Cover edge case when environment is being created with empty project name

src/poetry/utils/env.py

@@ -948,7 +948,8 @@ def create_venv(
 
         if venv_prompt is not None:
             venv_prompt = venv_prompt.format(
-                project_name=self._poetry.package.name, python_version=python_minor
+                project_name=self._poetry.package.name or "virtualenv",
+                python_version=python_minor,
             )
 
         if not venv.exists():

tests/fixtures/no_name_project/README.rst

@@ -0,0 +1,2 @@
+No name project
+===============

tests/fixtures/no_name_project/pyproject.toml

@@ -0,0 +1,18 @@
+[tool.poetry]
+name = ""
+version = "1.2.3"
+description = "This project has no name"
+authors = [
+    "Sébastien Eustace <[email protected]>"
+]
+license = "MIT"
+
+readme = "README.rst"
+
+
+# Requirements
+[tool.poetry.dependencies]
+python = "~2.7 || ^3.6"
+
+[tool.poetry.group.dev.dependencies]
+pytest = "~3.4"

tests/utils/test_env.py

@@ -1415,3 +1415,43 @@ def test_build_environment_not_called_without_build_script_specified(
     with build_environment(poetry, project_env) as env:
         assert env == project_env
         assert not env.executed
+
+
+def test_create_venv_project_name_empty_sets_correct_prompt(
+    project_factory: ProjectFactory,
+    config: Config,
+    mocker: MockerFixture,
+    config_virtualenvs_path: Path,
+):
+    if "VIRTUAL_ENV" in os.environ:
+        del os.environ["VIRTUAL_ENV"]
+
+    fixture = Path(__file__).parent.parent / "fixtures" / "no_name_project"
+    poetry = project_factory("no", source=fixture)
+    manager = EnvManager(poetry)
+
+    poetry.package.python_versions = "^3.7"
+    venv_name = manager.generate_env_name("", str(poetry.file.parent))
+
+    mocker.patch("sys.version_info", (2, 7, 16))
+    mocker.patch(
+        "subprocess.check_output",
+        side_effect=check_output_wrapper(Version.parse("3.7.5")),
+    )
+    m = mocker.patch(
+        "poetry.utils.env.EnvManager.build_venv", side_effect=lambda *args, **kwargs: ""
+    )
+
+    manager.create_venv(NullIO())
+
+    m.assert_called_with(
+        config_virtualenvs_path / f"{venv_name}-py3.7",
+        executable="python3",
+        flags={
+            "always-copy": False,
+            "system-site-packages": False,
+            "no-pip": False,
+            "no-setuptools": False,
+        },
+        prompt="virtualenv-py3.7",
+    )