Feature transitivity?

I have a bin crate and a library crate together in a workspace
and the lib has a feature on it. bin depends on the lib.
when I run 'cargo build --features x' the library is not
transitively receiving this feature.
(this was after I moved the feature dependent code out of the bin
into the lib)
rust-by-example lists the regex library as demonstrating re-export of features but I don't for the life of me see it!
searching elsewhere has yielded nothing so I think this must be so basic as to not be an issue for anyone else.
sorry about the basicness but I'm at my wits end after days of searching/experimenting.

This section of the Cargo book describes how to enable features of dependencies:


If you want to hide the feature of your dependency (your lib crate) behind a feature of your binary crate, you could add something like this to the binary crate package's Cargo.toml:

lib = "0.1.0"

x = ["lib/x"]

Then when you enable the x feature of your binary crate, it will also enable the x feature of your library crate.


'x=[lib/x]' is the first thing I did and it didn't work!
I'm basing my 'not working' on the fact that
(cd lib; cargo expand --features x)
shows a macro expansion after a #[cfg(x)]
while 'cargo build --features x' from workspace directory fails in a way that can only mean 'x' was not seen.

I must be doing something stupid. here's minimal setup:

resolver = "2"
# directories!
members = ["lib"]

name = "test"
authors = ["{{authors}}"]
version = "0.1.0"
edition = "2021"




fn main(){


name = "lib"
version = "0.1.0"
edition = "2021"

crate-type = ["rlib", "dylib"]




mod g {
    fn h(){ println!("h ok") }

use g::*;

pub fn f(){ h() }

Your cfg macro isn't the right syntax to enable f when feature x is present:

- #[cfg(x)]
+ #[cfg(feature = "x")]
pub fn f(){ println!("ok") }

ah, I wrote a non-minimal example by missing that out.
corrected above.
in any case problem solved - the list of errors from compiler put the real error down the list and I didn't look at that far until now.