[Ada] Spurious error when instance of generic is used as formal package

This patch removes a spurious bug on the use of the current instance of
a generic package G as the actual in a nested instantiation of a generic
unit GU that has a formal package whose generic_package name is G. This
is only legal if G has no generic formal part, and the formal package
declaration is declared with a box or without a formal_paxkage_actual
part.

2019-07-09  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* sem_ch12.adb (Instantiate_Formal_Package): Handle properly the
	case where the actual for a formal package in an instance is the
	current instance of an enclosing generic package.
	(Check_Formal_Packages): If the formal package declaration is
	box-initialized or lacks associations altogether, no internal
	instance was created to verify conformance, and there is no
	validating package to remove from tree.

gcc/testsuite/

	* gnat.dg/generic_inst5.adb, gnat.dg/generic_inst6.adb,
	gnat.dg/generic_inst6_g1-c.adb, gnat.dg/generic_inst6_g1-c.ads,
	gnat.dg/generic_inst6_g1.ads, gnat.dg/generic_inst6_i1.ads,
	gnat.dg/generic_inst6_i2.ads, gnat.dg/generic_inst6_x.ads: New
	testcases.

From-SVN: r273275

2 files changed, 37 insertions, 3 deletions

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index b74910d..c80c9e4 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,13 @@
+2019-07-09  Ed Schonberg  <schonberg@adacore.com>
+
+	* sem_ch12.adb (Instantiate_Formal_Package): Handle properly the
+	case where the actual for a formal package in an instance is the
+	current instance of an enclosing generic package.
+	(Check_Formal_Packages): If the formal package declaration is
+	box-initialized or lacks associations altogether, no internal
+	instance was created to verify conformance, and there is no
+	validating package to remove from tree.
+
 2019-07-09  Yannick Moy  <moy@adacore.com>
 
 	* freeze.adb (Build_Renamed_Body): Do not set body to inline in
diff --git a/gcc/ada/sem_ch12.adb b/gcc/ada/sem_ch12.adb
index 0df4d96..9afa095 100644
--- a/gcc/ada/sem_ch12.adb
+++ b/gcc/ada/sem_ch12.adb
@@ -6657,9 +6657,11 @@ package body Sem_Ch12 is
                Formal_Decl := Parent (Associated_Formal_Package (E));
 
                --  Nothing to check if the formal has a box or an others_clause
-               --  (necessarily with a box).
+               --  (necessarily with a box), or no associations altogether
 
-               if Box_Present (Formal_Decl) then
+               if Box_Present (Formal_Decl)
+                 or else No (Generic_Associations (Formal_Decl))
+               then
                   null;
 
                elsif Nkind (First (Generic_Associations (Formal_Decl))) =
@@ -10309,8 +10311,11 @@ package body Sem_Ch12 is
    begin
       Analyze (Actual);
 
+      --  The actual must be a package instance, or else a current instance
+      --  such as a parent generic within the body of a generic child.
+
       if not Is_Entity_Name (Actual)
-        or else Ekind (Entity (Actual)) /= E_Package
+        or else not Ekind_In (Entity (Actual), E_Package, E_Generic_Package)
       then
          Error_Msg_N
            ("expect package instance to instantiate formal", Actual);
@@ -10354,6 +10359,14 @@ package body Sem_Ch12 is
          then
             null;
 
+         --  If this is the current instance of an enclosing generic, that
+         --  unit is the generic package we need.
+
+         elsif In_Open_Scopes (Actual_Pack)
+           and then Ekind (Actual_Pack) = E_Generic_Package
+         then
+            null;
+
          else
             Error_Msg_NE
               ("actual parameter must be instance of&", Actual, Gen_Parent);
@@ -10487,6 +10500,17 @@ package body Sem_Ch12 is
 
                Next_Entity (Actual_Ent);
             end loop;
+
+            --  No conformance to check if the generic has no formal parameters
+            --  and the formal package has no generic associations.
+
+            if Is_Empty_List (Formals)
+              and then
+                (Box_Present (Formal)
+                   or else No (Generic_Associations (Formal)))
+            then
+               return Decls;
+            end if;
          end;
 
          --  If the formal is not declared with a box, reanalyze it as an