`cargo build` failed with RUSTFLAGS="--print sysroot"

[mssun]

cargo build will fail when passing RUSTFLAGS like --print sysroot, --print native-static-libs, etc.

I guess cargo will read stdout for other purposes?

For example:

$ cargo new hello_world --bin
     Created binary (application) `hello_world` project
$ cd hello_world
$ RUSTFLAGS="--print sysroot" cargo build
error: unexpected character in cfg `/`, expected parens, a comma, an identifier, or a string

Versions:

$ cargo -V
cargo 0.23.0-nightly (8118b02ac 2017-09-14)

[alexcrichton]

There's some initial stages where we parse some output from rustc that we still need to pass rustflags, how come you're passing these flags to all compliations? Shouldn't it just be the final compilation?

[mssun]

I intended to use a rustc flags (--print native-static-libs) to print out if my project relies on any native static libraries.

[mssun]

@alexcrichton I misunderstand the usage of the --print native-static-libs flag. Sorry for the trouble. Please close this issue if you think relying stdout from rustc is not an problem. Thanks.

[alexcrichton]

Ok, thanks for the update!