Fix #18714: [Docs] python -c "import tvm; print(tvm.file)" fail

[JiwaniZakir]

Closes #18714

Before

Following the source installation docs, users who set up PYTHONPATH with only $TVM_HOME/python would hit an importlib.metadata.PackageNotFoundError: apache-tvm-ffi when running python -c "import tvm". This happened because tvm_ffi/__init__.py calls libinfo.load_lib_ctypes("apache-tvm-ffi", ...), which uses importlib.metadata.distribution("apache-tvm-ffi") to locate the shared library — a lookup that requires the apache-tvm-ffi package to be registered in the Python environment, not just present on PYTHONPATH.

After

The tvm-ffi package at 3rdparty/tvm-ffi is installed into the active Python environment via pip install before any import tvm is attempted. The PYTHONPATH export in docs/install/from_source.rst is also updated to include $TVM_HOME/3rdparty/tvm-ffi/python alongside $TVM_HOME/python, matching the environment layout expected by the FFI loader.

Changes

• docs/install/from_source.rst (line ~165–166): Added pip install $TVM_HOME/3rdparty/tvm-ffi step before the export PYTHONPATH line in the "set environment variable" path. Updated the PYTHONPATH export to append $TVM_HOME/3rdparty/tvm-ffi/python, ensuring both the package metadata (from the pip install) and the Python sources are resolvable.

Testing

Manual verification on a from-source build with the updated instructions:

$ pip install $TVM_HOME/3rdparty/tvm-ffi
$ export PYTHONPATH=$TVM_HOME/python:$TVM_HOME/3rdparty/tvm-ffi/python:$PYTHONPATH
$ python -c "import tvm; print(tvm.__file__)"
/path-to-tvm/python/tvm/__init__.py

No PackageNotFoundError is raised; importlib.metadata.distribution("apache-tvm-ffi") resolves correctly after the pip install step.

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This PR was created with AI assistance (Claude). The changes were reviewed by quality gates and a critic model before submission.

[gemini-code-assist]

Code Review

This pull request updates the TVM source installation documentation to include the installation of the tvm-ffi dependency and its addition to the PYTHONPATH. The reviewer suggested using an editable installation for tvm-ffi to ensure the package remains synchronized with the source tree and to avoid redundant entries in the PYTHONPATH.

[gemini-code-assist]

Using an editable install (pip install -e) for tvm-ffi is a more robust approach for a source-based installation. It registers the necessary package metadata to resolve the PackageNotFoundError while keeping the package linked to the source directory. This ensures that tvm-ffi stays in sync with your source tree (e.g., after a git pull) and removes the need to manually add its path to PYTHONPATH. Having the same package in both site-packages and PYTHONPATH is redundant and can lead to import conflicts or version mismatches.

Suggested change

	pip install $TVM_HOME/3rdparty/tvm-ffi
	export PYTHONPATH=$TVM_HOME/python:$TVM_HOME/3rdparty/tvm-ffi/python:$PYTHONPATH
	pip install -e $TVM_HOME/3rdparty/tvm-ffi
	export PYTHONPATH=$TVM_HOME/python:$PYTHONPATH