fix(multivers): read the correct RUSTFLAGS variable

There was a typo that lead to `RUSTFLAGS` being ignored and overwritten.

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
+### Fixed
+
+- `RUSTFLAGS` is no longer overwritten completely (discarding it previous value). There was a typo when reading its current value (`RUST_FLAGS` instead of `RUSTFLAGS`).
+
 [Unreleased]: https://github.com/ronnychevalier/cargo-multivers/compare/v0.6.0...HEAD
 
 ## [0.6.0] - 15-12-2023

src/multivers.rs

@@ -134,7 +134,7 @@ impl Multivers {
             Triple::from_str(&self.target).context("Failed to parse the target")?;
         let manifest_path = package.manifest_path.as_std_path().to_path_buf();
         let features_list = self.features.features.join(" ");
-        let mut rust_flags = std::env::var("RUST_FLAGS").unwrap_or_default();
+        let mut rust_flags = std::env::var("RUSTFLAGS").unwrap_or_default();
 
         let metadata = MultiversMetadata::from_package(package)
             .context("Failed to parse package's metadata")?;