Fix --sw crash when first file in cmdline fails to collect

Fix #5444

changelog/5444.bugfix.rst

@@ -0,0 +1 @@
+Fix ``--stepwise`` mode when the first file passed on the command-line fails to collect.

src/_pytest/stepwise.py

@@ -28,6 +28,7 @@ class StepwisePlugin:
         self.config = config
         self.active = config.getvalue("stepwise")
         self.session = None
+        self.report_status = ""
 
         if self.active:
             self.lastfailed = config.cache.get("cache/stepwise", None)
@@ -103,7 +104,7 @@ class StepwisePlugin:
                     self.lastfailed = None
 
     def pytest_report_collectionfinish(self):
-        if self.active and self.config.getoption("verbose") >= 0:
+        if self.active and self.config.getoption("verbose") >= 0 and self.report_status:
             return "stepwise: %s" % self.report_status
 
     def pytest_sessionfinish(self, session):

testing/test_stepwise.py

@@ -156,14 +156,18 @@ def test_change_testfile(stepwise_testdir):
     assert "test_success PASSED" in stdout
 
 
-def test_stop_on_collection_errors(broken_testdir):
-    result = broken_testdir.runpytest(
-        "-v",
-        "--strict-markers",
-        "--stepwise",
-        "broken_testfile.py",
-        "working_testfile.py",
-    )
+@pytest.mark.parametrize("broken_first", [True, False])
+def test_stop_on_collection_errors(broken_testdir, broken_first):
+    """Stop during collection errors. We have two possible messages depending on the order (#5444),
+    so test both cases."""
+    files = ["working_testfile.py", "broken_testfile.py"]
+    if broken_first:
+        files.reverse()
+    result = broken_testdir.runpytest("-v", "--strict-markers", "--stepwise", *files)
 
-    stdout = result.stdout.str()
-    assert "errors during collection" in stdout
+    if broken_first:
+        result.stdout.fnmatch_lines(
+            "*Error when collecting test, stopping test execution*"
+        )
+    else:
+        result.stdout.fnmatch_lines("*errors during collection*")