unpack_strategy/dmg: use diskutil image on macOS 14+

[p-linnane]

hdiutil is deprecated on macOS 27 and prints a deprecation warning on every attach, imageinfo, and convert call, each one pointing at diskutil image as the replacement (also reported in #23401). diskutil image attach was added in macOS 13, while image creation was added in macOS 14. Because SLA conversion requires diskutil image create from, this moves the DMG unpack strategy to diskutil image on macOS 14 and newer and retains the existing hdiutil path for older releases.

On macOS 14 and newer we detect images with diskutil image info --plist, attach read-only with nobrowse into an isolated temporary mount point, fall back to a plain attach when an image has multiple mountable volumes (--mountPoint only supports a single mountable entity), and convert SLA-bearing images with diskutil image create from. Both tools emit the same system-entities/mount-point plist structure, so mount handling and ejection are unchanged.

One detection difference is worth calling out. diskutil image info exits nonzero after printing the license agreement for an SLA-bearing image. When that occurs, detection confirms the file has a valid koly UDIF trailer directly. This avoids treating arbitrary failure output as a disk image without falling back to deprecated hdiutil on the new path.

Validated end-to-end on macOS 27 beta build 26A5388g, including SLA-bearing, multi-volume, and combined SLA/multi-volume images. The macOS 14 floor is based on the capability history documented by diskutil(8); macOS 14 through 26 have not been exercised directly. diskutil image create from --format UDRO preserves embedded SLAs, while RAW strips them like the legacy UDTO conversion. This is observed prerelease behavior and should be rechecked before macOS 27 GA.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

Claude Code (Opus 5) drafted the implementation and tests; I reviewed the diff, verified the new tests fail without the fix and pass with it, exercised real SLA-bearing and multi-volume disk images end-to-end on macOS 27, and ran brew lgtm + targeted specs.

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[Copilot]

Pull request overview

This PR updates Homebrew’s DMG unpack strategy to avoid hdiutil deprecation warnings on macOS 27+ by switching to diskutil image for image detection, attachment, and SLA-handling conversion while retaining the existing hdiutil behavior on older macOS versions.

Changes:

• Add an OS-gated diskutil image code path for .can_extract? and DMG mounting/attachment on macOS 27+.
• Introduce helpers to attach images with an isolated mount point and to convert SLA-bearing images for mounting.
• Add macOS 27-specific unit tests and OS extension hooks to enable the new behavior only on macOS.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/unpack_strategy/dmg.rb	Switch DMG detection/attach/convert to diskutil image on macOS 27+ and factor out helpers.
Library/Homebrew/test/unpack_strategy/dmg_spec.rb	Add specs covering diskutil vs hdiutil selection, isolated mount point, fallback attach, and SLA conversion.
Library/Homebrew/extend/os/unpack_strategy/dmg.rb	Add OS-specific loader for DMG unpack strategy extensions on macOS.
Library/Homebrew/extend/os/mac/unpack_strategy/dmg.rb	Define the macOS 27+ predicate (diskutil_image?) used to switch implementations.

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[MikeMcQuaid]

Thanks! If possible let's see what other macOS versions this works on?

[MikeMcQuaid]

Thanks, sorry, few more nits.

[MikeMcQuaid]

Thanks!