fix: throw error message in case of target rule that depends on a pip…

…e. (#1532)

* fix: throw error message in case of target rule that depends on a pipe.

* skip on win

snakemake/dag.py

@@ -1308,6 +1308,12 @@ def handle_pipes_and_services(self):
                             "a dead lock.".format(f),
                             rule=job.rule,
                         )
+                    elif is_pipe and depending[0].is_norun:
+                        raise WorkflowError(
+                            f"Output file {f} is marked as pipe but is requested by a rule that "
+                            "does not execute anything. This is not allowed because it would lead "
+                            "to a dead lock."
+                        )
 
                     for dep in depending:
                         if dep.is_run:

tests/test_pipe_depend/Snakefile

@@ -0,0 +1,11 @@
+rule all:
+    input:
+        "test.txt"
+
+
+rule a:
+    output:
+        pipe("test.txt")
+    shell:
+        "echo test > {output}"
+

tests/tests.py

@@ -1565,3 +1565,13 @@ def test_service_jobs():
 
 def test_incomplete_params():
     run(dpath("test_incomplete_params"), dryrun=True, printshellcmds=True)
+
+
+@skip_on_windows  # no pipe support on windows
+def test_pipe_depend():
+    run(dpath("test_pipe_depend"), shouldfail=True)
+
+
+@skip_on_windows  # no pipe support on windows
+def test_pipe_depend_target_file():
+    run(dpath("test_pipe_depend"), targets=["test.txt"], shouldfail=True)