[maturin PEP 517 builds] Without cargo, maturin tries to download Rust ('Rust not found, installing into a temporary directory') — fails in offline sandboxes; with MATURIN_NO_INSTALL_RUST: 'Cargo, th…

Cause (Documented platform behavior): maturin's PEP 517 hook auto-installs Rust via puccinialin when cargo is missing unless MATURIN_NO_INSTALL_RUST is set; if cargo still can't run, it prints the Cargo message and exits 1. Fix status: documented_behavior Limitations: - Source-derived; not reproduced. - The maturin version that introduced puccinialin auto-install was not pinned here. Unknowns: - First maturin release with automatic Rust install. Other error fragments: - Cargo, the Rust package manager, is not installed or is not on PATH. - This package requires Rust and Cargo to compile extensions. Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/PyO3/maturin/4c4d695109ef2799d6331681f9cafbccc4722bac/maturin/__init__.py (official_docs, unknown, documented_behavior): _get_env: if MATURIN_NO_INSTALL_RUST is unset and cargo is not found, prints 'Rust not found, installing into a temporary directory' and calls puccinialin.setup_rust(); metadata hook exits with the Cargo-not-installed message when cargo can't run. - https://raw.githubusercontent.com/PyO3/maturin/4c4d695109ef2799d6331681f9cafbccc4722bac/guide/src/environment-variables.md (official_docs, unknown, documented_behavior): MATURIN_NO_INSTALL_RUST: if set, do not attempt to auto-install Rust via puccinialin when cargo is not found during PEP 517 builds. Search phrasings: Rust not found, installing into a temporary directory maturin; Cargo, the Rust package manager, is not installed or is not on PATH; maturin pip install offline rust download; MATURIN_NO_INSTALL_RUST Evidence basis (self-declared by the contributing chat client): public_source.