[bug #59795] interaction of .na and '.ad l' documented incorrectly

[G. Branden Robinson]

Follow-up Comment #10, bug #59795 (project groff):

Bjarni is correct.  I was attempting to infer groff (and Heirloom) behavior in
black-box fashion, and did not contrive enough experimental cases.

But the implementation is sufficiently strange that it's easier to get an
understanding by quoting the code.

>From src/roff/troff/env.cpp:


void adjust()
{
  curenv->adjust_mode |= 1;
  if (has_arg()) {
    switch (tok.ch()) {
    case 'l':
      curenv->adjust_mode = ADJUST_LEFT;
      break;
    case 'r':
      curenv->adjust_mode = ADJUST_RIGHT;
      break;
    case 'c':
      curenv->adjust_mode = ADJUST_CENTER;
      break;
    case 'b':
    case 'n':
      curenv->adjust_mode = ADJUST_BOTH;
      break;
    default:
      int n;
      if (get_integer(&n)) {
        if (n < 0)
          warning(WARN_RANGE, "negative adjustment mode");
        else if (n > 5) {
          curenv->adjust_mode = 5;
          warning(WARN_RANGE, "adjustment mode '%1' out of range", n);
        }
        else
          curenv->adjust_mode = n;
      }
    }
  }
  skip_line();
}

void no_adjust()
{
  curenv->adjust_mode &= ~1;
  skip_line();
}


>From this we can see that adjustment enablement is simply the least
significant bit of the adjustment mode.  Where things get weird is the value
of the ADJUST_LEFT constant, but we shouldn't scar users' minds with that.

I'm dubious about this bit:


        else if (n > 5) {
          curenv->adjust_mode = 5;
          warning(WARN_RANGE, "adjustment mode '%1' out of range", n);
        }


This should be comparing to an ADJUST_MAX constant instead of a literal.  It
also smells a little funny to start right-adjusting if the adjustment mode is
out of range (that's what adjust_mode = 5 means).  I'll have to see if AT&T
troff supported numeric adjustment modes; it is already known that V7 troff
did not support the .j register.



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