京公网安备11010502063487号build.rs 是 Cargo 在编译 crate 之前先运行的一段 Rust 程序。它什么时候运行、能生成什么、改了哪些文件会触发重跑、失败了会怎样?这篇用一个最小项目把每个问题都跑出结果。
cargo build 输出(只保留关键行):
Compiling app v0.3.1 (<实验目录>/proj/u85)
warning: app@0.3.1: build.rs 运行了:读到 1 行
warning: unexpected `cfg` condition name: `has_data`
= help: or consider adding `println!("cargo::rustc-check-cfg=cfg(has_data)");` to the top of the `build.rs`
warning: unexpected `cfg` condition name: `has_data`
= help: or consider adding `println!("cargo::rustc-check-cfg=cfg(has_data)");` to the top of the `build.rs`
warning: `app` (bin "app") generated 2 warnings
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.58s
运行 app:
LINES = 1 FIRST = "alpha"
BUILT_BY = build.rs-0.3.1
cfg(has_data) 为真
OUT_DIR 里生成的 gen.rs 内容:
pub const LINES: usize = 1;
pub const FIRST: &str = "alpha";build.rs 属于 Cargo,更多配置见Cargo Build Script。上一篇中遇到的「读文件却没触发重编译」问题见函数式宏。
第一次 build 之后:1 次;没改动再 build:1 次;改了 data.txt 之后 build:2 次(运行 app:LINES = 3 FIRST = "alpha");只改 main.rs 之后 build:2 次
去掉 rerun-if-changed 并 build 一次后累计 3 次;只改 main.rs 再 build:累计 4 次(新增 1)
退出码 101
error: failed to run custom build command for `app v0.3.1 (<实验目录>/proj/u85)`
Caused by:
process didn't exit successfully: `<实验目录>/target/debug/build/app-571b150f2e5c57c7/build-script-build` (exit status: 101)
--- stderr
thread 'main' (7161489) panicked at build.rs:1:13:
build.rs 故意失败
note: run with `RUST_BACKTRACE=1` environment variable to display a backtracewarning: app@0.3.1: CARGO_PKG_NAME=app warning: app@0.3.1: CARGO_PKG_VERSION=0.3.1 warning: app@0.3.1: TARGET=aarch64-apple-darwin warning: app@0.3.1: HOST=aarch64-apple-darwin warning: app@0.3.1: PROFILE=debug warning: app@0.3.1: OPT_LEVEL=0 warning: app@0.3.1: CARGO_MANIFEST_DIR=<实验目录>/proj/u85 warning: app@0.3.1: cwd 是 manifest 目录: true