Allow required_variable to only enforce on certain modes

gcp-metadata mod can use this, as it does not need `hostlist` when run
in local mode.

lib/ramble/ramble/application.py

@@ -829,7 +829,7 @@ def build_modifier_instances(self):
             self._modifier_instances.append(mod_inst)
 
             # Add this modifiers required variables for validation
-            self.keywords.update_keys(mod_inst.required_vars)
+            self.keywords.update_keys(mod_inst.get_required_variables())
 
         # Ensure no expand vars are set correctly for modifiers
         for mod_inst in self._modifier_instances:

lib/ramble/ramble/language/modifier_language.py

@@ -256,19 +256,23 @@ def _env_var_modification(mod):
 
 
 @modifier_directive("required_vars")
-def required_variable(var: str, results_level="variable"):
+def required_variable(var: str, results_level="variable", modes=None):
     """Mark a variable as being required by this modifier
 
     Args:
         var (str): Variable name to mark as required
         results_level (str): 'variable' or 'key'. If 'key', variable is promoted to
                              a key within JSON or YAML formatted results.
+        modes (list[str] | None): modes that the required check should be applied. The
+                            default None means apply to all modes.
     """
 
     def _mark_required_var(mod):
         mod.required_vars[var] = {
             "type": ramble.keywords.key_type.required,
             "level": ramble.keywords.output_level.variable,
+            # Extra prop that's only used for filtering
+            "modes": set(modes) if modes is not None else None,
         }
 
     return _mark_required_var

lib/ramble/ramble/modifier.py

@@ -284,6 +284,22 @@ def _prepare_analysis(self, workspace):
         """
         pass
 
+    def get_required_variables(self):
+        """Get all the required variables based on the mode."""
+        required_vars = self.required_vars
+        filtered_vars = {}
+        if required_vars:
+            mode = self._usage_mode
+            for var_name, var_props in required_vars.items():
+                modes = var_props["modes"]
+                if modes is None or mode in modes:
+                    filtered_vars[var_name] = {
+                        # Exclude the extra modes prop
+                        k: var_props[k]
+                        for k in var_props.keys() - {"modes"}
+                    }
+        return filtered_vars
+
 
 class ModifierError(RambleError):
     """

lib/ramble/ramble/test/modifier_functionality/required_variables.py

@@ -0,0 +1,69 @@
+# Copyright 2022-2024 The Ramble Authors
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+import os
+
+import pytest
+
+import ramble.workspace
+import ramble.experiment_set
+from ramble.main import RambleCommand
+
+workspace = RambleCommand("workspace")
+
+
+@pytest.mark.parametrize(
+    "test_name,mode,expect_error",
+    [
+        (
+            "standard_require_hostlist",
+            "standard",
+            ramble.experiment_set.RambleVariableDefinitionError,
+        ),
+        ("local_no_require_hostlist", "local", None),
+    ],
+)
+def test_required_variables(
+    test_name, mode, expect_error, mutable_mock_workspace_path, mutable_applications
+):
+    workspace_name = test_name
+
+    test_config = f"""
+ramble:
+  variables:
+    mpi_command: ''
+    batch_submit: 'batch_submit {{execute_experiment}}'
+    processes_per_node: 1
+  applications:
+    hostname:
+      workloads:
+        local:
+          experiments:
+            test:
+              variables:
+                n_nodes: 1
+  modifiers:
+  - name: gcp-metadata
+    mode: {mode}
+"""
+
+    with ramble.workspace.create(workspace_name) as ws:
+        ws.write()
+
+        config_path = os.path.join(ws.config_dir, ramble.workspace.config_file_name)
+
+        with open(config_path, "w+") as f:
+            f.write(test_config)
+
+        ws._re_read()
+
+        if expect_error:
+            with pytest.raises(expect_error):
+                workspace("setup", "--dry-run", global_args=["-D", ws.root])
+        else:
+            workspace("setup", "--dry-run", global_args=["-D", ws.root])

var/ramble/repos/builtin/modifiers/gcp-metadata/modifier.py

@@ -34,7 +34,7 @@ class GcpMetadata(BasicModifier):
 
     software_spec("pdsh", pkg_spec="pdsh", package_manager="spack*")
 
-    required_variable("hostlist")
+    required_variable("hostlist", modes=["standard"])
 
     modifier_variable(
         "metadata_parallel_prefix",