Raise error when non-existing task paths are added to the config.

docs/source/changes.md

@@ -8,6 +8,9 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 ## 0.4.5 - 2023-12-xx
 
 - {pull}`515` enables tests with graphviz in CI. Thanks to {user}`NickCrews`.
+- {pull}`517` raises an error when the configuration file contains a non-existing path
+  (fixes #514). Also adds a warning if the path is configured as a string and not a list
+  of strings.
 
 ## 0.4.4 - 2023-12-04
 

src/_pytask/shared.py

@@ -2,6 +2,7 @@
 from __future__ import annotations
 
 import glob
+import warnings
 from pathlib import Path
 from typing import Any
 from typing import Iterable
@@ -46,17 +47,29 @@ def to_list(scalar_or_iter: Any) -> list[Any]:
 
 def parse_paths(x: Any | None) -> list[Path] | None:
     """Parse paths."""
-    if x is not None:
-        paths = [Path(p) for p in to_list(x)]
-        paths = [
-            Path(p).resolve()
-            for path in paths
-            for p in glob.glob(path.as_posix())  # noqa: PTH207
-        ]
-        out = paths
-    else:
-        out = None
-    return out
+    if x is None:
+        return None
+
+    if isinstance(x, str):
+        msg = (
+            "Specifying paths as a string in 'pyproject.toml' is deprecated and will "
+            "result in an error in v0.5. Please use a list of strings instead: "
+            f'["{x}"].'
+        )
+        warnings.warn(msg, category=FutureWarning, stacklevel=1)
+        x = [x]
+
+    paths = [Path(p) for p in to_list(x)]
+    for p in paths:
+        if not p.exists():
+            msg = f"The path '{p}' does not exist."
+            raise FileNotFoundError(msg)
+
+    return [
+        Path(p).resolve()
+        for path in paths
+        for p in glob.glob(path.as_posix())  # noqa: PTH207
+    ]
 
 
 def reduce_names_of_multiple_nodes(

tests/test_config.py

@@ -4,6 +4,7 @@
 
 import pytest
 from pytask import build
+from pytask import cli
 from pytask import ExitCode
 
 
@@ -59,3 +60,15 @@ def test_passing_paths_via_configuration_file(tmp_path, file_or_folder):
 
     assert session.exit_code == ExitCode.OK
     assert len(session.tasks) == 1
+
+
+def test_not_existing_path_in_config(runner, tmp_path):
+    config = """
+    [tool.pytask.ini_options]
+    paths = "not_existing_path"
+    """
+    tmp_path.joinpath("pyproject.toml").write_text(textwrap.dedent(config))
+
+    with pytest.warns(FutureWarning, match="Specifying paths as a string"):
+        result = runner.invoke(cli, [tmp_path.as_posix()])
+    assert result.exit_code == ExitCode.CONFIGURATION_FAILED