Crate cfg_version 

Conditional compilation based on dependency versions.

Parses Cargo.lock at macro expansion time to determine the resolved version of any dependency, then conditionally includes or excludes the annotated item. When a dependency appears multiple times in the lock file (e.g., syn 1.x and 2.x), only the version actually used by the current crate is considered.

Usage

# Cargo.toml
[dependencies]
cfg-version = "0.1"

use cfg_version::cfg_version;

// Include only when indexmap >= 2.8.0, < 3.0.0
#[cfg_version(indexmap = "^2.8")]
fn needs_indexmap_2_8() { }

// Include only when indexmap >= 2.0.0
#[cfg_version(indexmap = ">=2")]
fn needs_indexmap_2() { }

// Include only when indexmap < 2.8.0
#[cfg_version(indexmap = "<2.8")]
fn old_indexmap_fallback() { }

Version requirements use Cargo’s semver syntax: ^, ~, *, >=, >, <, <=, =, and comma-separated combinations.

Attribute Macros

cfg_version

Conditionally include an item based on a dependency’s resolved version.