different feature sets use the same output directory ($OUT_DIR)

[japaric]

they should use different output directory so build scripts that generate files whose contents vary with Cargo features will work correctly (otherwise you will only one instance of such files across different builds that use different feature sets)

cc @alexcrichton

[japaric]

Example where you can observe this bug:

$ tail -n5 Cargo.toml
build = "build.rs"

[features]
a = []
default = ["a"]

$ cat build.rs
use std::env;
use std::fs::File;
use std::io::Write;
use std::path::PathBuf;

fn main() {
    let outfile = PathBuf::from(env::var_os("OUT_DIR").unwrap()).join("foo.txt");

    writeln!(File::create(outfile).unwrap(),
             "{:?}",
             env::var_os("CARGO_FEATURE_A")).unwrap();

    println!("cargo:rerun-if-changed=build.rs");
}

$ cargo clean

$ cargo build

$ cat **/foo.txt
Some("1")

$ cargo build --no-default-features

$ cat **/foo.txt
None

$ cargo build

# Expected `Some("1")`!
$ cat **/foo.txt
None

[japaric]

To elaborate: The second cargo build command doesn't run the build script and that's fine. The problem is that both feature sets, "a" (the default) and "" (no-default-features), use the same $OUT_DIR so the cargo build --no-default-features command overwrites the foo.txt file that cargo build generated.

[alexcrichton]

Fixed in #3310