unable to build older releases due to MSRV conflict

[tones111]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Rust Version

1.62.1

Clap Version

v4.0.32

Minimal reproducible code

N/A

Steps to reproduce the bug with the above code

cargo new --bin args
cd args
cargo add clap@=4.0.32
cargo +1.62.1 check

Actual Behaviour

error: package `clap_lex v0.3.3` cannot be built because it requires rustc 1.64.0 or newer, while the currently active rustc version is 1.62.1

Expected Behaviour

Since the MSRV for clap v4.0.32 is rust 1.60.0 I expect to be able to compile with the 1.62.1 compiler.

Additional Context

It looks like the version numbers for dependencies need to be constrained to prevent cargo from picking a version with an incompatible MSRV. In this case clap_lex should be fixed to v0.3.0 since v0.3.1 bumped the MSRV to rust 1.64.0. There may be other incompatibilities... this is just the first error presented.

Debug Output

No response

[tones111]

It looks like I'm able to build by adding the constraint described above to v4.0.32.

-clap_lex = { path = "./clap_lex", version = "0.3.0" }
+clap_lex = { path = "./clap_lex", version = "=0.3.0" }

however, I'm unable to create a pull request since there's no branch at that point in the repo. Would it be possible to tag a v4.0.33 with this change?

[epage]

The way to solve this is for you to run cargo update -p clap_lex --precise 0.3.0. Newer versions of cargo should include that suggestion in the error.

Unfortunately, crates can only be responsible that they can build for the MSRV but should not be responsible for all of versions of dependencies to build for the MSRV

• One way is for everyone to treat a change to MSRV as a breaking change but this is quite disruptive and leads to multiple copies of crates in dependency graphs
• Another way is to use version constraints, as you mentioned, but this has repercussions on the ecosystem, for example
  • Cargo is unable to resolve dependency versions rust-lang/cargo#6584 (comment)
  • https://www.reddit.com/r/rust/comments/p8clcx/how_to_fix_cargo_dependency_issue/

The ideal long term solution is for cargo to handle this automatically which I'm working towards: rust-lang/cargo#9930