Panic when piping --check to head

[YaLTeR]

rustfmt 0.99.2-nightly (5c9a2b6 2018-08-07)

└─ env RUST_BACKTRACE=1 cargo +nightly fmt -- --check | head
Diff in /home/yalter/Source/rust/yalter-bot/src/bot.rs at line 21:
     pub fn new(discord: Discord, modules: Vec<Box<Module>>) -> Self {
         // Connect.
         let (connection, ready) = discord.connect().expect("Connect failed");
-        println!(
-            "[Ready] {} is serving {} servers.",
-            ready.user.username,
-            ready.servers.len()
-        );
+        println!("[Ready] {} is serving {} servers.",
thread 'main' panicked at 'failed printing to stdout: Broken pipe (os error 32)', libstd/io/stdio.rs:696:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:475
   5: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:390
   6: std::panicking::begin_panic_fmt
             at libstd/panicking.rs:345
   7: std::io::stdio::_print
             at libstd/io/stdio.rs:696
             at libstd/io/stdio.rs:705
   8: rustfmt_nightly::rustfmt_diff::OutputWriter::writeln
   9: rustfmt_nightly::filemap::write_file
  10: <rustfmt_nightly::Session<'b, T> as rustfmt_nightly::formatting::FormatHandler>::handle_formatted_file
  11: rustfmt_nightly::formatting::format_project
  12: syntax::with_globals
  13: <rustfmt_nightly::Session<'b, T>>::format
  14: rustfmt::format_and_emit_report
  15: <rustfmt_nightly::Session<'b, T>>::override_config
  16: rustfmt::execute
  17: rustfmt::main
  18: std::rt::lang_start::{{closure}}
  19: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  20: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  21: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  22: main
  23: __libc_start_main
  24: <unknown>

[max-sixty]

Haven't diagnosed, but a couple findings to move this forward:

• Only panics with that specific rustfmt.toml
• With that rustfmt.toml, the formatting isn't stable - it switches back & forth each time cargo fmt is run

[YaLTeR]

Actually after noticing this on one of my projects it seems to be rust-lang/rust#46016 which affects anything using print*!().

[ytmimi]

Confirming this is still an issue using rustfmt 1.5.1-nightly (2f3ddd9f 2022-06-27).

run cargo +nightly fmt -- --emit stdout | head from the root of the rustfmt repo:

output

rustfmt/build.rs:

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::{Path, PathBuf};
use std::process::Command;

fn main() {
    // Only check .git/HEAD dirty status if it exists - doing so when
Error writing files: io error: rustfmt/src/bin/main.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/src/cargo-fmt/main.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/src/format-diff/main.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/src/git-rustfmt/main.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/src/attr/doc_comment.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/tests/cargo-fmt/main.rs: Broken pipe (os error 32)
Error writing files: io error: rustfmt/tests/rustfmt/main.rs: Broken pipe (os error 32)
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }', src/tools/rustfmt/src/bin/main.rs:34:31
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This might be related to #5114

[ytmimi]

Also seems tangentially related to #2696