jdx/mise · error · ShimUnsupportedError

formula uses `#{feature}`, which mise's source-build shim do

Error message

formula uses `#{feature}`, which mise's source-build shim does not support

What it means

mise can source-build Homebrew formulae without Homebrew by evaluating the formula's .rb in its own Formula-DSL shim (shim.rb, invoked from src/system/packages/brew/source.rs). It implements 'the commonly-used subset of the Formula DSL; formulae that reach outside it fail loudly with a clear message rather than miscompiling silently' (file header). When a formula's install code uses something outside that subset, `shim_unsupported!` raises ShimUnsupportedError with `formula uses \`X\`, which mise's source-build shim does not support`. Concrete raisers in shim.rb: resource patches (line 405), resources declaring a non-nil download strategy `using:` (line 410), unknown `on_system :macos =>` condition symbols (line 614), inline `patch` strings via `:DATA`-style sources (line 659), `testpath` (line 718), and any unknown install-time helper method called inside `def install` (line 858).

Source

Thrown at src/system/packages/brew/shim.rb:63

def ohai(*args)
  $stdout.puts "==> #{args.join(" ")}"
  $stdout.flush
end

def opoo(message)
  $stderr.puts "Warning: #{message}"
end

def odie(message)
  $stderr.puts "Error: #{message}"
  exit 1
end

class ShimUnsupportedError < StandardError; end

def shim_unsupported!(feature)
  raise ShimUnsupportedError,
        "formula uses `#{feature}`, which mise's source-build shim does not support"
end

module MiseDownload
  module_function

  # download with redirects into the cache, verify, return the path
  def fetch(url, sha256, context)
    raise "#{context}: missing sha256" if sha256.to_s.strip.empty?
    sha256 = sha256.to_s.strip.downcase
    raise "#{context}: malformed sha256" unless sha256.match?(/\A[0-9a-f]{64}\z/)

    MISE_BREW_CACHE.mkpath
    dest = MISE_BREW_CACHE + "#{sha256}--#{File.basename(URI(url).path)}"
    unless dest.file? && Digest::SHA256.file(dest).hexdigest == sha256
      ohai "Downloading #{url}"
      tmp = Pathname.new("#{dest}.incomplete")
      URI.open(url, "rb", redirect: true) do |remote|

View on GitHub (pinned to 6bd4a54fad)

Solutions

Update mise to the newest release first — the shim's DSL subset expands as formulae require it
Install the formula with real Homebrew (`brew install <formula>`) so the full Formula DSL is available, or use a tool backend that ships binaries (aqua/github releases) instead of source-building the brew formula
If bottles exist for your platform, let mise pour the bottle rather than source-building (bottle pour paths don't evaluate install code and never hit this shim)
Inspect the formula (github.com/Homebrew/homebrew-core/blob/HEAD/Formula/<first-letter>/<formula>.rb) to find the offending stanza and file an issue at github.com/jdx/mise naming the formula so support can be added

Example fix

# before (source-build shim rejects the formula's DSL)
mise use brew:niche-formula
# after (real Homebrew handles full DSL)
brew install niche-formula

Defensive patterns

Strategy: fallback

Validate before calling

# before source-building, check the formula for DSL the shim rejects
ruby -e '
  src = File.read(ARGV[0])
  abort "uses testpath in install" if src.match?(/^\s*def install.*?testpath/m)
  abort "uses inline patch (:DATA)" if src.include?("patch :DATA") || src.match?(/patch\s+do\s*\n\s*s\s*=/)
  abort "resource uses download strategy" if src.match?(/using:\s*:/)
' Formula/foo.rb 2>/dev/null || echo "formula likely needs real brew"

Type guard

# ruby: formula source is shim-compatible when no flagged constructs appear
FORMULA_SHIM_UNSUPPORTED = [
  /testpath/,
  /patch\s+:DATA/,
  /using:\s*:/,          # resource download strategies
  /patch\s+("|')/,       # inline patch strings
  /on_system\s+:macos\s*=>\s*:(?!ventura_or_older|ventura_or_newer|sonoma_or_older|sonoma_or_newer|monterey_or_older|monterey_or_newer|big_sur_or_older|big_sur_or_newer|catalina_or_older|catalina_or_newer|sequoia_or_older|sequoia_or_newer|tahoe_or_older|tahoe_or_newer)[a-z_]+/
].freeze
def shim_compatible_formula?(src)
  FORMULA_SHIM_UNSUPPORTED.none? { |re| src.match?(re) }
end

Try / catch

# shell: on shim rejection, fall back to real Homebrew
out=$(mise use "brew:$FORMULA" 2>&1)
if [ $? -ne 0 ] && printf '%s' "$out" | grep -q 'source-build shim does not support'; then
  brew install "$FORMULA"
else
  printf '%s\n' "$out"
fi

Prevention

Prefer bottles/derived backends over source-building formulae: bottle pours skip the formula install DSL entirely
Keep Homebrew available as fallback for formulae with git/svn resources or rich patch sets, which the shim rejects by design
Update mise when source-build failures appear after homebrew/core formula updates — the DSL subset tracks upstream evolution
Read the exact feature name in the error (e.g. 'resource with download strategy :git') to decide between updating mise, pinning an older formula, or using brew

When it happens

Trigger: Source-building a formula through mise's brew system-packages integration (e.g. `mise use brew:<formula>` when no bottle is poured/available, or a build mode that forces source) where the formula's `install` block or its resources/patches use unsupported DSL: a `resource do ... using: :git ... end`, a `test do testpath ... end` referenced at install time, a patch with an inline string source, or a helper method the shim never defined.

Common situations: Linux machines or containers source-building formulae that Homebrew serves as bottles on macOS; niche formulae with git/cvs resources or heavy patch sets; a formula update in homebrew/core suddenly adopting a new DSL method the shim lacks; build-from-source forced by settings or missing bottles for the platform.

Related errors

AI-assisted analysis of jdx/mise@6bd4a54fad (2026-08-16). Data as JSON: /api/errors/126a3a6318e78c30. Report an issue: GitHub.