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

[Douglas Gregor]

Looks great, thanks!

Sent from my iPhone

On Jun 5, 2011, at 10:31 AM, Richard Smith <richard at metafoo.co.uk> wrote:

> 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
> <pr10053.diff>