Implement --show-errors-immediately. (#156)

Author: tobiasraabe

docs/source/changes.rst

@@ -22,6 +22,7 @@ all releases are available on `PyPI <https://pypi.org/project/pytask>`_ and
   days, hours, minutes and seconds.
 - :gh:`155` implements functions to check for optional packages and programs and raises
   errors for requirements to draw the DAG earlier.
+- :gh:`156` adds an option to print/show errors as soon as they occur.
 
 
 0.1.1 - 2021-08-25

docs/source/reference_guides/configuration.rst

@@ -147,6 +147,20 @@ The options
         pdb = True
 
 
+.. confval:: show_errors_immediately
+
+    If you want to print the exception and tracebacks of errors as soon as they occur,
+    set this value to true.
+
+    .. code-block:: console
+
+        pytask build --show-errors-immediately
+
+    .. code-block:: ini
+
+        show_errors_immediately = True
+
+
 .. confval:: show_locals
 
     If you want to print local variables of each stack frame in the tracebacks, set this

src/_pytask/build.py

@@ -94,6 +94,12 @@ def main(config_from_cli):
     help="Stop after the first failure.",
 )
 @click.option("--max-failures", default=None, help="Stop after some failures.")
+@click.option(
+    "--show-errors-immediately",
+    is_flag=True,
+    default=None,
+    help="Print errors with tracebacks as soon as the task fails.",
+)
 def build(**config_from_cli):
     """Collect and execute tasks and report the results.
 

src/_pytask/execute.py

@@ -16,12 +16,30 @@
 from _pytask.outcomes import Persisted
 from _pytask.outcomes import Skipped
 from _pytask.report import ExecutionReport
+from _pytask.shared import get_first_non_none_value
 from _pytask.shared import reduce_node_name
 from _pytask.traceback import format_exception_without_traceback
 from _pytask.traceback import remove_traceback_from_exc_info
 from _pytask.traceback import render_exc_info
 
 
+@hookimpl
+def pytask_post_parse(config):
+    if config["show_errors_immediately"]:
+        config["pm"].register(ShowErrorsImmediatelyPlugin)
+
+
+@hookimpl
+def pytask_parse_config(config, config_from_cli, config_from_file):
+    config["show_errors_immediately"] = get_first_non_none_value(
+        config_from_cli,
+        config_from_file,
+        key="show_errors_immediately",
+        default=False,
+        callback=lambda x: x if x is None else bool(x),
+    )
+
+
 @hookimpl
 def pytask_execute(session):
     """Execute tasks."""
@@ -172,10 +190,17 @@ def pytask_execute_task_log_end(report):
     console.print(report.symbol, style=report.color, end="")
 
 
+class ShowErrorsImmediatelyPlugin:
+    @staticmethod
+    @hookimpl(tryfirst=True)
+    def pytask_execute_task_log_end(session, report):
+        if not report.success:
+            _print_errored_task_report(session, report)
+
+
 @hookimpl
 def pytask_execute_log_end(session, reports):
     session.execution_end = time.time()
-    show_locals = session.config["show_locals"]
 
     n_failed = len(reports) - sum(report.success for report in reports)
     n_skipped = sum(
@@ -195,27 +220,7 @@ def pytask_execute_log_end(session, reports):
 
     for report in reports:
         if not report.success:
-
-            task_name = reduce_node_name(report.task, session.config["paths"])
-            if len(task_name) > console.width - 15:
-                task_name = report.task.base_name
-            console.rule(
-                f"[{ColorCode.FAILED}]Task {task_name} failed", style=ColorCode.FAILED
-            )
-
-            console.print()
-
-            if report.exc_info and isinstance(report.exc_info[1], Exit):
-                console.print(format_exception_without_traceback(report.exc_info))
-            else:
-                console.print(render_exc_info(*report.exc_info, show_locals))
-
-            console.print()
-            show_capture = session.config["show_capture"]
-            for when, key, content in report.sections:
-                if key in ("stdout", "stderr") and show_capture in (key, "all"):
-                    console.rule(f"Captured {key} during {when}", style=None)
-                    console.print(content)
+            _print_errored_task_report(session, report)
 
     session.hook.pytask_log_session_footer(
         session=session,
@@ -235,6 +240,28 @@ def pytask_execute_log_end(session, reports):
     return True
 
 
+def _print_errored_task_report(session, report):
+    """Print the traceback and the exception of an errored report."""
+    task_name = reduce_node_name(report.task, session.config["paths"])
+    if len(task_name) > console.width - 15:
+        task_name = report.task.base_name
+    console.rule(f"[{ColorCode.FAILED}]Task {task_name} failed", style=ColorCode.FAILED)
+
+    console.print()
+
+    if report.exc_info and isinstance(report.exc_info[1], Exit):
+        console.print(format_exception_without_traceback(report.exc_info))
+    else:
+        console.print(render_exc_info(*report.exc_info, session.config["show_locals"]))
+
+    console.print()
+    show_capture = session.config["show_capture"]
+    for when, key, content in report.sections:
+        if key in ("stdout", "stderr") and show_capture in (key, "all"):
+            console.rule(f"Captured {key} during {when}", style=None)
+            console.print(content)
+
+
 def _update_states_in_database(dag, task_name):
     """Update the state for each node of a task in the database."""
     for name in node_and_neighbors(dag, task_name):

src/_pytask/live.py

@@ -132,7 +132,7 @@ def pytask_execute_task_log_start(self, task):
         self.update_running_tasks(task)
         return True
 
-    @hookimpl(tryfirst=True)
+    @hookimpl
     def pytask_execute_task_log_end(self, report):
         self.update_reports(report)
         return True

tests/test_execute.py

@@ -1,3 +1,4 @@
+import re
 import subprocess
 import textwrap
 
@@ -265,7 +266,7 @@ def task_y(): pass
 
 
 @pytest.mark.end_to_end
-def test_scheduling_w_mixed_priorities(tmp_path):
+def test_scheduling_w_mixed_priorities(runner, tmp_path):
     source = """
     import pytask
 
@@ -275,6 +276,32 @@ def task_mixed(): pass
     """
     tmp_path.joinpath("task_dummy.py").write_text(textwrap.dedent(source))
 
-    session = main({"paths": tmp_path})
+    result = runner.invoke(cli, [tmp_path.as_posix()])
+
+    assert result.exit_code == 4
+    assert "Failures during resolving dependencies" in result.output
+    assert "'try_first' and 'try_last' cannot be applied" in result.output
+
+
+@pytest.mark.end_to_end
+@pytest.mark.parametrize("show_errors_immediately", [True, False])
+def test_show_errors_immediately(runner, tmp_path, show_errors_immediately):
+    source = """
+    def task_succeed(): pass
+    def task_error(): raise ValueError
+    """
+    tmp_path.joinpath("task_error.py").write_text(textwrap.dedent(source))
+
+    args = [tmp_path.as_posix()]
+    if show_errors_immediately:
+        args.append("--show-errors-immediately")
+    result = runner.invoke(cli, args)
+
+    assert result.exit_code == 1
+    assert "::task_succeed │ ." in result.output
 
-    assert session.exit_code == 4
+    matches_traceback = re.findall("Traceback", result.output)
+    if show_errors_immediately:
+        assert len(matches_traceback) == 2
+    else:
+        assert len(matches_traceback) == 1