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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - PCH not preserving defaults for template parameters"
href="https://bugs.llvm.org/show_bug.cgi?id=34728">34728</a>
</td>
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<tr>
<th>Summary</th>
<td>PCH not preserving defaults for template parameters
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</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>steve@obrien.cc
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Precompiling this code:
template <int foo=0, class T>
int func(T const&);
template <int foo, class T>
int func(T const&) {
return foo;
}
then using the precompiled header with `-include-pch`, with this main .cpp:
int main(int, char**) { return func(3.14); }
results in an error:
main.cpp:1:32: error: no matching function for call to 'func'
int main(int, char**) { return func(3.14); }
^~~~
/Users/steveo/pchfix/func.h:7:7: note: candidate template ignored: couldn't
infer template argument 'foo'
int func(T const&) {
^
It seems that this breaks when...
(1) there's a template function with its first arg which is defaulted, other
args after it, with no default;
(2) when the declaration (with the default, non-type value is separate),
followed by the body of the function, as it is in this example;
(3) when precompiled + used later on.
I'm not completely sure this covers all the needed conditions.
These examples somehow don't break:
// works: two defaulted non-type params
template <int foo=0, int bar=1> int func(double);
template <int foo, int bar> int func(double) { return foo; }
// works: two defaulted type params
template <class A=int, class T=double> int func(T);
template <class A, class T> int func(T) { return A(); }
// works: two type params, either kind, with defaults
template <int foo=0, class T=double> int func(T);
template <int foo, class T> int func(T) { return foo; }
// works: all-in-one decl+defn
template <class A=int, class T> int func(T) { return A(); }
// works: one default arg, all-in-one
template <class A=int> int func(double) { return A(); }
// works: one default arg, separate decl+defn
template <class A=int> int func(double);
template <class A> int func(double) { return A(); }
// works: no precompiling, everything in same main TU
template <int foo=0, class T> int func(T const&);
template <int foo, class T> int func(T const&) { return foo; }
int main(int, char**) { return func(3.14159); }</pre>
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