[cfe-dev] How to handle -f flags

[Reid Kleckner]

How about we model "-f" as a prefix similar to "--", and then use some
tablegen construct to create the -f and -fno- versions, as well as
potentially populating a .def file from it like you suggest?

The only problem I see with this is that I commonly search the .td files
for "ffoo", and that wouldn't fire anymore.

On Fri, Sep 27, 2013 at 8:36 AM, Rafael Espíndola <
rafael.espindola at gmail.com> wrote:

> There are some special -f options that are not really flags. For
> example, -fprofile-dir=PATH. It takes a value and there is no such
> thing as -fno-profile-dir. For these special cases it looks like we
> have a fairly reasonable infrastructure, since they will need some
> custom handling anyway.
>
> But the vast majority are just simple flags that have the form of the
> pair -ffoo and -fno-foo. Right now we have quiet a large amount of
> boilerplate to implement those.
>
> * Add both to Options.td:
>
> def fshow_column : Flag<["-"], "fshow-column">, Group<f_Group>,
> Flags<[CC1Option]>;
> def fno_show_column : Flag<["-"], "fno-show-column">, Group<f_Group>,
> Flags<[CC1Option]>,
>   HelpText<"Do not include column number on diagnostics">;
>
> * Add it to some .def file.
>
> DIAGOPT(ShowColumn, 1, 1)       /// Show column number on diagnostics.
>
> * Parse the option:
>
> Opts.ShowColumn = Args.hasFlag(OPT_fshow_column,
>                                  OPT_fno_show_column,
>                                  /*Default=*/true);
>
> * Actually use the option for what it is intended.
>
> Because of this, most -f options have some bug in their
> implementation. In the above fshow-column example the help text is out
> of sync, the negative of -ffunction-sections is missing completely,
> etc.
>
> I think that to fix this we need something more like the way we handle
> warnings:
>
> * Add a catch all -f* option to Options.td.
> * Add a include/Basic/FFlags.td with entries like
>
> def show_column : FFlag<"Include column number on diagnostics", 1>;
>
> Where 1 is the default value.
>
> * Have tablegen produce a FFlags.def file and a function for setting
> the flags from the command line options.
>
> * Produce a -f specific error if we see one that we don't know what it
> is ("unknown flag: 'foobar'", instead of "unknown argument:
> '-ffoobar'").
>
> Can anyone see a problem with this? The main difference (other than
> the refactoring) would be that all the f flags are in singe .def file
> and object, not split in CodeGenOptions.def/CodeGenOptions,
> DiagnosticOptions.def/DiagnosticOptions, etc.
>
> Cheers,
> Rafael
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