1 files changed, 79 insertions, 0 deletions
diff --git a/clang/test/SemaCXX/cxx2c-fold-exprs.cpp b/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
index 0674135..4806143 100644
--- a/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
+++ b/clang/test/SemaCXX/cxx2c-fold-exprs.cpp
@@ -305,3 +305,82 @@ static_assert(__is_same_as(_Three_way_comparison_result_with_tuple_like<tuple<in
 static_assert(__is_same_as(_Three_way_comparison_result_with_tuple_like<tuple<int>, 0>::type, long));
 
 }
+
+namespace GH88866 {
+
+template <typename...Ts> struct index_by;
+
+template <typename T, typename Indices>
+concept InitFunc = true;
+
+namespace ExpandsBoth {
+
+template <typename Indices, InitFunc<Indices> auto... init>
+struct LazyLitMatrix; // expected-note {{here}}
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices>> auto... init
+>
+struct LazyLitMatrix<index_by<Indices...>, init...> {
+};
+
+// FIXME: Explain why we didn't pick up the partial specialization - pack sizes don't match.
+template struct LazyLitMatrix<index_by<int, char>, 42>;
+// expected-error@-1 {{instantiation of undefined template}}
+template struct LazyLitMatrix<index_by<int, char>, 42, 43>;
+
+}
+
+namespace ExpandsRespectively {
+
+template <typename Indices, InitFunc<Indices> auto... init>
+struct LazyLitMatrix;
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices...>> auto... init
+>
+struct LazyLitMatrix<index_by<Indices...>, init...> {
+};
+
+template struct LazyLitMatrix<index_by<int, char>, 42>;
+template struct LazyLitMatrix<index_by<int, char>, 42, 43>;
+
+}
+
+namespace TypeParameter {
+
+template <typename Indices, InitFunc<Indices>... init>
+struct LazyLitMatrix; // expected-note {{here}}
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices>>... init
+>
+struct LazyLitMatrix<index_by<Indices...>, init...> {
+};
+
+// FIXME: Explain why we didn't pick up the partial specialization - pack sizes don't match.
+template struct LazyLitMatrix<index_by<int, char>, float>;
+// expected-error@-1 {{instantiation of undefined template}}
+template struct LazyLitMatrix<index_by<int, char>, unsigned, float>;
+
+}
+
+namespace Invalid {
+
+template <typename Indices, InitFunc<Indices>... init>
+struct LazyLitMatrix;
+
+template <
+    typename...Indices,
+    InitFunc<index_by<Indices>> init
+    // expected-error@-1 {{unexpanded parameter pack 'Indices'}}
+>
+struct LazyLitMatrix<index_by<Indices...>, init> {
+};
+
+}
+
+}