[cfe-commits] [PATCH] PR10053 Improved two-stage lookup diagnostic

[Richard Smith]

Oops, forgot the patch!

On Sun, June 5, 2011 18:31, Richard Smith wrote:
> On Sun, June 5, 2011 04:16, Douglas Gregor wrote:
>> On Jun 4, 2011, at 1:37 PM, Richard Smith wrote:
>>> The attached patch improves our error recovery when handling code
>>> which some versions of gcc incorrectly accept, due to an incomplete
>>> implementation of two-stage name lookup.
>>>
>>> This example from the compatibility section on the www:
>>>
>>>
>>>
>>> template <typename T> T Squared(T x) { return Multiply(x, x); }
>>>
>>>
>>> int Multiply(int x, int y) { return x * y; }
>>>
>>>
>>> int main() { Squared(5); }
>>>
>>>
>>>
>>> Now produces the following diagnostics:
>>>
>>>
>>>
>>> my_file.cpp:2:10: error: use of undeclared identifier 'Multiply'
>>> return Multiply(x, x); ^ my_file.cpp:10:3: note: in instantiation of
>>> function template specialization 'Squared<int>' requested here
>>> Squared(5);
>>> ^
>>> my_file.cpp:5:5: note: viable function not candidate: declared after
>>> template was defined and not in an associated namespace int
>>> Multiply(int
>>> x, int y) { ^
>>
>> The code looks good, but I think the diagnostic wording could be
>> improved considerably. The error message should say what the problem is,
>> and the note should suggest the solution. For example:
>>
>> error: call to function 'Multiply' that is neither visible in the
>> template definition nor found by argument dependent lookup
>>
>> note: 'Multiply' should be declared prior to the call site or in the
>> namespace of one of its arguments
>
> The attached, revised patch produces this in the case where there are no
> associated namespaces:
>
> my_file.cpp:2:10: error: call to function 'Multiply' that is neither
> visible in the template definition nor found by argument dependent lookup
> return Multiply(x, x); ^
> my_file.cpp:10:3: note: in instantiation of function template
> specialization 'Squared<int>' requested here Squared(5);
> ^
> my_file.cpp:5:5: note: 'Multiply' should be declared prior to the call
> site int Multiply(int x, int y) { ^
>
>
> In the case where there is a single associated namespace (excluding those
>  within namespace std), we produce this:
>
> my_file2.cpp:5:13: error: call to function 'operator<<' that is neither
> visible in the template definition nor found by argument dependent lookup
> std::cout << value << "\n";
> ^
> my_file2.cpp:17:3: note: in instantiation of function template
> specialization 'Dump<ns::Data>' requested here Dump(ns::Data());
> ^
> my_file2.cpp:12:15: note: 'operator<<' should be declared prior to the
> call site or in namespace 'ns' std::ostream& operator<<(std::ostream& out,
> ns::Data data) {
> ^
>
>
> Finally, if there are multiple associated namespaces for the call, we
> produce a slightly tweaked version of the diagnostic you suggested:
>
> my_file3.cpp:5:10: error: call to function 'operator!' that is neither
> visible in the template definition nor found by argument dependent lookup
> return !value; ^
> my_file3.cpp:18:3: note: in instantiation of function template
> specialization 'Negate<ns2::S<ns::Data> >' requested here
> Negate(ns2::S<ns::Data>());
> ^
> my_file3.cpp:15:18: note: 'operator!' should be declared prior to the
> call site or in an associated namespace of one of its arguments
> ns2::S<ns::Data> operator!(ns2::S<ns::Data>);
> ^
>
>
>>> This patch only diagnoses normal unqualified names; diagnostics for
>>> names with scope specifiers and for overloaded operators are not
>>> similarly improved.
>
> I've extended the patch to also cover overloaded operators. We don't
> fully recover in that case, but we do produce the improved diagnostic.
>
> Comments?
>
>
> Thanks,
> Richard
-------------- next part --------------
A non-text attachment was scrubbed...
Name: pr10053.diff
Type: text/x-patch
Size: 17993 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20110605/6220f34c/attachment.bin>