[Ada] Allow assignment to wide string.

Given the following variable declaration...

   Www : Wide_String := "12345";

... this patch allows the following assignment to work:

   (gdb) set variable www := "qwert"

Without this patch, the debugger rejects the assignment because
the size of the array elements are different:

   (gdb) set www := "asdfg"
   Incompatible types in assignment

(on the lhs, we have an array of 2-bytes elements, and on the rhs,
we have a standard 1-byte string).

gdb/ChangeLog:

        * ada-lang.c (ada_same_array_size_p): New function.
        (ada_promote_array_of_integrals): New function.
        (coerce_for_assign): Add handling of arrays where the elements
        are integrals of a smaller size than the size of the target
        array element type.

gdb/testsuite/ChangeLog:

        * gdb.ada/set_wstr: New testcase.

1 files changed, 81 insertions, 3 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 9f329df..edef6bd 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -8629,6 +8629,72 @@ cast_from_fixed (struct type *type, struct value *arg)
   return value_from_double (type, val);
 }
 
+/* Given two array types T1 and T2, return nonzero iff both arrays
+   contain the same number of elements.  */
+
+static int
+ada_same_array_size_p (struct type *t1, struct type *t2)
+{
+  LONGEST lo1, hi1, lo2, hi2;
+
+  /* Get the array bounds in order to verify that the size of
+     the two arrays match.  */
+  if (!get_array_bounds (t1, &lo1, &hi1)
+      || !get_array_bounds (t2, &lo2, &hi2))
+    error (_("unable to determine array bounds"));
+
+  /* To make things easier for size comparison, normalize a bit
+     the case of empty arrays by making sure that the difference
+     between upper bound and lower bound is always -1.  */
+  if (lo1 > hi1)
+    hi1 = lo1 - 1;
+  if (lo2 > hi2)
+    hi2 = lo2 - 1;
+
+  return (hi1 - lo1 == hi2 - lo2);
+}
+
+/* Assuming that VAL is an array of integrals, and TYPE represents
+   an array with the same number of elements, but with wider integral
+   elements, return an array "casted" to TYPE.  In practice, this
+   means that the returned array is built by casting each element
+   of the original array into TYPE's (wider) element type.  */
+
+static struct value *
+ada_promote_array_of_integrals (struct type *type, struct value *val)
+{
+  struct type *elt_type = TYPE_TARGET_TYPE (type);
+  LONGEST lo, hi;
+  struct value *res;
+  LONGEST i;
+
+  /* Verify that both val and type are arrays of scalars, and
+     that the size of val's elements is smaller than the size
+     of type's element.  */
+  gdb_assert (TYPE_CODE (type) == TYPE_CODE_ARRAY);
+  gdb_assert (is_integral_type (TYPE_TARGET_TYPE (type)));
+  gdb_assert (TYPE_CODE (value_type (val)) == TYPE_CODE_ARRAY);
+  gdb_assert (is_integral_type (TYPE_TARGET_TYPE (value_type (val))));
+  gdb_assert (TYPE_LENGTH (TYPE_TARGET_TYPE (type))
+	      > TYPE_LENGTH (TYPE_TARGET_TYPE (value_type (val))));
+
+  if (!get_array_bounds (type, &lo, &hi))
+    error (_("unable to determine array bounds"));
+
+  res = allocate_value (type);
+
+  /* Promote each array element.  */
+  for (i = 0; i < hi - lo + 1; i++)
+    {
+      struct value *elt = value_cast (elt_type, value_subscript (val, lo + i));
+
+      memcpy (value_contents_writeable (res) + (i * TYPE_LENGTH (elt_type)),
+	      value_contents_all (elt), TYPE_LENGTH (elt_type));
+    }
+
+  return res;
+}
+
 /* Coerce VAL as necessary for assignment to an lval of type TYPE, and
    return the converted value.  */
 
@@ -8653,9 +8719,21 @@ coerce_for_assign (struct type *type, struct value *val)
   if (TYPE_CODE (type2) == TYPE_CODE_ARRAY
       && TYPE_CODE (type) == TYPE_CODE_ARRAY)
     {
-      if (TYPE_LENGTH (type2) != TYPE_LENGTH (type)
-          || TYPE_LENGTH (TYPE_TARGET_TYPE (type2))
-          != TYPE_LENGTH (TYPE_TARGET_TYPE (type2)))
+      if (!ada_same_array_size_p (type, type2))
+	error (_("cannot assign arrays of different length"));
+
+      if (is_integral_type (TYPE_TARGET_TYPE (type))
+	  && is_integral_type (TYPE_TARGET_TYPE (type2))
+	  && TYPE_LENGTH (TYPE_TARGET_TYPE (type2))
+	       < TYPE_LENGTH (TYPE_TARGET_TYPE (type)))
+	{
+	  /* Allow implicit promotion of the array elements to
+	     a wider type.  */
+	  return ada_promote_array_of_integrals (type, val);
+	}
+
+      if (TYPE_LENGTH (TYPE_TARGET_TYPE (type2))
+          != TYPE_LENGTH (TYPE_TARGET_TYPE (type)))
         error (_("Incompatible types in assignment"));
       deprecated_set_value_type (val, type);
     }