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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Type diffing should not expand (& should maybe even contract) types to canonical form where possible"
href="http://llvm.org/bugs/show_bug.cgi?id=16613">16613</a>
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<th>Summary</th>
<td>Type diffing should not expand (& should maybe even contract) types to canonical form where possible
</td>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C++
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>dblaikie@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu, rtrieu@google.com
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Given:
template<typename T>
class foo {
};
void func(foo<std::string>);
int main() {
foo<const std::string> f;
func(f);
}
Clang prints the expanded (& then abbreviated with [...]) form of the type in
the type diff'd diagnostic:
"candidate function not viable: no known conversion from 'foo<const
basic_string<[...]>>' to 'foo<basic_string<[...]>>' for 1st argument"
It would be nice if we could print "foo<std::string>" here.
I'm not sure if it's the right thing to do, but even better would be if one of
the types was canonical & the other wasn't, but they were the same actual type,
we could still print the shorter, non-canonical type out.
(this comes from some callback-like code with type deduction:
void func(std::string);
callback<const std::string&> c = MakeCallback(func); // MakeCallback's type
uses type deduction & presumably ends up with the raw canonical type, not
std::string so even without template type diffing we print out the expanded
type rather than the std::string typedef
)
The "aka" (provided in cases where template type diffing doesn't trigger) is
useful but I fear it's noisier than necessary in many cases - especially when
the same sugared type is used on both sides of a type diff (in which case we
could at least provide a single aka, rather than redundantly print it on both
sides)</pre>
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