[cfe-dev] [ycm-dev] libclang: diagnostics not reported for template instantiations

[Val Markovic via cfe-dev]

Could this be related to the Incomplete flag we started passing to libclang
a while ago?

On Sun, Nov 1, 2015 at 9:11 AM, Manuel Klimek <klimek at google.com> wrote:

> +Benjamin
>
> On Tue, Oct 27, 2015 at 5:15 PM Val Markovic <val at markovic.io> wrote:
>
>> +klimek
>>
>> On Mon, Oct 26, 2015 at 3:09 PM, Ben Jackson <puremourning at gmail.com>
>> wrote:
>>
>>> Hi there,
>>>
>>> An issue was raised against ycmd that we were not reporting errors as a
>>> result of failed template instantiations. This is because, seemingly,
>>> libclang does not report diagnostics for template instantiations where
>>> instantiation fails (in the sense that the generated code is not valid).
>>>
>>> A fairly canonical test case is as follows:
>>>
>>>     template<typename T>
>>>     void get_size(const T& t)
>>>     {
>>>         return t.size();
>>>     }
>>>
>>>     struct Test
>>>     {
>>>         void not_size() const;
>>>     };
>>>
>>>     int run_test()
>>>     {
>>>         Test t;
>>>
>>>         get_size(t);
>>>
>>>         return "not_an_int";
>>>     }
>>>
>>> Expected: a diagnostic reported at the line ‘get_size(t)’ as struct Test
>>> does not have a size()const method. However, no diagnostic is reported.
>>>
>>> The ‘return “not_an_int”’ is just to prove that diagnostics reporting is
>>> working in general in the test case.
>>>
>>> When running the above with ‘c-index-test -index-file’, grepping for
>>> ‘[diagnostic]’, the result is :
>>>
>>>     $ ./bin/c-index-test -index-file
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp  |
>>> grep '\[diagnostic\]'
>>>
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp:18:12:
>>> error: cannot initialize return object of type 'int' with an lvalue of type
>>> 'const char [11]'
>>> [diagnostic]:
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp:18:12:
>>> error: cannot initialize return object of type ‘int' with an lvalue of type
>>> 'const char [11]'
>>>
>>> However, when running clang directly, we get the diagnostic for
>>> get_size(t):
>>>
>>>      clang++
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp
>>>
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp:18:12:
>>> error: cannot initialize return object of type 'int' with an lvalue of type
>>> 'const char [11]'
>>>         return "not_an_int";
>>>            ^~~~~~~~~~~~
>>>
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp:4:14:
>>> error: no member named 'size' in 'Test'
>>>         return t.size();
>>>            ~ ^
>>>
>>> ../llvm/tools/clang/test/Index/diagnostics-template-instantiation.cpp:16:5:
>>> note: in instantiation of function template specialization 'get_size<Test>'
>>> requested here
>>>         get_size(t);
>>>     ^
>>>     2 errors generated.
>>>
>>> Is this a bug or simply a limitation of the libclang interface? Or is
>>> there something required to get these diagnostics to report. Apologies, I
>>> must confess I have not looked into this in detail within clang.
>>>
>>
> I'd expect there to be a way to drive libclang to get those diagnostics.
> On the other hand, it would probably mean a significant slow-down, because
> template instantiation can be a significant amount of the parse time.
>
>
>>
>>> Many thanks and kind regards,
>>> Ben
>>>
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>>
>>
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