Xtrig arg validate (cylc#5955)

* Xtrigger function arg validation.
* Add integration tests for xtrigger validation, which provides simple examples for each of the built in xtriggers.
- Xrandom validate function
- Init test xrandom validate function
- Add unit tests for validation of built in xtriggers
- Automatically validate xtrigger function signature

---------

Co-authored-by: Hilary James Oliver <hilary.j.oliver@gmail.com>

* Apply suggestions from code review

Co-authored-by: Ronnie Dutta <61982285+MetRonnie@users.noreply.github.com>

* fix flake8

* Improve xtrigger validation (#60)

* Improve xtrigger validation

* wall_clock: use placeholder function for signature validation & autodocs

* Fix docstring for autodoc [skip ci]

---------

Co-authored-by: Hilary Oliver <hilary.j.oliver@gmail.com>
Co-authored-by: Ronnie Dutta <61982285+MetRonnie@users.noreply.github.com>

changes.d/5955.feat.md

@@ -0,0 +1 @@
+Support xtrigger argument validation.

cylc/flow/config.py

@@ -57,6 +57,7 @@
 from cylc.flow.id import Tokens
 from cylc.flow.cycling.integer import IntegerInterval
 from cylc.flow.cycling.iso8601 import ingest_time, ISO8601Interval
+
 from cylc.flow.exceptions import (
     CylcError,
     InputError,
@@ -1718,28 +1719,25 @@ def generate_triggers(self, lexpression, left_nodes, right, seq,
                 if label != 'wall_clock':
                     raise WorkflowConfigError(f"xtrigger not defined: {label}")
                 else:
-                    # Allow "@wall_clock" in the graph as an undeclared
-                    # zero-offset clock xtrigger.
-                    xtrig = SubFuncContext(
-                        'wall_clock', 'wall_clock', [], {})
+                    # Allow "@wall_clock" in graph as implicit zero-offset.
+                    xtrig = SubFuncContext('wall_clock', 'wall_clock', [], {})
 
-            if xtrig.func_name == 'wall_clock':
-                if self.cycling_type == INTEGER_CYCLING_TYPE:
-                    raise WorkflowConfigError(
-                        "Clock xtriggers require datetime cycling:"
-                        f" {label} = {xtrig.get_signature()}"
-                    )
-                else:
-                    # Convert offset arg to kwarg for certainty later.
-                    if "offset" not in xtrig.func_kwargs:
-                        xtrig.func_kwargs["offset"] = None
-                        with suppress(IndexError):
-                            xtrig.func_kwargs["offset"] = xtrig.func_args[0]
+            if (
+                xtrig.func_name == 'wall_clock'
+                and self.cycling_type == INTEGER_CYCLING_TYPE
+            ):
+                raise WorkflowConfigError(
+                    "Clock xtriggers require datetime cycling:"
+                    f" {label} = {xtrig.get_signature()}"
+                )
 
-            if self.xtrigger_mgr is None:
-                XtriggerManager.validate_xtrigger(label, xtrig, self.fdir)
-            else:
+            # Generic xtrigger validation.
+            XtriggerManager.check_xtrigger(label, xtrig, self.fdir)
+
+            if self.xtrigger_mgr:
+                # (not available during validation)
                 self.xtrigger_mgr.add_trig(label, xtrig, self.fdir)
+
             self.taskdefs[right].add_xtrig_label(label, seq)
 
     def get_actual_first_point(self, start_point):
@@ -2427,10 +2425,10 @@ def upgrade_clock_triggers(self):
             # Derive an xtrigger label.
             label = '_'.join(('_cylc', 'wall_clock', task_name))
             # Define the xtrigger function.
-            xtrig = SubFuncContext(label, 'wall_clock', [], {})
-            xtrig.func_kwargs["offset"] = offset
+            args = [] if offset is None else [offset]
+            xtrig = SubFuncContext(label, 'wall_clock', args, {})
             if self.xtrigger_mgr is None:
-                XtriggerManager.validate_xtrigger(label, xtrig, self.fdir)
+                XtriggerManager.check_xtrigger(label, xtrig, self.fdir)
             else:
                 self.xtrigger_mgr.add_trig(label, xtrig, self.fdir)
             # Add it to the task, for each sequence that the task appears in.

cylc/flow/exceptions.py

@@ -241,13 +241,12 @@ class XtriggerConfigError(WorkflowConfigError):
 
     """
 
-    def __init__(self, label: str, trigger: str, message: str):
+    def __init__(self, label: str, message: str):
         self.label: str = label
-        self.trigger: str = trigger
         self.message: str = message
 
-    def __str__(self):
-        return f'[{self.label}] {self.message}'
+    def __str__(self) -> str:
+        return f'[@{self.label}] {self.message}'
 
 
 class ClientError(CylcError):

cylc/flow/scripts/function_run.py

@@ -18,10 +18,13 @@
 
 (This command is for internal use.)
 
-Run a Python function "<name>(*args, **kwargs)" in the process pool. It must be
-defined in a module of the same name. Positional and keyword arguments must be
-passed in as JSON strings. <src-dir> is the workflow source dir, needed to find
-local xtrigger modules.
+Run a Python xtrigger function "<name>(*args, **kwargs)" in the process pool.
+It must be in a module of the same name. Positional and keyword arguments must
+be passed in as JSON strings.
+
+Python entry points are the preferred way to make xtriggers available to the
+scheduler, but local xtriggers can be stored in <src-dir>.
+
 """
 import sys
 

cylc/flow/subprocpool.py

@@ -41,7 +41,8 @@
 from cylc.flow.task_proxy import TaskProxy
 from cylc.flow.wallclock import get_current_time_string
 
-_XTRIG_FUNCS: dict = {}
+_XTRIG_MOD_CACHE: dict = {}
+_XTRIG_FUNC_CACHE: dict = {}
 
 
 def _killpg(proc, signal):
@@ -66,68 +67,86 @@ def _killpg(proc, signal):
     return True
 
 
-def get_func(func_name, src_dir):
-    """Find and return an xtrigger function from a module of the same name.
+def get_xtrig_mod(mod_name, src_dir):
+    """Find, cache, and return a named xtrigger module.
 
-    These locations are checked in this order:
-    - <src_dir>/lib/python/
-    - `$CYLC_PYTHONPATH`
-    - defined via a `cylc.xtriggers` entry point for an
-      installed Python package.
+    Locations checked in this order:
+    - <src_dir>/lib/python (prepend to sys.path)
+    - $CYLC_PYTHONPATH (already in sys.path)
+    - `cylc.xtriggers` entry point
 
-    Workflow source directory passed in as this is executed in an independent
-    process in the command pool and therefore doesn't know about the workflow.
+    (Check entry point last so users can override with local implementations).
+
+    Workflow source dir passed in - this executes in an independent subprocess.
+
+    Raises:
+        ImportError, if the module is not found
 
     """
-    if func_name in _XTRIG_FUNCS:
-        return _XTRIG_FUNCS[func_name]
+    if mod_name in _XTRIG_MOD_CACHE:
+        # Found and cached already.
+        return _XTRIG_MOD_CACHE[mod_name]
 
     # First look in <src-dir>/lib/python.
     sys.path.insert(0, os.path.join(src_dir, 'lib', 'python'))
-    mod_name = func_name
     try:
-        mod_by_name = __import__(mod_name, fromlist=[mod_name])
+        _XTRIG_MOD_CACHE[mod_name] = __import__(mod_name, fromlist=[mod_name])
     except ImportError:
-        # Look for xtriggers via entry_points for external sources.
-        # Do this after the lib/python and PYTHONPATH approaches to allow
-        # users to override entry_point definitions with local/custom
-        # implementations.
+        # Then entry point.
         for entry_point in iter_entry_points('cylc.xtriggers'):
-            if func_name == entry_point.name:
-                _XTRIG_FUNCS[func_name] = entry_point.load()
-                return _XTRIG_FUNCS[func_name]
-
+            if mod_name == entry_point.name:
+                _XTRIG_MOD_CACHE[mod_name] = entry_point.load()
+                return _XTRIG_MOD_CACHE[mod_name]
         # Still unable to find anything so abort
         raise
 
-    try:
-        _XTRIG_FUNCS[func_name] = getattr(mod_by_name, func_name)
-    except AttributeError:
-        # Module func_name has no function func_name, nor an entry_point entry.
-        raise
-    return _XTRIG_FUNCS[func_name]
+    return _XTRIG_MOD_CACHE[mod_name]
+
+
+def get_xtrig_func(mod_name, func_name, src_dir):
+    """Find, cache, and return a function from an xtrigger module.
+
+    Raises:
+        ImportError, if the module is not found
+        AttributeError, if the function is not found in the module
+
+    """
+    if (mod_name, func_name) in _XTRIG_FUNC_CACHE:
+        return _XTRIG_FUNC_CACHE[(mod_name, func_name)]
+
+    mod = get_xtrig_mod(mod_name, src_dir)
+
+    _XTRIG_FUNC_CACHE[(mod_name, func_name)] = getattr(mod, func_name)
+
+    return _XTRIG_FUNC_CACHE[(mod_name, func_name)]
 
 
 def run_function(func_name, json_args, json_kwargs, src_dir):
     """Run a Python function in the process pool.
 
     func_name(*func_args, **func_kwargs)
 
+    The function is presumed to be in a module of the same name.
+
     Redirect any function stdout to stderr (and workflow log in debug mode).
     Return value printed to stdout as a JSON string - allows use of the
     existing process pool machinery as-is. src_dir is for local modules.
 
     """
     func_args = json.loads(json_args)
     func_kwargs = json.loads(json_kwargs)
+
     # Find and import then function.
-    func = get_func(func_name, src_dir)
+    func = get_xtrig_func(func_name, func_name, src_dir)
+
     # Redirect stdout to stderr.
     orig_stdout = sys.stdout
     sys.stdout = sys.stderr
     res = func(*func_args, **func_kwargs)
+
     # Restore stdout.
     sys.stdout = orig_stdout
+
     # Write function return value as JSON to stdout.
     sys.stdout.write(json.dumps(res))