fixtures: more tweaks

[bluetech]

A few more small fixture cleanups/improvements from looking at #11243.

The second commit is picked from #11243 authored by @sadra-barikbin. The idea is to make #11243 a bit smaller after it's rebased on top of this (which I'll be happy to do if @sadra-barikbin prefers).

The last commits are some doctest cleanups after checking its fixture handling. If we ever want to provide a proper interface for (non-Function) items to support fixtures, DoctestItem can be our model case.

[bluetech]

I also wrote another commit, making getfixtureclosure a bit faster by avoiding all of the repetitive work and linear searches it does. However I scrapped it because it will likely conflict further with @sadra-barikbin's plan to change getfixtureclosure from BFS to DFS (as stated in #11234). Here it is for reference:

patch

commit 95ca3bbe7f03380470092c1f3446b921cd93ddac
Author: Ran Benita <ran@unusedvar.com>
Date:   Tue Sep 5 00:30:36 2023 +0300

    fixtures: avoid linear searches in getfixtureclosure
    
    Previously did an inefficient fixpoint algorithm. Replace it with a work
    queue so we only check "new" argnames.

diff --git a/src/_pytest/fixtures.py b/src/_pytest/fixtures.py
index 80b965b81..ce006151c 100644
--- a/src/_pytest/fixtures.py
+++ b/src/_pytest/fixtures.py
@@ -1544,23 +1544,23 @@ class FixtureManager:
         # (discovering matching fixtures for a given name/node is expensive).
 
         parentid = parentnode.nodeid
-        fixturenames_closure = list(initialnames)
+        closure: dict[str, None] = dict.fromkeys(initialnames)
 
         arg2fixturedefs: Dict[str, Sequence[FixtureDef[Any]]] = {}
-        lastlen = -1
-        while lastlen != len(fixturenames_closure):
-            lastlen = len(fixturenames_closure)
-            for argname in fixturenames_closure:
-                if argname in ignore_args:
-                    continue
-                if argname in arg2fixturedefs:
-                    continue
-                fixturedefs = self.getfixturedefs(argname, parentid)
-                if fixturedefs:
-                    arg2fixturedefs[argname] = fixturedefs
-                    for arg in fixturedefs[-1].argnames:
-                        if arg not in fixturenames_closure:
-                            fixturenames_closure.append(arg)
+        work = deque(initialnames)
+        while work:
+            argname = work.popleft()
+            if argname in ignore_args:
+                continue
+            if argname in arg2fixturedefs:
+                continue
+            fixturedefs = self.getfixturedefs(argname, parentid)
+            if fixturedefs:
+                arg2fixturedefs[argname] = fixturedefs
+                for arg in fixturedefs[-1].argnames:
+                    if arg not in closure:
+                        closure[arg] = None
+                        work.append(arg)
 
         def sort_by_scope(arg_name: str) -> Scope:
             try:
@@ -1570,7 +1570,7 @@ class FixtureManager:
             else:
                 return fixturedefs[-1]._scope
 
-        fixturenames_closure.sort(key=sort_by_scope, reverse=True)
+        fixturenames_closure = sorted(closure, key=sort_by_scope, reverse=True)
         return fixturenames_closure, arg2fixturedefs
 
     def pytest_generate_tests(self, metafunc: "Metafunc") -> None:

[nicoddemus]

LGTM!

[sadra-barikbin]

Thanks @bluetech. Looks good to me.

[RonnyPfannschmidt]

Love to see this land, it's just awesome to see all the collaboration on enhancing those details happen, thanks!