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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Invalid type in constraint substitution results in hard error instead of substitution failure"
href="https://bugs.llvm.org/show_bug.cgi?id=49513">49513</a>
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<th>Summary</th>
<td>Invalid type in constraint substitution results in hard error instead of substitution failure
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>11.0
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++2a
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>barry.revzin@gmail.com
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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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<p>
<div>
<pre>From StackOverflow (<a href="https://stackoverflow.com/q/66562184/2069064">https://stackoverflow.com/q/66562184/2069064</a>):
template<class T>
struct A {
constexpr bool operator()() requires T::value { return T::value; }
constexpr bool operator()() { return false; }
};
static_assert(!A<void>()());
clang rejects this, saying:
<source>:3:42: error: type 'void' cannot be used prior to '::' because it has
no members
constexpr bool operator()() requires T::value { return T::value; }
^
<source>:7:16: note: in instantiation of template class 'A<void>' requested
here
static_assert(!A<void>()());
^
But the rule in [temp.constr.atomic] is that "if substitution results in an
invalid type or expression, the constraint is not satisfied." Which is what
should happen here. gcc and msvc accept.</pre>
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