Fix lint

Author: wenscarl

jax/_src/dtypes.py

@@ -730,6 +730,12 @@ def _least_upper_bound(jax_numpy_dtype_promotion: str, *nodes: JAXType) -> JAXTy
         "promotion path. To avoid unintended promotion, 8-bit floats do not support "
         "implicit promotion. If you'd like your inputs to be promoted to another type, "
         "you can do so explicitly using e.g. x.astype('float32')")
+    elif any(n in _float4_dtypes for n in nodes):
+      msg = (
+        f"Input dtypes {tuple(str(n) for n in nodes)} have no available implicit dtype "
+        "promotion path. To avoid unintended promotion, 4-bit floats do not support "
+        "implicit promotion. If you'd like your inputs to be promoted to another type, "
+        "you can do so explicitly using e.g. x.astype('float32')")
     elif any(n in _intn_dtypes for n in nodes):
       msg = (
         f"Input dtypes {tuple(str(n) for n in nodes)} have no available implicit dtype "

tests/dtypes_test.py

@@ -989,7 +989,8 @@ def testFloat8PromotionError(self):
   def testFloat4PromotionError(self):
     for dtype in fp4_dtypes:
       if dtype == dtypes.float4_e2m1fn and jtu.test_device_matches(['tpu']):
-        self.skipTest("TPU does not support float4_e2m1fn.")
+        # TPU does not support float4_e2m1fn.
+        continue
       x = jnp.array(1, dtype=dtype)
       y = jnp.array(1, dtype='float32')
       with self.assertRaisesRegex(dtypes.TypePromotionError,
@@ -1055,7 +1056,7 @@ def testArrayRepr(self, dtype, weak_type):
     if dtype == dtypes.float8_e8m0fnu and jtu.test_device_matches(['tpu']):
       self.skipTest('TPU does not support float8_e8m0fnu.')
     if dtype == dtypes.float4_e2m1fn and jtu.test_device_matches(['tpu']):
-      self.skipTest('TPU does not support float4_e2m1fn.')      
+      self.skipTest('TPU does not support float4_e2m1fn.')
     val = lax_internal._convert_element_type(0, dtype, weak_type=weak_type)
     rep = repr(val)
     self.assertStartsWith(rep, 'Array(')