c++: Fix implicit friend operator==.

It seems that in writing testcases for the operator<=> proposal I didn't
include any tests for implicitly declared friend operator==, and
consequently it didn't work.

2020-02-11  Jason Merrill  <jason@redhat.com>

	PR c++/93675
	* class.c (add_implicitly_declared_members): Use do_friend.
	* method.c (implicitly_declare_fn): Fix friend handling.
	(decl_remember_implicit_trigger_p): New.
	(synthesize_method): Use it.
	* decl2.c (mark_used): Use it.

gcc/cp/ChangeLog

 2020-02-11  Jason Merrill  <jason@redhat.com>
 
+	PR c++/93675
+	* class.c (add_implicitly_declared_members): Use do_friend.
+	* method.c (implicitly_declare_fn): Fix friend handling.
+	(decl_remember_implicit_trigger_p): New.
+	(synthesize_method): Use it.
+	* decl2.c (mark_used): Use it.
+
+2020-02-11  Jason Merrill  <jason@redhat.com>
+
 	PR c++/93650
 	PR c++/90691
 	* constexpr.c (maybe_constant_value): Correct earlier change.

gcc/cp/class.c

@@ -3241,6 +3241,10 @@ add_implicitly_declared_members (tree t, tree* access_decls,
       {
 	tree eq = implicitly_declare_fn (sfk_comparison, t, false, space,
 					 NULL_TREE);
+	if (DECL_FRIEND_P (space))
+	  do_friend (NULL_TREE, DECL_NAME (eq), eq,
+		     NULL_TREE, NO_SPECIAL, true);
+	else
 	  add_method (t, eq, false);
       }
 

gcc/cp/cp-tree.h

@@ -6801,6 +6801,7 @@ extern void after_nsdmi_defaulted_late_checks   (tree);
 extern bool maybe_explain_implicit_delete	(tree);
 extern void explain_implicit_non_constexpr	(tree);
 extern void deduce_inheriting_ctor		(tree);
+extern bool decl_remember_implicit_trigger_p	(tree);
 extern void synthesize_method			(tree);
 extern tree lazily_declare_fn			(special_function_kind,
 						 tree);

gcc/cp/decl2.c

@@ -5650,7 +5650,7 @@ mark_used (tree decl, tsubst_flags_t complain)
       /* Remember the current location for a function we will end up
 	 synthesizing.  Then we can inform the user where it was
 	 required in the case of error.  */
-      if (DECL_ARTIFICIAL (decl))
+      if (decl_remember_implicit_trigger_p (decl))
 	DECL_SOURCE_LOCATION (decl) = input_location;
 
       /* Synthesizing an implicitly defined member function will result in

gcc/cp/method.c

@@ -1463,6 +1463,22 @@ build_comparison_op (tree fndecl, tsubst_flags_t complain)
     --cp_unevaluated_operand;
 }
 
+/* True iff DECL is an implicitly-declared special member function with no real
+   source location, so we can use its DECL_SOURCE_LOCATION to remember where we
+   triggered its synthesis.  */
+
+bool
+decl_remember_implicit_trigger_p (tree decl)
+{
+  if (!DECL_ARTIFICIAL (decl))
+    return false;
+  special_function_kind sfk = special_function_p (decl);
+  /* Inherited constructors have the location of their using-declaration, and
+     operator== has the location of the corresponding operator<=>.  */
+  return (sfk != sfk_inheriting_constructor
+	  && sfk != sfk_comparison);
+}
+
 /* Synthesize FNDECL, a non-static member function.   */
 
 void
@@ -1479,7 +1495,7 @@ synthesize_method (tree fndecl)
 
   /* Reset the source location, we might have been previously
      deferred, and thus have saved where we were first needed.  */
-  if (DECL_ARTIFICIAL (fndecl) && !DECL_INHERITED_CTOR (fndecl))
+  if (decl_remember_implicit_trigger_p (fndecl))
     DECL_SOURCE_LOCATION (fndecl)
       = DECL_SOURCE_LOCATION (TYPE_NAME (DECL_CONTEXT (fndecl)));
 
@@ -2717,9 +2733,15 @@ implicitly_declare_fn (special_function_kind kind, tree type,
     type_set_nontrivial_flag (type, kind);
 
   /* Create the function.  */
+  if (friend_p)
+    fn_type = build_function_type (return_type, parameter_types);
+  else
+    {
       tree this_type = cp_build_qualified_type (type, this_quals);
       fn_type = build_method_type_directly (this_type, return_type,
 					    parameter_types);
+    }
+
   if (raises)
     {
       if (raises != error_mark_node)
@@ -2794,12 +2816,19 @@ implicitly_declare_fn (special_function_kind kind, tree type,
 	 inheriting constructor doesn't satisfy the requirements.  */
       constexpr_p = DECL_DECLARED_CONSTEXPR_P (inherited_ctor);
     }
+
+  if (friend_p)
+    DECL_CONTEXT (fn) = DECL_CONTEXT (pattern_fn);
+  else
+    {
       /* Add the "this" parameter.  */
       this_parm = build_this_parm (fn, fn_type, this_quals);
       DECL_CHAIN (this_parm) = DECL_ARGUMENTS (fn);
       DECL_ARGUMENTS (fn) = this_parm;
 
       grokclassfn (type, fn, kind == sfk_destructor ? DTOR_FLAG : NO_SPECIAL);
+    }
+
   DECL_IN_AGGR_P (fn) = 1;
   DECL_ARTIFICIAL (fn) = 1;
   DECL_DEFAULTED_FN (fn) = 1;

gcc/testsuite/g++.dg/cpp2a/spaceship-synth2a.C

+// Test with only spaceship defaulted.
+// { dg-do run { target c++2a } }
+
+#include <compare>
+
+struct D
+{
+  int i;
+  friend auto operator<=>(const D&, const D&) = default;
+  // friend auto operator==(const D& x, const D&) = default;
+  // friend auto operator!=(const D& x, const D&) = default;
+  // friend auto operator< (const D& x, const D&) = default;
+  // friend auto operator<=(const D& x, const D&) = default;
+  // friend auto operator> (const D& x, const D&) = default;
+  // friend auto operator>=(const D& x, const D&) = default;
+};
+
+#define assert(X) do { if (!(X)) __builtin_abort(); } while (0)
+
+int main()
+{
+  D d{42};
+  D d2{24};
+
+  assert (is_eq (d <=> d));
+  assert (is_lteq (d <=> d));
+  assert (is_gteq (d <=> d));
+  assert (is_lt (d2 <=> d));
+  assert (is_lteq (d2 <=> d));
+  assert (is_gt (d <=> d2));
+  assert (is_gteq (d <=> d2));
+
+  assert (d == d);
+  assert (!(d2 == d));
+  assert (!(d == d2));
+  assert (d != d2);
+  assert (!(d2 != d2));
+
+  assert (d2 < d);
+  assert (d2 <= d);
+  assert (d > d2);
+  assert (d >= d2);
+}

gcc/testsuite/g++.dg/cpp2a/spaceship-synth2b.C

+// Test with only spaceship defaulted.
+// { dg-do run { target c++2a } }
+
+#include <compare>
+
+struct D
+{
+  int i;
+  friend auto operator<=>(D, D) = default;
+  // friend auto operator==(D, D) = default;
+  // friend auto operator!=(D, D) = default;
+  // friend auto operator< (D, D) = default;
+  // friend auto operator<=(D, D) = default;
+  // friend auto operator> (D, D) = default;
+  // friend auto operator>=(D, D) = default;
+};
+
+#define assert(X) do { if (!(X)) __builtin_abort(); } while (0)
+
+int main()
+{
+  D d{42};
+  D d2{24};
+
+  assert (is_eq (d <=> d));
+  assert (is_lteq (d <=> d));
+  assert (is_gteq (d <=> d));
+  assert (is_lt (d2 <=> d));
+  assert (is_lteq (d2 <=> d));
+  assert (is_gt (d <=> d2));
+  assert (is_gteq (d <=> d2));
+
+  assert (d == d);
+  assert (!(d2 == d));
+  assert (!(d == d2));
+  assert (d != d2);
+  assert (!(d2 != d2));
+
+  assert (d2 < d);
+  assert (d2 <= d);
+  assert (d > d2);
+  assert (d >= d2);
+}