Merge master

news/9117.bugfix.rst

@@ -0,0 +1,2 @@
+New resolver: The "Requirement already satisfied" log is not printed only once
+for each package during resolution.

news/9249.feature.rst

@@ -0,0 +1 @@
+Add a mechanism to delay resolving certain packages, and use it for setuptools.

src/pip/_internal/resolution/resolvelib/factory.py

@@ -97,9 +97,11 @@ class Factory(object):
         self._force_reinstall = force_reinstall
         self._ignore_requires_python = ignore_requires_python
 
+        self._build_failures = {}  # type: Cache[InstallationError]
         self._link_candidate_cache = {}  # type: Cache[LinkCandidate]
         self._editable_candidate_cache = {}  # type: Cache[EditableCandidate]
-        self._build_failures = {}  # type: Cache[InstallationError]
+        self._installed_candidate_cache = {
+        }  # type: Dict[str, AlreadyInstalledCandidate]
 
         if not ignore_installed:
             self._installed_dists = {
@@ -121,7 +123,11 @@ class Factory(object):
         template,  # type: InstallRequirement
     ):
         # type: (...) -> Candidate
-        base = AlreadyInstalledCandidate(dist, template, factory=self)
+        try:
+            base = self._installed_candidate_cache[dist.key]
+        except KeyError:
+            base = AlreadyInstalledCandidate(dist, template, factory=self)
+            self._installed_candidate_cache[dist.key] = base
         if extras:
             return ExtrasCandidate(base, extras)
         return base

src/pip/_internal/resolution/resolvelib/provider.py

@@ -117,7 +117,18 @@ class PipProvider(AbstractProvider):
         restrictive = _get_restrictive_rating(req for req, _ in information)
         transitive = all(parent is not None for _, parent in information)
         key = next(iter(candidates)).name if candidates else ""
-        return (restrictive, transitive, key)
+
+        # HACK: Setuptools have a very long and solid backward compatibility
+        # track record, and extremely few projects would request a narrow,
+        # non-recent version range of it since that would break a lot things.
+        # (Most projects specify it only to request for an installer feature,
+        # which does not work, but that's another topic.) Intentionally
+        # delaying Setuptools helps reduce branches the resolver has to check.
+        # This serves as a temporary fix for issues like "apache-airlfow[all]"
+        # while we work on "proper" branch pruning techniques.
+        delay_this = (key == "setuptools")
+
+        return (delay_this, restrictive, transitive, key)
 
     def find_matches(self, requirements):
         # type: (Sequence[Requirement]) -> Iterable[Candidate]