rustup: rust-analyzer fallback recursively executes Homebrew wrapper

[tamird]

Description of issue

When Homebrew's rustup wrapper is first in PATH and the active toolchain has no rust-analyzer component, rust-analyzer --version repeatedly falls back to that same wrapper and exits with error: infinite recursion detected. A working standalone Homebrew rust-analyzer is later in PATH at /opt/homebrew/bin/rust-analyzer.

The expected behavior is to skip the rustup proxy and run the standalone analyzer.

This reproduces with Homebrew 7.0.8 and rustup 1.29.1, the current rustup formula version. The installed standalone analyzer is Homebrew's 2026-09-28 build. brew update updated Homebrew and the public taps but exited unsuccessfully because of authentication for an unrelated private tap. brew doctor reports an unrelated unlinked keg. This is being reported in Discussions because the homebrew-core issue checklist cannot truthfully be completed.

The diagnostics and this report were prepared by OpenAI Codex (GPT-6) at the reporter's request.

Reproduction

With the Homebrew rustup and rust-analyzer formulae installed, and an active toolchain without the rust-analyzer component:

export PATH="$(brew --prefix rustup)/bin:$PATH"
command -v rust-analyzer
rustup show active-toolchain
rustup component list --installed
rust-analyzer --version

The command resolves to /opt/homebrew/opt/rustup/bin/rust-analyzer. The active toolchain is stable-aarch64-apple-darwin (default). Installed components:

cargo-aarch64-apple-darwin
clippy-aarch64-apple-darwin
rust-docs-aarch64-apple-darwin
rust-src
rust-std-aarch64-apple-darwin
rust-std-aarch64-unknown-linux-musl
rust-std-armv7-unknown-linux-musleabihf
rust-std-riscv64gc-unknown-linux-gnu
rustc-aarch64-apple-darwin
rustfmt-aarch64-apple-darwin

Complete failing command output, exit status 1:

$ rust-analyzer --version
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/opt/rustup/bin/rust-analyzer"
error: infinite recursion detected

Running the standalone analyzer directly succeeds, exit status 0:

$ /opt/homebrew/bin/rust-analyzer --version
rust-analyzer 0.0.0 (03fcb77246 2026-09-27)

Cause and controlled comparison

The rustup formula's env_script_all_files call creates this shell wrapper at /opt/homebrew/opt/rustup/bin/rust-analyzer:

#!/bin/bash
RUSTUP_OVERRIDE_UNIX_FALLBACK_SETTINGS="/opt/homebrew/etc/rustup/settings.toml" exec "/opt/homebrew/Cellar/rustup/1.29.1/libexec/bin/rust-analyzer"  "$@"

The underlying proxy resolves to /opt/homebrew/Cellar/rustup/1.29.1/libexec/bin/rustup. The wrapper and that executable are different files.

Rustup's fallback implementation excludes PATH candidates by comparing their file identity with env::current_exe(). It therefore accepts the shell wrapper as an external analyzer, executes it, and re-enters the proxy.

As a controlled comparison, executing the underlying proxy with Homebrew's fallback-settings environment preserved and only the wrapper directory removed from the child PATH succeeds:

(
    export RUSTUP_OVERRIDE_UNIX_FALLBACK_SETTINGS=/opt/homebrew/etc/rustup/settings.toml
    export PATH="$(printf '%s' "$PATH" | tr ':' '\n' | awk '$0 != "/opt/homebrew/opt/rustup/bin"' | paste -sd ':' -)"
    /opt/homebrew/opt/rustup/libexec/bin/rust-analyzer --version
)

Output, exit status 0:

info: `rust-analyzer` is unavailable for the active toolchain
info: falling back to "/opt/homebrew/bin/rust-analyzer"
rust-analyzer 0.0.0 (03fcb77246 2026-09-27)

Related wrapper behavior is discussed in discussion 7086; that thread concerns caller-selected argv[0] rather than this fallback recursion.

Output of brew config

Local proxy configuration is redacted.

HOMEBREW_VERSION: 7.0.8
ORIGIN: https://github.com/Homebrew/brew
HEAD: a57af195cf9d7addb48bdb1204c9151313cd0057
Last commit: 2 days ago
Branch: stable
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /opt/homebrew
all_proxy: [local proxy configuration redacted]
ftp_proxy: [local proxy configuration redacted]
http_proxy: [local proxy configuration redacted]
https_proxy: [local proxy configuration redacted]
no_proxy: [local proxy configuration redacted]
Homebrew Ruby: 4.0.7 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.7/bin/ruby
CPU: 18-core 64-bit dunno
Clang: 21.0.0 build 2100
Git: 2.56.0 => /opt/homebrew/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.7.1-arm64
CLT: 27.0.0.0.1788430756
Xcode: 27.0
Metal Toolchain: N/A

Output of brew doctor

The unrelated formula's name is redacted. No ownership or linking changes were made.

Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: You have unlinked kegs in your Cellar.
Leaving kegs unlinked can lead to build-trouble and cause formulae that depend on
those kegs to fail to run properly once built.

Run `brew link` on these:
  [unrelated formula name redacted]

[SMillerDev]

Have you tried reporting this upstream? They're in a better position to comment on fixes for this than Homebrew is.