Re: [PATCH] driver: Improve the generated help text for alias options with arguments

[Lewis Hyatt <lhyatt@gmail.com>]

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On Tue, Mar 17, 2020 at 11:52:13AM +0000, Richard Sandiford wrote:
> Lewis Hyatt <lhyatt@gmail.com> writes:
> > On Mon, Mar 16, 2020 at 06:11:08PM +0000, Richard Sandiford wrote:
> >> Lewis Hyatt via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> > ...
> >> > FWIW there are three other options currently affected by this change
> >> > (-Wimplicit-fallthrough, -fcf-protection, and -flive-patching). The change for
> >> > -Wimplicit-fallthrough I think is particularly helpful:
> >> >
> >> > -Wimplicit-fallthrough      Same as -Wimplicit-fallthrough=.  Use the latter option instead.
> >> > becomes
> >> > -Wimplicit-fallthrough      Same as -Wimplicit-fallthrough=3 (or, in negated form, -Wimplicit-fallthrough=0).
> >> 
> >> I also see:
> >> 
> >> -  -ftail-call-workaround      Same as -ftail-call-workaround=.  Use the latter option instead.
> >> +  -ftail-call-workaround      Same as -ftail-call-workaround=1 (or, in negated form, -ftail-call-workaround=0).
> >>    -ftail-call-workaround=<0,2> Disallow tail call optimization when a calling routine may have omitted character lengths.
> >> ...
> >>    --imacros                   Same as -imacros.  Use the latter option instead.
> >>    --imacros=                  Same as -imacros.  Use the latter option instead.
> >>    --include                   Same as -include.  Use the latter option instead.
> >> -  --include-barrier           Same as -I.  Use the latter option instead.
> >> +  --include-barrier           Same as -I-.
> >>    --include-directory         Same as -I.  Use the latter option instead.
> >>    --include-directory-after   Same as -idirafter.  Use the latter option instead.
> >>    --include-directory-after=  Same as -idirafter.  Use the latter option instead.
> >> ...
> >> -  -Wnormalized                Same as -Wnormalized=.  Use the latter option instead.
> >> +  -Wnormalized                Same as -Wnormalized=nfc (or, in negated form, -Wnormalized=none).
> >>    -Wnormalized=[none|id|nfc|nfkc] Warn about non-normalized Unicode strings.
> >> 
> >> I agree all of these look like improvements, especially the
> >> --include-barrier one.  But I think the include ones also show
> >> that the "Use the latter option instead." decision is independent
> >> of whether the option is defined to be an alias.
> 
> Gah, I meant an Alias() with an argument here.
> 
> >> 
> >> FWIW, there's also:
> >> 
> >> Wmissing-format-attribute
> >> C ObjC C++ ObjC++ Warning Alias(Wsuggest-attribute=format)
> >> ;
> >> 
> >> which still ends up as:
> >> 
> >>   -Wmissing-format-attribute  Same as -Wsuggest-attribute=format.  Use the latter option instead.
> >> 
> >> Not really my area though, so I don't have any specific suggestion
> >> about how to separate the cases.
> >> 
> >
> > Right, sorry, in my first email I only mentioned the options output by
> > --help=common, but there were a few more as well. Thanks very much for trying
> > it out and for the feedback.
> >
> > The rule I implemented was to change the help output for all alias options
> > with no documentation if they also specify the extra 2nd option (or 2nd and
> > 3rd options) to the Alias directive. For example, -include-barrier is like this:
> >
> > -include-barrier C ObjC C++ ObjC++ Alias(I, -)
> >
> > It serves to provide the argument '-' to the option '-I', so it is eligible for
> > the new text. The others are like this one:
> >
> > -include-directory-after C ObjC C++ ObjC++ Separate Alias(idirafter) MissingArgError(missing path after %qs)
> >
> > Since that one doesn't pass the extra args to Alias, I interpreted it to
> > mean this is the case for which the "Use the latter option" directive was
> > intended to apply. (-idirafter has been designated as preferable to
> > -include-directory-after).
> 
> Yeah, I get why you did it like this.  It's just that the end effect
> is to make --include-barrier seem less disparaged than the other
> --include-* options, but I'm not sure there's supposed to be any
> difference between them in that respect.
> 
> Perhaps we should drop the "Use the latter option instead." thing
> altogether for aliases.  I'm not sure that it really helps, and this
> thread shows that adding it automatically can lead to some odd corner
> cases.
> 
> In practice we shouldn't remove any of these aliases unless we're
> also removing the option that they're an alias of.  And if we do that,
> the options should go through the usual deprecation cycle, just like
> options without aliases.
> 
> If there are specific options that we want to steer users away
> from without deprecation, then we should probably have a specific
> tag for that.

Thanks, it makes sense to me. That would amount to changing just one line of
the patch then, so it would look instead like the attached.

-Lewis

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gcc/ChangeLog:

2020-03-19  Lewis Hyatt  <lhyatt@gmail.com>

	* opts.c (print_filtered_help): Improve the help text for alias
	options.

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commit 7a74dd55098e2ec8c2b87dc172ac34f91eefc0c1
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Wed Feb 12 13:52:28 2020 -0500

    driver: Improve the generated help text for alias options
    
diff --git a/gcc/opts.c b/gcc/opts.c
index ac160ed8404..5dc7d65dedd 100644
--- a/gcc/opts.c
+++ b/gcc/opts.c
@@ -1315,14 +1315,31 @@ print_filtered_help (unsigned int include_flags,
       if (option->alias_target < N_OPTS
 	  && cl_options [option->alias_target].help)
 	{
+	  const struct cl_option *target = cl_options + option->alias_target;
 	  if (option->help == NULL)
 	    {
-	      /* For undocumented options that are aliases for other options
-		 that are documented, point the reader to the other option in
-		 preference of the former.  */
-	      snprintf (new_help, sizeof new_help,
-			_("Same as %s.  Use the latter option instead."),
-			cl_options [option->alias_target].opt_text);
+	      /* The option is undocumented but is an alias for an option that
+		 is documented.  If the option has alias arguments, then its
+		 purpose is to provide certain arguments to the other option, so
+		 inform the reader of this.  Otherwise, point the reader to the
+		 other option in preference to the former.  */
+
+	      if (option->alias_arg)
+		{
+		  if (option->neg_alias_arg)
+		    snprintf (new_help, sizeof new_help,
+			      _("Same as %s%s (or, in negated form, %s%s)."),
+			      target->opt_text, option->alias_arg,
+			      target->opt_text, option->neg_alias_arg);
+		  else
+		    snprintf (new_help, sizeof new_help,
+			      _("Same as %s%s."),
+			      target->opt_text, option->alias_arg);
+		}
+	      else
+		snprintf (new_help, sizeof new_help,
+			  _("Same as %s."),
+			  target->opt_text);
 	    }
 	  else
 	    {