Automatically validate xtrigger function signature

cylc/flow/subprocpool.py

@@ -116,10 +116,7 @@ def get_xtrig_func(mod_name, func_name, src_dir):
 
     mod = get_xtrig_mod(mod_name, src_dir)
 
-    try:
-        _XTRIG_FUNC_CACHE[(mod_name, func_name)] = getattr(mod, func_name)
-    except AttributeError:
-        raise
+    _XTRIG_FUNC_CACHE[(mod_name, func_name)] = getattr(mod, func_name)
 
     return _XTRIG_FUNC_CACHE[(mod_name, func_name)]
 

cylc/flow/xtrigger_mgr.py

@@ -16,6 +16,7 @@
 
 from contextlib import suppress
 from enum import Enum
+from inspect import signature
 import json
 import re
 from copy import deepcopy
@@ -279,12 +280,22 @@ def check_xtrigger(
                 fname,
                 f"'{fname}' not found in xtrigger module '{fname}'",
             )
+
         if not callable(func):
             raise XtriggerConfigError(
                 label,
                 fname,
                 f"'{fname}' not callable in xtrigger module '{fname}'",
             )
+        if func is not wall_clock:
+            # Validate args and kwargs against the function signature
+            # (but not for wall_clock because it's a special case).
+            try:
+                signature(func).bind(*fctx.func_args, **fctx.func_kwargs)
+            except TypeError as exc:
+                raise XtriggerConfigError(
+                    label, fname, f"{fctx.get_signature()}: {exc}"
+                )
 
         # Check any string templates in the function arg values (note this
         # won't catch bad task-specific values - which are added dynamically).

cylc/flow/xtriggers/xrandom.py

@@ -112,21 +112,6 @@ def validate(f_args, f_kwargs, f_signature):
     If f_args used, convert to f_kwargs for clarity.
 
     """
-    n_args = len(f_args)
-    n_kwargs = len(f_kwargs)
-
-    if n_args + n_kwargs > 3:
-        raise WorkflowConfigError(f"Too many args: {f_signature}")
-
-    if n_args + n_kwargs < 1:
-        raise WorkflowConfigError(f"Wrong number of args: {f_signature}")
-
-    if n_kwargs:
-        # kwargs must be "secs" and "_"
-        kw = next(iter(f_kwargs))
-        if kw not in ("secs", "_"):
-            raise WorkflowConfigError(f"Illegal arg '{kw}': {f_signature}")
-
     # convert to kwarg
     f_kwargs["percent"] = f_args[0]
     del f_args[0]

tests/integration/test_config.py

@@ -16,17 +16,18 @@
 
 from pathlib import Path
 import sqlite3
-from typing import TYPE_CHECKING
+from typing import Any
 import pytest
 
-from cylc.flow.exceptions import ServiceFileError, WorkflowConfigError
+from cylc.flow.exceptions import (
+    ServiceFileError,
+    WorkflowConfigError,
+    XtriggerConfigError,
+)
 from cylc.flow.parsec.exceptions import ListValueError
 from cylc.flow.pathutil import get_workflow_run_pub_db_path
 
-if TYPE_CHECKING:
-    from types import Any
-
-    Fixture = Any
+Fixture = Any
 
 
 @pytest.mark.parametrize(
@@ -353,7 +354,7 @@ def test_xtrig_validation_wall_clock(
     flow: 'Fixture',
     validate: 'Fixture',
 ):
-    """If an xtrigger module has a `validate_config` it is called.
+    """If an xtrigger module has a `validate()` function is called.
 
     https://github.com/cylc/cylc-flow/issues/5448
     """
@@ -376,14 +377,13 @@ def test_xtrig_validation_echo(
     flow: 'Fixture',
     validate: 'Fixture',
 ):
-    """If an xtrigger module has a `validate_config` it is called.
+    """If an xtrigger module has a `validate()` function is called.
 
     https://github.com/cylc/cylc-flow/issues/5448
     """
     id_ = flow({
         'scheduler': {'allow implicit tasks': True},
         'scheduling': {
-            'initial cycle point': '1012',
             'xtriggers': {'myxt': 'echo()'},
             'graph': {'R1': '@myxt => foo'},
         }
@@ -399,21 +399,20 @@ def test_xtrig_validation_xrandom(
     flow: 'Fixture',
     validate: 'Fixture',
 ):
-    """If an xtrigger module has a `validate_config` it is called.
+    """If an xtrigger module has a `validate()` function it is called.
 
     https://github.com/cylc/cylc-flow/issues/5448
     """
     id_ = flow({
         'scheduler': {'allow implicit tasks': True},
         'scheduling': {
-            'initial cycle point': '1012',
-            'xtriggers': {'myxt': 'xrandom()'},
+            'xtriggers': {'myxt': 'xrandom(200)'},
             'graph': {'R1': '@myxt => foo'},
         }
     })
     with pytest.raises(
         WorkflowConfigError,
-        match=r'Wrong number of args: xrandom\(\)'
+        match=r"'percent' should be a float between 0 and 100:"
     ):
         validate(id_)
 
@@ -423,29 +422,30 @@ def test_xtrig_validation_custom(
     validate: 'Fixture',
     monkeypatch: 'Fixture',
 ):
-    """If an xtrigger module has a `validate_config`
+    """If an xtrigger module has a `validate()` function
     an exception is raised if that validate function fails.
 
     https://github.com/cylc/cylc-flow/issues/5448
-
-    Rather than create our own xtrigger module on disk
-    and attempt to trigger a validation failure we
-    mock our own exception, xtrigger and xtrigger
-    validation functions and inject these into the
-    appropriate locations:
     """
+    # Rather than create our own xtrigger module on disk
+    # and attempt to trigger a validation failure we
+    # mock our own exception, xtrigger and xtrigger
+    # validation functions and inject these into the
+    # appropriate locations:
     GreenExc = type('Green', (Exception,), {})
 
-    def kustom_mock(suite):
+    def kustom_xt(feature):
         return True, {}
 
     def kustom_validate(args, kwargs, sig):
         raise GreenExc('This is only a test.')
 
+    # Patch xtrigger func
     monkeypatch.setattr(
         'cylc.flow.xtrigger_mgr.get_xtrig_func',
-        lambda *args: kustom_mock,
+        lambda *args: kustom_xt,
     )
+    # Patch xtrigger's validate func
     monkeypatch.setattr(
         'cylc.flow.config.get_xtrig_func',
         lambda *args: kustom_validate if "validate" in args else ''
@@ -463,3 +463,22 @@ def kustom_validate(args, kwargs, sig):
     Path(id_)
     with pytest.raises(GreenExc, match=r'This is only a test.'):
         validate(id_)
+
+
+def test_xtrig_signature_validation(
+    flow: 'Fixture',
+    validate: 'Fixture',
+):
+    """Test automatic xtrigger function signature validation."""
+    id_ = flow({
+        'scheduler': {'allow implicit tasks': True},
+        'scheduling': {
+            'xtriggers': {'myxt': 'xrandom()'},
+            'graph': {'R1': '@myxt => foo'},
+        }
+    })
+    with pytest.raises(
+        XtriggerConfigError,
+        match=r"xrandom\(\): missing a required argument: 'percent'"
+    ):
+        validate(id_)

tests/unit/xtriggers/test_xrandom.py

@@ -27,13 +27,10 @@ def test_validate_good_path():
 
 @pytest.mark.parametrize(
     'args, kwargs, err', (
-        param([100], {'f': 1.1, 'b': 1, 'x': 2}, 'Too', id='too-many-args'),
-        param([], {}, 'Wrong number', id='too-few-args'),
-        param(['foo'], {}, '\'percent', id='percent-not-numeric'),
-        param([101], {}, '\'percent', id='percent>100'),
-        param([-1], {}, '\'percent', id='percent<0'),
-        param([100], {'egg': 1}, 'Illegal', id='invalid-kwarg'),
-        param([100], {'secs': 1.1}, "'secs'", id='secs-not-int'),
+        param(['foo'], {}, r"'percent", id='percent-not-numeric'),
+        param([101], {}, r"'percent", id='percent>100'),
+        param([-1], {}, r"'percent", id='percent<0'),
+        param([100], {'secs': 1.1}, r"'secs'", id='secs-not-int'),
     )
 )
 def test_validate_exceptions(args, kwargs, err):