[PATCH] D85545: [Diagnostics] Diagnose missing comma in string array initialization

[Dávid Bolvanský via cfe-commits]

For your godbolt example, you hit the heuristic to not warn, if
literals count is <= 2. (motivated by many false positives; and I
didnt see a true positive case, so..)

>> you could emit the warning only if exactly one comma was missing.

This could work.

ut 11. 8. 2020 o 0:04 Arthur O'Dwyer <arthur.j.odwyer at gmail.com> napísal(a):
>
> To decrease the number of false-positives, you could emit the warning only if exactly one comma was missing.
>
>     const char *likely_a_bug[] = { "a", "b", "c" "d", "e", "f", "g", "h", "i" };
>     const char *likely_not_a_bug[] = { "a", "b" "c", "d" "e", "f" "g" };
>     const char *oops_still_a_bug[] = { "a", "b", "c" "d", "e", "f" "g", "h", "i" };
>
> However, as `oops_still_a_bug` shows, that tactic would also decrease the number of true positives, and it would confuse the end-user, for whom predictability is key.
>
> I still think it would be appropriate to stop issuing the warning for structs, though.
> Here's my struct example from below in Godbolt: https://godbolt.org/z/6jjv6a
> Speaking of predictability, I don't understand why `struct Y` avoids the warning whereas `struct X` hits it.
> After removing the warning for structs, neither `X` nor `Y` should hit it, and that should fix pretty much all the Firefox hits as I understand them.
>
> –Arthur
>
>
> On Mon, Aug 10, 2020 at 5:51 PM Dávid Bolvanský <david.bolvansky at gmail.com> wrote:
>>
>> Something like this:
>>   const char *Sources[] = {
>>     "// \\tparam aaa Bbb\n",
>>     "// \\tparam\n"
>>     "//     aaa Bbb\n",
>>     "// \\tparam \n"
>>     "//     aaa Bbb\n",
>>     "// \\tparam aaa\n"
>>     "// Bbb\n"
>>   };
>>
>> annoys me :/ Any idea/heuristic how to avoid warning here?
>>
>> po 10. 8. 2020 o 23:48 Dávid Bolvanský <david.bolvansky at gmail.com> napísal(a):
>> >
>> > For your cases, we currently do not warn. If possible, fetch the
>> > latest Clang trunk and re-evaluate on Firefox.
>> >
>> > po 10. 8. 2020 o 23:46 Arthur O'Dwyer <arthur.j.odwyer at gmail.com> napísal(a):
>> > >
>> > > It looks to me as if all of the false-positives so far have been not arrays but structs.
>> > >
>> > > struct X { int a; const char *b; int c; };
>> > > X x = { 41, "forty" "two", 43 };  // false-positive here
>> > >
>> > > The distinguishing feature here is that if you did insert a comma as suggested by the compiler, then the result would no longer type-check.
>> > > X x = { 41, "forty", "two", 43 };  // this is ill-formed because "two" is not a valid initializer for `int c`
>> > >
>> > > Dávid, can you use this in some way?
>> > > IMHO it would be appropriate to just turn the warning off if the entity being initialized is a struct — leave the warning enabled only for initializers of arrays.
>> > >
>> > > my $.02,
>> > > –Arthur
>> > >
>> > >
>> > > On Mon, Aug 10, 2020 at 5:38 PM Dávid Bolvanský <david.bolvansky at gmail.com> wrote:
>> > >>
>> > >> I moved it to -Wextra due to false positives.
>> > >>
>> > >> > Should there be some exception for line length
>> > >>
>> > >> Yeah, but sure how to define the threshold or so. :/
>> > >>
>> > >> po 10. 8. 2020 o 23:21 dmajor via Phabricator
>> > >> <reviews at reviews.llvm.org> napísal(a):
>> > >> >
>> > >> > dmajor added a comment.
>> > >> >
>> > >> > In the Firefox repo this warning is firing on a number of strings that were broken up by clang-format (or humans) for line length, for example https://searchfox.org/mozilla-central/rev/ab81b8552f4aa9696a2524f97fdfeb59d4dc31c1/security/certverifier/ExtendedValidation.cpp#176-178 or https://searchfox.org/mozilla-central/rev/ab81b8552f4aa9696a2524f97fdfeb59d4dc31c1/xpcom/tests/gtest/TestEscape.cpp#103-104 or https://searchfox.org/mozilla-central/rev/ab81b8552f4aa9696a2524f97fdfeb59d4dc31c1/js/src/jsapi-tests/testXDR.cpp#115.
>> > >> >
>> > >> > Do you consider these to be false positives in your view? Should there be some exception for line length, perhaps?
>> > >> >
>> > >> >
>> > >> > Repository:
>> > >> >   rG LLVM Github Monorepo
>> > >> >
>> > >> > CHANGES SINCE LAST ACTION
>> > >> >   https://reviews.llvm.org/D85545/new/
>> > >> >
>> > >> > https://reviews.llvm.org/D85545
>> > >> >