brew-cask: AeroSpace tap Ruby metadata evaluation rejects postflight_steps on 2026.9.4

[soodoh]

Problem

On mise 2026.9.4, a dry-run for brew-cask:nikitabobko/tap/aerospace fails while evaluating the tap's Ruby definition:

-e:271:in 'CaskMetadata#method_missing': unsupported cask metadata DSL `postflight_steps` (RuntimeError)
	from Casks/aerospace.rb:13:in 'block in <main>'

Expected: resolve metadata and produce a dry-run plan. Actual: evaluation fails before installation or lifecycle execution.

Environment

• macOS 26.6.2 (25G83), arm64; Bash 3.2.57.
• mise 2026.9.4 macos-arm64 (2026-09-09), standalone release binary.
• Ruby 4.0.6 (03b6d3f889, precompiled arm64-darwin23), with real Ruby/mise binaries on PATH, not shims.

Tested with isolated HOME and mise config/data/cache/state under /private/tmp, empty global/system configs, and copies of existing binaries. No packages were installed, upgraded, or removed; the existing Homebrew prefix was only inspected.

Reproduction

Minimal mise.toml:

[settings]
experimental = true

[tools]
ruby = "4.0.6"

[bootstrap.packages]
"brew-cask:nikitabobko/tap/aerospace" = { version = "latest", os = "macos" }

With Ruby 4.0.6 already available on PATH:

ruby --version
mise --version
mise --verbose bootstrap packages apply --dry-run brew-cask:nikitabobko/tap/aerospace

The command exited 1 on both runs, with the error above; the first used a fresh cache. The verbose log confirms API JSON returned 404, followed by successful retrieval of AeroSpace 0.21.3-Beta at tap commit 9ac0bfc08904719c52a63101fa7e1e133a23bda2. Its postflight_steps block contains two run commands.

Reduced metadata-only test

Under the same sandbox profile, the unmodified v2026.9.4 metadata shim, verified against the embedded shim, fails on this fixture:

cask "aerospace" do
  version "1.0"
  sha256 "0000000000000000000000000000000000000000000000000000000000000000"
  url "https://example.invalid/aerospace.zip"
  postflight_steps do
  end
end

Removing only the empty postflight_steps block produces valid JSON and exit 0; keeping it produces the same exception and exit 1. Both variants were tested twice. This is metadata-only: the dummy URL is never fetched.

The shim defines postflight, but not postflight_steps. It is unchanged at main commit 5df41faaa8b5a3f6b119b9e22ab5dd7825b3cfa2; main was not built or run.

Related work and question

• feat(brew): evaluate ordinary third-party taps #12774 added third-party tap Ruby evaluation.
• brew-cask: Homebrew's cask metadata migration (command_wrapper artifacts, run flight steps) breaks previously-working casks #11462 / fix(brew): support cask command wrappers and run steps #11472 address JSON-described lifecycle execution; this fails earlier, extracting metadata from Ruby, despite fix(brew): support cask command wrappers and run steps #11472 being included in 2026.9.4.
• macOS: tap metadata sandbox prevents Ruby 4.0.6 startup (`rb_check_realpath_internal` / EPERM) #12937 / fix(sandbox): allow metadata access to macOS private directory #12940 concern sandbox startup. Ruby starts successfully here and reaches the cask DSL.

Is representing structured postflight_steps in the tap metadata shim within the intended scope, or is there a supported alternative for this cask? This would mean extracting metadata, not executing hooks during a dry-run.

mise doctor

Full output below, with the temporary root replaced by <REPRO>. Exit 1; the activation warning reflects the explicit-PATH test setup.

mise doctor output

version: 2026.9.4 macos-arm64 (2026-09-09)
activated: no
shims_on_path: no
self_update_available: yes

build_info:
  Target: aarch64-apple-darwin
  Features: openssl, rustls-native-roots, self_update
  Built: Wed, 9 Sep 2026 20:03:11 +0000
  Rust Version: rustc 1.98.1 (48a229cea 2026-09-01)
  Profile: release

shell:
  /bin/bash
  GNU bash, version 3.2.57(1)-release (arm64-apple-darwin25)
  Copyright (C) 2007 Free Software Foundation, Inc.

aqua:
  baked in registry: aquaproj/aqua-registry@85b9f0cee7c3274257a594dbb0a552a586be382e
  baked in registry tools: 2290

dirs:
  cache: <REPRO>/cache
  config: <REPRO>
  data: <REPRO>/data
  shims: <REPRO>/data/shims
  system_shims: /usr/local/share/mise/shims
  state: <REPRO>/state

config_files:
  <REPRO>/system.toml
  <REPRO>/global.toml
  <REPRO>/mise.toml

env_files:
  (none)

ignored_config_files: (none)

backends:
  aqua
  asdf
  cargo
  conda
  core
  dotnet
  forgejo
  gem
  github
  gitlab
  go
  npm
  packslip
  pipx
  pkgx
  spm
  http
  s3
  ubi
  vfox

plugins:

toolset:
  core:ruby@4.0.6

path:
  <REPRO>/data/installs/ruby/4.0.6/bin
  <REPRO>/bin
  /usr/bin
  /bin
  /usr/sbin
  /sbin
-e:271:in 'CaskMetadata#method_missing': unsupported cask metadata DSL `postflight_steps` (RuntimeError)
	from Casks/aerospace.rb:13:in 'block in <main>'
	from -e:287:in 'BasicObject#instance_eval'
	from -e:287:in 'Object#cask'
	from Casks/aerospace.rb:1:in '<main>'
	from -e:290:in 'Kernel#eval'
	from -e:290:in '<main>'

system_packages:

env_vars:
  MISE_DATA_DIR=<REPRO>/data
  MISE_CACHE_DIR=<REPRO>/cache
  MISE_STATE_DIR=<REPRO>/state
  MISE_CONFIG_DIR=<REPRO>
  MISE_GLOBAL_CONFIG_FILE=<REPRO>/global.toml
  MISE_SYSTEM_CONFIG_FILE=<REPRO>/system.toml
  MISE_TRUSTED_CONFIG_PATHS=<REPRO>
  MISE_COLOR=0

settings:
  experimental  true <REPRO>/mise.toml

1 warning found:

1. failed to check brew-cask system packages: published cask metadata was unavailable (failed to fetch Homebrew cask 'aerospace' directly. mise needs API metadata at api/cask/aerospace.json; for a third-party tap that means a JSON file on the tap's default branch, which most taps do not publish. mise will not proxy to the brew CLI; install it with `brew`, or see https://mise.jdx.dev/bootstrap/packages/brew.html#third-party-taps) and mise could not evaluate Casks/aerospace.rb

1 problem found:

1. mise is not activated, run mise help activate or
   read documentation at https://mise.jdx.dev for activation instructions.
   Alternatively, add the shims directory <REPRO>/data/shims to PATH.
   Using the shims directory is preferred for non-interactive setups.

AI-assisted — Tool: Pi; model: openai-codex/gpt-6-astra; version: 0.85.1.

[jdx]

Opened #13060 to address the structured flight-step metadata gap.

The tap metadata shim now collects preflight_steps / postflight_steps containing run commands into structured artifacts without executing the commands. It preserves version interpolation and path placeholders. The Rust runner also honors the explicit must_succeed: false used by the two AeroSpace commands; ordinary lifecycle evaluation skips structured blocks so they are not run twice.

The focused regression tests pass, including sandboxed metadata extraction with Ruby 4.0.6, and mise run lint-fix / Cargo check pass.

One limitation surfaced when checking the complete cask pinned in this report: with this patch, evaluation advances beyond postflight_steps and fails on the existing unsupported HOMEBREW_PREFIX constant in its completion targets. So this PR fixes the reported flight-step gap, but does not yet make the full AeroSpace cask work. I have kept that limitation explicit in the PR rather than claiming an end-to-end fix.

AI-assisted — Tool: Codex; model: openai/unavailable; version: unavailable.