Clean-up: tests: bt2 plug-ins: modernize the plug-ins

By virtue of their use of the C Babeltrace 2 APIs, the test plug-ins
perform a fair amount of manual resource management.

To make it possible to adopt a more modern C++ style in those plug-ins,
a number of helpers are introduced.

Introduce reference wrappers for the Babeltrace 2 interface:
  - value_ref: wraps a bt_value reference using std::unique_ptr
  - message_const_ref: wraps a constant message reference using a
    unique_ptr
  - message_iterator_ref: wraps a message iterator reference using a
    unique_ptr
  - event_class_const_ref: wraps a constant event class reference using
    a unique_ptr

A specialized random_access_container_wrapper is specialized to wrap
bt_value arrays of strings.

In doing so, it is possible to eliminate the use of gotos and manual
reference management on error paths. Some struct/classes are renamed to
eliminate ambiguities that arose over the refactoring.

The changes allow some simplifications of the code flow in places which
are applied directly.

Change-Id: I25c148d7970cb89add55a86f2c162973d3d27e4a
Signed-off-by: Jérémie Galarneau <[email protected]>

src/common/container-wrapper.hpp

@@ -117,6 +117,11 @@ class random_access_container_wrapper {
  return ContainerOperations::size(_container);
  }
 
+ bool empty() const
+ {
+ return size() == 0;
+ }
+
  typename std::conditional<std::is_pointer<ElementType>::value, ElementType, ElementType&>::type
  operator[](std::size_t index)
  {
@@ -144,7 +149,7 @@ class random_access_container_wrapper {
  operator[](std::size_t index) const
  {
  if (index >= ContainerOperations::size(_container)) {
- LTTNG_THROW_INVALID_ARGUMENT_ERROR(lttng::format(
+ throw std::invalid_argument(lttng::format(
  "Out of bound access through random_access_container_wrapper: index={}, size={}",
  index,
  size()));

tests/utils/bt2_plugins/Makefile.am

@@ -16,7 +16,9 @@ lttngtest_la_CXXFLAGS = \
  -fvisibility=default
 
 lttngtest_la_SOURCES = \
- lttngtest-plugin.cpp
+ lttngtest-plugin.cpp \
+ fmt.hpp \
+ utils.hpp
 
 lttngtest_la_LDFLAGS = \
  $(AM_LDFLAGS) \