feat: add fish shell support for venv activation instructions

Detect the user's shell (fish, zsh, bash) and show the correct
venv activation command. Fish shell users now see
'source .venv/bin/activate.fish' instead of the bash-only
'source .venv/bin/activate'.

Closes #36

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

Author: isaacbmiller

src/dspy_cli/server/runner.py

@@ -221,7 +221,8 @@ def notify_cli(msg: str, level: str = "info"):
         click.echo("  2. Subclass dspy.Module")
         click.echo("  3. Are not named with a leading underscore")
         click.echo("  4. If you are using external dependencies:")
-        click.echo("     - Ensure your venv is activated")
+        from dspy_cli.utils.venv import venv_activate_command
+        click.echo(f"     - Ensure your venv is activated ({venv_activate_command()})")
         click.echo("     - Make sure you have dspy-cli as a local dependency")
         click.echo("     - Install them using pip install -e .")
 

src/dspy_cli/utils/venv.py

@@ -143,8 +143,42 @@ def validate_python_version(python: Path, min_version: tuple = (3, 9)) -> tuple[
         return False, ""
 
 
+def detect_shell() -> str:
+    """Detect the current shell type.
+
+    Returns:
+        Shell name: "fish", "zsh", "bash", or "sh" (default fallback).
+    """
+    if os.environ.get("FISH_VERSION"):
+        return "fish"
+
+    shell = os.environ.get("SHELL", "")
+    for name in ("fish", "zsh", "bash"):
+        if shell.endswith(f"/{name}"):
+            return name
+
+    return "sh"
+
+
+def venv_activate_command(venv_dir: str = ".venv") -> str:
+    """Return the shell-appropriate venv activation command.
+
+    Args:
+        venv_dir: Virtual environment directory name.
+
+    Returns:
+        Activation command string for the current shell.
+    """
+    shell = detect_shell()
+    if shell == "fish":
+        return f"source {venv_dir}/bin/activate.fish"
+    return f"source {venv_dir}/bin/activate"
+
+
 def show_venv_warning():
     """Display warning and guidance when no venv is detected."""
+    activate_cmd = venv_activate_command()
+
     click.echo(click.style("⚠ Warning: No virtual environment detected", fg="yellow"))
     click.echo()
     click.echo("Running without a project venv may cause import errors if dependencies")
@@ -154,7 +188,7 @@ def show_venv_warning():
     click.echo("  1. Add dspy-cli to your project:")
     click.echo("     uv add dspy-cli")
     click.echo("  2. Create and activate a venv:")
-    click.echo("     uv sync  (or python -m venv .venv && source .venv/bin/activate)")
+    click.echo(f"     uv sync  (or python -m venv .venv && {activate_cmd})")
     click.echo("  3. Use a task runner:")
     click.echo("     uv run dspy-cli serve")
     click.echo("  4. Specify Python interpreter:")

tests/test_venv_utils.py

@@ -7,7 +7,12 @@
 from pathlib import Path
 
 
-from dspy_cli.utils.venv import sanitize_env_for_exec, validate_python_version
+from dspy_cli.utils.venv import (
+    detect_shell,
+    sanitize_env_for_exec,
+    validate_python_version,
+    venv_activate_command,
+)
 
 
 class TestValidatePythonVersion:
@@ -119,3 +124,49 @@ def test_preserves_other_vars(self):
 
         # Cleanup
         os.environ.pop("MY_CUSTOM_VAR", None)
+
+
+class TestDetectShell:
+    """Tests for shell detection."""
+
+    def test_fish_via_fish_version(self, monkeypatch):
+        monkeypatch.setenv("FISH_VERSION", "3.6.1")
+        monkeypatch.setenv("SHELL", "/bin/bash")
+        assert detect_shell() == "fish"
+
+    def test_fish_via_shell_env(self, monkeypatch):
+        monkeypatch.delenv("FISH_VERSION", raising=False)
+        monkeypatch.setenv("SHELL", "/usr/local/bin/fish")
+        assert detect_shell() == "fish"
+
+    def test_bash_via_shell_env(self, monkeypatch):
+        monkeypatch.delenv("FISH_VERSION", raising=False)
+        monkeypatch.setenv("SHELL", "/bin/bash")
+        assert detect_shell() == "bash"
+
+    def test_zsh_via_shell_env(self, monkeypatch):
+        monkeypatch.delenv("FISH_VERSION", raising=False)
+        monkeypatch.setenv("SHELL", "/bin/zsh")
+        assert detect_shell() == "zsh"
+
+    def test_fallback_to_sh(self, monkeypatch):
+        monkeypatch.delenv("FISH_VERSION", raising=False)
+        monkeypatch.delenv("SHELL", raising=False)
+        assert detect_shell() == "sh"
+
+
+class TestVenvActivateCommand:
+    """Tests for shell-aware activation command."""
+
+    def test_fish_uses_activate_fish(self, monkeypatch):
+        monkeypatch.setenv("FISH_VERSION", "3.6.1")
+        assert venv_activate_command() == "source .venv/bin/activate.fish"
+
+    def test_bash_uses_activate(self, monkeypatch):
+        monkeypatch.delenv("FISH_VERSION", raising=False)
+        monkeypatch.setenv("SHELL", "/bin/bash")
+        assert venv_activate_command() == "source .venv/bin/activate"
+
+    def test_custom_venv_dir(self, monkeypatch):
+        monkeypatch.setenv("FISH_VERSION", "3.6.1")
+        assert venv_activate_command("venv") == "source venv/bin/activate.fish"