fix(ruby): reject non-MRI Ruby engines on Windows with clear error

[jdx]

Summary

• On Windows, the Ruby plugin uses RubyInstaller2 which only distributes standard MRI Ruby
• When a user requests a non-MRI engine (jruby, truffleruby, etc.), the plugin would construct an invalid download URL and fail with a confusing 404 error
• Now fails early with a clear error message explaining that only MRI Ruby is supported on Windows

Fixes #8537

Test plan

• Verify mise use ruby@jruby-9 on Windows now shows a clear error instead of a 404
• Verify standard MRI Ruby versions still install correctly on Windows

🤖 Generated with Claude Code

---

Note

Low Risk
Small, localized change to Windows Ruby installation flow that only adds an upfront validation and error message; minimal impact on successful MRI installs.

Overview
Adds an early Windows-only guard in the Ruby installer to reject non-MRI engine version strings (e.g., JRuby/TruffleRuby) before attempting a RubyInstaller2 download.

This replaces a confusing downstream 404 from a constructed RubyInstaller2 URL with a clear bail! error message explaining that only standard MRI Ruby is supported on Windows.

^{Written by Cursor Bugbot for commit a1c623b. This will update automatically on new commits. Configure here.}

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refines the Ruby plugin's behavior on Windows by introducing a validation step during installation. Previously, attempting to install non-MRI Ruby engines like JRuby or TruffleRuby on Windows would lead to a cryptic 404 error due to an invalid download URL. The change now proactively checks the requested Ruby engine and, if it's not a standard MRI version, it immediately fails with a user-friendly error message, clarifying that only MRI Ruby is supported on Windows via RubyInstaller2.

Highlights

• Error Handling: Implemented an early exit mechanism for unsupported Ruby engines on Windows, preventing confusing 404 errors during installation.
• Platform Specificity: Ensured that only standard MRI Ruby versions are supported and installable on Windows, aligning with RubyInstaller2's distribution.
• User Experience: Provided a clear and informative error message when a user attempts to install a non-MRI Ruby engine on Windows.

Changelog

• src/plugins/core/ruby_windows.rs
  • Added a check to prevent installation of non-MRI Ruby engines on Windows.
  • Introduced an early exit with a descriptive error message for unsupported Ruby engines.

Activity

• The pull request addresses issue mise on Windows incorrectly trying to download jruby releases from rubyinstaller #8537, which likely reported the confusing 404 error.
• A test plan is outlined to verify the new error message for non-MRI engines and confirm continued correct installation of standard MRI Ruby versions on Windows.

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[greptile-apps]

Greptile Summary

This PR adds a focused early-exit guard in the Windows Ruby plugin (ruby_windows.rs) that rejects non-MRI Ruby engines (jruby, truffleruby, etc.) with a human-readable error message before any network I/O is attempted. Previously, the plugin would construct an invalid RubyInstaller2 download URL and fail with a confusing 404.

Key changes:

• Added bail! at the top of install_version_ that checks ruby_common::is_mri_version(&tv.version) and surfaces a clear error explaining that only MRI Ruby is supported on Windows via RubyInstaller2.
• Updated the eyre import to include bail.
• The is_mri_version helper (in the unchanged ruby_common.rs) uses a simple first-character digit check, which correctly distinguishes 3.2.0 (MRI) from jruby-9.4.0.0 (non-MRI).

Minor concerns:

• No unit test covers the new rejection path in install_version_.
• The pre-existing test_list_versions_matching test asserts that TruffleRuby versions are retrievable from the Windows backend, which may be misleading now that installing such versions produces an immediate error.
• resolve_rubyinstaller_lock_info in ruby_common.rs (unchanged) silently returns an empty PlatformInfo for non-MRI versions rather than an error — a mild inconsistency with the new install_version_ behaviour.

Confidence Score: 4/5

• This PR is safe to merge — the change is minimal, correct, and improves UX; no regressions to the happy path.
• The fix is a single-function early guard using a well-defined helper (is_mri_version) that already exists. MRI version detection is straightforward (digit-prefix check), the error message is clear, and the change does not touch the download, checksum, or install logic for valid MRI versions. Minor gaps (missing test, potentially misleading existing test assertions) prevent a perfect score.
• The existing test_list_versions_matching assertions for TruffleRuby in ruby_windows.rs deserve a second look to confirm they still reflect the intended behaviour after this change.

Important Files Changed

Filename	Overview
src/plugins/core/ruby_windows.rs	Adds an early bail in install_version_ to reject non-MRI Ruby engines with a clear error message; logic is correct and the is_mri_version helper is well-defined. Minor: no new test for the rejection path, and existing TruffleRuby listing assertions may now be misleading.
src/plugins/core/ruby_common.rs	Pre-existing file (unchanged by this PR) providing is_mri_version, rubyinstaller_url, and resolve_rubyinstaller_lock_info. Note that resolve_rubyinstaller_lock_info silently returns PlatformInfo::default() for non-MRI versions (no error), creating a mild inconsistency with the new bail in install_version_.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["install_version_ called\n(ruby_windows.rs)"] --> B{"is_mri_version\n(tv.version)?"}
    B -- "No\n(e.g. jruby-9, truffleruby-23)" --> C["bail! with clear error\n'Ruby engine X is not supported\non Windows'"]
    B -- "Yes\n(e.g. 3.2.0, 3.3.1)" --> D["download RubyInstaller2 .7z\n(rubyinstaller_url)"]
    D --> E["verify_checksum"]
    E --> F["install (un7z + rename)"]
    F --> G["verify (ruby -v)"]
    G --> H["install_rubygems_hook"]
    H --> I["test_gem (gem -v)"]
    I --> J["install_default_gems"]
    J --> K["Ok(tv)"]
    C --> L["Err returned to caller"]

Loading

Comments Outside Diff (1)

1. src/plugins/core/ruby_windows.rs, line 286-313 (link)

   Existing test may be misleading after this change

   The test_list_versions_matching test asserts that TruffleRuby version strings (e.g. truffleruby-24) return non-empty results on the Windows backend. However, _list_remote_versions only fetches from oneclick/rubyinstaller2, whose release tags match RubyInstaller-([0-9.]+)-.* — so only MRI versions are ever listed from that source. After this PR, users on Windows can potentially be shown TruffleRuby versions (from a fallback source) but will immediately hit the bail error when trying to install them.

   If the Windows backend is intended to list only MRI Ruby versions, the TruffleRuby assertions in this test are misleading and should either be removed or converted to negative assertions (is_empty()). Conversely, if TruffleRuby versions are intentionally still shown in the listing for discoverability, a comment explaining this UX decision would help future readers.

   

_{Last reviewed commit: a1c623b}

[greptile-apps]

No unit test for the new rejection behavior

There is no test that verifies a non-MRI version string (e.g. jruby-9.4.0.0, truffleruby-23) produces the expected bail error. Consider adding a small unit test for install_version_ that mocks a non-MRI ToolVersion and asserts the error message contains "is not supported on Windows". This would guard against regressions to the early-exit path and make the intent explicit.

[gemini-code-assist]

Code Review

This pull request correctly adds a check to prevent installation of non-MRI Ruby engines on Windows, providing a much clearer error message to the user. My only feedback is a minor formatting issue in the new error message string which would cause unintended indentation in the output.

_{Note: Security Review did not run due to the size of the PR.}

[gemini-code-assist]

The indentation on the second line of this multi-line string literal will be included in the error message, which is likely not intended. This will cause the second line of the error message to be indented with several spaces. It's better to put the string on a single line or remove the indentation on the continued line to fix the output format.

                "Ruby engine '{}' is not supported on Windows.\nOnly standard MRI Ruby versions can be installed via RubyInstaller2.",

[github-actions]

Hyperfine Performance

mise x -- echo

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
mise-2026.3.5 x -- echo	26.0 ± 0.6	25.1	32.4	1.00
mise x -- echo	26.4 ± 1.0	25.7	36.8	1.02 ± 0.05

mise env

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
mise-2026.3.5 env	25.7 ± 1.2	24.6	36.9	1.00
mise env	26.2 ± 1.8	25.0	39.4	1.02 ± 0.09

mise hook-env

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
mise-2026.3.5 hook-env	26.5 ± 0.9	25.6	34.4	1.00
mise hook-env	27.8 ± 2.7	25.7	52.0	1.05 ± 0.11

mise ls

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
mise-2026.3.5 ls	25.6 ± 0.9	24.7	33.4	1.00 ± 0.04
mise ls	25.5 ± 0.4	24.9	30.8	1.00

xtasks/test/perf

Command	mise-2026.3.5	mise	Variance
install (cached)	161ms	161ms	+0%
ls (cached)	88ms	87ms	+1%
bin-paths (cached)	91ms	90ms	+1%
task-ls (cached)	846ms	817ms	+3%