2 from Jim Wilson <wilson at gcc dot gnu.org> ---
I ran into this with a riscv toolchain make check.

Debugging, I discovered that if my terminal window is 80 characters wide, then
context->max_caret_width gets set to 78 in diagnostic.c, and then in
diagnostic-show-locus.c m_x_offset_display gets set to 9, and then in
print_trailing_fixits it calls move_to_column with column set to 9 which causes
an extra unnecessary newline to be emitted.  This extra newline leads to the "1
blank lines in output" error.  Also, I suspect that there is a contributing bug
in the dg-{begin,end}-multiline-output support that causes it to fail when an
error is followed by two newlines.  This causes the "expected multiline pattern
lines 550-551" failure.

A bit of experimenting with the testcase in isolation shows that if my screen
is 88 chars wide there is no extra newline, and if my screen is 87 chars wide I
get the extra newline.

A bit of experimenting with RUNTESTFLAGS="plugin.exp" show that the testcase
fails every time when my screen is 80 characters wide and works everytime when
my screen is 81 characters wide.  I don't know why this number is different
than above.

A testcase whose success depends on screen width is very annoying.

One way to work around the problem is to make the line shorter.  If I delete
one tab char from line 548 of gcc.dg/plugin/diagnostic-test-expressions-1.c and
8 space characters from the two matching error lines 550 and 551, then the
testcase does work with an 80 character wide terminal.  However, it does now
fail with a 77 char wide screen due to a different line 415-416.  So this isn't
an ideal solution.  But it works for me as my screens are always 80 characters
wide.

ideally there should be a way to turn off the max_caret_width stuff when
running the testsuite so results don't depend on screen width.  Someone who
knows the diagnostic code should probably look at this.

Or maybe print_trailing_fixits can be fixed?  It isn't obvious why it needs to
call move_to_column at the end.