[c++20] Implement P0482R6: enable -fchar8_t by default in C++20 mode.
This unfortunately results in a substantial breaking change when
switching to C++20, but it's not yet clear what / how much we should
do about that. We may want to add a compatibility conversion from
u8 string literals to const char*, similar to how C++98 provided a
compatibility conversion from string literals to non-const char*,
but that's not handled by this patch.
The feature can be disabled in C++20 mode with -fno-char8_t.
llvm-svn: 346892
diff --git a/clang/test/SemaCXX/cxx2a-compat.cpp b/clang/test/SemaCXX/cxx2a-compat.cpp
index 53043d6..d51f1e6 100644
--- a/clang/test/SemaCXX/cxx2a-compat.cpp
+++ b/clang/test/SemaCXX/cxx2a-compat.cpp
@@ -21,3 +21,19 @@
#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