[Bug c/68187] New: Poor error message from -Wmisleading-indentation on glibc's ../stdlib/strtol_l.c

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68187

            Bug ID: 68187
           Summary: Poor error message from -Wmisleading-indentation on
                    glibc's ../stdlib/strtol_l.c
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dmalcolm at gcc dot gnu.org
  Target Milestone: ---

Building glibc (a9224562cbe9cfb0bd8d9e637a06141141f9e6e3) on x86_64, with gcc
r229364 patched to add -Wmisleading-indentation added to -Wall:

../stdlib/strtol_l.c: In function ‘____strtoul_l_internal’:
../stdlib/strtol_l.c:356:9: error: statement is indented as if it were guarded
by... [-Werror=misleading-indentation]
         cnt < thousands_len; })
         ^
../stdlib/strtol_l.c:353:9: note: ...this ‘for’ clause, but it is not
   && ({ for (cnt = 0; cnt < thousands_len; ++cnt)
         ^

The code is question looks like this:

   348            for (c = *end; c != L_('\0'); c = *++end)
   349              if (((STRING_TYPE) c < L_('0') || (STRING_TYPE) c >
L_('9'))
   350  # ifdef USE_WIDE_CHAR
   351                  && (wchar_t) c != thousands
   352  # else
   353                  && ({ for (cnt = 0; cnt < thousands_len; ++cnt)
   354                        if (thousands[cnt] != end[cnt])
   355                          break;
   356                        cnt < thousands_len; })
   357  # endif
   358                  && (!ISALPHA (c)
   359                      || (int) (TOUPPER (c) - L_('A') + 10) >= base))
   360                break;


It looks like lines 354 and 355 are poorly indented, leading to the warning
from -Wmisleading-indentation at line 356.

It could be argued that the warning is reasonable here, though I don't like the
wording of our warning here: line 356 isn't indented as if guarded by line 353,
it's more that lines 354 and 355 *aren't* indented.

Specifically:

(gdb) call inform (guard_tinfo.location, "guard_tinfo")
../stdlib/strtol_l.c:353:9: note: guard_tinfo
   && ({ for (cnt = 0; cnt < thousands_len; ++cnt)
         ^

(gdb) call inform (body_tinfo.location, "body_tinfo")
../stdlib/strtol_l.c:354:9: note: body_tinfo
         if (thousands[cnt] != end[cnt])
         ^
(gdb) call inform (next_tinfo.location, "next_tinfo")
../stdlib/strtol_l.c:356:9: note: next_tinfo
         cnt < thousands_len; })
         ^

(gdb) p guard_exploc
$11 = {file = 0x1dd40a0 "../stdlib/strtol_l.c", line = 353, column = 9, data =
0x0, sysp = false}
(gdb) p body_exploc
$12 = {file = 0x1dd40a0 "../stdlib/strtol_l.c", line = 354, column = 9, data =
0x0, sysp = false}
(gdb) p next_stmt_exploc
$13 = {file = 0x1dd40a0 "../stdlib/strtol_l.c", line = 356, column = 9, data =
0x0, sysp = false}

(gdb) p guard_vis_column
$14 = 22
(gdb) p body_vis_column 
$15 = 22
(gdb) p next_stmt_vis_column 
$16 = 22

(gdb) p body_type
$17 = CPP_KEYWORD

I believe it's entering this clause:

          /* Don't warn if they are aligned on the same column
             as the guard itself (suggesting autogenerated code that doesn't
             bother indenting at all).  We consider the column of the first


but:

(gdb) p guard_line_first_nws 
$18 = 16
(gdb) p body_vis_column 
$19 = 22

due to the "&& ({ " before the "for" on line 353 and hence it fails the tests,
and reaches:

          /* Otherwise, they are visually aligned: issue a warning.  */
          return true;