#7938 - [Plugin: Stepwise][Enhancements] Refactoring, smarter registration & --sw-skip functionality (#7939)

* adding --sw-skip shorthand for stepwise skip

* be explicit rather than implicit with default args for stepwise

* add constant for sw cache dir; only register plugin if necessary rather check check activity always;

* use str format; remove unused args in hooks

* assert cache upfront, allow stepwise to have a reference to the cache

* type hinting lf, skip, move literal strings into module constants

* convert parametrized option into a list

* add a sessionfinish hook for stepwise to keep backwards behaviour the same

* add changelog for #7938

* Improve performance of stepwise modifyitems & address PR feedback

* add test for stepwise deselected based on performance enhancements

* Apply suggestions from code review

* delete from items, account for edge case where failed_index = 0

Co-authored-by: Bruno Oliveira <nicoddemus@gmail.com>

1 files changed, 37 insertions, 40 deletions

diff --git a/src/_pytest/stepwise.py b/src/_pytest/stepwise.py
index 97eae18fd..197577c79 100644
--- a/src/_pytest/stepwise.py
+++ b/src/_pytest/stepwise.py
@@ -1,5 +1,6 @@
 from typing import List
 from typing import Optional
+from typing import TYPE_CHECKING
 
 import pytest
 from _pytest import nodes
@@ -8,6 +9,11 @@ from _pytest.config.argparsing import Parser
 from _pytest.main import Session
 from _pytest.reports import TestReport
 
+if TYPE_CHECKING:
+    from _pytest.cacheprovider import Cache
+
+STEPWISE_CACHE_DIR = "cache/stepwise"
+
 
 def pytest_addoption(parser: Parser) -> None:
     group = parser.getgroup("general")
@@ -15,12 +21,15 @@ def pytest_addoption(parser: Parser) -> None:
         "--sw",
         "--stepwise",
         action="store_true",
+        default=False,
         dest="stepwise",
         help="exit on test failure and continue from last failing test next time",
     )
     group.addoption(
+        "--sw-skip",
         "--stepwise-skip",
         action="store_true",
+        default=False,
         dest="stepwise_skip",
         help="ignore the first failing test but stop on the next failing test",
     )
@@ -28,63 +37,56 @@ def pytest_addoption(parser: Parser) -> None:
 
 @pytest.hookimpl
 def pytest_configure(config: Config) -> None:
-    config.pluginmanager.register(StepwisePlugin(config), "stepwiseplugin")
+    # We should always have a cache as cache provider plugin uses tryfirst=True
+    if config.getoption("stepwise"):
+        config.pluginmanager.register(StepwisePlugin(config), "stepwiseplugin")
+
+
+def pytest_sessionfinish(session: Session) -> None:
+    if not session.config.getoption("stepwise"):
+        assert session.config.cache is not None
+        # Clear the list of failing tests if the plugin is not active.
+        session.config.cache.set(STEPWISE_CACHE_DIR, [])
 
 
 class StepwisePlugin:
     def __init__(self, config: Config) -> None:
         self.config = config
-        self.active = config.getvalue("stepwise")
         self.session: Optional[Session] = None
         self.report_status = ""
-
-        if self.active:
-            assert config.cache is not None
-            self.lastfailed = config.cache.get("cache/stepwise", None)
-            self.skip = config.getvalue("stepwise_skip")
+        assert config.cache is not None
+        self.cache: Cache = config.cache
+        self.lastfailed: Optional[str] = self.cache.get(STEPWISE_CACHE_DIR, None)
+        self.skip: bool = config.getoption("stepwise_skip")
 
     def pytest_sessionstart(self, session: Session) -> None:
         self.session = session
 
     def pytest_collection_modifyitems(
-        self, session: Session, config: Config, items: List[nodes.Item]
+        self, config: Config, items: List[nodes.Item]
     ) -> None:
-        if not self.active:
-            return
         if not self.lastfailed:
             self.report_status = "no previously failed tests, not skipping."
             return
 
-        already_passed = []
-        found = False
-
-        # Make a list of all tests that have been run before the last failing one.
-        for item in items:
+        # check all item nodes until we find a match on last failed
+        failed_index = None
+        for index, item in enumerate(items):
             if item.nodeid == self.lastfailed:
-                found = True
+                failed_index = index
                 break
-            else:
-                already_passed.append(item)
 
         # If the previously failed test was not found among the test items,
         # do not skip any tests.
-        if not found:
+        if failed_index is None:
             self.report_status = "previously failed test not found, not skipping."
-            already_passed = []
         else:
-            self.report_status = "skipping {} already passed items.".format(
-                len(already_passed)
-            )
-
-        for item in already_passed:
-            items.remove(item)
-
-        config.hook.pytest_deselected(items=already_passed)
+            self.report_status = f"skipping {failed_index} already passed items."
+            deselected = items[:failed_index]
+            del items[:failed_index]
+            config.hook.pytest_deselected(items=deselected)
 
     def pytest_runtest_logreport(self, report: TestReport) -> None:
-        if not self.active:
-            return
-
         if report.failed:
             if self.skip:
                 # Remove test from the failed ones (if it exists) and unset the skip option
@@ -109,14 +111,9 @@ class StepwisePlugin:
                     self.lastfailed = None
 
     def pytest_report_collectionfinish(self) -> Optional[str]:
-        if self.active and self.config.getoption("verbose") >= 0 and self.report_status:
-            return "stepwise: %s" % self.report_status
+        if self.config.getoption("verbose") >= 0 and self.report_status:
+            return f"stepwise: {self.report_status}"
         return None
 
-    def pytest_sessionfinish(self, session: Session) -> None:
-        assert self.config.cache is not None
-        if self.active:
-            self.config.cache.set("cache/stepwise", self.lastfailed)
-        else:
-            # Clear the list of failing tests if the plugin is not active.
-            self.config.cache.set("cache/stepwise", [])
+    def pytest_sessionfinish(self) -> None:
+        self.cache.set(STEPWISE_CACHE_DIR, self.lastfailed)