c++: ICE with defaulted comparison operator [PR94478]

Here we ICE because early_check_defaulted_comparison passed a null
ctx to same_type_p.  The attached test is ill-formed according to
[class.compare.default]/1, so fixed by detecting this case early.

	PR c++/94478 - ICE with defaulted comparison operator
	* method.c (early_check_defaulted_comparison): Give an error when the
	context is null.

	* g++.dg/cpp2a/spaceship-err4.C: New test.

gcc/cp/ChangeLog

+2020-04-08  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94478 - ICE with defaulted comparison operator
+	* method.c (early_check_defaulted_comparison): Give an error when the
+	context is null.
+
 2020-04-08  Tobias Burnus  <tobias@codesourcery.com>
 
 	PR middle-end/94120

gcc/cp/method.c

@@ -1102,6 +1102,17 @@ early_check_defaulted_comparison (tree fn)
       return false;
     }
 
+  if (!ctx)
+    {
+      if (DECL_OVERLOADED_OPERATOR_IS (fn, SPACESHIP_EXPR))
+	error_at (loc, "three-way comparison operator can only be defaulted "
+		  "in a class definition");
+      else
+	error_at (loc, "equality comparison operator can only be defaulted "
+		  "in a class definition");
+      return false;
+    }
+
   if (!DECL_OVERLOADED_OPERATOR_IS (fn, SPACESHIP_EXPR)
       && !same_type_p (TREE_TYPE (TREE_TYPE (fn)), boolean_type_node))
     {

gcc/testsuite/ChangeLog

+2020-04-08  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/94478 - ICE with defaulted comparison operator
+	* g++.dg/cpp2a/spaceship-err4.C: New test.
+
 2020-04-08  Alexandre Oliva <oliva@adacore.com>
 
 	* gcc.target/arm/polytypes.c: Add quotes around

gcc/testsuite/g++.dg/cpp2a/spaceship-err4.C

+// PR c++/94478 - ICE with defaulted comparison operator.
+// { dg-do compile { target c++2a } }
+
+struct B {};
+bool operator!=(const B&, const B&) = default; // { dg-error "equality comparison operator can only be defaulted in a class definition" }
+bool operator==(const B&, const B&) = default; // { dg-error "equality comparison operator can only be defaulted in a class definition" }
+bool operator<=>(const B&, const B&) = default; // { dg-error "three-way comparison operator can only be defaulted in a class definition" }