[m-rev.] for review: simplify options_file error handling

[Julien Fischer]

On Sun, 23 Jan 2022, Zoltan Somogyi wrote:

> Make options_file.m return either info or error.
> 
> compiler/options_file.m:
>     Change the interface of three lookup predicates to return
>     either the information they are intended to look up, or a list of
>     error_specs, but not both. The old code would have made sense
>     if some error_specs generated during the lookup could be warnings,
>     but they are always errors.

...

> diff --git a/compiler/options_file.m b/compiler/options_file.m
> index f27be9384..95643faad 100644
> --- a/compiler/options_file.m
> +++ b/compiler/options_file.m

...

> @@ -1264,29 +1261,39 @@ lookup_mercury_stdlib_dir(Variables, MaybeMerStdlibDir) :-

...

> +lookup_mmc_maybe_module_options(Variables, MaybeModuleName, Result) :-
>      VariableTypes = options_variable_types,
>      list.map_foldl(
>          lookup_options_variable(Variables, MaybeModuleName),
>          VariableTypes, VariableTypesMaybeValues, [], Specs),
> -    Result = list.condense(
> -        list.map(convert_to_mmc_options, VariableTypesMaybeValues)).
> +    (
> +        Specs = [],
> +        MmcOptLists =
> +            list.map(convert_to_mmc_options, VariableTypesMaybeValues),
> +        list.condense(MmcOptLists, MmcOpts),
> +        Result = ok1(MmcOpts)
> +    ;
> +        Specs = [_ | _],
> +        % Returning error1 here is correct because all specs the Specs

   ... all spec in Specs

> +        % will have severity_error. There is (as of this writing) exactly
> +        % one place in this module that generates an error_spec whose
> +        % severity is NOT severity_error, but it is not reachable from
> +        % lookup_options_variable.
> +        Result = error1(Specs)
> +    ).

The rest looks fine.

Julien.