Adding ndarray-linalg as unused dependency breaks build

[grothesque]

The following program builds and runs with cargo run. This is on current Debian stable with current Rust from rustup. The project was started from a fresh cargo new.

src/main.rs:

use ndarray as nd;

fn main() {
    let a = nd::arr2(&[[1.0, 2.0], [3.0, 4.0]]);
    let b = a.dot(&a);
    dbg!(b);
}

Cargo.toml:

[package]
name = "matmul"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
ndarray = "0.15.6"

However, when the following dependency line is added to Cargo.toml

ndarray-linalg = { version = "0.16.0", features = ["openblas-system"] }

cargo build fails with the following linker error:

error: linking with `cc` failed: exit status: 1
  |
  = note: LC_ALL="C" PATH="/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/cwg/.cargo/bin:/home/cwg/local/bin:/home/cwg/sys/bin:/home/cwg/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games" VSLANG="1033" "cc" "-m64" "/tmp/rustcvTd5ry/symbols.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.12rijkjv0x41cjbz.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.13zpo2a8nbmhezo6.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.18mwf38722fgdy2r.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1aulkdo8yfo6ihe3.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1ecocs5yuozxilmd.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1f7nyf4sn87xzaeq.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1fscnlrszql1dx22.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1g9982xymiazplzt.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1gn7rlw3e0d00jy7.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1h75op7sa9k7iynp.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1htow7tq8fl054u1.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1mpbuhv5lz3hq8vc.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1pq7vses7fawrpw5.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1q2dfthqogtb4973.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1rei7w7vfghwcm06.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1s0cev0krhm1nhli.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1v4mntwzpnbzlj7e.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1x8dahilfep9z896.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.1z9wqh15t745i2lu.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2476p408ijlio2aw.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.25zmx5z4ite7p93j.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.26zmyc0tqt5w8kp.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.295wsp3neqca3vq1.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2ehfwqz7fchblmoj.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2gj3qnetq34b5t25.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2llxqdmvpmyaw5tu.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2pr2xhkd4kum3ou0.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2y0vmyequpityodr.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2yfjbf68nlk12tkk.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2yi0z30et38wrvz3.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.2yj1k6s5zr8tke29.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.323o19iavd61zegj.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.33diw2qg26c5h3fa.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3bfbbia7767bgi9q.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3chmf4xfctqyqoxz.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3cxwcdlcjhvofqjw.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3er1zjezmko0ldc6.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3iwgrdt7o7qs655c.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3ojuwlzkujzr5ofk.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.42vkbpy0wns7q6b6.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.43sivngp0qeg9fo2.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.47fffcu23i8420ji.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.4lpp2rihs6fjz7uk.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.4ooads6hzvl3x9my.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.4tezgwp05waflge3.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.4tg3ihci1x6vfruf.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.4z4566ttclw6xyvv.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.52uo2hu8276a261m.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.55ukw19rwbfqk3ff.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.587cg4f0hsp9jvt7.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.5e71hbpcqf1hqyrd.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.785rbqjn06o4vau.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.9cssaprb5odwrpa.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.d6j127m8bb6cvpe.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.dnksvzmb461opu9.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.ft41rhofy1okclq.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.g0qqcxss02unjop.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.jo240miv0pmekn6.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.m6kcwgjgcso7rkw.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.qhkcypped3s2239.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.qkck8ljwzx8hq7p.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.rrl7vpmrjcugxxp.rcgu.o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3bx3kcxg016rjf94.rcgu.o" "-Wl,--as-needed" "-L" "/tmp/matmul/target/debug/deps" "-L" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "/tmp/matmul/target/debug/deps/libndarray-023ca636ca46b8eb.rlib" "/tmp/matmul/target/debug/deps/libmatrixmultiply-c16e1aba180dc4e2.rlib" "/tmp/matmul/target/debug/deps/libapprox-8319bcbed4fd7e02.rlib" "/tmp/matmul/target/debug/deps/libnum_complex-65da99b25716bc26.rlib" "/tmp/matmul/target/debug/deps/libserde-1c762bfd80303691.rlib" "/tmp/matmul/target/debug/deps/librand-4959d6cec0f8d469.rlib" "/tmp/matmul/target/debug/deps/librand_chacha-b22197ade9f74797.rlib" "/tmp/matmul/target/debug/deps/libppv_lite86-9f808eb911999ef2.rlib" "/tmp/matmul/target/debug/deps/librand_core-fe980624cf1fe49e.rlib" "/tmp/matmul/target/debug/deps/libgetrandom-70ffb9e79a3d1149.rlib" "/tmp/matmul/target/debug/deps/libcfg_if-61dc7a6799e72b18.rlib" "/tmp/matmul/target/debug/deps/libnum_integer-6761fe06578db2d2.rlib" "/tmp/matmul/target/debug/deps/libnum_traits-aa75f3964f70d2b4.rlib" "/tmp/matmul/target/debug/deps/librawpointer-fd99f7762ca119b4.rlib" "/tmp/matmul/target/debug/deps/libcblas_sys-33b52a1f1355ee0d.rlib" "/tmp/matmul/target/debug/deps/liblibc-a9fa19dd18f65bfc.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-90f6ddbf82de36ec.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-480c41e9d4e1f677.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-db744c0ca03eed1d.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libmemchr-8ba652dc7d4b285a.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-d5f4520a9ebc0d58.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-4ad84de58f0cb463.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-0d10aae2e0f38735.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd_detect-0c17cff739e6745b.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-b29e17139dde1aa8.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-1f975299829cc7bd.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-86bae3bc3079f89b.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-321b82c30dffdf5f.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-3dd8a6810a0bdfef.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-eb39a61c0c879984.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-aa769569f91c3548.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-510a192a50a983ed.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-0577018320f99037.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-193cf992125ccd4c.rlib" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-8e138eaf26ebb4a8.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "/home/cwg/cb/autostow/rust/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "/tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: /usr/bin/ld: /tmp/matmul/target/debug/deps/matmul-df71ff3b22c784a0.3bfbbia7767bgi9q.rcgu.o: in function `ndarray::linalg::impl_linalg::mat_mul_impl':
          /home/cwg/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ndarray-0.15.6/src/linalg/impl_linalg.rs:484: undefined reference to `cblas_zgemm'
          /usr/bin/ld: /home/cwg/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ndarray-0.15.6/src/linalg/impl_linalg.rs:483: undefined reference to `cblas_cgemm'
          /usr/bin/ld: /home/cwg/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ndarray-0.15.6/src/linalg/impl_linalg.rs:481: undefined reference to `cblas_dgemm'
          /usr/bin/ld: /home/cwg/.cargo/registry/src/index.crates.io-6f17d22bba15001f/ndarray-0.15.6/src/linalg/impl_linalg.rs:480: undefined reference to `cblas_sgemm'
          collect2: error: ld returned 1 exit status

  = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)

error: could not compile `matmul` (bin "matmul") due to previous error

This problem disappears when the following use declaration is added to the program

use ndarray_linalg;

(However rustc warns about an "unused import"...)

I reckon that ndarray and ndarray-linalg have a tricky job here dealing with different sources of BLAS/LAPACK and a fallback implementation of matrix multiplication provided by the matrixmultiply crate. Still, it seems to me that the problem described above should be addressed in some way, at least by improving documentation.

It is very surprising when a program stops working after an unused dependency is added, and then can be made to build again by adding a needless use declaration.

[bluss]

It's the same problem as the one described here https://github.com/rust-ndarray/ndarray?tab=readme-ov-file#how-to-enable-blas-integration in the Readme - at least I think it is. It says "your program must also link to blas_src by using it".

This is not great, but that's ndarray's design for blas right now to enable loose coupling between ndarray and blas versions. So we have some tangential docs. It happens that using ndarray_linalg is interchangeable with using blas_src.

Not sure how to improve this, probably add back a fixed requirement on blas src version and so on?

[grothesque]

Thanks for the reply. I do not yet understand the problem completely, so I'm unable to suggest a fix at this time.

I spent some time trying to understand what's going on. Starting from the toy project described in the topmost post, I can obtain the same error message by replacing the following chunk in Cargo.toml

[dependencies]
ndarray = "0.15.6"

by

[dependencies.ndarray]
default-features = false
features = ["blas", "approx", "std"]
version = "0.15.2"

This latter chunk is taken directly from Cargo.toml of ndarray-linalg.

It is indeed the "blas" feature of ndarray that triggers the problem.

Now looking, as you suggest, at the readme file of ndarray (I note in passing that the subsection title "How to enable blas integration" does not render correctly on github), it suggests to use

[dependencies]
ndarray = { version = "0.15.0", features = ["blas"] }
blas-src = { version = "0.8", features = ["openblas"] }
openblas-src = { version = "0.10", features = ["cblas", "system"] }

for system openblas.

However, this does not work on my box (neither as the only dependencies, or together with

ndarray-linalg = { version = "0.16.0", features = ["openblas-system"] }

So, disregarding ndarray-linalg for a moment, is the suggestion in the readme file of ndarray on how to use system openblas out of date, or am I missing something?