cargo recompile all crates when building cross architecture with specifying `+crt-static` in rustflags on Windows

[metaworm]

Problem

I specify rustflags in .cargo/config.toml in my project directory like this

[target.i686-pc-windows-msvc]
rustflags = ["-C", "target-feature=+crt-static"]
[target.x86_64-pc-windows-msvc]
rustflags = ["-C", "target-feature=+crt-static"]

Every time when i build project using cargo build --target <target-triple> and switch one target to another, cargo will recompile all crates rather than reuse the compiled result in the target/<target-triple> directory

Steps

1. Put these configuration into .cargo/config.toml in your project directory

   [target.i686-pc-windows-msvc]
   rustflags = ["-C", "target-feature=+crt-static"]
   [target.x86_64-pc-windows-msvc]
   rustflags = ["-C", "target-feature=+crt-static"]

2. Build the x86_64 version which is the default on Windows using cargo build
3. Build the x86 version using cargo build --target i686-pc-windows-msvc
4. Build the x86_64 version again using cargo build, cargo will recompile all crates

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.66.0-nightly (b332991a5 2022-10-13)

[ehuss]

Thanks for the report! This is a known issue where running cargo build and cargo build --target share the same build-script/proc-macro artifacts, but use different RUSTFLAGS and thus cause a rebuild.

Workarounds involve always using --target, separate target directories, or target-applies-to-host.

Closing as a duplicate of #9453 (and #3739, and #6375, and #8716).