Allow pre configure plugin to access compat mode info in cylc install.

CHANGES.md

@@ -30,7 +30,6 @@ enhancements to ``cylc lint``:
   * __Only__ check for missing Jinja2 shebangs in ``flow.cylc`` and
     ``suite.rc`` files.
 
-### Fixes
 ### Breaking Changes
 
 [#5600](https://github.com/cylc/cylc-flow/pull/5600) -
@@ -53,6 +52,9 @@ for `cylc play` when called by `cylc vip` or `cylc vr`.
 Enabled the "stop", "poll", "kill" and "message" commands to be issued from
 the UI whilst the workflow is in the process of shutting down.
 
+[#5582](https://github.com/cylc/cylc-flow/pull/5582) - Set Cylc 7 compatibility
+mode before running pre-configure plugins.
+
 ## __cylc-8.1.4 (<span actions:bind='release-date'>Released 2023-05-04</span>)__
 
 ### Fixes

cylc/flow/scripts/install.py

@@ -108,7 +108,8 @@
 from cylc.flow.workflow_files import (
     install_workflow,
     parse_cli_sym_dirs,
-    search_install_source_dirs
+    search_install_source_dirs,
+    check_deprecation,
 )
 from cylc.flow.terminal import cli_function
 
@@ -290,6 +291,11 @@ def install(
             "options --no-run-name and --run-name are mutually exclusive."
         )
     source = get_source_location(reg)
+
+    # Check deprecation to allow plugins to have access to correct flags
+    # for compatibility mode:
+    check_deprecation(source)
+
     for entry_point in iter_entry_points(
         'cylc.pre_configure'
     ):

cylc/flow/scripts/validate_install_play.py

@@ -28,6 +28,8 @@
 
 """
 
+import sys
+
 from cylc.flow.scripts.validate import (
     VALIDATE_OPTIONS,
     _main as validate_main
@@ -111,5 +113,5 @@ def main(parser: COP, options: 'Values', workflow_id: Optional[str] = None):
     )
 
     set_timestamps(LOG, options.log_timestamp)
-    log_subcommand('play', workflow_id)
+    log_subcommand(*sys.argv[1:])
     _play(parser, options, workflow_id)

cylc/flow/workflow_files.py

@@ -1237,8 +1237,12 @@ def check_deprecation(path, warn=True):
     Path can point to config file or parent directory (i.e. workflow name).
     """
     if (
-        path.resolve().name == WorkflowFiles.SUITE_RC
-        or (path / WorkflowFiles.SUITE_RC).is_file()
+        # Don't want to log if it's already been set True.
+        not cylc.flow.flags.cylc7_back_compat
+        and (
+            path.resolve().name == WorkflowFiles.SUITE_RC
+            or (path / WorkflowFiles.SUITE_RC).is_file()
+        )
     ):
         cylc.flow.flags.cylc7_back_compat = True
         if warn:

tests/integration/test_install.py

@@ -148,3 +148,43 @@ def test_install_scan_ping(
     out = capsys.readouterr().out
     assert INSTALLED_MSG.format(wfrun='w2/run1') in out
     assert WF_ACTIVE_MSG.format(wf='w2') not in out
+
+
+def test_install_gets_back_compat_mode_for_plugins(
+    src_run_dirs: Callable,
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture,
+):
+    """Assert that pre cylc install will detect whether a workflow
+    should use back compat mode _before_ running pre_configure plugins
+    so that those plugins can use that information.
+    """
+    class failIfDeprecated:
+        """A fake Cylc Plugin entry point"""
+        @staticmethod
+        def resolve():
+            return failIfDeprecated.raiser
+
+        @staticmethod
+        def raiser(*_, **__):
+            import cylc.flow.flags
+            if cylc.flow.flags.cylc7_back_compat:
+                print('Plugin:True')
+                return True
+            print('Plugin:False')
+            return False
+
+    # Monkeypatch our fake entry point into iter_entry_points:
+    monkeypatch.setattr(
+        'cylc.flow.scripts.install.iter_entry_points',
+        lambda x: [failIfDeprecated]
+    )
+    opts = InstallOptions()
+
+    monkeypatch.setattr('cylc.flow.flags.cylc7_back_compat', False)
+    install_cli(opts, reg='w1')
+    assert capsys.readouterr()[0].split('\n')[0] == 'Plugin:False'
+
+    monkeypatch.setattr('cylc.flow.flags.cylc7_back_compat', True)
+    install_cli(opts, reg='w1')
+    assert capsys.readouterr()[0].split('\n')[0] == 'Plugin:True'