rsmith added a comment.
I think you'll also need to update the `ASTDeclReader` to merge `VarDecl`
definitions together if it reads a definition and there already is one in the
AST. I note that right now `Sema::AddInitializerToDecl` permits multiple
definitions of a `VarDecl`, which doesn't seem like what we want here; we'll
probably want to merge those as we parse them, too.
Now, we have a problem here: unlike with classes and functions, we can't always
convert a variable definition to a declaration by just dropping the
initializer. Perhaps we can add a flag to `VarDecl` to indicate "this is just a
declaration, even though it looks like a definition", to handle that case?
(This would also be useful for `VarTemplateSpecializationDecl`s, where we
currently reject valid code such as "template<typename> int n; int k = n<int>;"
because we have no way to represent the difference between a mere declaration
and a definition of `n<int>`.)
================
Comment at: lib/Sema/SemaTemplate.cpp:505
@@ -499,3 +504,3 @@
Instantiation->setInvalidDecl();
} else if (InstantiatedFromMember) {
if (isa<FunctionDecl>(Instantiation)) {
----------------
Why do we not issue a diagnostic in this case for a `VarDecl` when `Complain`
is true and no definition is available? It seems like we should either be
diagnosing this or asserting that it can't happen.
================
Comment at: lib/Sema/SemaTemplate.cpp:528
@@ +527,3 @@
+ Note = diag::note_template_decl_here;
+ } else if (isa<VarDecl>(Instantiation)) {
+ if (isa<VarTemplateSpecializationDecl>(Instantiation)) {
----------------
`else` + `assert` would make more sense here. No other kind of declaration
should get here.
================
Comment at: lib/Sema/SemaType.cpp:6898-6899
@@ +6897,4 @@
+ } else if (auto *VD = dyn_cast<VarDecl>(D)) {
+ // FIXME: Handle the case where D is a VarTemplateSpecializationDecl, i.e.
D
+ // is not a static data member.
+ if (auto *Pattern = VD->getInstantiatedFromStaticDataMember())
----------------
We should add a `getTemplateInstantiationPattern()` to `VarDecl` and use it
from here.
https://reviews.llvm.org/D24508
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