Always check_if_exists for editable

But only when pip has collected the editable package's metadata.

closes #1548

CHANGES.txt

@@ -1,5 +1,8 @@
 **8.2.0 (unreleased)**
 
+* Uninstall existing packages when performing an editable installation of
+  the same packages (:issue:`1548`).
+
 * Pip show is less verbose by default. `--verbose` prints multiline fields
 
 * Added optional column formatting to ``pip list`` (:issue:`3651`).

pip/req/req_set.py

@@ -489,6 +489,7 @@ class RequirementSet(object):
                 abstract_dist.prep_for_dist()
                 if self.is_download:
                     req_to_install.archive(self.download_dir)
+                req_to_install.check_if_exists()
             elif req_to_install.satisfied_by:
                 if require_hashes:
                     logger.debug(

tests/functional/test_install.py

@@ -201,10 +201,34 @@ def test_install_editable_uninstalls_existing(data, script, tmpdir):
     )
     result.assert_installed('pip-test-package', with_files=['.git'])
     assert 'Found existing installation: pip-test-package 0.1' in result.stdout
-    assert 'Uninstalling pip-test-package:' in result.stdout
+    assert 'Uninstalling pip-test-package-' in result.stdout
     assert 'Successfully uninstalled pip-test-package' in result.stdout
 
 
+def test_install_editable_uninstalls_existing_from_path(script, data):
+    """
+    Test that installing an editable uninstalls a previously installed
+    non-editable version from path
+    """
+    to_install = data.src.join('simplewheel-1.0')
+    result = script.pip_install_local(to_install)
+    assert 'Successfully installed simplewheel' in result.stdout
+    simple_folder = script.site_packages / 'simple'
+    result.assert_installed('simple', editable=False)
+    assert simple_folder in result.files_created, str(result.stdout)
+
+    result = script.pip(
+        'install', '-e',
+        to_install,
+    )
+    install_path = script.site_packages / 'simplewheel.egg-link'
+    assert install_path in result.files_created, str(result)
+    assert 'Found existing installation: simplewheel 1.0' in result.stdout
+    assert 'Uninstalling simplewheel-' in result.stdout
+    assert 'Successfully uninstalled simplewheel' in result.stdout
+    assert simple_folder in result.files_deleted, str(result.stdout)
+
+
 def test_install_editable_from_hg(script, tmpdir):
     """Test cloning from Mercurial."""
     pkg_path = _create_test_package(script, name='testpackage', vcs='hg')