Re: [committed] diagnostics: support compact printing of secondary locations

[Richard Sandiford <richard.sandiford@linaro.org>]

David Malcolm <dmalcolm@redhat.com> writes:
> On Mon, 2017-07-03 at 19:57 +0100, Richard Sandiford wrote:
>> [Thanks for all your diagnostic work btw.]
>> 
>> David Malcolm <dmalcolm@redhat.com> writes:
>> > clang can also print notes about matching opening symbols
>> > e.g. the note here:
>> > 
>> >   missing-symbol-2.c:25:22: error: expected ']'
>> >     const char test [42;
>> >                        ^
>> >   missing-symbol-2.c:25:19: note: to match this '['
>> >     const char test [42;
>> >                     ^
>> > which, although somewhat redundant for this example, seems much
>> > more
>> > useful if there's non-trivial nesting of constructs, or more than a
>> > few
>> > lines separating the open/close symbols (e.g. showing a stray
>> > "namespace {"
>> > that the user forgot to close).
>> > 
>> > I'd like to implement both of these ideas as followups, but in
>> > the meantime, is the fix-it hint patch OK for trunk?
>> > (successfully bootstrapped & regrtested on x86_64-pc-linux-gnu)
>> 
>> Just wondering: how easy would it be to restrict the note to the
>> kinds
>> of cases you mention?  TBH I think clang goes in for extra notes too
>> much, and it's not always that case that an "expected 'foo'" message
>> really is caused by a missing 'foo'.  It'd be great if there was some
>> way of making the notes a bit more discerning. :-)
>> 
>> Or maybe do something like restrict the extra note to cases in which
>> the
>> opening character is on a different line and use an underlined range
>> when the opening character is on the same line?
>> 
>> Thanks,
>> Richard
>
> Thanks.
>
> This patch implements a new method:
>
>    bool gcc_rich_location::add_location_if_nearby (location_t);
>
> to make it easy for a diagnostic to compactly print secondary locations
> for these kinds of cases, falling back to printing them via a note
> otherwise.
>
> Usage example (adapted from the one in the header):
>
>   gcc_rich_location richloc (primary_loc);
>   bool added secondary = richloc.add_location_if_nearby (secondary_loc);
>   error_at_rich_loc (&richloc, "missing %qs", "}");
>   if (!added secondary)
>     inform (secondary_loc, "here's the associated %qs", "{");
>
> When primary_loc and secondary_loc are on the same line this will print:
>
>   test.c:1:39: error: missing '}'
>    struct same_line { double x; double y; ;
>                     ~                    ^
>
> When they are on different lines, this will print:
>
>   test.c:6:1: error: missing '}'
>    ;
>    ^
>   test.c:3:1: note: here's the associated '{'
>    {
>    ^

Thanks, this looks great!

Richard