Separate Parsec ItemNotFoundError into two

ItemNotFoundError - Where an item could be defined, but isn't (in sparse mode).
NotAConfigItemError - Where an item is not part of a config to be defined.

move get_manyparents to init

create unit test for get_manyparents

CHANGES.md

@@ -104,6 +104,8 @@ now accepts ``&`` and ``|`` as valid line breaks in the same way as ``=>``.
 renamed to `CYLC_WORKFLOW_ID`. `CYLC_WORKFLOW_NAME` re-added as
 `CYLC_WORKFLOW_ID` shorn of any trailing `runX`.
 
+[#4471](https://github.com/cylc/cylc-flow/pull/4471) - Users now get a different
+error for a config item that doesn't exist to be set, to one that isn't set.
 
 ### Fixes
 

cylc/flow/parsec/config.py

@@ -17,11 +17,13 @@
 from copy import deepcopy
 import re
 from textwrap import dedent
+from typing import Union
 
 from cylc.flow.context_node import ContextNode
 from cylc.flow.parsec.exceptions import (
     ItemNotFoundError,
-    NotSingleItemError
+    NotSingleItemError,
+    NotAConfigItemError,
 )
 from cylc.flow.parsec.fileparse import parse
 from cylc.flow.parsec.util import printcfg
@@ -44,6 +46,8 @@ def __init__(self, spec, upgrader=None, output_fname=None, tvars=None,
         if validator is None:
             validator = parsec_validate
         self.validator = validator
+        # Get a list of config items which have a private name ``__MANY__``:
+        self.manyparents = self._get_namespace_parents()
 
     def loadcfg(self, rcfile, title=""):
         """Parse a config file, upgrade or deprecate items if necessary,
@@ -110,12 +114,18 @@ def get(self, keys=None, sparse=False):
         parents = []
         if keys:
             for key in keys:
-                try:
-                    cfg = cfg[key]
-                except (KeyError, TypeError):
-                    raise ItemNotFoundError(itemstr(parents, key))
+                if (
+                    key not in self.dense
+                    and not parents or parents in self.manyparents
+                ):
+                    raise NotAConfigItemError(key)
                 else:
-                    parents.append(key)
+                    try:
+                        cfg = cfg[key]
+                    except (KeyError, TypeError):
+                        raise ItemNotFoundError(itemstr(parents, key))
+                    else:
+                        parents.append(key)
 
         return cfg
 
@@ -162,6 +172,29 @@ def dump(self, keys=None, sparse=False, prefix='', none_str=''):
         cfg = self.get(keys, sparse)
         printcfg(cfg, prefix=prefix, level=len(keys), none_str=none_str)
 
+    def _get_namespace_parents(self) -> Union[list, None]:
+        """get a list of the parents of config items which can be user defined.
+
+        For example, where
+
+        .. code-block:: cylc
+
+           [runtime]
+               [[my_task]]  # Custom task names.
+               [[my_other_task]]
+
+        this function will return ``[runtime]``.
+        """
+        try:
+            manyparents = [
+                list(key[1].parents())[0].name
+                for key in self.spec.walk()
+                if key[1].name == '__MANY__'
+            ]
+        except AttributeError:
+            manyparents = None
+        return manyparents
+
 
 class ConfigNode(ContextNode):
     """A Cylc configuration schema, section, or setting.

cylc/flow/parsec/exceptions.py

@@ -35,7 +35,17 @@ def __init__(self, item):
         self.item = item
 
     def __str__(self):
-        return f'item not found: {self.item}'
+        return f'You have not set \"{self.item}\" in this config.'
+
+
+class NotAConfigItemError(ParsecError, KeyError):
+    """Error raised for missing configuration items."""
+
+    def __init__(self, item):
+        self.item = item
+
+    def __str__(self):
+        return f'You cannot set  \"{self.item}\" in this config.'
 
 
 class NotSingleItemError(ParsecError, TypeError):

tests/functional/cylc-get-config/08-item-not-found.t

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#-------------------------------------------------------------------------------
+# Test cylc config
+. "$(dirname "$0")/test_header"
+#-------------------------------------------------------------------------------
+set_test_number 7
+#-------------------------------------------------------------------------------
+cat >>'global.cylc' <<__HERE__
+[platforms]
+    [[foo]]
+__HERE__
+
+OLD="$CYLC_CONF_PATH"
+export CYLC_CONF_PATH="${PWD}"
+
+# Control Run
+run_ok "${TEST_NAME_BASE}-ok" cylc config -i "[platforms]foo"
+
+# If item not settable in config (platforms is mis-spelled):
+run_fail "${TEST_NAME_BASE}-not-in-config-spec" cylc config -i "[platfroms]foo"
+grep_ok "NotAConfigItemError" "${TEST_NAME_BASE}-not-in-config-spec.stderr"
+
+# If item not defined, item not found.
+run_fail "${TEST_NAME_BASE}-not-defined" cylc config -i "[scheduler]"
+grep_ok "ItemNotFoundError" "${TEST_NAME_BASE}-not-defined.stderr"
+
+# If item settable in config, item not found.
+run_fail "${TEST_NAME_BASE}-not-defined__MULTI__" cylc config -i "[platforms]bar"
+grep_ok "ItemNotFoundError" "${TEST_NAME_BASE}-not-defined__MULTI__.stderr"
+
+rm global.cylc
+export CYLC_CONF_PATH="$OLD"
+
+exit

tests/unit/parsec/test_config.py

@@ -14,12 +14,17 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from os import spawnl
 import tempfile
+from _pytest.config import Config
 
 import pytest
 
 from cylc.flow.parsec import config
-from cylc.flow.parsec.config import ConfigNode as Conf
+from cylc.flow.parsec.config import (
+    ConfigNode as Conf,
+    ParsecConfig
+)
 from cylc.flow.parsec.OrderedDict import OrderedDictWithDefaults
 from cylc.flow.parsec.upgrade import upgrader
 from cylc.flow.parsec.validate import (
@@ -256,7 +261,7 @@ def test_get_item(sample_spec_2):
 
 def test_item_not_found_error():
     error = config.ItemNotFoundError("internal error")
-    assert 'item not found: internal error' == str(error)
+    assert 'You have not set "internal error" in this config.' == str(error)
 
 
 def test_not_single_item_error():
@@ -314,3 +319,15 @@ def test_mdump_oneline(parse_config, sample_spec, capsys):
 def test_get_none(parse_config):
     cfg = parse_config(sample_spec, '')  # blank config
     assert cfg.get(sparse=True) == {}
+
+
+def test__get_namespace_parents(parse_config):
+    """It returns a list of parents and nothing else"""
+    def spec_():
+        with Conf('myconfig') as myconf:
+            with Conf('manythings'):
+                Conf('<thing>')
+
+        return myconf
+    cfg = ParsecConfig(spec_())
+    assert cfg.manyparents == ['manythings']