[PATCH] D150285: Fix CRTP partial specialization instantiation crash.

[Erich Keane via Phabricator via cfe-commits]

erichkeane created this revision.
erichkeane added reviewers: alexander-shaposhnikov, clang-language-wg.
Herald added a project: All.
erichkeane requested review of this revision.

Fixes #60778.

When instantiating the body of a class template specialization that was
instantiated from a partial specialization, we were incorrectly
collecting template arguments from the primary template, which resulted
in the template arguments list being inaccurate.  In the example from
the issue, we were trying to substitute the boolean 'false' into the
type on Nested, which caused an assertion.


https://reviews.llvm.org/D150285

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/Sema/SemaTemplateInstantiate.cpp
  clang/test/SemaTemplate/partial-spec-instantiate.cpp


Index: clang/test/SemaTemplate/partial-spec-instantiate.cpp
===================================================================
--- clang/test/SemaTemplate/partial-spec-instantiate.cpp
+++ clang/test/SemaTemplate/partial-spec-instantiate.cpp
@@ -134,3 +134,23 @@
 
   _Static_assert(S::value, "");
 }
+
+namespace GH60778 {
+  template <bool B = false> class ClassTemplate {
+  public:
+      template <typename T, typename = void> class Nested {};
+  };
+
+  template <typename DerivedType> class Base {};
+
+  template <>
+  template <typename T>
+  class ClassTemplate<>::Nested<T> : public Base<ClassTemplate<>::Nested<T>> {};
+
+  void use() {
+    // This should instantiate the body of Nested with the template arguments
+    // from the Partial Specialization. This would previously get confused and 
+    // get the template arguments from the primary template instead.
+    ClassTemplate<>::Nested<int> instantiation;
+  }
+}
Index: clang/lib/Sema/SemaTemplateInstantiate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -163,6 +163,14 @@
     assert(ClassTemplSpec->getSpecializedTemplate() && "No class template?");
     if (ClassTemplSpec->getSpecializedTemplate()->isMemberSpecialization())
       return Response::Done();
+
+    // If this was instantiated from a partial template specialization, we need
+    // to get the next level of declaration context from the partial
+    // specialization, as the ClassTemplateSpecializationDecl's
+    // DeclContext/LexicalDeclContext will be for the primary template.
+    if (auto *InstFromPartialTempl = ClassTemplSpec->getSpecializedTemplateOrPartial()
+                      .dyn_cast<ClassTemplatePartialSpecializationDecl *>())
+      return Response::ChangeDecl(InstFromPartialTempl->getLexicalDeclContext());
   }
   return Response::UseNextDecl(ClassTemplSpec);
 }
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -391,6 +391,10 @@
   at the point where it is required. This fixes:
   (`#62224 <https://github.com/llvm/llvm-project/issues/62224>`_) and
   (`#62596 <https://github.com/llvm/llvm-project/issues/62596>`_)
+- Fix an assertion when instantiating the body of a Class Template Specialization
+  when it had been instantiated from a partial template specialization with different
+  template arguments on the containing class. This fixes:
+  (`#60778 <https://github.com/llvm/llvm-project/issues/60778>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


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