`cargo fmt` failure on Windows, too many command line args

[riverar]

Summary

cargo fmt fails with The filename or extension is too long. (os error 206) when the workspace contains a deep hierarchy, many files, and/or many crates resulting in a rustfmt command line length that exceeds ~32K.

We are currently hitting this in https://github.com/microsoft/windows-rs. (I have a smaller repro below.)

Related: #5975

Expected behavior

cargo fmt to format all code as it does with smaller crates

Actual behavior

The filename or extension is too long. (os error 206)

Configuration

N/A

Reproduction Steps

1. git clone https://github.com/riverar/repro-a1326fb90c2c on a Windows machine.
2. cd repro-a1326fb90c2c
3. cargo fmt
4. Observe error

Meta

rustfmt --version:

rustfmt 1.9.0-nightly (cced03bfd6 2026-05-28)

[jieyouxu]

Notes for myself: probably need to do sth like rust-lang/cargo#13131

[riverar]

Note this is not a long path issue so a manifest won't help.