c++: parse trivial DMI immediately [PR96645]

The recent change to reject __is_constructible for nested classes with DMI
is, unsurprisingly, breaking some code.  Let's allow simple cases by
immediately parsing DMI that do no name lookup; then being in complete class
scope makes no difference.

	PR c++/96645

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_early_parsing_nsdmi): New.
	(cp_parser_member_declaration): Call it.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/nsdmi10.C: Now OK.
	* g++.dg/ext/is_constructible3.C: Likewise.
	* g++.dg/ext/is_constructible7.C: Likewise.

4 files changed, 31 insertions, 6 deletions

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 7e1c777..63c8af1 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -2701,6 +2701,8 @@ static tree cp_parser_late_parse_one_default_arg
   (cp_parser *, tree, tree, tree);
 static void cp_parser_late_parsing_nsdmi
   (cp_parser *, tree);
+static bool cp_parser_early_parsing_nsdmi
+  (cp_parser *, tree);
 static void cp_parser_late_parsing_default_args
   (cp_parser *, tree);
 static tree cp_parser_sizeof_operand
@@ -27478,7 +27480,8 @@ cp_parser_member_declaration (cp_parser* parser)
 	      if (DECL_DECLARES_FUNCTION_P (decl))
 		cp_parser_save_default_args (parser, STRIP_TEMPLATE (decl));
 	      else if (TREE_CODE (decl) == FIELD_DECL
-		       && DECL_INITIAL (decl))
+		       && DECL_INITIAL (decl)
+		       && !cp_parser_early_parsing_nsdmi (parser, decl))
 		/* Add DECL to the queue of NSDMI to be parsed later.  */
 		vec_safe_push (unparsed_nsdmis, decl);
 	    }
@@ -32292,6 +32295,29 @@ cp_parser_late_parsing_nsdmi (cp_parser *parser, tree field)
   DECL_INITIAL (field) = def;
 }
 
+/* If the DEFERRED_PARSE for FIELD is safe to parse immediately, do so.
+   Returns true if deferred parsing is no longer needed.  */
+
+static bool
+cp_parser_early_parsing_nsdmi (cp_parser *parser, tree field)
+{
+  tree init = DECL_INITIAL (field);
+  if (TREE_CODE (init) != DEFERRED_PARSE)
+    return true;
+
+  cp_token_cache *tokens = DEFPARSE_TOKENS (init);
+  for (cp_token *p = tokens->first; p != tokens->last; ++p)
+    if (p->type == CPP_NAME
+	|| p->keyword == RID_THIS
+	|| p->keyword == RID_OPERATOR)
+      /* There's a name to look up or 'this', give up.  */
+      return false;
+
+  /* It's trivial, parse now.  */
+  cp_parser_late_parsing_nsdmi (parser, field);
+  return true;
+}
+
 /* FN is a FUNCTION_DECL which may contains a parameter with an
    unparsed DEFERRED_PARSE.  Parse the default args now.  This function
    assumes that the current scope is the scope in which the default
diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
index d8588b7..a965f7b 100644
--- a/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
+++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi10.C
@@ -6,7 +6,7 @@ struct A1 {
     int y1 = 1;
   };
 
-  A1(const B1& opts = B1()) {}  // { dg-error "default member initializer" }
+  A1(const B1& opts = B1()) {}
 };
 
 struct A2 {
@@ -14,5 +14,5 @@ struct A2 {
     int x2, y2 = 1;
   };
 
-  A2(const B2& opts = B2()) {}  // { dg-error "default member initializer" }
+  A2(const B2& opts = B2()) {}
 };
diff --git a/gcc/testsuite/g++.dg/ext/is_constructible3.C b/gcc/testsuite/g++.dg/ext/is_constructible3.C
index 305751d..c7c5874 100644
--- a/gcc/testsuite/g++.dg/ext/is_constructible3.C
+++ b/gcc/testsuite/g++.dg/ext/is_constructible3.C
@@ -8,7 +8,7 @@ struct A {
     B() = default;
   };
 
-  static constexpr bool v = __is_constructible (B); // { dg-error "member initializer" }
+  static constexpr bool v = __is_constructible (B);
 
 };
 
diff --git a/gcc/testsuite/g++.dg/ext/is_constructible7.C b/gcc/testsuite/g++.dg/ext/is_constructible7.C
index 76a63bb..013a1df 100644
--- a/gcc/testsuite/g++.dg/ext/is_constructible7.C
+++ b/gcc/testsuite/g++.dg/ext/is_constructible7.C
@@ -12,7 +12,7 @@ using true_type = bool_constant<true>;
 
 template<typename T>
 struct is_default_constructible
-  : bool_constant<__is_constructible(T)> // { dg-error "default member init" }
+  : bool_constant<__is_constructible(T)>
 { };
 
 void testVarStruct()
@@ -22,7 +22,6 @@ void testVarStruct()
       int number = 5; // compiles, if remove initialization
     };
 
-    // { dg-prune-output "could not convert" }
     is_default_constructible<A>::type t = true_type{};
   };
 }