function `print` is used but why it warn me `unused`? - rust

Question

Here is the function lies in huangjj27:env_logger/src/writer/wasm.rs
//! logging functions from wasm-bindgen.
//!
//! Here use the one-param logging functions, all messages should be transformed
//! to string before passing to the functions. Note that we only need this
//! module for `wasm32-unknown-unknown` target
#![cfg(all(target_arch = "wasm32", target_vendor = "unknown"))]
// use log::Level;
use wasm_bindgen::prelude::*;
use crate::fmt::glob::Target;
pub(in crate::fmt::writer) fn print(msg: &str, t: Target) {
// work around for unused variable
let _ = t;
log(&msg);
}
As is shown above, the wasm module will only compile with wasm32-unknown-unknown target. And the print function is used in huangjj27:env_loggersrc\fmt\writer\termcolor\shim_impl.rs:
// huangjj27:env_loggersrc\fmt\writer\termcolor\shim_impl.rs: 32-48
pub(in crate::fmt::writer) fn print(&self, buf: &Buffer) -> io::Result<()> {
// This impl uses the `eprint` and `print` macros
// instead of using the streams directly.
// This is so their output can be captured by `cargo test`
let log = String::from_utf8_lossy(&buf.0);
#[cfg(all(target_arch = "wasm32", target_vendor = "unknown"))]
wasm::print(&log, self.target);
#[cfg(not(all(target_arch = "wasm32", target_vendor = "unknown")))]
match self.target {
Target::Stderr => eprint!("{}", log),
Target::Stdout => print!("{}", log),
}
Ok(())
}
then I test it with the node:
wasm-pack test --node -- --no-default-features --test node
then I get this confusing denied unused issue:
[INFO]: Checking for the Wasm target...
Compiling env_logger v0.8.2 (C:\Users\huangjj27\Documents\codes\env_logger)
error: function is never used: `print`
--> src\fmt\writer\wasm.rs:13:31
|
13 | pub(in crate::fmt::writer) fn print(msg: &str, t: Target) {
| ^^^^^
|
note: lint level defined here
--> src\lib.rs:280:54
|
280 | #![deny(missing_debug_implementations, missing_docs, warnings)]
| ^^^^^^^^
= note: `#[deny(dead_code)]` implied by `#[deny(warnings)]`
error: function is never used: `print`
--> src\fmt\writer\wasm.rs:13:31
|
13 | pub(in crate::fmt::writer) fn print(msg: &str, t: Target) {
| ^^^^^
|
note: lint level defined here
--> src\lib.rs:280:54
|
280 | #![deny(missing_debug_implementations, missing_docs, warnings)]
| ^^^^^^^^
= note: `#[deny(dead_code)]` implied by `#[deny(warnings)]`
error: aborting due to previous error
error: could not compile `env_logger`.
warning: build failed, waiting for other jobs to finish...
error: aborting due to previous error
error: could not compile `env_logger`.
To learn more, run the command again with --verbose.
Error: Compilation of your program failed
Caused by: failed to execute `cargo build`: exited with exit code: 101
full command: "cargo" "build" "--tests" "--target" "wasm32-unknown-unknown"
My questions are:
Why does the warning come out, while I indeed use the function wasm::print somewhere?
How could I deal with this problem? Working around or fixing it is ok (but I still need to keep the lint config enabled).

Answer 1

If you only use a function in other unused functions, then it will still give you the warning. If you want to disable the warning on that one function, you can do that by putting #[allow(dead_code)] on the line before the function header.