使用不稳定库功能“iter_nth_back”的 Rust 包

我有一个我不太了解的 Rust 应用程序，我正在从我正在开发的 Python 程序中调用它。我没有更改 Rust 源代码中的任何内容，但这两个项目的构建过程只是停止工作并出现如下错误：

[... several similar errors]
error[E0658]: use of unstable library feature 'iter_nth_back'
   --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/ndarray-0.13.0/src/iterators/mod.rs:585:46
    |
585 |         either_mut!(self.inner, iter => iter.nth_back(n))
    |                                              ^^^^^^^^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/56995

error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0658`.
error: Could not compile `ndarray`.

我查看了名单ndarray 版本，几天前发布了 0.13.0 版本，所以我怀疑它与我的构建环境不兼容。

我怎样才能让我的构建再次运行？

以下是重现该问题的完整步骤：

$ sudo docker run -it --rm rust:1.36.0
# USER=foo cargo new hello_world --bin
     Created binary (application) `hello_world` package
# cd hello_world/
# echo 'bio = "^0"' >> Cargo.toml
# cargo build
    Updating crates.io index
  Downloaded bio v0.29.0
  Downloaded [... many more ...]
  Downloaded ndarray v0.13.0
  Downloaded [... many more ...]
   Compiling proc-macro2 v1.0.4
   Compiling [... many more ...]
   Compiling ndarray v0.13.0
   Compiling [... many more ...]
   Compiling statrs v0.11.0
error[E0658]: use of unstable library feature 'iter_nth_back'
   --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/ndarray-0.13.0/src/iterators/mod.rs:134:5
    |
134 | /     fn nth_back(&mut self, n: usize) -> Option<*mut A> {
135 | |         let index = self.index?;
136 | |         let len = self.dim[0] - index[0];
137 | |         if n < len {
...   |
147 | |         }
148 | |     }
    | |_____^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/56995
[... other, similar errors ...]
   Compiling serde_derive v1.0.101
   Compiling strum_macros v0.16.0
   Compiling snafu-derive v0.5.0
error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0658`.
error: Could not compile `ndarray`.
warning: build failed, waiting for other jobs to finish...
error: build failed
#

有趣的是，如果我运行最新的 rust docker 镜像 1.38，我不会看到错误。然而，我的构建过程是从 Ubuntu Xenial 的包管理器安装 Rust，所以我可能无法轻松升级它。

新答案：升级 Rust

事实证明，升级 rust 并没有我想象的那么难，然后我就不用改 Rust 源代码了。

In my .travis.yml文件，我替换了这个：

- sudo apt-get install -y cargo

有了这个：

- sudo curl https://sh.rustup.rs -sSf | sh -s -- -y
- source ~/.cargo/env

原始答案：引脚依赖性

我尝试添加一个明确的ndarray依赖性并将其固定在 0.12，但这不起作用。然后我注意到bio最近几天也发布了新版本。固定这种依赖是有效的。

$ sudo docker run -it --rm rust:1.36.0
# USER=foo cargo new hello_world --bin
     Created binary (application) `hello_world` package
# cd hello_world/
# echo 'bio = "~0.28.2"' >> Cargo.toml
# cargo build
    Updating crates.io index
  Downloaded bio v0.28.2
  Downloaded [... many more ...]
  Downloaded ndarray v0.12.1
  Downloaded [... many more ...]
   Compiling proc-macro2 v1.0.4
   Compiling [... many more ...]
   Compiling ndarray v0.12.1
   Compiling [... many more ...]
   Compiling csv v1.1.1
   Compiling hello_world v0.1.0 (/hello_world)
    Finished dev [unoptimized + debuginfo] target(s) in 14m 15s
#