`cargo build --features "X"` doesn't update binary mtime when list of features change

Problem

Cargo doesn't appear to be updating the mtime on the binary in the ./target/debug directory when grabbing that file from the cache. This is breaking my using cargo inside a Makefile because the Makefile believes the built binary is older than it actually is.

Steps

1. Create a repo with the following source

   # Cargo.toml
   [package]
   name = "minrepro"
   version = "0.1.0"
   edition = "2021"
   
   [dependencies]
   
   [features]
   feature_a = []
   feature_b = []
   

   // src/main.rs
   fn main() {
       #[cfg(feature = "feature_a")]
       println!("Hello, Feature A!");
       #[cfg(feature = "feature_b")]
       println!("Hello, Feature B!");
   
       println!("Hello, world!");
   }
   

   # Makefile to show the problem
   FEATURES :=
   
   ifeq ($(FEATURE),A)
   FEATURES += "feature_a"
   endif
   
   ifeq ($(FEATURE),B)
   FEATURES += "feature_b"
   endif
   
   .PHONY: all FORCE
   
   all: bin
   	./bin
   
   bin: target/debug/minrepro
   	cp target/debug/minrepro bin
   
   target/debug/minrepro: FORCE
   	cargo build --features="$(FEATURES)"
   

2. Check the current time

   bash$ date
   Fri Mar 14 10:55:00 PM PDT 202
   

3. Build the crate with feature a

   cargo build --features feature_a
     Compiling minrepro v0.1.0 (/home/matsch/dev/minrepro)
     Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.12s
   

4. stat the built binary

   bash$ stat ./target/debug/minrepro
   stat ./target/debug/minrepro
   File: ./target/debug/minrepro
   Size: 3946232   	Blocks: 7712       IO Block: 4096   regular file
   Device: 253,1	Inode: 58468456    Links: 2
   Access: (0755/-rwxr-xr-x)  Uid: (1155901/  matsch)   Gid: (89939/primarygroup)
   Access: 2025-03-14 22:55:51.930800853 -0700
   Modify: 2025-03-14 22:55:51.930800853 -0700
   Change: 2025-03-14 22:55:51.938800874 -0700
   Birth: 2025-03-14 22:55:51.874800711 -0700
   

5. Build the crate with feature b

   cargo build --features feature_b
     Compiling minrepro v0.1.0 (/home/matsch/dev/minrepro)
     Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.12s
   

6. stat the built binary again

   stat ./target/debug/minrepro
   File: ./target/debug/minrepro
   Size: 3946216   	Blocks: 7712       IO Block: 4096   regular file
   Device: 253,1	Inode: 58470933    Links: 2
   Access: (0755/-rwxr-xr-x)  Uid: (1155901/  matsch)   Gid: (89939/primarygroup)
   Access: 2025-03-14 23:01:12.287611878 -0700
   Modify: 2025-03-14 23:01:12.287611878 -0700
   Change: 2025-03-14 23:01:12.295611898 -0700
   Birth: 2025-03-14 23:01:12.231611736 -0700
   

7. Build the crate with feature a again

   cargo build --features feature_a
     Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.12s
   

8. stat the built binary again

   stat ./target/debug/minrepro
   File: ./target/debug/minrepro
   Size: 3946232   	Blocks: 7712       IO Block: 4096   regular file
   Device: 253,1	Inode: 58468456    Links: 2
   Access: (0755/-rwxr-xr-x)  Uid: (1155901/  matsch)   Gid: (89939/primarygroup)
   Access: 2025-03-14 22:55:51.930800853 -0700
   Modify: 2025-03-14 22:55:51.930800853 -0700
   Change: 2025-03-14 23:02:43.063840777 -0700
   Birth: 2025-03-14 22:55:51.874800711 -0700
   

Notice that the "Modify" time is now older than step 5, even though the file on disk has been updated since step "5"

Using the Makefile, I can produce the same issue:

# The first time it works
bash$ FEATURE=B make
cargo build --features=""feature_b""
   Compiling minrepro v0.1.0 (/home/matsch/dev/minrepro)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s
cp target/debug/minrepro bin
./bin
Hello, Feature B!
Hello, world!

# Same with feature A
bash$ FEATURE=A make
cargo build --features=""feature_a""
   Compiling minrepro v0.1.0 (/home/matsch/dev/minrepro)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
cp target/debug/minrepro bin
./bin
Hello, Feature A!
Hello, world!

# But now we go back to feature B and it still outputs feature A
# This is because make has determined the `cp` is not needed because the mtime of `./target/debug/minrepro` is older than `bin`
bash$ FEATURE=B make
cargo build --features=""feature_b""
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
./bin
Hello, Feature A!
Hello, world!

Possible Solution(s)

No response

Notes

No response

Version

cargo --version --verbose
cargo 1.85.0 (d73d2caf9 2024-12-31)
release: 1.85.0
commit-hash: d73d2caf9e41a39daf2a8d6ce60ec80bf354d2a7
commit-date: 2024-12-31
host: x86_64-unknown-linux-gnu
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Debian n/a (rodete) [64-bit]

Reproduce the issue with the provided minimal crate and alternating feature builds, then trace how Cargo handles cached artifacts and the target/debug binary. Done means switching between feature_a and feature_b updates the binary's mtime when the cached artifact is restored, so the Makefile copies and runs the current build.