fix #4775 Consider environment variable PIP_TARGET when calculate depndancy delta.

news/4775.bugfix.rst

@@ -0,0 +1 @@
+If `PIP_TARGET` is set to environment variables,  Refer specified directory for calculate delta, instead default directory

pipenv/environment.py

@@ -540,7 +540,7 @@ class Environment:
         :rtype: iterator
         """
 
-        libdirs = self.base_paths["libdirs"].split(os.pathsep)
+        libdirs = os.environ.get('PIP_TARGET', self.base_paths["libdirs"].split(os.pathsep))
         dists = (pkg_resources.find_distributions(libdir) for libdir in libdirs)
         yield from itertools.chain.from_iterable(dists)
 

tests/integration/test_sync.py

@@ -111,3 +111,30 @@ requests = "*"
         c = p.pipenv('sync --sequential --verbose')
         for package in p.lockfile['default']:
             assert f'Successfully installed {package}' in c.stdout
+
+
+@pytest.mark.sync
+def test_sync_consider_pip_target(PipenvInstance):
+    """
+    """
+    with PipenvInstance(chdir=True) as p:
+        with open(p.pipfile_path, 'w') as f:
+            f.write("""
+[packages]
+six = "*"
+            """.strip())
+
+        # Perform initial lock.
+        c = p.pipenv('lock')
+        assert c.returncode == 0
+        lockfile_content = p.lockfile
+        assert lockfile_content
+        c = p.pipenv('sync')
+        assert c.returncode == 0
+
+        pip_target_dir = 'target_dir'
+        os.environ['PIP_TARGET'] = pip_target_dir
+        c = p.pipenv('sync')
+        assert c.returncode == 0
+        assert 'six.py' in os.listdir(os.path.join(p.path, pip_target_dir))
+        os.environ.pop('PIP_TARGET')