[Ada] Spurious error on discriminant of incomplete type

[Pierre-Marie de Rodat <derodat at adacore dot com>]

This patch corrects the conformance verification of discriminants to
provide symmetry between the analysis of incomplete and full view
discriminants. As a result, types of discriminants always resolve to the
proper view.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-07-10  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* sem_ch6.adb (Check_Discriminant_Conformance): Use Find_Type to
	discover the type of a full view discriminant.

gcc/testsuite/

	* gnat.dg/incomplete7.adb, gnat.dg/incomplete7.ads: New testcase.

--- gcc/ada/sem_ch6.adb
+++ gcc/ada/sem_ch6.adb
@@ -5960,7 +5960,7 @@ package body Sem_Ch6 is
               Access_Definition (N, Discriminant_Type (New_Discr));
 
          else
-            Analyze (Discriminant_Type (New_Discr));
+            Find_Type (Discriminant_Type (New_Discr));
             New_Discr_Type := Etype (Discriminant_Type (New_Discr));
 
             --  Ada 2005: if the discriminant definition carries a null

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/incomplete7.adb
@@ -0,0 +1,5 @@
+--  { dg-do compile }
+
+package body Incomplete7 is
+   procedure Foo is null;
+end Incomplete7;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/incomplete7.ads
@@ -0,0 +1,31 @@
+package Incomplete7 is
+   type Color;
+   type Color is (red, green, blue);
+
+   type Action (C : Color := Color'(red));
+   type Action (C : Color := Color'(red)) is record
+      case C is
+         when red =>
+            Stop_Time : Positive;
+
+         when others =>
+            Go_For_It : Integer;
+      end case;
+   end record;
+
+   type Num;
+   type Num is new Integer;
+
+   type Rec (N : Num := Num'(1));
+   type Rec (N : Num := Num'(1)) is record
+      case N is
+         when 1 =>
+            One : Integer;
+
+         when others =>
+            null;
+      end case;
+   end record;
+
+   procedure Foo;
+end Incomplete7;