[Ada] Clean up error handling of 'Image

2020-06-15  Bob Duff  <duff@adacore.com>

gcc/ada/

	* sem_attr.adb (Check_Image_Type): New procedure for checking
	the type, depending on language version. Disable the Ada 2020
	support until the corresponding expander work is done.
	(Analyze_Image_Attribute): Call Check_Image_Type.  Rearrange the
	code to be simplier and more logical.  When P_Type is modified,
	modify P_Base_Type accordingly.
	* sem_util.adb (Is_Object_Image): Do not return False if the
	prefix is a type. X'Image should be considered an image of an
	object iff X is an object (albeit illegal pre-2020 if
	nonscalar).

2 files changed, 39 insertions, 37 deletions

diff --git a/gcc/ada/sem_attr.adb b/gcc/ada/sem_attr.adb
index 2c3cd50..801c445 100644
--- a/gcc/ada/sem_attr.adb
+++ b/gcc/ada/sem_attr.adb
@@ -1414,56 +1414,65 @@ package body Sem_Attr is
       -----------------------------
 
       procedure Analyze_Image_Attribute (Str_Typ : Entity_Id) is
+         procedure Check_Image_Type (Image_Type : Entity_Id);
+         --  Check that Image_Type is legal as the type of a prefix of 'Image.
+         --  Legality depends on the Ada language version.
+
+         procedure Check_Image_Type (Image_Type : Entity_Id) is
+         begin
+            if False -- ???Disable 2020 feature until expander work is done
+              and then Ada_Version >= Ada_2020
+            then
+               null; -- all types are OK
+            elsif not Is_Scalar_Type (Image_Type) then
+               if Ada_Version >= Ada_2012 then
+                  Error_Attr_P
+                    ("prefix of % attribute must be a scalar type or a scalar "
+                       & "object name");
+               else
+                  Error_Attr_P ("prefix of % attribute must be a scalar type");
+               end if;
+            end if;
+         end Check_Image_Type;
+
+      --  Start of processing for Analyze_Image_Attribute
+
       begin
          --  AI12-0124: The ARG has adopted the GNAT semantics of 'Img for
          --  scalar types, so that the prefix can be an object, a named value,
          --  or a type. If the prefix is an object, there is no argument.
 
-         if Attr_Id = Attribute_Img
-           or else (Ada_Version >= Ada_2012 and then Is_Object_Image (P))
-         then
+         if Is_Object_Image (P) then
             Check_E0;
             Set_Etype (N, Str_Typ);
+            Check_Image_Type (Etype (P));
 
-            if Attr_Id = Attribute_Img and then not Is_Object_Image (P) then
-               Error_Attr_P
-                 ("prefix of % attribute must be a scalar object name");
+            if Attr_Id /= Attribute_Img and then Ada_Version < Ada_2012 then
+               Error_Attr_P ("prefix of % attribute must be a scalar type");
             end if;
          else
             Check_E1;
             Set_Etype (N, Str_Typ);
 
-            --  Check that the prefix type is scalar - much in the same way as
-            --  Check_Scalar_Type but with custom error messages to denote the
-            --  variants of 'Image attributes.
+            --  ???It's not clear why 'Img should behave any differently than
+            --  'Image.
 
-            if Is_Entity_Name (P)
-              and then Is_Type (Entity (P))
-              and then Ekind (Entity (P)) = E_Incomplete_Type
+            if Attr_Id = Attribute_Img then
+               Error_Attr_P
+                 ("prefix of % attribute must be a scalar object name");
+            end if;
+
+            pragma Assert (Is_Entity_Name (P) and then Is_Type (Entity (P)));
+
+            if Ekind (Entity (P)) = E_Incomplete_Type
               and then Present (Full_View (Entity (P)))
             then
                P_Type := Full_View (Entity (P));
+               P_Base_Type := Base_Type (P_Type);
                Set_Entity (P, P_Type);
             end if;
 
-            if not Is_Entity_Name (P)
-              or else not Is_Type (Entity (P))
-              or else not Is_Scalar_Type (P_Type)
-            then
-               if Ada_Version >= Ada_2012 then
-                  Error_Attr_P
-                    ("prefix of % attribute must be a scalar type or a scalar "
-                     & "object name");
-               else
-                  Error_Attr_P ("prefix of % attribute must be a scalar type");
-               end if;
-
-            elsif Is_Protected_Self_Reference (P) then
-               Error_Attr_P
-                 ("prefix of % attribute denotes current instance "
-                  & "(RM 9.4(21/2))");
-            end if;
-
+            Check_Image_Type (P_Type);
             Resolve (E1, P_Base_Type);
             Validate_Non_Static_Attribute_Function_Call;
          end if;
diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
index d7d43c9..a1bf0ae 100644
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -16797,13 +16797,6 @@ package body Sem_Util is
 
    function Is_Object_Image (Prefix : Node_Id) return Boolean is
    begin
-      --  When the type of the prefix is not scalar, then the prefix is not
-      --  valid in any scenario.
-
-      if not Is_Scalar_Type (Etype (Prefix)) then
-         return False;
-      end if;
-
       --  Here we test for the case that the prefix is not a type and assume
       --  if it is not then it must be a named value or an object reference.
       --  This is because the parser always checks that prefixes of attributes