[gcc r13-548] [Ada] Subprogram renaming fails to hide homograph

[Pierre-Marie de Rodat <pmderodat@gcc.gnu.org>]

https://gcc.gnu.org/g:de0665fc7f195e12ede10abb6a98b10011e70807

commit r13-548-gde0665fc7f195e12ede10abb6a98b10011e70807
Author: Gary Dismukes <dismukes@adacore.com>
Date:   Mon Mar 28 19:15:30 2022 -0400

    [Ada] Subprogram renaming fails to hide homograph
    
    The compiler failed to detect an error where the first prefix of an
    expanded name given as the renamed subprogram in a subprogram renaming
    declaration denotes a unit with the same name as the name given for the
    subprogram renaming. Such a unit must be hidden by the renaming itself.
    An error check is added to catch this case.
    
    gcc/ada/
    
            * sem_ch8.adb (Analyze_Subprogram_Renaming): Add error check for
            the case of a renamed subprogram given by an expanded name whose
            outermost prefix names a unit that is hidden by the name of the
            renaming.
            (Ult_Expanded_Prefix): New local expression function to return
            the ultimate prefix of an expanded name.

Diff:
---
 gcc/ada/sem_ch8.adb | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/gcc/ada/sem_ch8.adb b/gcc/ada/sem_ch8.adb
index 60c2ce6e3bc..1cf34117a30 100644
--- a/gcc/ada/sem_ch8.adb
+++ b/gcc/ada/sem_ch8.adb
@@ -3967,6 +3967,31 @@ package body Sem_Ch8 is
                  ("implicit operation& is not visible (RM 8.3 (15))",
                   Nam, Old_S);
             end if;
+
+         --  Check whether an expanded name used for the renamed subprogram
+         --  begins with the same name as the renaming itself, and if so,
+         --  issue an error about the prefix being hidden by the renaming.
+         --  We exclude generic instances from this checking, since such
+         --  normally illegal renamings can be constructed when expanding
+         --  instantiations.
+
+         elsif Nkind (Nam) = N_Expanded_Name then
+            declare
+               function Ult_Expanded_Prefix (N : Node_Id) return Node_Id is
+                 (if Nkind (N) /= N_Expanded_Name
+                  then N
+                  else Ult_Expanded_Prefix (Prefix (N)));
+               --  Returns the ultimate prefix of an expanded name
+
+            begin
+               if Chars (Entity (Ult_Expanded_Prefix (Nam))) = Chars (New_S)
+                 and then not In_Instance
+               then
+                  Error_Msg_Sloc := Sloc (N);
+                  Error_Msg_NE
+                    ("& is hidden by declaration#", Nam, New_S);
+               end if;
+            end;
          end if;
 
          Set_Convention (New_S, Convention (Old_S));