<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -Wunneeded-internal-declaration warned on needed function"
href="https://bugs.llvm.org/show_bug.cgi?id=43598">43598</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>-Wunneeded-internal-declaration warned on needed function
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>leonardchan@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>For this code:
```
1 #include <type_traits>
2
3 namespace {
4
5 // Check if Op is convertible to bool.
6 template <typename Op>
7 using enable_relop_t = std::enable_if_t<(std::is_convertible<Op,
bool>::value), bool>;
8
9 // Chek if can do == with T and U.
10 template <typename T, typename U,
11 enable_relop_t<decltype(std::declval<T>() == std::declval<U>())> =
true>
12 constexpr bool is_comparable(T&&, U&&) {
13 return true;
14 }
15
16 struct comparable_a {};
17
18 constexpr bool operator==(const comparable_a&, const comparable_a&) {
return true; }
19
20 static_assert(is_comparable(comparable_a{}, comparable_a{}));
21
22 }
```
We get this warning on line 18: warning: function 'operator==' is not needed
and will not be emitted [-Wunneeded-internal-declaration]. If the function were
truly unneeded, I would assume I should just be able to comment out line 18 and
everything should still compile, but I would get an `error no matching function
for call to 'is_comparable'` meaning it was used.
Compiled with `bin/clang++ ~/misc/test.cpp -c -std=c++17 -Wall` from ToT clang.
I'm noticing that this compiles without warnings also if I don't wrap
everything in an unnamed namespace or mark operator== with
__attrubute__((used)).</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>