Add Python support for dynamic types

This changes the gdb Python API to add support for dynamic types.  In
particular, this adds an attribute to gdb.Type, and updates some
attributes to reflect dynamic sizes and field offsets.

There's still no way to get the dynamic type from one of its concrete
instances.  This could perhaps be added if needed.

gdb/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	PR python/23662:
	* python/py-type.c (convert_field): Handle
	FIELD_LOC_KIND_DWARF_BLOCK.
	(typy_get_sizeof): Handle TYPE_HAS_DYNAMIC_LENGTH.
	(typy_get_dynamic): Nw function.
	(type_object_getset): Add "dynamic".
	* NEWS: Add entry.

gdb/doc/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	PR python/23662:
	* python.texi (Types In Python): Document new features.

gdb/testsuite/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	PR python/23662:
	* gdb.ada/variant.exp: Add Python checks.
	* gdb.rust/simple.exp: Add dynamic type checks.

1 files changed, 10 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.ada/variant.exp b/gdb/testsuite/gdb.ada/variant.exp
index 490956a..da51f7b 100644
--- a/gdb/testsuite/gdb.ada/variant.exp
+++ b/gdb/testsuite/gdb.ada/variant.exp
@@ -14,6 +14,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 load_lib "ada.exp"
+load_lib "gdb-python.exp"
 
 standard_ada_testfile pkg
 
@@ -43,4 +44,13 @@ foreach_with_prefix scenario {none all minimal} {
 	" = \\(one => 3, two => 0, str => \"zzz\", onevalue => 33, str2 => \"\"\\)"
     gdb_test "print nav3" \
 	" = \\(one => 3, two => 7, str => \"zzz\", onevalue => 33, str2 => \"qqqqqqq\", twovalue => 88\\)"
+
+    # This is only supported for the DWARF encoding.
+    if {$scenario == "minimal" && ![skip_python_tests]} {
+	gdb_test_no_output \
+	    "python t = gdb.lookup_type('nested_and_variable')" \
+	    "fetch type for python"
+	gdb_test "python print(t.dynamic)" "True"
+	gdb_test "python print(t\['onevalue'\].bitpos)" "None"
+    }
 }