Add warning when non-matching files are passed to pytask.

docs/source/changes.md

@@ -13,6 +13,9 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`619` makes coiled an optional import for tests. Thanks to {user}`erooke`.
 - {pull}`620` makes tests more flexible about their location. Thanks to {user}`erooke`.
 - {pull}`621` fixes the pull requests template.
+- {pull}`627` adds a warning when users explicitly pass files to pytask that pytask is
+  going to ignore because they do not match a pattern. Happens quite often when the task
+  module's name does not start with `task_`.
 
 ## 0.5.0 - 2024-05-26
 

src/_pytask/config.py

@@ -7,6 +7,7 @@
 from typing import TYPE_CHECKING
 from typing import Any
 
+from _pytask.console import console
 from _pytask.pluginmanager import hookimpl
 from _pytask.shared import parse_markers
 from _pytask.shared import parse_paths
@@ -115,3 +116,16 @@ def pytask_parse_config(config: dict[str, Any]) -> None:
 def pytask_post_parse(config: dict[str, Any]) -> None:
     """Sort markers alphabetically."""
     config["markers"] = {k: config["markers"][k] for k in sorted(config["markers"])}
+
+    # Show a warning to the user if they passed a path pointing to a Python module that
+    # does not match the task file pattern.
+    for path in config["paths"]:
+        if path.is_file() and not any(
+            path.match(pattern) for pattern in config["task_files"]
+        ):
+            msg = (
+                f"Warning: The path '{path}' does not match any of the task file "
+                f"patterns in {config['task_files']}. Rename the file or configure a "
+                "different 'task_files' pattern if you want to collect it."
+            )
+            console.print(msg, style="warning")

tests/test_collect.py

@@ -582,3 +582,17 @@ def task_example() -> Annotated[str, Path("file.txt")]: ...
     result = runner.invoke(cli, [tmp_path.as_posix()])
     assert result.exit_code == ExitCode.COLLECTION_FAILED
     assert "The task uses multiple ways to parse" in result.output
+
+
+@pytest.mark.end_to_end()
+def test_print_warning_if_non_matching_path_is_passed(runner, tmp_path):
+    tmp_path.joinpath("task.py").write_text("def task_example(): pass")
+    result = runner.invoke(cli, [tmp_path.as_posix()])
+    assert result.exit_code == ExitCode.OK
+    assert "Collected 0 tasks" in result.output
+    assert "Warning: The path" not in result.output
+
+    result = runner.invoke(cli, [tmp_path.joinpath("task.py").as_posix()])
+    assert result.exit_code == ExitCode.OK
+    assert "Collected 0 tasks" in result.output
+    assert "Warning: The path" in result.output