[cfe-commits] [Patch] Update Sema Diagnostics to use %diff

Richard Smith richard at metafoo.co.uk
Fri Jul 13 17:09:54 PDT 2012

On Fri, Jul 13, 2012 at 3:41 PM, Richard Trieu <rtrieu at google.com> wrote:

> On Thu, Jul 12, 2012 at 5:32 PM, Richard Smith <richard at metafoo.co.uk>wrote:
>> On Thu, Jul 12, 2012 at 4:53 PM, Richard Trieu <rtrieu at google.com> wrote:
>>> On Thu, Jul 12, 2012 at 3:22 PM, Richard Smith <richard at metafoo.co.uk>wrote:
>>>> On Thu, Jul 12, 2012 at 2:07 PM, Richard Trieu <rtrieu at google.com>wrote:
>>>>> Change diagnostic messages in DiagnosticsSemaKinds.td to use %diff
>>>>> when two QualType's are required.  This will enable template type diffing
>>>>> for all Sema messages.  The default text of the diff matches the old
>>>>> message so no test cases need to be updated.  Some tests have been added
>>>>> for the modified messages.
>>>>> Patch attached and also available at:
>>>>> http://llvm-reviews.chandlerc.com/D6
>>>> This looks awesome! I have a few questions:
>>>> 1) A few of the diagnostics contain multiple %diff{...}s, for instance,
>>>> err_init_conversion_failed. How well does that work in tree mode?
>>> The current diagnostics can't print two trees.  For the
>>> err_init_conversion_failed, the first %diff prints if args 1 & 3 are
>>> templates.  The other %diff's only print if 1 & 3 are function pointer
>>> types.  Skimming the code, it appears that it does allow two trees to be
>>> printed, but problems may arise if only one tree is requested.  I think
>>> that printing the first possible tree, then ignoring any further trees
>>> should be the way to go.
>> Sounds good to me.
> r160193
>>>  2) How should we handle diagnostics which refer only to built-in
>>>> types? (Examples: the warn_impcast_* and most of the err_typecheck_*
>>>> diagnostics.)
>>>> Is the diff valuable here? Are there cases where this will cause worse
>>>> diagnostics? More generally, how hesitant should we be before adding %diff
>>>> to a diagnostic, and are there any rules we should be following?
>>> The diff will almost always fall back to standard printing for some of
>>> the diagnostics.  I applied the changes as broadly as possible in case
>>> anybody else wanted to improve the %diff for other cases.
>> OK, this seems reasonable, and I suppose a diff for
>> IdentityAliasTemplate<int> vs IdentityAliasTemplate<long> might be nice.
>>> I'm not overly fond of the "between types" wording in the tree case for
>>>> the warn_impcast_* set (it seems redundant to say that a cast is between
>>>> types, although I see that you need some way to introduce the type tree). I
>>>> wonder if something like this would read more naturally:
>>>> 'implicit conversion changes value from %2 to %3; types are:
>>>> <tree>'
>>> That is certainly possible to do, but also means that the diagnostic
>>> will be longer since the full types are printed.
>> In the above example, %2 and %3 there aren't the types in question, and
>> I'm only suggesting changing the tree form of the diagnostic. If my
>> counting is right, the tweak should make that diagnostic 1 character
>> shorter.
>>> 3) How should we handle diagnostics are just naming two types which
>>>> weren't expected to be the same, rather than comparing them to each other?
>>>> (Examples: most of the cases where the diagnostic concerns an explicit
>>>> cast.)
>>>> In such a case, I would expect the way that the types differ would be
>>>> uninteresting. My concern in such cases is mainly that adding a diff might
>>>> make the diagnostic less clear, in the case where the diff either performs
>>>> some desugaring or produces a tree.
>>>> This also applies to err_ovl_ambiguous_oper_binary
>>>> and err_typecheck_invalid_operands. Those are a little more interesting,
>>>> because I suppose it will frequently be the case that the operands to a
>>>> binary operator were supposed to be the same. However, I think it could be
>>>> confusing to produce a type tree for these, since the diagnostic is
>>>> fundamentally trying to list two types, not point out the difference
>>>> between two types.
>>> Like I said, I applied the diff to as many places as I could.  I don't
>>> mind changing the wording or removing %diff's if that makes things better.
>>  I think it would be useful to have a general policy for this. For that,
>> I suggest: "%diff should be used when a diagnostic contains two types which
>> the user might reasonably have expected to be the same. It should not be
>> used when a diagnostic contains two types which were likely to have been
>> intentionally different." -- unless we have a motivating example for
>> wanting a diff in the latter case.
> Removed %diff from diagnostics where the types are expected to be
> different.  Let me know if there should be more removed.

Thanks, LGTM!
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