lucifer1004 opened a new pull request, #825:
URL: https://github.com/apache/tvm-ffi/pull/825
## Why
`tvm-ffi-sys/build.rs` decides whether it is building documentation with
`env::var("RUSTDOC").is_ok()`. Cargo sets `RUSTDOC` for every build script
([Cargo: environment variables set for build
scripts](https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts)),
so the check is always true. It was meant for the Rust docs build in
`docs/conf.py` (#160).
As a result, a normal `cargo build` without a working `tvm-ffi-config`
doesn't fail. It prints "tvm-ffi-config not available, skipping for
documentation build" and emits no `rustc-link-*` directives. The first sign of
trouble is a link error in a dependent crate:
```
rust-lld: error: undefined symbol: TVMFFIEnvGetStream
```
Cargo also caches the empty build-script output. The build script declares
no `rerun-if-*`, so it reruns only when the package's own files change, and the
build keeps failing after tvm-ffi is installed until `cargo clean -p
tvm-ffi-sys`.
## What
- **Documentation builds:** detected by `DOCS_RS`, which docs.rs sets.
`docs/conf.py` now sets it too for its `cargo doc`, so docs still build without
tvm-ffi installed. In that case the build script emits a `cargo:warning` naming
the reason and doesn't link.
- **Every other build:** fails in the build script, with the reason and the
fix, when `tvm-ffi-config` cannot be run, exits non-zero (its stderr is
included), or prints no library directory:
```
could not run `tvm-ffi-config`: No such file or directory (os error 2).
tvm-ffi-sys links libtvm_ffi from the directory that `tvm-ffi-config --libdir`
prints: install tvm-ffi (e.g. `pip install apache-tvm-ffi`) and put
tvm-ffi-config on PATH. To build documentation only, set DOCS_RS=1.
```
- **Rerunning:** the build script declares its inputs with
`cargo:rerun-if-env-changed` (`DOCS_RS`, `PATH`, and the library-path variable
it reads) plus `rerun-if-changed=build.rs`, so output from one environment
isn't reused in another.
## Tests
A scratch crate that depends on `tvm-ffi-sys` and calls `TVMFFIEnvGetStream`:
- **On `main`, without `tvm-ffi-config`:** the build script runs with
`RUSTDOC=…/rustdoc` in its environment (`cargo build -vv`), its output has no
link directives, and the link fails with the undefined symbol above.
- **With this change:**
- Without `tvm-ffi-config`, the build fails in the build script with the
message above.
- `DOCS_RS=1 cargo doc` without `tvm-ffi-config` still builds, with the
warning.
- With `tvm-ffi-config`, the crate builds and runs, including right after
that `DOCS_RS=1` build: the build script reruns and links.
- `cargo test` in `rust/` passes (25 suites).
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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