Merge with develop.

poetry/installation/installer.py

@@ -11,7 +11,6 @@
 from poetry.puzzle.operations import Uninstall
 from poetry.puzzle.operations import Update
 from poetry.puzzle.operations.operation import Operation
-from poetry.puzzle.provider import Provider
 from poetry.repositories import Pool
 from poetry.repositories import Repository
 from poetry.repositories.installed_repository import InstalledRepository
@@ -206,17 +205,36 @@ def _do_install(self, local_repo):
             root = root.clone()
             del root.dev_requires[:]
 
-        if self._remove_untracked:
-            locked_names = {locked.name for locked in locked_repository.packages}
+        if self._io.is_verbose():
+            self._io.write_line("")
+            self._io.write_line(
+                "<info>Finding the necessary packages for the current system</>"
+            )
 
-            for installed in self._installed_repository.packages:
-                if installed.name == self._package.name:
-                    continue
-                if installed.name in Provider.UNSAFE_PACKAGES:
-                    # Never remove pip, setuptools etc.
-                    continue
-                if installed.name not in locked_names:
-                    ops.append(Uninstall(installed))
+        # We resolve again by only using the lock file
+        pool = Pool(ignore_repository_names=True)
+
+        # Making a new repo containing the packages
+        # newly resolved and the ones from the current lock file
+        repo = Repository()
+        for package in local_repo.packages + locked_repository.packages:
+            if not repo.has_package(package):
+                repo.add_package(package)
+
+        pool.add_repository(repo)
+
+        # We whitelist all packages to be sure
+        # that the latest ones are picked up
+        whitelist = []
+        for pkg in locked_repository.packages:
+            whitelist.append(pkg.name)
+
+        solver = Solver(
+            root, pool, self._installed_repository, locked_repository, NullIO()
+        )
+
+        with solver.use_environment(self._env):
+            ops = solver.solve(use_latest=whitelist)
 
         # We need to filter operations so that packages
         # not compatible with the current system,