Fix pip install . -e when buck2 is not installed (pytorch#11842)

If the installation goes through regular './install_executorch.sh' path,
it sets the -DBUCK2 cmake config, but if you directly call `pip install
.` it
doesn't resolve buck dependency.

Test Plan:

Run 

- `./install_requirement.sh` and `pip install . --no-build-isolation -v`
- `./install_requirement.sh` and `pip install -e . --no-build-isolation
-v`
- ./install_executorch.sh


cc @larryliu0820 @jathu

Author: mergennachin

docs/source/using-executorch-building-from-source.md

@@ -64,8 +64,8 @@ Or alternatively, [install conda on your machine](https://conda.io/projects/cond
    # Intel-based macOS systems require building PyTorch from source (see below)
    ./install_executorch.sh
    ```
-  
-   See the [PyTorch instructions](https://github.com/pytorch/pytorch#installation) on how to build PyTorch from source.  
+
+   See the [PyTorch instructions](https://github.com/pytorch/pytorch#installation) on how to build PyTorch from source.
 
    Use the [`--use-pt-pinned-commit` flag](../../install_executorch.py) to install ExecuTorch with an existing PyTorch build:
 
@@ -90,7 +90,7 @@ Or alternatively, [install conda on your machine](https://conda.io/projects/cond
 
    # Or you can directly do the following if dependencies are already installed
    # either via a previous invocation of `./install_executorch.sh` or by explicitly installing requirements via `./install_requirements.sh` first.
-   pip install -e .
+   pip install -e . --no-build-isolation
    ```
 
    If C++ files are being modified, you will still have to reinstall ExecuTorch from source.
@@ -243,7 +243,7 @@ Install ClangCL for Windows from the [official website](https://learn.microsoft.
 To check if conda is detected by the powershell prompt, try `conda list` or `conda --version`
 
 If conda is not detected, you could run the powershell script for conda named `conda-hook.ps1`.
-To verify that Conda is available in the in the powershell environment, run try `conda list` or `conda --version`. 
+To verify that Conda is available in the in the powershell environment, run try `conda list` or `conda --version`.
 If Conda is not available, run conda-hook.ps1 as follows:
 ```bash
 $miniconda_dir\\shell\\condabin\\conda-hook.ps1

install_executorch.py

@@ -19,7 +19,6 @@
     install_optional_example_requirements,
     install_requirements,
     python_is_compatible,
-    TORCH_NIGHTLY_URL,
 )
 
 # Set up logging
@@ -208,8 +207,6 @@ def main(args):
             ".",
             "--no-build-isolation",
             "-v",
-            "--extra-index-url",
-            TORCH_NIGHTLY_URL,
         ]
     )
     subprocess.run(cmd, check=True)

pyproject.toml

@@ -7,6 +7,7 @@ requires = [
   "tomli",  # Imported by extract_sources.py when using python < 3.11.
   "wheel",  # For building the pip package archive.
   "zstd",  # Imported by resolve_buck.py.
+  "certifi",  # Imported by resolve_buck.py.
 ]
 build-backend = "setuptools.build_meta"
 
@@ -49,7 +50,7 @@ classifiers = [
 ]
 
 # Python dependencies required for use.
-# coremltools has issue with python 3.13, see https://github.com/apple/coremltools/issues/2487 
+# coremltools has issue with python 3.13, see https://github.com/apple/coremltools/issues/2487
 requires-python = ">=3.10,<3.13"
 dependencies=[
   "expecttest",

requirements-dev.txt

@@ -7,6 +7,7 @@ setuptools>=63  # For building the pip package contents.
 tomli  # Imported by extract_sources.py when using python < 3.11.
 wheel  # For building the pip package archive.
 zstd  # Imported by resolve_buck.py.
+certifi  # Imported by resolve_buck.py.
 lintrunner==0.12.7
 lintrunner-adapters==0.12.4
 hydra-core>=1.3.0

tools/cmake/Utils.cmake

@@ -128,7 +128,7 @@ function(resolve_buck2)
 
   set(resolve_buck2_command
       ${PYTHON_EXECUTABLE} ${executorch_root}/tools/cmake/resolve_buck.py
-      --cache_dir=buck2-bin
+      --cache_dir=${executorch_root}/buck2-bin
   )
 
   if(NOT ${BUCK2} STREQUAL "")