1 files changed, 39 insertions, 0 deletions
diff --git a/test/SemaCXX/cxx2a-compat.cpp b/test/SemaCXX/cxx2a-compat.cpp
new file mode 100644
index 000000000000..d51f1e6aab13
--- /dev/null
+++ b/test/SemaCXX/cxx2a-compat.cpp
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -Wc++2a-compat-pedantic -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++2a -pedantic -verify %s
+
+struct A { // expected-note 0+{{candidate}}
+  A() = default; // expected-note 0+{{candidate}}
+  int x, y;
+};
+A a1 = {1, 2};
+#if __cplusplus <= 201703L
+  // expected-warning@-2 {{aggregate initialization of type 'A' with user-declared constructors is incompatible with C++2a}}
+#else
+  // expected-error@-4 {{no matching constructor}}
+#endif
+A a2 = {};
+
+struct B : A { A a; };
+B b1 = {{}, {}}; // ok
+B b2 = {1, 2, 3, 4};
+#if __cplusplus <= 201703L
+  // expected-warning@-2 2{{aggregate initialization of type 'A' with user-declared constructors is incompatible with C++2a}}
+#else
+  // expected-error@-4 2{{no viable conversion from 'int' to 'A'}}
+#endif
+
+// Essentially any use of a u8 string literal in C++<=17 is broken by C++20.
+// Just warn on all such string literals.
+struct string { string(const char*); }; // expected-note 0+{{candidate}}
+char u8arr[] = u8"hello";
+const char *u8ptr = "wo" u8"rld";
+string u8str = u8"test" u8"test";
+#if __cplusplus <= 201703L
+// expected-warning@-4 {{type of UTF-8 string literal will change}} expected-note@-4 {{remove 'u8' prefix}}
+// expected-warning@-4 {{type of UTF-8 string literal will change}} expected-note@-4 {{remove 'u8' prefix}}
+// expected-warning@-4 {{type of UTF-8 string literal will change}} expected-note@-4 {{remove 'u8' prefix}}
+#else
+// expected-error@-8 {{ISO C++20 does not permit initialization of char array with UTF-8 string literal}}
+// expected-error@-8 {{cannot initialize a variable of type 'const char *' with an lvalue of type 'const char8_t [6]'}}
+// expected-error@-8 {{no viable conversion from 'const char8_t [9]' to 'string'}}
+#endif