Ignore artificial fields in Ada

A user found an unusual Ada situation that DWARF does not readily
support.  Consider this type:

   type Discrete_Typ is tagged null record;
   type Int_Typ (Is_Static : Boolean) is new Discrete_Typ with null record;

   type Signed_Int_Typ (Is_Static : Boolean) is
      new Int_Typ (Is_Static => Is_Static)
                    with record
      case Is_Static is
         when True =>
            Field : Integer;
         when others =>
            null;
      end case;
   end record;

Here, Signed_Int_Typ has a variant part where the discriminant is
stored in a superclass.

Anyway, this code caused gnat-llvm to crash.  While fixing the crash,
I decided to fix this by emitting an anonymous field in Signed_Int_Typ
that represents the discriminant.  This would allow member DIEs to
refer to it -- which I suppose is possibly why DWARF specified that
the discriminant should be a member of the variant (though I don't
really know; this decision always seemed very strange to me).

Making the field anonymous lead to the strange error:

    Type ... is not a structure or union type.

... which comes from lookup_struct_elt, which fails when an anonymous
member of a structure has a non-composite type.  This patch includes a
fix for this issue.

After fixing that, though I decided it would be better if the
artificial discriminant were still given a name.  So, this patch
includes a change to ada_is_ignored_field to ignore artificial fields.

Approved-By: Andrew Burgess <aburgess@redhat.com>

gdb/ada-lang.c

@@ -6261,10 +6261,12 @@ ada_is_ignored_field (struct type *type, int field_num)
   {
     const char *name = type->field (field_num).name ();
 
-    /* Anonymous field names should not be printed.
-       brobecker/2007-02-20: I don't think this can actually happen
-       but we don't want to print the value of anonymous fields anyway.  */
-    if (name == NULL)
+    /* Anonymous field names should not be printed.  */
+    if (name == nullptr || name[0] == '\0')
+      return 1;
+
+    /* Skip artificial fields.  */
+    if (type->field (field_num).is_artificial ())
       return 1;
 
     /* Normally, fields whose name start with an underscore ("_")

gdb/gdbtypes.c

@@ -1821,12 +1821,18 @@ lookup_struct_elt (struct type *type, const char *name, int noerr)
 	}
       else if (!t_field_name || *t_field_name == '\0')
 	{
-	  struct_elt elt
-	    = lookup_struct_elt (type->field (i).type (), name, 1);
-	  if (elt.field != NULL)
+	  struct type *field_type = type->field (i).type ();
+	  enum type_code field_code = check_typedef (field_type)->code ();
+
+	  if (field_code == TYPE_CODE_STRUCT || field_code == TYPE_CODE_UNION)
 	    {
-	      elt.offset += type->field (i).loc_bitpos ();
-	      return elt;
+	      struct_elt elt
+		= lookup_struct_elt (type->field (i).type (), name, 1);
+	      if (elt.field != NULL)
+		{
+		  elt.offset += type->field (i).loc_bitpos ();
+		  return elt;
+		}
 	    }
 	}
     }

gdb/testsuite/gdb.dwarf2/ada-artificial-field.c

@@ -0,0 +1,22 @@
+/* Copyright 2025 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+unsigned char bytes[] = { 1, 2, 3 };
+
+int
+main (void)
+{
+  return 0;
+}

gdb/testsuite/gdb.dwarf2/ada-artificial-field.exp

@@ -0,0 +1,95 @@
+# Copyright 2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that Ada does not display artificial fields.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+require dwarf2_support
+
+standard_testfile .c -dw.S
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    cu {} {
+	DW_TAG_compile_unit {
+	    DW_AT_language @DW_LANG_Ada95
+	    DW_AT_name fd.adb
+	    DW_AT_comp_dir /tmp
+	} {
+	    declare_labels byte array disc struct
+
+	    byte: DW_TAG_base_type {
+		DW_AT_byte_size 1 DW_FORM_sdata
+		DW_AT_encoding @DW_ATE_unsigned
+		DW_AT_name byte
+	    }
+
+	    struct: DW_TAG_structure_type {
+		DW_AT_name anonfield
+		DW_AT_byte_size 3 DW_FORM_sdata
+	    } {
+		DW_TAG_member {
+		    DW_AT_name one
+		    DW_AT_type :$byte
+		    DW_AT_data_member_location 0 DW_FORM_sdata
+		}
+		DW_TAG_member {
+		    DW_AT_name discr
+		    DW_AT_type :$byte
+		    DW_AT_data_member_location 1 DW_FORM_sdata
+		    DW_AT_artificial 1 DW_FORM_flag
+		}
+		DW_TAG_member {
+		    DW_AT_type :$byte
+		    DW_AT_data_member_location 1 DW_FORM_sdata
+		}
+		DW_TAG_member {
+		    DW_AT_name two
+		    DW_AT_type :$byte
+		    DW_AT_data_member_location 2 DW_FORM_sdata
+		}
+	    }
+
+	    DW_TAG_variable {
+		DW_AT_name "value"
+		DW_AT_type :$struct
+		DW_AT_external 1 DW_FORM_flag
+		DW_AT_location {
+		    DW_OP_addr [gdb_target_symbol "bytes"]
+		} SPECIAL_expr
+	    }
+	}
+    }
+}
+
+if {[prepare_for_testing ${testfile}.exp ${testfile} \
+	 [list $srcfile $asm_file] {nodebug}]} {
+    return
+}
+
+gdb_test_no_output "set language ada"
+
+gdb_test "print value" \
+    [string_to_regexp " = (one => 1, two => 3)"]
+
+gdb_test "ptype value" \
+    [multi_line \
+	 "type = record" \
+	 "    one: byte;" \
+	 "    two: byte;" \
+	 "end record"]