[clang] Add a C++17 deduction guide testcase.

[hokein]

Summary

From https://bugs.llvm.org/show_bug.cgi?id=47219.

It was crashing before the commit 1e14588d0f68.

[adamcz]

Thanks, adding this test is a very good idea.

clang/test/PCH/cxx17-deduction-guide-decl.cpp

16

You can drop these 3 lines, they're not needed for the crash repro. Also, c-tor doesn't have to be explicit. Probably best to keep the code as short as possible.

[hokein]

address comment, simplify the test.

clang/test/PCH/cxx17-deduction-guide-decl.cpp

16

yeah, thanks!

clang/test/PCH/cxx17-deduction-guide-decl.cpp

+// Test with pch.
+// RUN: %clang_cc1 -emit-pch -std=c++17  -o %t %s
+// RUN: %clang_cc1 -include-pch %t -emit-llvm -std=c++17 -o - %s
+
+#ifndef HEADER
+#define HEADER
+
+namespace RP47219 {
+typedef int MyInt;
+template <typename T>
+class Some {
+ public:
+  explicit Some(T, MyInt) {}
+};
+
+// Class template argument deduction
+template <typename T>
+Some(T) -> Some<T>;
+
+struct Foo {};
+void ParseNatural() {
+  Some(Foo(), 1);
+}
+}
+
+#else
+
+#endif