ldionne added inline comments.
================
Comment at: clang/include/clang/Basic/DiagnosticSemaKinds.td:4683-4686
+ "Member '%0' marked with 'exclude_from_explicit_instantiation' attribute is "
+ "not defined but an explicit template instantiation declaration exists. "
+ "Reliance on this member being defined by an explicit template instantiation
"
+ "will lead to link errors.">;
----------------
rsmith wrote:
> Diagnostics should start with a lowercase letter and not end with a period.
>
> That said, I'm not sure I see why this diagnostic is correct / useful. If the
> entity is never used, then there's no link error. And if it is ever used,
> then you should get an implicit instantiation like normal, and we already
> have a diagnostic for the case where an entity is implicitly instantiated and
> no definition is available.
> Diagnostics should start with a lowercase letter and not end with a period.
Done.
> That said, I'm not sure I see why this diagnostic is correct / useful. If the
> entity is never used, then there's no link error. And if it is ever used,
> then you should get an implicit instantiation like normal, and we already
> have a diagnostic for the case where an entity is implicitly instantiated and
> no definition is available.
This is not what happens right now. If you don't provide a definition but you
try to call the function, an extern call will be produced (and that will result
in a link error because any potential explicit instantiation won't provide the
function). For example:
```
cat <<EOF | ./install/bin/clang++ -cc1 -stdlib=libc++ -xc++ -emit-llvm -o - -
template <class T>
struct Foo {
__attribute__((exclude_from_explicit_instantiation)) static void
static_member_function();
};
extern template struct Foo<int>;
int main() {
Foo<int>::static_member_function();
}
EOF
```
Results in the following LLVM IR:
```
; Function Attrs: noinline norecurse nounwind optnone
define i32 @main() #0 {
entry:
call void @_ZN3FooIiE22static_member_functionEv()
ret i32 0
}
declare void @_ZN3FooIiE22static_member_functionEv() #1
```
I guess we should be getting a warning or an error on the point of implicit
instantiation instead, or is this behavior acceptable?
================
Comment at: clang/lib/Sema/SemaTemplateInstantiate.cpp:2581-2582
+ if (Function->hasAttr<ExcludeFromExplicitInstantiationAttr>()) {
+ if (TSK == TSK_ExplicitInstantiationDeclaration &&
+ !Pattern->isDefined()) {
+ Diag(Function->getLocation(),
----------------
rsmith wrote:
> Nit: we prefer to left-align continuation lines (clang-format will do that
> for you).
Thanks for the heads up. I ran clang-format on all the lines I touched in this
file.
Repository:
rC Clang
https://reviews.llvm.org/D51789
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