Expose current 'print' settings to Python

PR python/17291 asks for access to the current print options.  While I
think this need is largely satisfied by the existence of
Value.format_string, it seemed to me that a bit more could be done.

First, while Value.format_string uses the user's settings, it does not
react to temporary settings such as "print/x".  This patch changes
this.

Second, there is no good way to examine the current settings (in
particular the temporary ones in effect for just a single "print").
This patch adds this as well.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=17291

gdb/python/py-prettyprint.c

@@ -39,6 +39,10 @@ enum gdbpy_string_repr_result
     string_repr_ok
   };
 
+/* If non-null, points to options that are in effect while
+   printing.  */
+const struct value_print_options *gdbpy_current_print_options;
+
 /* Helper function for find_pretty_printer which iterates over a list,
    calls each function and inspects output.  This will return a
    printer object if one recognizes VALUE.  If no printer is found, it
@@ -604,6 +608,9 @@ gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
   if (printer == Py_None)
     return EXT_LANG_RC_NOP;
 
+  scoped_restore set_options = make_scoped_restore (&gdbpy_current_print_options,
+						    options);
+
   /* If we are printing a map, we want some special formatting.  */
   gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
 
@@ -632,8 +639,12 @@ gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
 gdbpy_ref<>
 apply_varobj_pretty_printer (PyObject *printer_obj,
 			     struct value **replacement,
-			     struct ui_file *stream)
+			     struct ui_file *stream,
+			     const value_print_options *opts)
 {
+  scoped_restore set_options = make_scoped_restore (&gdbpy_current_print_options,
+						    opts);
+
   *replacement = NULL;
   gdbpy_ref<> py_str = pretty_print_one_value (printer_obj, replacement);
 
@@ -688,3 +699,88 @@ gdbpy_default_visualizer (PyObject *self, PyObject *args)
 
   return find_pretty_printer (val_obj).release ();
 }
+
+/* Helper function to set a boolean in a dictionary.  */
+static int
+set_boolean (PyObject *dict, const char *name, bool val)
+{
+  gdbpy_ref<> val_obj (PyBool_FromLong (val));
+  if (val_obj == nullptr)
+    return -1;
+  return PyDict_SetItemString (dict, name, val_obj.get ());
+}
+
+/* Helper function to set an integer in a dictionary.  */
+static int
+set_unsigned (PyObject *dict, const char *name, unsigned int val)
+{
+  gdbpy_ref<> val_obj = gdb_py_object_from_ulongest (val);
+  if (val_obj == nullptr)
+    return -1;
+  return PyDict_SetItemString (dict, name, val_obj.get ());
+}
+
+/* Implement gdb.print_options.  */
+PyObject *
+gdbpy_print_options (PyObject *unused1, PyObject *unused2)
+{
+  gdbpy_ref<> result (PyDict_New ());
+  if (result == nullptr)
+    return nullptr;
+
+  value_print_options opts;
+  gdbpy_get_print_options (&opts);
+
+  if (set_boolean (result.get (), "raw",
+		   opts.raw) < 0
+      || set_boolean (result.get (), "pretty_arrays",
+		      opts.prettyformat_arrays) < 0
+      || set_boolean (result.get (), "pretty_structs",
+		      opts.prettyformat_structs) < 0
+      || set_boolean (result.get (), "array_indexes",
+		      opts.print_array_indexes) < 0
+      || set_boolean (result.get (), "symbols",
+		      opts.symbol_print) < 0
+      || set_boolean (result.get (), "unions",
+		      opts.unionprint) < 0
+      || set_boolean (result.get (), "address",
+		      opts.addressprint) < 0
+      || set_boolean (result.get (), "deref_refs",
+		      opts.deref_ref) < 0
+      || set_boolean (result.get (), "actual_objects",
+		      opts.objectprint) < 0
+      || set_boolean (result.get (), "static_members",
+		      opts.static_field_print) < 0
+      || set_boolean (result.get (), "deref_refs",
+		      opts.deref_ref) < 0
+      || set_unsigned (result.get (), "max_elements",
+		       opts.print_max) < 0
+      || set_unsigned (result.get (), "max_depth",
+		       opts.max_depth) < 0
+      || set_unsigned (result.get (), "repeat_threshold",
+		       opts.repeat_count_threshold) < 0)
+    return nullptr;
+
+  if (opts.format != 0)
+    {
+      char str[2] = { (char) opts.format, 0 };
+      gdbpy_ref<> fmtstr = host_string_to_python_string (str);
+      if (fmtstr == nullptr)
+	return nullptr;
+      if (PyDict_SetItemString (result.get (), "format", fmtstr.get ()) < 0)
+	return nullptr;
+    }
+
+  return result.release ();
+}
+
+/* Helper function that either finds the prevailing print options, or
+   calls get_user_print_options.  */
+void
+gdbpy_get_print_options (value_print_options *opts)
+{
+  if (gdbpy_current_print_options != nullptr)
+    *opts = *gdbpy_current_print_options;
+  else
+    get_user_print_options (opts);
+}