[PATCH] D56974: [SemaCXX] Fix ICE with structure bindings to members of template

[Daniele Di Proietto via Phabricator via cfe-commits]

ddiproietto created this revision.
ddiproietto added a reviewer: clang.
ddiproietto added a project: clang.
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Trying to use structure binding with a structure that doesn't implement
std::tuple_size, should unpack the data members. When the struct is a
template though, clang might hit an assertion (if the type has not been
completed before), because CXXRecordDecl::DefinitionData is nullptr.

This commit fixes the problem by completing the type while trying to
decompose the structured binding.

The ICE happens in real world code, for example, when trying to iterate
a protobuf generated map with a range-based for loop and structure
bindings (because google::protobuf::MapPair is a template and doesn't
support std::tuple_size).

Reported-by: nicholas.sun at nlsun.com


Repository:
  rC Clang

https://reviews.llvm.org/D56974

Files:
  clang/lib/Sema/SemaDeclCXX.cpp
  clang/test/SemaCXX/cxx1z-decomposition.cpp


Index: clang/test/SemaCXX/cxx1z-decomposition.cpp
===================================================================
--- clang/test/SemaCXX/cxx1z-decomposition.cpp
+++ clang/test/SemaCXX/cxx1z-decomposition.cpp
@@ -81,4 +81,21 @@
   void f() { static auto [a] = *this; } // expected-error {{cannot be declared 'static'}}
 };
 
+namespace instantiate_template {
+
+template <typename T1, typename T2>
+struct pair {
+  T1 a;
+  T2 b;
+};
+
+const pair<int, int> &f1();
+
+int f2() {
+  const auto &[a, b] = f1();
+  return a + b;
+}
+
+} // namespace instantiate_template
+
 // FIXME: by-value array copies
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -1300,6 +1300,10 @@
 static bool checkMemberDecomposition(Sema &S, ArrayRef<BindingDecl*> Bindings,
                                      ValueDecl *Src, QualType DecompType,
                                      const CXXRecordDecl *OrigRD) {
+  if (S.RequireCompleteType(Src->getLocation(), DecompType,
+                            diag::err_incomplete_type))
+    return true;
+
   CXXCastPath BasePath;
   DeclAccessPair BasePair =
       findDecomposableBaseClass(S, Src->getLocation(), OrigRD, BasePath);


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