================
@@ -9180,6 +9180,12 @@ bool Sema::hasAcceptableDefinition(NamedDecl *D,
NamedDecl **Suggested,
if (!getLangOpts().Modules && !getLangOpts().ModulesLocalVisibility)
return true;
+ // The external source may have additional definitions of this entity that
are
+ // visible, so complete the redeclaration chain now.
+ if (auto *Source = Context.getExternalSource()) {
+ Source->CompleteRedeclChain(D);
+ }
----------------
mpark wrote:
Further findings: in this case, what I'm seeing is that
[`LazyGenerationalUpdatePtr::get`](https://github.com/llvm/llvm-project/blob/main/clang/include/clang/AST/ExternalASTSource.h#L487-L497)
is called twice for [4].
The first invocation, the generation numbers don't match, and
`CompleteRedeclChain` is called (*outside* of the deserialization stage) and
gets to
[`DC->lookup(Name);`](https://github.com/llvm/llvm-project/blob/c6d95c441a29a45782ff72d6cb82839b86fd0e4a/clang/lib/Serialization/ASTReader.cpp#L7862).
We don't discover the definition in the first invocation.
The second invocation is from
[here](https://github.com/llvm/llvm-project/blob/c6d95c441a29a45782ff72d6cb82839b86fd0e4a/clang/lib/Sema/SemaType.cpp#L9174)
(via the `getMostRecentDecl()` call within `getDefinition`). This time, the
generation numbers **match**, and `CompleteRedeclChain` is **not** called.
However, if I explicitly invoke `CompleteRedeclChain` on it, it gets to the
same `DC->lookup(Name);` line as before with exactly the same values for `DC`
and `Name`. However, this time the definition **is** found. To be clear, this
is invoking `CompleteRedeclChain` on [4] **directly** rather than on [1], [2]
or [3], and also not **indirectly** via something like `getMostRecentDecl()` or
`redecls()` since `CompleteRedeclChain` will not be called through those
functions because the generation numbers match.
In short, I'm seeing that the `DC->lookup(Name)` has different behaviors
between two invocations, without either generation numbers changing. I wonder
if maybe another module was loaded in between the two calls, and the
`ExternalASTSource`'s generation number should have been incremented but it
wasn't for some reason...
https://github.com/llvm/llvm-project/pull/129982
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