Fix shell detection failure

news/2187.bugfix.md

@@ -0,0 +1 @@
+Default behavior for pdm venv activate when shell detection fails.

src/pdm/cli/commands/venv/activate.py

@@ -45,7 +45,10 @@ def handle(self, project: Project, options: argparse.Namespace) -> None:
         project.core.ui.echo(self.get_activate_command(venv))
 
     def get_activate_command(self, venv: VirtualEnv) -> str:  # pragma: no cover
-        shell, _ = shellingham.detect_shell()
+        try:
+            shell, _ = shellingham.detect_shell()
+        except shellingham.ShellDetectionFailure:
+            shell = None
         if shell == "fish":
             command, filename = "source", "activate.fish"
         elif shell == "csh":

tests/cli/test_venv.py

@@ -5,6 +5,7 @@
 from unittest.mock import ANY
 
 import pytest
+import shellingham
 
 from pdm.cli.commands.venv import backends
 from pdm.cli.commands.venv.utils import get_venv_prefix
@@ -168,6 +169,26 @@ def test_venv_activate_error(pdm, project):
     assert "Can't activate a non-venv Python" in result.stderr
 
 
+@pytest.mark.usefixtures("venv_backends")
+def test_venv_activate_no_shell(pdm, mocker, project):
+    project.project_config["venv.in_project"] = False
+    result = pdm(["venv", "create"], obj=project)
+    assert result.exit_code == 0, result.stderr
+    venv_path = re.match(r"Virtualenv (.+) is created successfully", result.output).group(1)
+    key = os.path.basename(venv_path)[len(get_venv_prefix(project)) :]
+
+    mocker.patch("shellingham.detect_shell", side_effect=shellingham.ShellDetectionFailure())
+    result = pdm(["venv", "activate", key], obj=project)
+    assert result.exit_code == 0, result.stderr
+    backend = project.config["venv.backend"]
+
+    if backend == "conda":
+        assert result.output.startswith("conda activate")
+    else:
+        assert result.output.strip("'\"\n").endswith("activate")
+        assert result.output.startswith("source")
+
+
 @pytest.mark.usefixtures("fake_create")
 @pytest.mark.parametrize("keep_pypackages", [True, False])
 def test_venv_auto_create(pdm, mocker, project, keep_pypackages):