Cargo build --release and cargo install use different features

[nmattia]

Problem

The command cargo build --release uses different features than cargo install.

Steps

1. go in this directory
2. cargo build --release

   Compiling lazy_static v1.3.0
   Compiling thread_local v0.3.6
   Compiling regex v1.1.8
  ...

3. cargo install

   Compiling lazy_static v1.3.0
   Compiling thread_local v0.3.6
   Compiling regex v1.1.8
...

Notes

Output of cargo version:

$ ./target/debug/cargo  --version
cargo 1.37.0
$ git rev-parse HEAD
c3ee836e92eed0db7f403ff9954ede138cd57082

I've added some debug logs to compute_metadata, in particular when hashing in the features:

diff --git a/src/cargo/core/compiler/context/compilation_files.rs b/src/cargo/core/compiler/context/compilation_files.rs
index ed3232ea..f63ca6be 100644
--- a/src/cargo/core/compiler/context/compilation_files.rs
+++ b/src/cargo/core/compiler/context/compilation_files.rs
...
@@ -525,12 +531,16 @@ fn compute_metadata<'a, 'cfg>(
         .stable_hash(bcx.ws.root())
         .hash(&mut hasher);
 
 ...
     // Also mix in enabled features to our metadata. This'll ensure that
     // when changing feature sets each lib is separately cached.
     bcx.resolve
         .features_sorted(unit.pkg.package_id())
         .hash(&mut hasher);
 
+    info!("{}: Features: {:#?}", tname, bcx.resolve.features_sorted(unit.pkg.package_id()));
+
     // Mix in the target-metadata of all the dependencies of this target.
     {
         let mut deps_metadata = cx

The cargo build --release gives:

[2019-08-26T19:18:50Z INFO  cargo::core::compiler::context::compilation_files] lazy_static: Features: [
    "spin",
    "spin_no_std",
]

and cargo install gives:

[2019-08-26T19:19:21Z INFO  cargo::core::compiler::context::compilation_files] lazy_static: Features: []

[ehuss]

This is caused by cargo install ignoring the Cargo.lock file by default. If you pass --locked, you should get the same behavior. Or run cargo update to use the most current dependencies.

[nmattia]

Unfortunately that doesn't seem to be the issue:

$  cargo build  --release -j 8
   Compiling bar v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/bar)
   Compiling foo v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/foo)
    Finished release [optimized] target(s) in 0.51s
running tests
$  cargo test --release
   Compiling bar v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/bar)
   Compiling foo v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/foo)
    Finished release [optimized] target(s) in 0.52s
     Running target/release/deps/bar-07370ca6dcd302b1

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/release/deps/foo-95cd32c8408c7a13

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

$ cargo install --locked --path bar --bins --root /nix/store/56wbjv24nifdp3ki61mpl0yy80qs0dch-bar-and-others
  Installing bar v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/bar)
   Compiling lazy_static v1.3.0
   Compiling thread_local v0.3.6
   Compiling regex v1.1.8
   Compiling bar v0.1.0 (/tmp/nix-build-bar-and-others.drv-0/workspace/bar)
    Finished release [optimized] target(s) in 10.98s

[ehuss]

Ah, I didn't realize you were comparing to cargo build in the root of the workspace. This happens because foo depends on rand > getrandom > lazy_static, and getrandom enables the spin_no_std feature of lazy_static for the uefi target. This is a known issue where unused targets activate features during feature unification (tracked in issues like #1197 and #2524).

Newer versions of getrandom do not specify its dependencies that way, so that may help.

[nmattia]

You're right, that seems to be the issue. cargo build -p bar ... doesn't help, but pushd bar; cargo build ... does!