[cfe-dev] Odd error in the modules-enabled LLVM build

[Richard Smith via cfe-dev]

Looks like we're doing ... something ... wrong when computing visibility
for a default template argument. Perhaps we're not correctly taking into
account that the lexical parent of the default template argument might have
been merged with definitions from other modules (and if so, the default
template argument should be considered available whenever any of the merged
copies of the enclosing lexical context are visible).

I think the bug is somewhere here:
https://github.com/llvm-mirror/clang/blob/master/lib/Sema/SemaLookup.cpp#L1550
(I think that comment is just wrong, and we should always be checking for
any visible definition of the enclosing lexical context. But I suspect if
we make that change we'll find a test case that shows why we need something
more subtle here.)

On 26 March 2018 at 09:36, David Blaikie via cfe-dev <cfe-dev at lists.llvm.org
> wrote:

> ping
>
> On Wed, Mar 21, 2018 at 9:50 AM David Blaikie <dblaikie at gmail.com> wrote:
>
>> Hey Richard (or anyone else who wants to weigh in on this), I'm seeing
>> something I can't quite explain - figured I'd check if I was missing
>> something obvious, or whether this is worth/requires more investigation.
>>
>> Trying to test the modules enabled LLVM build (LLVM_ENABLE_MODULES=ON) I
>> came across an error:
>>
>> In module 'LLVM_Utils' imported from lib/DebugInfo/PDB/Native/
>> ModuleDebugStream.cpp:11:
>> /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/shared_ptr.h:278:4:
>> error: no matching constructor for initialization
>>  of '__shared_ptr<llvm::msf::MappedBlockStream>'
>>         : __shared_ptr<_Tp>(std::move(__r)) { }
>>           ^                 ~~~~~~~~~~~~~~
>>
>> ...
>>
>> /usr/lib/gcc/x86_64-linux-gnu/7.3.0/../../../../include/c++/
>> 7.3.0/bits/shared_ptr_base.h:1157:2: note: candidate template ignored:
>> substitution failure [with _Yp = llvm::msf::MappedBlockStream, _Del =
>> std::default_delete<llvm::msf::MappedBlockStream>]: default argument of
>> '_UniqCompatible' must be imported from module 'LLVM_DebugInfo_PDB.IPDBEnumChildren'
>> before it is required
>>         __shared_ptr(unique_ptr<_Yp, _Del>&& __r)
>>         ^
>>
>> I guess I should be using libcxx if I want to use modules, rather than
>> using my system libstdc++? But even then, this seems like a rather strange
>> error that may be indicative of a bug?
>>
>> Including IPDBEnumChildren.h does fix the error - but it seems like a
>> wholely unrelated header to have to include here...
>>
>> - Dave
>>
>
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