Identify/decide minimum supported version of Rust

[DanielEScherzer]

C.f. #1238

If I understand correctly:

git2-rs/Cargo.toml

Line 16 in 7415113

edition = "2021"

means that MSRV >= 1.56.0

git2-rs/Cargo.toml

Line 20 in 7415113

bitflags = "2.1.0"

means MSRV >= 1.56.0 (https://docs.rs/crate/bitflags/2.1.0/source/Cargo.toml#55)

git2-rs/Cargo.lock

Lines 474 to 476 in 7415113

	[[package]]
	name = "libc"
	version = "0.2.174"

means MSRV >= 1.63.0 (https://docs.rs/crate/libc/0.2.174/source/Cargo.toml#52)

git2-rs/src/cred.rs

Line 301 in 7415113

|| cfg!(windows) && path.chars().nth(1).is_some_and(|x| x == ':')

means MSRV >= 1.70.0 (https://blog.rust-lang.org/2023/06/01/Rust-1.70.0/) (unless we want to say that there is a different MSRV depending on which features are enabled?)

git2-rs/src/opts.rs

Line 527 in 7415113

assert!(get_cached_memory().is_ok_and(|m| m.1 == 20 * 1024 * 1024));

means tests are MSRV >= 1.70.0 for the same reason

[DanielEScherzer]

If we go with 1.81+ we can use #[expect] with a lint reason, so I would prefer that in order to work towards adding clippy, but regardless of what version we use, we should probably add it to CI to ensure that we don't accidentally lose support

[weihanglo]

Thanks for the analysis! Maybe we can run https://crates.io/crates/cargo-msrv and figure out?

[DanielEScherzer]

• cargo lockfile version 4 is default since 1.83, supported since 1.78, https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-183-2024-11-28
• str::from_utf8() is 1.87.0+, https://blog.rust-lang.org/2025/05/15/Rust-1.87.0/

root@406fa489d8c6:/rust/git2-rs# cargo install cargo-msrv --locked
...
root@406fa489d8c6:/rust/git2-rs# cargo msrv find
  [Meta]   cargo-msrv 0.19.3  

Compatibility Check #1: Rust 1.76.0
  [FAIL]   Is incompatible 
                                                                                                                                         
  ╭─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
  │ error: failed to parse lock file at: /rust/git2-rs/Cargo.lock                                                                       │
  │                                                                                                                                     │
  │ Caused by:                                                                                                                          │
  │   lock file version `4` was found, but this version of Cargo does not understand this lock file, perhaps Cargo needs to be updated? │
  │                                                                                                                                     │
  ╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
                                                                                                                                         

Compatibility Check #2: Rust 1.86.0
  [FAIL]   Is incompatible 
                                                                                                          
  ╭──────────────────────────────────────────────────────────────────────────────────────────────────────╮
  │    Compiling libc v0.2.174                                                                           │
  │    Compiling shlex v1.3.0                                                                            │
  │    Compiling pkg-config v0.3.32                                                                      │
  │    Compiling vcpkg v0.2.15                                                                           │
  │     Checking bitflags v2.9.1                                                                         │
  │     Checking log v0.4.27                                                                             │
  │    Compiling jobserver v0.1.33                                                                       │
  │    Compiling cc v1.2.27                                                                              │
  │    Compiling libz-sys v1.1.22                                                                        │
  │    Compiling libgit2-sys v0.18.5+1.9.4 (/rust/git2-rs/libgit2-sys)                                   │
  │ warning: libgit2-sys@0.18.5+1.9.4: failed to probe system libgit2:                                   │
  │     Checking git2 v0.21.0 (/rust/git2-rs)                                                            │
  │ error[E0658]: use of unstable library feature `inherent_str_constructors`                            │
  │    --> src/blame.rs:207:25                                                                           │
  │     |                                                                                                │
  │ 207 |             Some(sb) => str::from_utf8(sb).map(|s| Some(s)).map_err(|e| e.into()),             │
  │     |                         ^^^^^^^^^^^^^^                                                         │
  │     |                                                                                                │
  │     = note: see issue #131114 <https://github.com/rust-lang/rust/issues/131114> for more information │
  │                                                                                                      │
  │ For more information about this error, try `rustc --explain E0658`.                                  │
  │ error: could not compile `git2` (lib) due to 1 previous error                                        │
  │                                                                                                      │
  ╰──────────────────────────────────────────────────────────────────────────────────────────────────────╯
                                                                                                          

Compatibility Check #3: Rust 1.91.1
  [OK]     Is compatible 

Compatibility Check #4: Rust 1.88.0
  [OK]     Is compatible 

Compatibility Check #5: Rust 1.87.0
  [OK]     Is compatible 

Result:
   Considered (min … max):   Rust 1.56.1 … Rust 1.96.0 
   Search method:            bisect                    
   MSRV:                     1.87.0                    
   Target:                   x86_64-unknown-linux-gnu  
                                                      

[weihanglo]

Thanks for that. 1.87 sounds good to me. Do we want to check MSRV of our major consumers on crates.io / GitHub, and see if it may piss people off?

[weihanglo]

Also, I guess we probably need to set for also libgit2-sys?

[DanielEScherzer]

Thanks for that. 1.87 sounds good to me. Do we want to check MSRV of our major consumers on crates.io / GitHub, and see if it may piss people off?

Given that this doesn't compile with 1.86 I think major consumers would have already complained if they were trying to use older Rust

Checked all crates with over a million downloads (there are 1832 reverse dependencies, not going to check them all)

• https://crates.io/crates/built -> requires 1.87+
• https://crates.io/crates/shadow-rs -> no MSRV but depends on ^0.20.0 so they just won't update if needed
• https://crates.io/crates/cargo -> requires 1.94+
• https://crates.io/crates/docify_macros -> 2024 edition -> 1.85+ but depends on ^0 so they just won't update if needed
• https://crates.io/crates/vergen-git2 -> requires 1.95+
• https://crates.io/crates/bat -> requires 1.87+
• https://crates.io/crates/cargo-cache -> requires 1.57+, but depends on ^0.14 so they just won't update if needed
• https://crates.io/crates/cargo-tarpaulin -> no MSRV but depends on ^0.20 so they just won't update if needed
• https://crates.io/crates/cargo-generate -> no MSRV but depends on ~0.21 so they just won't update if needed
• https://crates.io/crates/auth-git2 -> no MSRV but depends on >=0.21, <0.22 so they just won't update
• https://crates.io/crates/tokei -> requires 1.71+, documentation says "You can also build and install from source (requires the latest stable Rust compiler.)", they pin to ^0.19.0 so they just won't upgrade
• https://crates.io/crates/cargo-update -> requires 1.86+ but depends on ^0.20 so they just won't update if needed

[weihanglo]

I guess libgit2-sys can be a bit lower? That sys crate can be as low as 1.63.0 (pre sparse registry), thought I don't know if it is particularly useful.

We might also want to use the new ctest which requires 1.88 (#1262), though dev dependency doesn't really affect publish MSRV.

I am fine with 1.87 for all. @ehuss any thought?

[ehuss]

1.87 seems fine. I'm fine with an even newer version (like stable-3). Usually I just bump the rust version when there is some new feature I want/need.