Implement ignore_dependencies in new resolver

If this flag is set, simply report every candidate has no dependencies.

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

@@ -20,11 +20,13 @@ class PipProvider(AbstractProvider):
         self,
         finder,    # type: PackageFinder
         preparer,  # type: RequirementPreparer
+        ignore_dependencies,  # type: bool
         make_install_req  # type: InstallRequirementProvider
     ):
         # type: (...) -> None
         self._finder = finder
         self._preparer = preparer
+        self._ignore_dependencies = ignore_dependencies
         self._make_install_req = make_install_req
 
     def make_requirement(self, ireq):
@@ -72,6 +74,8 @@ class PipProvider(AbstractProvider):
 
     def get_dependencies(self, candidate):
         # type: (Candidate) -> Sequence[Requirement]
+        if self._ignore_dependencies:
+            return []
         return [
             make_requirement(
                 r,

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

@@ -37,6 +37,7 @@ class Resolver(BaseResolver):
         super(Resolver, self).__init__()
         self.finder = finder
         self.preparer = preparer
+        self.ignore_dependencies = ignore_dependencies
         self.make_install_req = make_install_req
         self._result = None  # type: Optional[Result]
 
@@ -45,6 +46,7 @@ class Resolver(BaseResolver):
         provider = PipProvider(
             finder=self.finder,
             preparer=self.preparer,
+            ignore_dependencies=self.ignore_dependencies,
             make_install_req=self.make_install_req,
         )
         reporter = BaseReporter()

tests/unit/resolution_resolvelib/conftest.py

@@ -58,5 +58,6 @@ def provider(finder, preparer):
     yield PipProvider(
         finder=finder,
         preparer=preparer,
+        ignore_dependencies=False,
         make_install_req=make_install_req,
     )