Unable to build hello world with Xargo (can't perform LTO when compiling incrementally)

[johnthagen]

Follow the instructions here to build the hello world xargo subproject.

On Mac:

$ xargo build --target x86_64-apple-darwin --release --verbose
+ "rustc" "--print" "sysroot"
+ RUSTFLAGS="--sysroot /Users/user/.xargo/HOST"
+ "cargo" "build" "--target" "x86_64-apple-darwin" "--release" "--verbose"
   Compiling min-sized-rust-xargo v0.1.0 (/Users/user/GitHub/min-sized-rust/xargo)
     Running `rustc --edition=2018 --crate-name min_sized_rust_xargo src/main.rs --color always --crate-type bin --emit=dep-info,link -C opt-level=z -C panic=abort -C lto -C codegen-units=1 -C metadata=2a6dbeac17463644 -C extra-filename=-2a6dbeac17463644 --out-dir /Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/deps --target x86_64-apple-darwin -C incremental=/Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/incremental -L dependency=/Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/deps -L dependency=/Users/user/GitHub/min-sized-rust/xargo/target/release/deps --sysroot /Users/user/.xargo/HOST`
error: can't perform LTO when compiling incrementally

error: aborting due to previous error

error: Could not compile `min-sized-rust-xargo`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name min_sized_rust_xargo src/main.rs --color always --crate-type bin --emit=dep-info,link -C opt-level=z -C panic=abort -C lto -C codegen-units=1 -C metadata=2a6dbeac17463644 -C extra-filename=-2a6dbeac17463644 --out-dir /Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/deps --target x86_64-apple-darwin -C incremental=/Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/incremental -L dependency=/Users/user/GitHub/min-sized-rust/xargo/target/x86_64-apple-darwin/release/deps -L dependency=/Users/user/GitHub/min-sized-rust/xargo/target/release/deps --sysroot /Users/user/.xargo/HOST` (exit code: 1)

What's strange is that this is after a xargo clean, so it shouldn't be an incremental build?

For a failed Linux build output see: https://travis-ci.org/johnthagen/min-sized-rust/jobs/486629156

Cargo.toml:

[package]
name = "min-sized-rust-xargo"
version = "0.1.0"
authors = ["johnthagen <[email protected]>"]
edition = "2018"

[dependencies]

[profile.release]
opt-level = 'z'     # Optimize for size.
lto = true          # Enable Link Time Optimization
codegen-units = 1   # Reduce number of codegen units to increase optimizations.
panic = 'abort'     # Abort on panic

Xargo.toml:

[dependencies]
std = {default-features=false}

[johnthagen]

Bisecting nightly versions, this problem started appearing with nightly-2019-01-28 (for macOS).

Though, it seems like Linux with versions before that are still failing: https://travis-ci.org/johnthagen/min-sized-rust/jobs/486680281

[phil-opp]

This is a bug in cargo that should be fixed in the current or upcoming nightly. It was reported in rust-lang/cargo#6564 (comment) and fixed in rust-lang/cargo#6610.

[johnthagen]

I'm still hitting this issue with rustc 1.34.0-nightly (8ae730a44 2019-02-04).

[phil-opp]

That's because cargo is a git submodule in the rustc repo which still uses the 9 day old commit 245818076 for cargo. You can see this when you run cargo --version.

There is an open PR that updates the cargo submodule, which should finally fix this issue: rust-lang/rust#58131.

[johnthagen]

This has been fixed on the latest nightlies.