[lldb/test] Add events listener helper function to lldbtest

This patch introduces 2 new lldb utility functions:
- lldbutil.start_listening_from: This can be called in the test setup to
  create a listener and set it up for a specific event mask and add it
  to the user-provided broadcaster's list.
- lldbutil.fetch_next_event: This will use fetch a single event from the
  provided istener and return it if it matches the provided broadcaster.

The motivation behind this is to easily test new kinds of events
(i.e. Swift type-system progress events). However, this patch also
updates `TestProgressReporting.py` and `TestDiagnosticReporting.py`
to make use of these new helper functions.

Differential Revision: https://reviews.llvm.org/D122193

Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/lldbutil.py b/lldb/packages/Python/lldbsuite/test/lldbutil.py
index 117c624..af2c41d 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbutil.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbutil.py
@@ -1255,6 +1255,29 @@ def expect_state_changes(test, listener, process, states, timeout=30):
             lldb.SBProcess.GetStateFromEvent(event),
             expected_state)
 
+def start_listening_from(broadcaster, event_mask):
+    """Creates a listener for a specific event mask and add it to the source broadcaster."""
+
+    listener = lldb.SBListener("lldb.test.listener")
+    broadcaster.AddListener(listener, event_mask)
+    return listener
+
+def fetch_next_event(test, listener, broadcaster, timeout=10):
+    """Fetch one event from the listener and return it if it matches the provided broadcaster.
+    Fails otherwise."""
+
+    event = lldb.SBEvent()
+
+    if listener.WaitForEvent(timeout, event):
+        if event.BroadcasterMatchesRef(broadcaster):
+            return event
+
+        test.fail("received event '%s' from unexpected broadcaster '%s'." %
+                  (event.GetDescription(), event.GetBroadcaster().GetName()))
+
+    test.fail("couldn't fetch an event before reaching the timeout.")
+
+
 # ===================================
 # Utility functions related to Frames
 # ===================================