Can't install '.' requirement when virtualenv is local

[frostming]

Steps to replicate

$ git clone https://github.com/pallets/flask.git
$ cd flask
$ virtualenv venv
$ . venv/bin/activate
$ pipenv install -e .

Actual result

Courtesy Notice: Pipenv found itself running within a virtual environment, so it will automatically use that environment, instead of creating its own for any project. You can set PIPENV_IGNORE_VIRTUALENVS=1 to force pipenv to ignore that environment and create its own instead. You can set PIPENV_VERBOSITY=-1 to suppress this warning.
Installing -e .…
Adding setuptools to Pipfile's [packages]…
✔ Installation Succeeded
Pipfile.lock (0ba3fc) out of date, updating to (77786a)…
Locking [dev-packages] dependencies…
Locking [packages] dependencies…
Building requirements...
Traceback (most recent call last):
  File "/Users/fming/.local/bin/pipenv", line 11, in <module>
    load_entry_point('pipenv', 'console_scripts', 'pipenv')()
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/decorators.py", line 73, in new_func
    return ctx.invoke(f, obj, *args, **kwargs)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/click/decorators.py", line 21, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/Users/fming/wkspace/github/pipenv/pipenv/cli/command.py", line 252, in install
    site_packages=state.site_packages
  File "/Users/fming/wkspace/github/pipenv/pipenv/core.py", line 2201, in do_install
    skip_lock=skip_lock,
  File "/Users/fming/wkspace/github/pipenv/pipenv/core.py", line 1281, in do_init
    pypi_mirror=pypi_mirror,
  File "/Users/fming/wkspace/github/pipenv/pipenv/core.py", line 1114, in do_lock
    keep_outdated=keep_outdated
  File "/Users/fming/wkspace/github/pipenv/pipenv/utils.py", line 1318, in venv_resolve_deps
    deps, project, r=False, include_index=True
  File "/Users/fming/wkspace/github/pipenv/pipenv/utils.py", line 1434, in convert_deps_to_pip
    new_dep = Requirement.from_pipfile(dep_name, dep)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/requirementslib/models/requirements.py", line 2743, in from_pipfile
    r = FileRequirement.from_pipfile(name, pipfile)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/requirementslib/models/requirements.py", line 1843, in from_pipfile
    arg_dict["setup_info"] = arg_dict["parsed_line"].setup_info
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/requirementslib/models/requirements.py", line 813, in setup_info
    self.setup_info = self.get_setup_info()
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/requirementslib/models/requirements.py", line 802, in get_setup_info
    setup_info = SetupInfo.from_ireq(self.ireq, subdir=self.subdirectory)
  File "/Users/fming/wkspace/github/pipenv/pipenv/vendor/requirementslib/models/setup_info.py", line 1851, in from_ireq
    shutil.copytree(path, target)
  File "/Users/fming/Library/PythonUp/versions/3.7/lib/python3.7/shutil.py", line 368, in copytree
    raise Error(errors)
shutil.Error: [('/Users/fming/wkspace/github/flask/venv/bin/python3', '/var/folders/vh/5_b6mbg93vg2npbb21v03vwr0000gn/T/reqlib-src7cnho_yw/flask/venv/bin/python3', "[Errno 13] Permission denied: '/Users/fming/wkspace/github/flask/venv/bin/python3'"), ('/Users/fming/wkspace/github/flask/venv/bin/python', '/var/folders/vh/5_b6mbg93vg2npbb21v03vwr0000gn/T/reqlib-src7cnho_yw/flask/venv/bin/python', "[Errno 13] Permission denied: '/Users/fming/wkspace/github/flask/venv/bin/python'")]

It is caused by the copy_tree call introduced in recent releases.