MNT: fix lint formatting and skip UnstableRocketWarning for GenericSurface

black/ruff reformat the multi-name exception imports in rocketpy/__init__.py
and rocketpy/rocket/rocket.py.

evaluate_center_of_pressure ignores GenericSurface lift coefficients, so the
computed static margin does not reflect rockets that rely on them. Skip the
UnstableRocketWarning in that case to avoid false positives, echoing the
concern raised in the review of #764 that blocked a similar check.

Author: Gui-FernandesBR

rocketpy/__init__.py

@@ -1,6 +1,10 @@
 from .control import _Controller
 from .environment import Environment, EnvironmentAnalysis
-from .exceptions import InvalidInertiaError, InvalidParameterError, UnstableRocketWarning
+from .exceptions import (
+    InvalidInertiaError,
+    InvalidParameterError,
+    UnstableRocketWarning,
+)
 from .mathutils import (
     Function,
     PiecewiseFunction,

rocketpy/exceptions.py

@@ -16,4 +16,10 @@ class InvalidInertiaError(RocketPyError, ValueError):
 
 class UnstableRocketWarning(UserWarning):
     """Issued when the rocket's static margin is negative at motor ignition,
-    indicating an aerodynamically unstable configuration."""
+    indicating an aerodynamically unstable configuration.
+
+    Not issued when the rocket has any ``GenericSurface`` aerodynamic
+    surfaces, since their lift coefficient derivative is not accounted for
+    in the center of pressure calculation, making the static margin
+    unreliable for this check in that case.
+    """

rocketpy/rocket/rocket.py

@@ -23,7 +23,11 @@
 )
 from rocketpy.rocket.aero_surface.fins.free_form_fins import FreeFormFins
 from rocketpy.rocket.aero_surface.generic_surface import GenericSurface
-from rocketpy.exceptions import InvalidInertiaError, InvalidParameterError, UnstableRocketWarning
+from rocketpy.exceptions import (
+    InvalidInertiaError,
+    InvalidParameterError,
+    UnstableRocketWarning,
+)
 from rocketpy.rocket.components import Components
 from rocketpy.rocket.parachute import Parachute
 from rocketpy.tools import (
@@ -742,17 +746,26 @@ def evaluate_static_margin(self):
         self.static_margin.set_discrete(
             lower=0, upper=self.motor.burn_out_time, samples=200
         )
-        # Warn the user if the rocket is aerodynamically unstable at ignition
-        initial_static_margin = self.static_margin.get_value_opt(0)
-        if initial_static_margin < 0:
-            warnings.warn(
-                f"The rocket has a negative static margin ({initial_static_margin:.2f} cal) "
-                "at motor ignition (t=0), indicating an aerodynamically unstable "
-                "configuration. Check the placement of fins and nose cone relative "
-                "to the center of mass.",
-                UnstableRocketWarning,
-                stacklevel=2,
-            )
+        # Warn the user if the rocket is aerodynamically unstable at ignition.
+        # Skipped when GenericSurface instances are present: their lift
+        # coefficient derivative is not accounted for in
+        # evaluate_center_of_pressure, so the computed static margin does not
+        # reflect their contribution and cannot be trusted for this check.
+        has_generic_surface = any(
+            isinstance(aero_surface, GenericSurface)
+            for aero_surface, _position in self.aerodynamic_surfaces
+        )
+        if not has_generic_surface:
+            initial_static_margin = self.static_margin.get_value_opt(0)
+            if initial_static_margin < 0:
+                warnings.warn(
+                    f"The rocket has a negative static margin ({initial_static_margin:.2f} cal) "
+                    "at motor ignition (t=0), indicating an aerodynamically unstable "
+                    "configuration. Check the placement of fins and nose cone relative "
+                    "to the center of mass.",
+                    UnstableRocketWarning,
+                    stacklevel=2,
+                )
         return self.static_margin
 
     def evaluate_dry_inertias(self):

tests/unit/rocket/test_rocket.py

@@ -5,8 +5,12 @@
 import numpy as np
 import pytest
 
-from rocketpy import Function, NoseCone, Rocket, SolidMotor
-from rocketpy.exceptions import InvalidInertiaError, InvalidParameterError
+from rocketpy import Function, GenericSurface, NoseCone, Rocket, SolidMotor
+from rocketpy.exceptions import (
+    InvalidInertiaError,
+    InvalidParameterError,
+    UnstableRocketWarning,
+)
 from rocketpy.mathutils.vector_matrix import Vector
 from rocketpy.motors.empty_motor import EmptyMotor
 from rocketpy.motors.motor import Motor
@@ -878,3 +882,43 @@ def test_rocket_invalid_inertia_length_raises(inertia):
             power_on_drag=0.3,
             center_of_mass_without_motor=0,
         )
+
+
+def test_unstable_rocket_warning_raised(calisto):
+    """UnstableRocketWarning must be raised when the static margin at motor
+    ignition is negative."""
+    nose = NoseCone(
+        length=0.55829,
+        kind="vonkarman",
+        base_radius=0.0635,
+        rocket_radius=0.0635,
+        name="Nose Cone",
+    )
+    with pytest.warns(UnstableRocketWarning):
+        calisto.add_surfaces(nose, 1.16)
+    assert calisto.static_margin(0) < 0
+
+
+def test_unstable_rocket_warning_skipped_with_generic_surface(calisto):
+    """UnstableRocketWarning must not be raised when the rocket has a
+    GenericSurface, since its lift coefficient derivative is not accounted
+    for in the center of pressure calculation, making the static margin
+    unreliable for this check."""
+    nose = NoseCone(
+        length=0.55829,
+        kind="vonkarman",
+        base_radius=0.0635,
+        rocket_radius=0.0635,
+        name="Nose Cone",
+    )
+    generic_surface = GenericSurface(
+        reference_area=None,
+        reference_length=None,
+        coefficients={
+            "cL": lambda alpha, beta, mach, reynolds, pitch_rate, yaw_rate, roll_rate: 1
+        },
+    )
+    with warnings.catch_warnings():
+        warnings.simplefilter("error", UnstableRocketWarning)
+        calisto.add_surfaces([nose, generic_surface], [1.16, 0])
+    assert calisto.static_margin(0) < 0