Replace O(N) lookup with O(1) for task outputs (master)

CHANGES.md

@@ -164,7 +164,7 @@ variable `ISODATETIMEREF` (reference time for the `isodatetime` command from
 [metomi-isodatetime](https://github.com/metomi/isodatetime/)) in task jobs to
 have the same value as `CYLC_TASK_CYCLE_POINT`.
 
-[#3286](https://github.com/cylc/cylc-flow/pull/3249) -
+[#3286](https://github.com/cylc/cylc-flow/pull/3286) -
 Removed the `cylc check-triggering` command.
 Changed the `suite.rc` schema:
 * Removed `[cylc]log resolved dependencies`
@@ -173,6 +173,11 @@ Changed the `suite.rc` schema:
   `[cylc][[events]]abort if any task fails` so it lives with the other
   `abort if/on ...` settings.
 
+[#3351](https://github.com/cylc/cylc-flow/pull/3351) - sped up suite validation
+(which also affects responsiveness of suite controllers during suite startup,
+restarts, and reloads).  Impact of the speedup is most noticeable when dealing
+with suite configurations that contain tasks with many task outputs.
+
 ### Fixes
 
 [#3308](https://github.com/cylc/cylc-flow/pull/3308) - fix a long-standing bug

cylc/flow/config.py

@@ -1590,8 +1590,7 @@ def generate_taskdefs(self, orig_expr, left_nodes, right, seq):
 
             # Record custom message outputs.
             for item in self.cfg['runtime'][name]['outputs'].items():
-                if item not in taskdef.outputs:
-                    taskdef.outputs.append(item)
+                taskdef.outputs.add(item)
 
     def generate_triggers(self, lexpression, left_nodes, right, seq,
                           suicide, task_triggers):

cylc/flow/taskdef.py

@@ -64,7 +64,7 @@ def __init__(self, name, rtcfg, run_mode, start_point, spawn_ahead):
         self.expiration_offset = None
         self.namespace_hierarchy = []
         self.dependencies = {}
-        self.outputs = []
+        self.outputs = set()
         self.param_var = {}
         self.external_triggers = []
         self.xtrig_labels = {}  # {sequence: [labels]}