Do not allow plugins to act on global.cylc

cylc/flow/parsec/fileparse.py

@@ -30,6 +30,7 @@
       value type is known).
 """
 
+from copy import deepcopy
 import os
 from pathlib import Path
 import re
@@ -51,6 +52,7 @@
 
 if t.TYPE_CHECKING:
     from optparse import Values
+    from typing import Dict, Union
 
 
 # heading/sections can contain commas (namespace name lists) and any
@@ -105,6 +107,12 @@
 _UNCLOSED_MULTILINE = re.compile(
     r'(?<![\w>])\[.*\]'
 )
+TEMPLATING_DETECTED = 'templating_detected'
+EXTRA_VARS_TEMPLATE = {
+    'env': {},
+    'template_variables': {},
+    'templating_detected': None
+}
 
 
 def get_cylc_env_vars() -> t.Dict[str, str]:
@@ -242,7 +250,7 @@ def multiline(flines, value, index, maxline):
     return quot + newvalue + line, index
 
 
-def process_plugins(fpath, opts):
+def process_plugins(fpath: 'Union[str, Path]', opts: 'Values'):
     """Run a Cylc pre-configuration plugin.
 
     Plugins should return a dictionary containing:
@@ -263,12 +271,16 @@ def process_plugins(fpath, opts):
             'templating_detected': None
         }
     """
+    fpath = Path(fpath)
+
     # Set out blank dictionary for return:
-    extra_vars = {
-        'env': {},
-        'template_variables': {},
-        'templating_detected': None
-    }
+    extra_vars = deepcopy(EXTRA_VARS_TEMPLATE)
+
+    # Don't run this on global configs:
+    if fpath.name == 'global.cylc':
+        return extra_vars
+
+    fpath = fpath.parent
 
     # Run entry point pre_configure items, trying to merge values with each.:
     for entry_point in iter_entry_points(
@@ -302,26 +314,20 @@ def process_plugins(fpath, opts):
                     )
                 extra_vars[section].update(section_update)
 
+        templating_detected = plugin_result.get(TEMPLATING_DETECTED, None)
         if (
-            'templating_detected' in plugin_result and
-            plugin_result['templating_detected'] is not None and
-            extra_vars['templating_detected'] is not None and
-            extra_vars['templating_detected'] !=
-                plugin_result['templating_detected']
+            templating_detected is not None
+            and extra_vars[TEMPLATING_DETECTED] is not None
+            and extra_vars[TEMPLATING_DETECTED] != templating_detected
         ):
             # Don't allow subsequent plugins with different templating_detected
             raise ParsecError(
-                "Can't merge templating languages "
-                f"{extra_vars['templating_detected']} and "
-                f"{plugin_result['templating_detected']}"
+                "Can't merge templating languages"
+                f"{extra_vars[TEMPLATING_DETECTED]} and "
+                f"{templating_detected}"
             )
-        elif (
-            'templating_detected' in plugin_result and
-            plugin_result['templating_detected'] is not None
-        ):
-            extra_vars['templating_detected'] = plugin_result[
-                'templating_detected'
-            ]
+        elif plugin_result.get(TEMPLATING_DETECTED, None) is not None:
+            extra_vars[TEMPLATING_DETECTED] = templating_detected
 
     return extra_vars
 
@@ -352,7 +358,7 @@ def merge_template_vars(
         >>> merge_template_vars(a, b)
         {'FOO': 42, 'BAZ': 3.14159, 'BAR': 'Hello World'}
     """
-    if plugin_result['templating_detected'] is not None:
+    if plugin_result[TEMPLATING_DETECTED] is not None:
         plugin_tvars = plugin_result['template_variables']
         will_be_overwritten = (
             native_tvars.keys() &
@@ -456,7 +462,7 @@ def read_and_proc(
     do_jinja2 = True
     do_contin = True
 
-    extra_vars = process_plugins(Path(fpath).parent, opts)
+    extra_vars = process_plugins(fpath, opts)
 
     if not template_vars:
         template_vars = {}
@@ -483,12 +489,12 @@ def read_and_proc(
 
     # Fail if templating_detected ≠ hashbang
     process_with = hashbang_and_plugin_templating_clash(
-        extra_vars['templating_detected'], flines
+        extra_vars[TEMPLATING_DETECTED], flines
     )
     # process with EmPy
     if do_empy:
         if (
-            extra_vars['templating_detected'] == 'empy' and
+            extra_vars[TEMPLATING_DETECTED] == 'empy' and
             not process_with and
             process_with != 'empy'
         ):
@@ -508,7 +514,7 @@ def read_and_proc(
     # process with Jinja2
     if do_jinja2:
         if (
-            extra_vars['templating_detected'] == 'jinja2' and
+            extra_vars[TEMPLATING_DETECTED] == 'jinja2' and
             not process_with and
             process_with != 'jinja2'
         ):

tests/unit/parsec/test_fileparse.py

@@ -32,13 +32,15 @@
 )
 from cylc.flow.parsec.OrderedDict import OrderedDictWithDefaults
 from cylc.flow.parsec.fileparse import (
+    EXTRA_VARS_TEMPLATE,
     _prepend_old_templatevars,
     _get_fpath_for_source,
     get_cylc_env_vars,
     addict,
     addsect,
     multiline,
     parse,
+    process_plugins,
     read_and_proc,
     merge_template_vars
 )
@@ -741,7 +743,7 @@ def test_get_fpath_for_source(tmp_path):
 
 def test_user_has_no_cwd(tmp_path):
     """Test we can parse a config file even if cwd does not exist."""
-    cwd = tmp_path/"cwd"
+    cwd = tmp_path / "cwd"
     os.mkdir(cwd)
     os.chdir(cwd)
     os.rmdir(cwd)
@@ -765,15 +767,42 @@ def test_get_cylc_env_vars(monkeypatch):
         {
             "CYLC_VERSION": "betwixt",
             "CYLC_ENV_NAME": "between",
-            "CYLC_QUESTION": "que?", 
-            "CYLC_ANSWER": "42", 
+            "CYLC_QUESTION": "que?",
+            "CYLC_ANSWER": "42",
             "FOO": "foo"
         }
     )
     assert (
         get_cylc_env_vars() == {
-            "CYLC_QUESTION": "que?", 
-            "CYLC_ANSWER": "42", 
+            "CYLC_QUESTION": "que?",
+            "CYLC_ANSWER": "42",
         }
     )
 
+
+class EntryPointWrapper:
+    """Wraps a method to make it look like an entry point."""
+
+    def __init__(self, fcn):
+        self.name = fcn.__name__
+        self.fcn = fcn
+
+    def load(self):
+        return self.fcn
+
+
+@EntryPointWrapper
+def pre_configure_basic(*_, **__):
+    """Simple plugin that returns one env var and one template var."""
+    return {'env': {'foo': 44}, 'template_variables': {}}
+
+
+def test_plugins_not_called_on_global_config(monkeypatch):
+    monkeypatch.setattr(
+        'cylc.flow.parsec.fileparse.iter_entry_points',
+        lambda x: [pre_configure_basic]
+    )
+    result = process_plugins('/pennine/way/flow.cylc', {})
+    assert result != EXTRA_VARS_TEMPLATE
+    result = process_plugins('/appalachian/trail/global.cylc', {})
+    assert result == EXTRA_VARS_TEMPLATE

tests/unit/plugins/test_pre_configure.py

@@ -68,7 +68,7 @@ def test_pre_configure(monkeypatch):
         'cylc.flow.parsec.fileparse.iter_entry_points',
         lambda x: [pre_configure_basic]
     )
-    extra_vars = process_plugins(None, None)
+    extra_vars = process_plugins('/', None)
     assert extra_vars == {
         'env': {
             'ANSWER': '42'
@@ -90,7 +90,7 @@ def test_pre_configure_duplicate(monkeypatch):
         ]
     )
     with pytest.raises(ParsecError):
-        process_plugins(None, None)
+        process_plugins('/', None)
 
 
 def test_pre_configure_templating_detected(monkeypatch):
@@ -103,7 +103,7 @@ def test_pre_configure_templating_detected(monkeypatch):
         ]
     )
     with pytest.raises(ParsecError):
-        process_plugins(None, None)
+        process_plugins('/', None)
 
 
 def test_pre_configure_exception(monkeypatch):
@@ -113,7 +113,7 @@ def test_pre_configure_exception(monkeypatch):
         lambda x: [pre_configure_error]
     )
     with pytest.raises(PluginError) as exc_ctx:
-        process_plugins(None, None)
+        process_plugins('/', None)
     # the context of the original error should be preserved in the raised
     # exception
     assert exc_ctx.value.entry_point == 'cylc.pre_configure'