Add block['var'] accessor

Currently we support iteration on blocks; this patch extends that to make
subscript access work as well.

gdb/ChangeLog:

2019-08-05  Christian Biesinger  <cbiesinger@google.com>

	* NEWS: Mention dictionary access on blocks.
	* python/py-block.c (blpy_getitem): New function.
	(block_object_as_mapping): New struct.
	(block_object_type): Use new struct for tp_as_mapping field.

gdb/doc/ChangeLog:

2019-08-05  Christian Biesinger  <cbiesinger@google.com>

	* python.texi (Blocks In Python): Document dictionary access on blocks.

gdb/testsuite/ChangeLog:

2019-08-05  Christian Biesinger  <cbiesinger@google.com>

	* gdb.python/py-block.exp: Test dictionary access on blocks.

1 files changed, 44 insertions, 1 deletions

diff --git a/gdb/python/py-block.c b/gdb/python/py-block.c
index 90140eb..4dc47ff 100644
--- a/gdb/python/py-block.c
+++ b/gdb/python/py-block.c
@@ -224,6 +224,43 @@ blpy_is_static (PyObject *self, void *closure)
   Py_RETURN_FALSE;
 }
 
+/* Given a string, returns the gdb.Symbol representing that symbol in this
+   block.  If such a symbol does not exist, returns NULL with a Python
+   exception.  */
+
+static PyObject *
+blpy_getitem (PyObject *self, PyObject *key)
+{
+  const struct block *block;
+
+  BLPY_REQUIRE_VALID (self, block);
+
+  gdb::unique_xmalloc_ptr<char> name = python_string_to_host_string (key);
+  if (name == nullptr)
+    return nullptr;
+
+  lookup_name_info lookup_name (name.get(), symbol_name_match_type::FULL);
+
+  /* We use ALL_BLOCK_SYMBOLS_WITH_NAME instead of block_lookup_symbol so
+     that we can look up symbols irrespective of the domain, matching the
+     iterator. It would be confusing if the iterator returns symbols you
+     can't find via getitem.  */
+  struct block_iterator iter;
+  struct symbol *sym = nullptr;
+  ALL_BLOCK_SYMBOLS_WITH_NAME (block, lookup_name, iter, sym)
+    {
+      /* Just stop at the first match */
+      break;
+    }
+
+  if (sym == nullptr)
+    {
+      PyErr_SetObject (PyExc_KeyError, key);
+      return nullptr;
+    }
+  return symbol_to_symbol_object (sym);
+}
+
 static void
 blpy_dealloc (PyObject *obj)
 {
@@ -440,6 +477,12 @@ static gdb_PyGetSetDef block_object_getset[] = {
   { NULL }  /* Sentinel */
 };
 
+static PyMappingMethods block_object_as_mapping = {
+  NULL,
+  blpy_getitem,
+  NULL
+};
+
 PyTypeObject block_object_type = {
   PyVarObject_HEAD_INIT (NULL, 0)
   "gdb.Block",			  /*tp_name*/
@@ -453,7 +496,7 @@ PyTypeObject block_object_type = {
   0,				  /*tp_repr*/
   0,				  /*tp_as_number*/
   0,				  /*tp_as_sequence*/
-  0,				  /*tp_as_mapping*/
+  &block_object_as_mapping,	  /*tp_as_mapping*/
   0,				  /*tp_hash */
   0,				  /*tp_call*/
   0,				  /*tp_str*/