[C++20] [Modules] Handle reachability for deduction guide

Previously, we forget to handle reachability for deduction guide.
The deduction guide is a hint to the compiler. And the deduction guide
should be able to use if the corresponding template decl is reachable.

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 47c7a61..aa87a33 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -2087,6 +2087,13 @@ bool LookupResult::isAvailableForLookup(Sema &SemaRef, NamedDecl *ND) {
   if (isVisible(SemaRef, ND))
     return true;
 
+  // Deduction guide lives in namespace scope generally, but it is just a
+  // hint to the compilers. What we actually lookup for is the generated member
+  // of the corresponding template. So it is sufficient to check the
+  // reachability of the template decl.
+  if (auto *DeductionGuide = ND->getDeclName().getCXXDeductionGuideTemplate())
+    return SemaRef.hasReachableDefinition(DeductionGuide);
+
   auto *DC = ND->getDeclContext();
   // If ND is not visible and it is at namespace scope, it shouldn't be found
   // by name lookup.