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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang++ errors when trying to call a constructor that automatically deduces its class template parameters from a Callable -templated class"
href="https://bugs.llvm.org/show_bug.cgi?id=40183">40183</a>
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<th>Summary</th>
<td>clang++ errors when trying to call a constructor that automatically deduces its class template parameters from a Callable -templated class
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>7.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++'17
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>jacksonmcneillnospam@gmail.com
</td>
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Created <span class=""><a href="attachment.cgi?id=21279" name="attach_21279" title="output of clang, including source, compile commands, and terminal output on crash">attachment 21279</a> <a href="attachment.cgi?id=21279&action=edit" title="output of clang, including source, compile commands, and terminal output on crash">[details]</a></span>
output of clang, including source, compile commands, and terminal output on
crash
clang version 7.0.0-3 (tags/RELEASE_700/final)
Target: x86_64-pc-linux-gnu
This is best described with code.
/*!
* Compile with: [g++ or clang++] -std=c++17 bug_code.cpp
*/
//Minimal replacement for std::function to demonstrate bug
template<typename> class callable_templated_class;
template<typename return_t, typename args_t>
class callable_templated_class<return_t(args_t)>
{
public:
callable_templated_class()
{
}
};
// You can remove one of these and specify int inside the
callable_templated_class<...> callback and still get the error. Removing both
and specifying int on both will not exhibit the error.
template <typename return_t, typename args_t>
class bug_class
{
public:
bug_class(int please_see_comment,
callable_templated_class<return_t(args_t)> callback)
/*!
* The 'int' at the beginning of the function is necessary to trigger the
bug in GCC (but not clang). In my testing, it can by any type -- but it must be
present.
*/
{
}
};
template <typename return_t, typename args_t>
class no_gcc_bug
{
public:
no_gcc_bug(callable_templated_class<return_t(args_t)> callback)
{
}
};
int main()
{
auto instantiation = callable_templated_class<int(int)>();
auto this_is_fine_in_gcc = new no_gcc_bug(instantiation); //works in
gcc, does not work in clang(crash)
auto this_will_error = new bug_class(0,instantiation); //This is a bug
in both GCC and clang.
//In GCC: It errors - I don't think it should(check standard?). At the
very least, the error message is wrong/confusing.
//In Clang: It crashes.
return 0;
}
Clang will crash trying to call the constructor for `no_gcc_bug`. I believe
clang is crashing while trying to deduce `return_t` or `args_t` from
`callable_templated_class<return_t(args_t)`. I think this because clang will
not crash if you remove the template from `no_gcc_bug` and use
`callable_templated_class<int(int)>` instead. However, if you keep the template
for `return_t` and/or `args_t`, clang will crash.
A similar bug exists in GCC, so I will link to the gcc bugzilla post when it's
up. I'm not sure of the correct behavior here, but it shouldn't crash.</pre>
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