Should accept values other than string literals as version requirements?

[taiki-e]

const_fn attribute currently only accepts string literals as version requirements, like the current cfg_version does.

#[const_fn("1.36")]
const fn func() { /* ... */ }

Should we accept numeric literals directly, like the original RFC or rustversion crate?

#[const_fn(1.36)]
const fn func() { /* ... */ }

[taiki-e]

Stabilization report of cfg_version (rust-lang/rust#64796 (comment)) says:

Literal-free invocations like version(1.50) do cause errors just as version(foo) does.

Closing -- I prefer to keep the same api as cfg_version.