[Ada] Incorrect ineffective use type clause warning

This patch fixes an issue in the compiler whereby a use_type_clause
incorrectly gets flagged as ineffective when the use of it comes after a
generic package instantiation where the installation of private use
clauses are required and one such clause references the same type.

gcc/ada/

	* sem_ch8.adb (Use_One_Type): Remove code in charge of setting
	Current_Use_Clause when Id is known to be redundant, and modify
	the printing of errors associated with redundant use type
	clauses so that line number gets included in more cases.

1 files changed, 72 insertions, 109 deletions

diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
index 786df01..1818778 100644
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -10571,20 +10571,6 @@ package body Sem_Ch8 is
       --  even if it is redundant at the place of the instantiation.
 
       elsif Redundant_Use (Id) then
-
-         --  We must avoid incorrectly setting the Current_Use_Clause when we
-         --  are working with a redundant clause that has already been linked
-         --  in the Prev_Use_Clause chain, otherwise the chain will break.
-
-         if Present (Current_Use_Clause (T))
-           and then Present (Prev_Use_Clause (Current_Use_Clause (T)))
-           and then Parent (Id) = Prev_Use_Clause (Current_Use_Clause (T))
-         then
-            null;
-         else
-            Set_Current_Use_Clause (T, Parent (Id));
-         end if;
-
          Set_Used_Operations (Parent (Id), New_Elmt_List);
 
       --  If the subtype mark designates a subtype in a different package,
@@ -10689,121 +10675,98 @@ package body Sem_Ch8 is
                --  Start of processing for Use_Clause_Known
 
                begin
-                  --  If both current use_type_clause and the use_type_clause
-                  --  for the type are at the compilation unit level, one of
-                  --  the units must be an ancestor of the other, and the
-                  --  warning belongs on the descendant.
-
-                  if Nkind (Parent (Clause1)) = N_Compilation_Unit
-                       and then
-                     Nkind (Parent (Clause2)) = N_Compilation_Unit
-                  then
-                     --  If the unit is a subprogram body that acts as spec,
-                     --  the context clause is shared with the constructed
-                     --  subprogram spec. Clearly there is no redundancy.
-
-                     if Clause1 = Clause2 then
-                        return;
-                     end if;
+                  --  If the unit is a subprogram body that acts as spec, the
+                  --  context clause is shared with the constructed subprogram
+                  --  spec. Clearly there is no redundancy.
 
-                     Unit1 := Unit (Parent (Clause1));
-                     Unit2 := Unit (Parent (Clause2));
+                  if Clause1 = Clause2 then
+                     return;
+                  end if;
 
-                     --  If both clauses are on same unit, or one is the body
-                     --  of the other, or one of them is in a subunit, report
-                     --  redundancy on the later one.
+                  Unit1 := Unit (Enclosing_Comp_Unit_Node (Clause1));
+                  Unit2 := Unit (Enclosing_Comp_Unit_Node (Clause2));
 
-                     if Unit1 = Unit2 or else Nkind (Unit1) = N_Subunit then
-                        Error_Msg_Sloc := Sloc (Current_Use_Clause (T));
-                        Error_Msg_NE -- CODEFIX
-                          ("& is already use-visible through previous "
-                           & "use_type_clause #??", Clause1, T);
-                        return;
-
-                     elsif Nkind (Unit2) in N_Package_Body | N_Subprogram_Body
-                       and then Nkind (Unit1) /= Nkind (Unit2)
-                       and then Nkind (Unit1) /= N_Subunit
-                     then
-                        Error_Msg_Sloc := Sloc (Clause1);
-                        Error_Msg_NE -- CODEFIX
-                          ("& is already use-visible through previous "
-                           & "use_type_clause #??", Current_Use_Clause (T), T);
-                        return;
-                     end if;
+                  --  If both clauses are on same unit, or one is the body of
+                  --  the other, or one of them is in a subunit, report
+                  --  redundancy on the later one.
 
-                     --  There is a redundant use_type_clause in a child unit.
-                     --  Determine which of the units is more deeply nested.
-                     --  If a unit is a package instance, retrieve the entity
-                     --  and its scope from the instance spec.
+                  if Unit1 = Unit2
+                    or else Nkind (Unit1) = N_Subunit
+                    or else
+                      (Nkind (Unit2) in N_Package_Body | N_Subprogram_Body
+                        and then Nkind (Unit1) /= Nkind (Unit2)
+                        and then Nkind (Unit1) /= N_Subunit)
+                  then
+                     Error_Msg_Sloc := Sloc (Clause1);
+                     Error_Msg_NE -- CODEFIX
+                       ("& is already use-visible through previous "
+                        & "use_type_clause #??", Clause2, T);
+                     return;
+                  end if;
 
-                     Ent1 := Entity_Of_Unit (Unit1);
-                     Ent2 := Entity_Of_Unit (Unit2);
+                  --  There is a redundant use_type_clause in a child unit.
+                  --  Determine which of the units is more deeply nested. If a
+                  --  unit is a package instance, retrieve the entity and its
+                  --  scope from the instance spec.
 
-                     if Scope (Ent2) = Standard_Standard then
-                        Error_Msg_Sloc := Sloc (Current_Use_Clause (T));
-                        Err_No := Clause1;
+                  Ent1 := Entity_Of_Unit (Unit1);
+                  Ent2 := Entity_Of_Unit (Unit2);
 
-                     elsif Scope (Ent1) = Standard_Standard then
-                        Error_Msg_Sloc := Sloc (Id);
-                        Err_No := Clause2;
+                  if Scope (Ent2) = Standard_Standard then
+                     Error_Msg_Sloc := Sloc (Clause2);
+                     Err_No := Clause1;
 
-                     --  If both units are child units, we determine which one
-                     --  is the descendant by the scope distance to the
-                     --  ultimate parent unit.
+                  elsif Scope (Ent1) = Standard_Standard then
+                     Error_Msg_Sloc := Sloc (Id);
+                     Err_No := Clause2;
 
-                     else
-                        declare
-                           S1 : Entity_Id;
-                           S2 : Entity_Id;
-
-                        begin
-                           S1 := Scope (Ent1);
-                           S2 := Scope (Ent2);
-                           while Present (S1)
-                             and then Present (S2)
-                             and then S1 /= Standard_Standard
-                             and then S2 /= Standard_Standard
-                           loop
-                              S1 := Scope (S1);
-                              S2 := Scope (S2);
-                           end loop;
+                  --  If both units are child units, we determine which one is
+                  --  the descendant by the scope distance to the ultimate
+                  --  parent unit.
 
-                           if S1 = Standard_Standard then
-                              Error_Msg_Sloc := Sloc (Id);
-                              Err_No := Clause2;
-                           else
-                              Error_Msg_Sloc := Sloc (Current_Use_Clause (T));
-                              Err_No := Clause1;
-                           end if;
-                        end;
-                     end if;
+                  else
+                     declare
+                        S1 : Entity_Id;
+                        S2 : Entity_Id;
 
-                     if Parent (Id) /= Err_No then
-                        if Most_Descendant_Use_Clause
-                             (Err_No, Parent (Id)) = Parent (Id)
-                        then
-                           Error_Msg_Sloc := Sloc (Err_No);
-                           Err_No := Parent (Id);
+                     begin
+                        S1 := Scope (Ent1);
+                        S2 := Scope (Ent2);
+                        while Present (S1)
+                          and then Present (S2)
+                          and then S1 /= Standard_Standard
+                          and then S2 /= Standard_Standard
+                        loop
+                           S1 := Scope (S1);
+                           S2 := Scope (S2);
+                        end loop;
+
+                        if S1 = Standard_Standard then
+                           Error_Msg_Sloc := Sloc (Id);
+                           Err_No := Clause2;
+                        else
+                           Error_Msg_Sloc := Sloc (Clause2);
+                           Err_No := Clause1;
                         end if;
+                     end;
+                  end if;
 
-                        Error_Msg_NE -- CODEFIX
-                          ("& is already use-visible through previous "
-                           & "use_type_clause #??", Err_No, Id);
+                  if Parent (Id) /= Err_No then
+                     if Most_Descendant_Use_Clause
+                          (Err_No, Parent (Id)) = Parent (Id)
+                     then
+                        Error_Msg_Sloc := Sloc (Err_No);
+                        Err_No := Parent (Id);
                      end if;
 
-                  --  Case where current use_type_clause and use_type_clause
-                  --  for the type are not both at the compilation unit level.
-                  --  In this case we don't have location information.
-
-                  else
                      Error_Msg_NE -- CODEFIX
                        ("& is already use-visible through previous "
-                        & "use_type_clause??", Id, T);
+                        & "use_type_clause #??", Err_No, Id);
                   end if;
                end Use_Clause_Known;
 
-            --  Here if Current_Use_Clause is not set for T, another case where
-            --  we do not have the location information available.
+            --  Here Current_Use_Clause is not set for T, so we do not have the
+            --  location information available.
 
             else
                Error_Msg_NE -- CODEFIX