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

[Ben Jackson via cfe-dev]

Val, 

I think you might be right. I will try it out to confirm, but the docs look to point to exactly that:

CXTranslationUnit_Incomplete	
Used to indicate that the translation unit is incomplete. 

When a translation unit is considered "incomplete", semantic analysis that is typically performed at the end of the translation unit will be suppressed. For example, this suppresses the completion of tentative declarations in C and of instantiation of implicitly-instantiation function templates in C++. This option is typically used when parsing a header with the intent of producing a precompiled header.


Thanks,
Ben


> On 1 Nov 2015, at 17:12, Val Markovic <val at markovic.io> wrote:
> 
> 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 <mailto:klimek at google.com>> wrote:
> +Benjamin 
> 
> On Tue, Oct 27, 2015 at 5:15 PM Val Markovic <val at markovic.io <mailto:val at markovic.io>> wrote:
> +klimek
> 
> On Mon, Oct 26, 2015 at 3:09 PM, Ben Jackson <puremourning at gmail.com <mailto: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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