Fix index_select feature gating

Author: alvarobartt

backends/candle/src/layers/index_select.rs

@@ -1,20 +1,27 @@
 // SPDX-License-Identifier: MIT or Apache-2.0
 // First Published under RadixMLP and https://github.com/michaelfeil/candle-index-select-cu by Michael Feil
 
-use candle::{DType, Result, Tensor};
+use candle::{Result, Tensor};
+
+#[cfg(feature = "cuda")]
+use candle::DType;
 #[cfg(feature = "cuda")]
 use candle_index_select_cu;
 
 #[inline]
 #[allow(dead_code)]
 pub fn index_select(tensor: &Tensor, ids: &Tensor, dim: usize) -> Result<Tensor> {
-    if cfg!(feature = "cuda")
-        && matches!(tensor.dtype(), DType::F16 | DType::F32)
-        && matches!(ids.dtype(), DType::U32)
+    #[cfg(feature = "cuda")]
+    {
+        if matches!(tensor.dtype(), DType::F16 | DType::F32) && matches!(ids.dtype(), DType::U32) {
+            // NOTE: `candle-index-select-cu` supports f16/f32 data and u32 indices
+            candle_index_select_cu::index_select(tensor, ids, dim)
+        } else {
+            tensor.index_select(ids, dim)
+        }
+    }
+    #[cfg(not(feature = "cuda"))]
     {
-        // NOTE: `candle-index-select-cu` supports f16/f32 data and u32 indices
-        candle_index_select_cu::index_select(tensor, ids, dim)
-    } else {
         tensor.index_select(ids, dim)
     }
 }