c++: CWG 2359, wrong copy-init with designated init [PR91319]

This CWG clarifies that designated initializer support direct-initialization.
Just be careful what Note 2 in [dcl.init.aggr]/4.2 says: "If the
initialization is by designated-initializer-clause, its form determines
whether copy-initialization or direct-initialization is performed."  Hence
this patch sets CONSTRUCTOR_IS_DIRECT_INIT only when we are dealing with
".x{}", but not ".x = {}".

	PR c++/91319

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_initializer_list): Set CONSTRUCTOR_IS_DIRECT_INIT
	when the designated initializer is of the .x{} form.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/desig30.C: New test.

2 files changed, 31 insertions, 0 deletions

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index a192065..86c0bb1 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -25892,6 +25892,7 @@ cp_parser_initializer_list (cp_parser* parser, bool* non_constant_p,
       tree designator;
       tree initializer;
       bool clause_non_constant_p;
+      bool direct_p = false;
       location_t loc = cp_lexer_peek_token (parser->lexer)->location;
 
       /* Handle the C++20 syntax, '. id ='.  */
@@ -25914,6 +25915,8 @@ cp_parser_initializer_list (cp_parser* parser, bool* non_constant_p,
 	  if (cp_lexer_next_token_is (parser->lexer, CPP_EQ))
 	    /* Consume the `='.  */
 	    cp_lexer_consume_token (parser->lexer);
+	  else
+	    direct_p = true;
 	}
       /* Also, if the next token is an identifier and the following one is a
 	 colon, we are looking at the GNU designated-initializer
@@ -25991,6 +25994,12 @@ cp_parser_initializer_list (cp_parser* parser, bool* non_constant_p,
       if (clause_non_constant_p && non_constant_p)
 	*non_constant_p = true;
 
+      if (TREE_CODE (initializer) == CONSTRUCTOR)
+	/* This uses |= rather than = because C_I_D_I could have been set in
+	   cp_parser_functional_cast so we must be careful not to clear the
+	   flag.  */
+	CONSTRUCTOR_IS_DIRECT_INIT (initializer) |= direct_p;
+
       /* If we have an ellipsis, this is an initializer pack
 	 expansion.  */
       if (cp_lexer_next_token_is (parser->lexer, CPP_ELLIPSIS))
diff --git a/gcc/testsuite/g++.dg/cpp2a/desig30.C b/gcc/testsuite/g++.dg/cpp2a/desig30.C
new file mode 100644
index 0000000..d9292df
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/desig30.C
@@ -0,0 +1,22 @@
+// PR c++/91319
+// { dg-do compile { target c++20 } }
+
+struct X {
+    explicit X() { }
+};
+
+struct Aggr {
+    X x;
+};
+
+Aggr
+f ()
+{
+  return Aggr{.x{}};
+}
+
+Aggr
+f2 ()
+{
+  return Aggr{.x = {}}; // { dg-error "explicit constructor" }
+}