Be more careful when rewriting thick pointer array type

To handle thick pointers with -fgnat-encodings=minimal, gdb will
rewrite the underlying array type to remove the bounds.  However, if
the same DWARF type is used both for a thick pointer and for an
ordinary array, this will have the side effect of removing the bounds
from the array.  This breaks the printing of objects of this type.

This patch fixes the problem by copying the array type, its range, and
its bounds.

gdb/ChangeLog
2020-12-14  Tom Tromey  <tromey@adacore.com>

	* dwarf2/read.c (rewrite_array_type): New function.
        (quirk_ada_thick_pointer_struct): Use rewrite_array_type.

gdb/testsuite/ChangeLog
2020-12-14  Tom Tromey  <tromey@adacore.com>

	* gdb.dwarf2/ada-thick-pointer.exp: New file.

1 files changed, 58 insertions, 13 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 91f669b..4edd8d4 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -15890,6 +15890,55 @@ quirk_gcc_member_function_pointer (struct type *type, struct objfile *objfile)
   smash_to_methodptr_type (type, new_type);
 }
 
+/* Helper for quirk_ada_thick_pointer.  If TYPE is an array type that
+   requires rewriting, then copy it and return the updated copy.
+   Otherwise return nullptr.  */
+
+static struct type *
+rewrite_array_type (struct type *type)
+{
+  if (type->code () != TYPE_CODE_ARRAY)
+    return nullptr;
+
+  struct type *index_type = type->index_type ();
+  range_bounds *current_bounds = index_type->bounds ();
+
+  /* Handle multi-dimensional arrays.  */
+  struct type *new_target = rewrite_array_type (TYPE_TARGET_TYPE (type));
+  if (new_target == nullptr)
+    {
+      /* Maybe we don't need to rewrite this array.  */
+      if (current_bounds->low.kind () == PROP_CONST
+	  && current_bounds->high.kind () == PROP_CONST)
+	return nullptr;
+    }
+
+  /* Either the target type was rewritten, or the bounds have to be
+     updated.  Either way we want to copy the type and update
+     everything.  */
+  struct type *copy = copy_type (type);
+  int nfields = copy->num_fields ();
+  field *new_fields
+    = ((struct field *) TYPE_ZALLOC (copy,
+				     nfields * sizeof (struct field)));
+  memcpy (new_fields, copy->fields (), nfields * sizeof (struct field));
+  copy->set_fields (new_fields);
+  if (new_target != nullptr)
+    TYPE_TARGET_TYPE (copy) = new_target;
+
+  struct type *index_copy = copy_type (index_type);
+  range_bounds *bounds
+    = (struct range_bounds *) TYPE_ZALLOC (index_copy,
+					   sizeof (range_bounds));
+  *bounds = *current_bounds;
+  bounds->low.set_const_val (1);
+  bounds->high.set_const_val (0);
+  index_copy->set_bounds (bounds);
+  copy->set_index_type (index_copy);
+
+  return copy;
+}
+
 /* While some versions of GCC will generate complicated DWARF for an
    array (see quirk_ada_thick_pointer), more recent versions were
    modified to emit an explicit thick pointer structure.  However, in
@@ -15916,20 +15965,16 @@ quirk_ada_thick_pointer_struct (struct die_info *die, struct dwarf2_cu *cu,
   /* Make sure we're looking at a pointer to an array.  */
   if (type->field (0).type ()->code () != TYPE_CODE_PTR)
     return;
-  struct type *ary_type = TYPE_TARGET_TYPE (type->field (0).type ());
-
-  while (ary_type->code () == TYPE_CODE_ARRAY)
-    {
-      /* The Ada code already knows how to handle these types, so all
-	 that we need to do is turn the bounds into static bounds.  */
-      struct type *index_type = ary_type->index_type ();
 
-      index_type->bounds ()->low.set_const_val (1);
-      index_type->bounds ()->high.set_const_val (0);
-
-      /* Handle multi-dimensional arrays.  */
-      ary_type = TYPE_TARGET_TYPE (ary_type);
-    }
+  /* The Ada code already knows how to handle these types, so all that
+     we need to do is turn the bounds into static bounds.  However, we
+     don't want to rewrite existing array or index types in-place,
+     because those may be referenced in other contexts where this
+     rewriting is undesirable.  */
+  struct type *new_ary_type
+    = rewrite_array_type (TYPE_TARGET_TYPE (type->field (0).type ()));
+  if (new_ary_type != nullptr)
+    type->field (0).set_type (lookup_pointer_type (new_ary_type));
 }
 
 /* If the DIE has a DW_AT_alignment attribute, return its value, doing