cargo install always re-installs sccache even if the newest version is already present

[jonasbb]

Problem

Running cargo install sccache --no-default-features twice compiles sccache twice.
However, given that the first install installs the most recent version I would expect the second install to be a no-op, since no update is required.

Steps

1. Run cargo install sccache --no-default-features
2. Run cargo install sccache --no-default-features again

Possible Solution(s)
I instrumented the version f84f3f8 with some dbg! statements to pinpoint the problem.
As best as I can tell, the problem is that exe_names in src/cargo/ops/common_for_install_and_uninstall.rs does not take into account feature flags.
By default only the sccache binary will be installed, but the sccache crate can also install sccache-dist when given the correct feature flags (Lines common_for_install_and_uninstall.rs:498).
This leads the check in common_for_install_and_uninstall.rs:218 to fail, which marks sccache as dirty.

Here is the debug output:

[src/cargo/ops/common_for_install_and_uninstall.rs:636] filter = Default {
    required_features_filterable: true, 
}                 
[src/cargo/ops/common_for_install_and_uninstall.rs:215] dupe_pkg_id.version() == pkg.version() = true
[src/cargo/ops/common_for_install_and_uninstall.rs:216] dupe_pkg_id.source_id() == source_id = true
[src/cargo/ops/common_for_install_and_uninstall.rs:217] precise_equal = true
[src/cargo/ops/common_for_install_and_uninstall.rs:493] self.features == feature_set(&opts.features) = true
[src/cargo/ops/common_for_install_and_uninstall.rs:494] self.all_features == opts.all_features = true
[src/cargo/ops/common_for_install_and_uninstall.rs:495] self.no_default_features == opts.no_default_features = true
[src/cargo/ops/common_for_install_and_uninstall.rs:496] self.profile.as_str() == opts.build_config.requested_profile.as_str() = true                          
[src/cargo/ops/common_for_install_and_uninstall.rs:497] (self.target.is_none() || self.target.as_deref() == Some(target)) = true
[src/cargo/ops/common_for_install_and_uninstall.rs:498] &self.bins = {
    "sccache",
}
[src/cargo/ops/common_for_install_and_uninstall.rs:498] exes = {
    "sccache",
    "sccache-dist",
}
[src/cargo/ops/common_for_install_and_uninstall.rs:498] dbg!(& self . bins) == dbg!(exes) = false
[src/cargo/ops/common_for_install_and_uninstall.rs:218] info.is_up_to_date(opts, target, &exes) = false
[src/cargo/ops/common_for_install_and_uninstall.rs:223] Ok((Freshness::Dirty, duplicates)) = Ok(
    (
        Dirty,
        {
            "sccache": Some(
                PackageId {
                    name: "sccache",
                    version: "0.2.13",
                    source: "registry `https://github.com/rust-lang/crates.io-index`",
                },
            ),
        },
    ),
)
[src/cargo/ops/cargo_install.rs:544] freshness = Dirty

Notes

Output of cargo version:

Revision f84f3f8, cargo 1.46.0
also reproduces on stable cargo 1.45.0 (744bd1f 2020-06-15)

[ChrisJefferson]

I don't have to give ``--no-default-features, I get the same thing just running cargo install sccache` (which I was coming to report, but then found this bug.

[jonasbb]

@ehuss Do you know where a good place is to start solving this bug? The cargo codebase is quite large and I'm not familiar with it.

This might be the same issue as #8703.

[hampuslidin]

I missed this issue when looking for a similar issue that of #8703. I have made a quite rough POC of a fix for the bug, which resolves the dependency graph of the package before checking if the package is fresh or dirty, to get the activated features for the package, and I can confirm that this solves the issue fornushell. The diff can be found in this gist. You can try it out on sccache locally as well, to see if it solves it for you.

[weihanglo]

This is effectively the same as #8703. Given a Cargo team member commented there with some insights, let's close this in favor of that one. Thank you!