[Concepts] Instantiate invented template type parameter type-constraint along with function parameters

We previously instantiated type-constraints of template type parameters along with the type parameter itself,
this caused problems when the type-constraints created by abbreviated templates refreneced other parameters
in the abbreviated templates.

When encountering a template type parameter with a type constraint, if it is implicit, delay instantiation of
the type-constraint until the function parameter which created the invented template type parameter is
instantiated.

(cherry picked from commit eacca4824463d8b96e2e1c9f8bbf886055218a16)

1 files changed, 29 insertions, 0 deletions

diff --git a/clang/test/SemaTemplate/instantiate-abbreviated-template.cpp b/clang/test/SemaTemplate/instantiate-abbreviated-template.cpp
new file mode 100644
index 00000000000..a73b6ce3610
--- /dev/null
+++ b/clang/test/SemaTemplate/instantiate-abbreviated-template.cpp
@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -std=c++2a -x c++ %s -verify
+// expected-no-diagnostics
+
+template<typename...>
+concept C = true;
+
+template<typename T>
+struct S {
+    template<typename U>
+    static void foo1(U a, auto b);
+    static void foo2(T a, C<T> auto b);
+    static void foo3(T a, C<decltype(a)> auto b);
+    static void foo4(T a, C<decltype(a)> auto b, const C<decltype(b)> auto &&c);
+};
+
+using sf1 = decltype(S<int>::foo1(1, 2));
+using sf2 = decltype(S<int>::foo2(1, 2));
+using sf3 = decltype(S<int>::foo3(1, 2));
+using sf4 = decltype(S<int>::foo4(1, 2, 3));
+
+
+template<typename... T>
+struct G {
+    static void foo1(auto a, const C<decltype(a)> auto &&... b);
+    static void foo2(auto a, const C<decltype(a), T> auto &&... b);
+};
+
+using gf1 = decltype(G<int, char>::foo1('a', 1, 2, 3, 4));
+using gf2 = decltype(G<int, char>::foo2('a', 1, 2));