[build] add torch to tool.uv no-build-isolation-package (#24303)

Signed-off-by: youkaichao <youkaichao@gmail.com>
Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/getting_started/installation/gpu/cuda.inc.md

@@ -165,14 +165,14 @@ There are scenarios where the PyTorch dependency cannot be easily installed with
 - Building vLLM with PyTorch nightly or a custom PyTorch build.
 - Building vLLM with aarch64 and CUDA (GH200), where the PyTorch wheels are not available on PyPI. Currently, only the PyTorch nightly has wheels for aarch64 with CUDA. You can run `uv pip install --index-url https://download.pytorch.org/whl/nightly/cu128 torch torchvision torchaudio` to [install PyTorch nightly](https://pytorch.org/get-started/locally/) and then build vLLM on top of it.
 
-To build vLLM using an existing PyTorch installation:
+To build vLLM using an existing PyTorch installation, it is recommended to use `uv`, because it has [a unique mechanism](https://docs.astral.sh/uv/concepts/projects/config/#disabling-build-isolation) for disabling build isolation for specific packages and vLLM leverages this mechanism to specify `torch` as the package to disable build isolation.
 
 ```bash
+# install PyTorch first, either from PyPI or from source
 git clone https://github.com/vllm-project/vllm.git
 cd vllm
-python use_existing_torch.py
-uv pip install -r requirements/build.txt
-uv pip install --no-build-isolation -e .
+# pip install -e . does not work directly, only uv can do this
+uv pip install -e .
 ```
 
 ##### Use the local cutlass for compilation

pyproject.toml

@@ -345,3 +345,6 @@ extend-ignore-re = []
 windo = "windo"
 
 [tool.typos.type.vimscript.extend-words]
+
+[tool.uv]
+no-build-isolation-package = ["torch"]

use_existing_torch.py

 # SPDX-License-Identifier: Apache-2.0
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
-import glob
-
-requires_files = glob.glob('requirements/*.txt')
-requires_files += ["pyproject.toml"]
-for file in requires_files:
-    print(f">>> cleaning {file}")
-    with open(file) as f:
-        lines = f.readlines()
-    if "torch" in "".join(lines).lower():
-        print("removed:")
-        with open(file, 'w') as f:
-            for line in lines:
-                if 'torch' not in line.lower():
-                    f.write(line)
-                else:
-                    print(line.strip())
-    print(f"<<< done cleaning {file}")
-    print()
+print("vLLM is now using 'uv' to disable build isolation for 'torch'.")
+print("Please instead install vLLM with 'uv pip install -e .' (must use 'uv')")