Hope to improve the error messages and Improve error-handling abilities of rustup

[sakuraflows]

Problem you are trying to solve

When I was installing mdbook, the following error suddenly popped up:

\rustbook_zhcn-main> cargo install mdbook
error: process didn't exit successfully: rustc -vV (exit code: 1)
--- stderr
error: Missing manifest in toolchain '1.90-aarch64-pc-windows-msvc'

As someone not very familiar with the rust-lang toolchain architecture, I had no idea what happened. I asked AI and searched online, but all I got was content about how to configure the MSVC toolchain on Windows. But I had obviously already configured it, otherwise I wouldn't have successfully built and compiled other projects before. Later, I found it in the mirror list — 1.90-aarch64-pc-windows-msvc. It was under the rustup list, and I began to realize that perhaps during installation, the toolchain automatically executed rustup update, and coincidentally my device had network problems, causing 1.90-aarch64-pc-windows-msvc not to be installed properly.

Finally, I manually executed rustup update again:

info: downloading 6 components
        rustc installed                       68.52 MiB
        cargo installed                        9.25 MiB
     rust-std installed                       19.68 MiB
    rust-docs installed                       20.52 MiB
      rustfmt installed                        2.68 MiB
       clippy installed                        3.84 MiB
  stable-aarch64-pc-windows-msvc unchanged - rustc 1.95.0 (59807616e 2026-04-14)
    1.90-aarch64-pc-windows-msvc installed - rustc 1.90.0 (1159e78c4 2025-09-14)

I knew I had succeeded.

1.90-aarch64-pc-windows-msvc, this package name is very misleading, and the error message is not detailed enough. I hope Rust can improve them in the future. Thanks a lot.

Solution you'd like

1. Under the prompts from the forum reply, I learned that(Improve error message for incomplete toolchains #4819 ) has proposed relevant improvements, but I believe for people who are not familiar with Rust’s complex toolchain mechanism, they might still fail to realize the potential connection between the toolchain or something else and rustup, and therefore they would not carry out the inspection steps for rustup either.

2. Regarding improving rustup’s error-handling ability:
   In package managers of some programming languages (such as pip), if there is a sudden network change during the download and installation process that causes the download to fail, an error message like the following is usually shown:

Collecting anyio<5,>=3.5.0 (from openai)
  Downloading https://pypi.tuna.tsinghua.edu.cn/packages/da/42/e921fccf5015463e32a3cf6ee7f980a6ed0f395ceeaa45060b61d86486c2/anyio-4.13.0-py3-none-any.whl (114 kB)
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))': /simple/distro/

However, when I was running cargo install mdbook, I am certain that I did not receive any prompt about a download failure from rustup. I hope improvements can be made in this regard.

Notes

No response

[rami3l]

@sakuraflows Hello, thanks for reporting.

I'm not sure how you've got 1.90 installed, if it wasn't your intention, was it through rust-toolchain.toml in your repo?

If so, this is called "auto installation" and we think the current behavior is indeed confusing which is why we have provided ways of opting out via rustup set auto-install disable for example.

While auto installation is still enabled by default due to historical reasons, we indeed have plans to inform the user what is happening in more cases (#4445), and then probably flip the default in a future release.

[sakuraflows]

Sorry，I don’t know how I installed 1.90-aarch64-pc-windows-msvc, but I can confirm that I installed mdbook by downloading from a network mirror, not from local code or my own code repository.

cargo install mdbook
    Updating `ustc` index 
     Ignored package `mdbook v0.5.2` is already installed, use --force to override

In fact, I don’t really care how 1.90-aarch64-pc-windows-msvc is installed — most programming languages’ dependency management handles installation automatically. The key points are the following two:

1. The error messages related to 1.90-aarch64-pc-windows-msvc are unclear.
2. When network conditions change or other error scenarios occur, people should be able to clearly identify which part of the build dependencies has a problem — the MSVC build tools, rustc, rustup, or cargo — rather than just seeing “Missing manifest in toolchain '1.90-aarch64-pc-windows-msvc'”. I know this kind of requirement may be “hard”, but based on that error message, I truly couldn’t find any information about ‘1.90-aarch64-pc-windows-msvc’,toolchain and rustup's Relationship online. When similar situations happen, many people might think it’s an issue with cargo or the Windows MSVC build tools themselves.

Thanks a lot for your reply.

[ChrisDenton]

I think there's two issues here.

1. It wasn't obvious in the original error that the message came from rustup
2. It wasn't clear what action you should be taking

[rami3l]

@sakuraflows Thanks for your reply. The fact that you have no idea why 1.90 was installed actually means cargo install is calling rustup. What does rustup show give when located in your repo when you ran cargo install?

[sakuraflows]

@rami3l Hello,

Problem you are trying to solve

When I was installing mdbook, the following error suddenly popped up:当我在安装 mdbook 时，突然弹出了以下错误：

\rustbook_zhcn-main> cargo install mdbook
error: process didn't exit successfully: rustc -vV (exit code: 1)
--- stderr
error: Missing manifest in toolchain '1.90-aarch64-pc-windows-msvc'

That was the key error message output at the time. That's all I can remember.,Sorry.However,If there had been any more critical information than this, I would definitely have remembered it. I tried to reproduce the issue from back then, but unfortunately I wasn't successful.