read-zero-byte-vec if we assign to a var, post suggestion turns the assignment into () bc of the .resize call #15575
Description
Using the following flags
--force-warn clippy::read-zero-byte-vec
this code:
use std::net::TcpListener;
use std::io::Read;
fn main() {
let listener = TcpListener::bind("127.0.0.1:9010").unwrap();
let mut stream_and_addr = listener.accept().unwrap();
let mut buf = Vec::with_capacity(32);
let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
println!("Got {} bytes", num_bytes_received);
}caused the following diagnostics:
Checking _snippet_0 v0.1.0 (/tmp/icemaker_global_tempdir.W9mV5T7suTWy/icemaker_clippyfix_tempdir.Krho1Ov5Kvsw/_snippet_0)
warning: reading zero byte data to `Vec`
--> src/main.rs:9:30
|
9 | let num_bytes_received = stream_and_addr.0.read(&mut buf).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `buf.resize(32, 0); stream_and_addr.0.read(&mut buf)`
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#read_zero_byte_vec
= note: requested on the command line with `--force-warn clippy::read-zero-byte-vec`
warning: `_snippet_0` (bin "_snippet_0") generated 1 warning
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
However after applying these diagnostics, the resulting code:
use std::net::TcpListener;
use std::io::Read;
fn main() {
let listener = TcpListener::bind("127.0.0.1:9010").unwrap();
let mut stream_and_addr = listener.accept().unwrap();
let mut buf = Vec::with_capacity(32);
let num_bytes_received = buf.resize(32, 0); stream_and_addr.0.read(&mut buf).unwrap();
println!("Got {} bytes", num_bytes_received);
}no longer compiled:
Checking _snippet_0 v0.1.0 (/tmp/icemaker_global_tempdir.W9mV5T7suTWy/icemaker_clippyfix_tempdir.Krho1Ov5Kvsw/_snippet_0)
error[E0277]: `()` doesn't implement `std::fmt::Display`
--> src/main.rs:11:30
|
11 | println!("Got {} bytes", num_bytes_received);
| -- ^^^^^^^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
| |
| required by this formatting parameter
|
= help: the trait `std::fmt::Display` is not implemented for `()`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0277`.
error: could not compile `_snippet_0` (bin "_snippet_0") due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_snippet_0` (bin "_snippet_0" test) due to 1 previous error
Version:
rustc 1.91.0-nightly (91ee6a405 2025-08-26)
binary: rustc
commit-hash: 91ee6a4057ce4bf1ab6d2f932cae497488d67c81
commit-date: 2025-08-26
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0