Currently, cargo provides an environment variable CARGO_PKG_NAME containing the name of the crate. clap uses this in clap::crate_name to get the name of the crate to use as the program name.

However, this doesn't work for crates that build more than one binary. I'd like to have an environment variable specifying the name of the binary being built, such as CARGO_BIN_NAME, which clap could use for a more accurate idea of the name of the program.

For example, given the following Cargo.toml:

[package]
name = "cratename"
version = "0.1.0"
edition = "2018"

[[bin]]
name = "binname"
path = "src/main.rs"

[dependencies]
clap = "2.33.1"

When building src/main.rs, cargo should set CARGO_PKG_NAME=cratename and CARGO_BIN_NAME=binname.