Factor out logic for locating egg-info directories

Why: A named function brings clarity to expressing what is happening.

Author: pradyunsg

src/pip/_internal/req/req_install.py

@@ -673,6 +673,24 @@ def looks_like_virtual_env(path):
                 os.path.exists(os.path.join(path, 'Scripts', 'Python.exe'))
             )
 
+        def locate_editable_egg_info(base):
+            candidates = []
+            for root, dirs, files in os.walk(base):
+                for dir_ in vcs.dirnames:
+                    if dir_ in dirs:
+                        dirs.remove(dir_)
+                # Iterate over a copy of ``dirs``, since mutating
+                # a list while iterating over it can cause trouble.
+                # (See https://github.com/pypa/pip/pull/462.)
+                for dir_ in list(dirs):
+                    if looks_like_virtual_env(os.path.join(root, dir_)):
+                        dirs.remove(dir_)
+                    # Also don't search through tests
+                    elif dir_ == 'test' or dir_ == 'tests':
+                        dirs.remove(dir_)
+                candidates.extend(os.path.join(root, dir_) for dir_ in dirs)
+            return [f for f in candidates if f.endswith('.egg-info')]
+
         def depth_of_directory(dir_):
             return (
                 dir_.count(os.path.sep) +
@@ -681,23 +699,7 @@ def depth_of_directory(dir_):
 
         if self.editable:
             base = self.source_dir
-            filenames = []
-            for root, dirs, files in os.walk(base):
-                for dir in vcs.dirnames:
-                    if dir in dirs:
-                        dirs.remove(dir)
-                # Iterate over a copy of ``dirs``, since mutating
-                # a list while iterating over it can cause trouble.
-                # (See https://github.com/pypa/pip/pull/462.)
-                for dir in list(dirs):
-                    if looks_like_virtual_env(os.path.join(root, dir)):
-                        dirs.remove(dir)
-                    # Also don't search through tests
-                    elif dir == 'test' or dir == 'tests':
-                        dirs.remove(dir)
-                filenames.extend([os.path.join(root, dir)
-                                    for dir in dirs])
-            filenames = [f for f in filenames if f.endswith('.egg-info')]
+            filenames = locate_editable_egg_info(base)
         else:
             base = os.path.join(self.setup_py_dir, 'pip-egg-info')
             filenames = os.listdir(base)