Warn but don't die if a pipeline parameter is missing targets (#144)

* Add more commits to git-blame-ignore-revs

* Warn but don't die if a pipeline parameter is missing targets

.git-blame-ignore-revs

@@ -1,2 +1,8 @@
 # Reformatted with Black
 e77db53f6c52c37e8a0bfa79f7bf3f07f0fa19d8
+
+# Enable COM rule
+98bf400c9017be60841d15df306faccd2ba71c90
+
+# Reformat with ruff-format
+f02536612abdaefec2b9eaf19d5a5c4c3507a3cb

tests/__snapshots__/test_validation.ambr

@@ -202,3 +202,12 @@
 
   '''
 # ---
+# name: test_warning_examples_cli[targetless-pipeline-params.yaml]
+  '''
+  >>> targetless-pipeline-params.yaml
+  warning: Pipeline "Example Pipeline with Parameter with no Target" parameter "id": no targets.
+  ------------------------------------------------------------
+  *** 0 errors, 1 warnings
+
+  '''
+# ---

tests/warning_examples/targetless-pipeline-params.yaml

@@ -0,0 +1,20 @@
+- step:
+    name: train_step
+    image: python:3.10
+    command:
+      - pip install valohai-utils
+      - python ./train.py {parameters}
+    parameters:
+      - name: id
+        type: string
+
+- pipeline:
+    name: Example Pipeline with Parameter with no Target
+    parameters:
+      - name: id
+        default: 123
+    nodes:
+      - name: train
+        step: train_step
+        type: execution
+    edges: []

valohai_yaml/objs/pipelines/pipeline_parameter.py

@@ -17,13 +17,15 @@ def __init__(
         self,
         *,
         name: str,
-        targets: Union[List[str], str],
+        targets: Optional[Union[List[str], str]] = None,
         value: Optional[str] = None,
         default: Optional[str] = None,
     ) -> None:
         self.name = name
         self.default = default if value is None else value
-        if isinstance(targets, str):
+        if not targets:
+            self.targets = []
+        elif isinstance(targets, str):
             self.targets = [targets]
         else:
             self.targets = check_type_and_listify(targets, str)
@@ -45,6 +47,10 @@ def lint(self, lint_result: LintResult, context: LintContext) -> None:
         config: Config = context["config"]
         steps = config.steps
         node_map = pipeline.node_map
+        if not self.targets:
+            lint_result.add_warning(
+                f'Pipeline "{pipeline.name}" parameter "{self.name}": no targets.',
+            )
         for target in self.targets:
             target_node_name, socket_type, target_parameter_name = split_socket_str(
                 target,