<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 - Unhelpful diagnostics when template parameters accidentally repeated after name"
href="https://bugs.llvm.org/show_bug.cgi?id=39670">39670</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Unhelpful diagnostics when template parameters accidentally repeated after name
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>comexk@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>Here is some erroneous code where the list of template parameters is
accidentally repeated after the name of the item being declared:
--
// declaration #1
template <typename T>
void foo<T>() {}
struct X {
// declaration #2
template <typename T>
void foo<T>() {}
// declaration #3
template <typename T>
using Bar<T> = int;
};
--
(I sometimes make this error because writing the template parameters after the
name is necessary in C++ for partial specializations, and always done in some
other languages.)
However, the error messages are not as helpful as they could be:
--
/tmp/foo.cpp:2:6: error: variable has incomplete type 'void'
void foo<T>() {}
^
/tmp/foo.cpp:2:9: error: expected ';' at end of declaration
void foo<T>() {}
^
;
/tmp/foo.cpp:2:9: error: expected unqualified-id
/tmp/foo.cpp:6:10: error: function template partial specialization is not
allowed
void foo<T>() {}
^ ~~~
/tmp/foo.cpp:8:5: error: cannot template a using declaration
using Bar<T> = int;
^
/tmp/foo.cpp:8:14: error: expected member name or ';' after declaration
specifiers
using Bar<T> = int;
--
Declaration #1 gets parsed as a variable declaration for some reason, even
though variable templates are equally ineligible for partial specialization.
Declaration #2 is closest to having a useful diagnostic ("function template
partial specialization is not allowed"), but it would be nice if Clang had a
more specific diagnostic suggesting removing the <T>.
For Declaration #3, the error message "cannot template a using declaration" is
outright inaccurate. It *is* possible to template a using declaration, just
not to partially specialize one.</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>