Factor out static_assert constexpr string extraction for reuse

The only semantics changes are slightly more vague error messages
to generalize.

gcc/cp/ChangeLog:

	* cp-tree.h (class cexpr_str): Add.
	* semantics.cc (finish_static_assert): Convert to use cexpr_str.
	(cexpr_str::type_check): Extract constexpr string code to here.
	(cexpr_str::extract): ... and here.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp26/static_assert1.C: Update to new error message.
	* g++.dg/cpp0x/udlit-error1.C: Dito.

1 files changed, 18 insertions, 0 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 1ac31d0..62718ff 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -9015,6 +9015,24 @@ struct push_access_scope_guard
   }
 };
 
+/* Extracting strings from constexpr.  */
+
+class cexpr_str
+{
+public:
+  cexpr_str (tree message) : message (message) {}
+  cexpr_str (const cexpr_str &) = delete;
+  ~cexpr_str () { XDELETEVEC (buf); }
+
+  bool type_check (location_t location);
+  bool extract (location_t location, const char * & msg, int &len);
+  tree message;
+private:
+  tree message_data = NULL_TREE;
+  tree message_sz = NULL_TREE;
+  char *buf = nullptr;
+};
+
 /* True if TYPE is an extended floating-point type.  */
 
 inline bool