feat: support Icon Composer icons for macOS

[iamEvanYT]

closes #9254
closes #9278

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This PR updates the "icon" property to the electron-builder configuration which adds support for icons made with Icon Composer (.icon format).

On building, it will create an Assets.car with the icon which will be bundled inside the app's Resources folder.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2f9afb2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 8 packages

Name	Type
app-builder-lib	Major
dmg-builder	Major
electron-builder-squirrel-windows	Major
electron-builder	Major
electron-forge-maker-appimage	Major
electron-forge-maker-nsis-web	Major
electron-forge-maker-nsis	Major
electron-forge-maker-snap	Major

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[Kilian]

would this support shipping both a .icon for Tahoe+ and an .icns for older mac versions?

[mmaietta]

would this support shipping both a .icon for Tahoe+ and an .icns for older mac versions?

@Kilian Do you know if those are separate "fields" perceived by mac? e.g., if we package both an icns and an icon, only Taho can read the new value?
Basically, do we know if Mac will render an icon file on older versions of macOS or is it only macOS 26+ "visible"?

I haven't gotten around to updating my mac to Tahoe yet as I'm afraid it'll brick my current dev environment while I'm mid-project. This is indeed on the todo list though

[iamEvanYT]

@mmaietta @Kilian I have tested on macOS Sequoia and with both the .icon and .icns file bundled, it will choose the .icon file and display a static version on it. I assume its the same for other macOS versions, but haven't tested.

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Update 1:

The plist property seems to be available since macOS 10.13+, which should mean that the Liquid Glass icon will be visible since that macOS version.

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Update 2:

Tested with macOS Monterey and confirmed that it does show there.

[mmaietta]

Thank you @iamEvanYT !

In this case then, I'd like to refactor this PR to instead leverage the icon, but I still need to check dmg-builder to see if/how the .icon would be rendered. Will try to get back to this asap

Is there a minimum xcode or macos version required for supporting this CLI tool? Wondering if we need to throw a more descriptive error if the tool command doesn't exist

[iamEvanYT]

@mmaietta I did a few commits a few days ago to change to the icon property which should work. As for the minimum Xcode version, it should be Xcode 26. There is a check for macOS Tahoe in the icon-composer.ts file, which should cover errors in CI.

[mmaietta]

This is looking solid! Any chance we can add a .icon test fixture to integrate this into one of the mac unit tests?

[iamEvanYT]

@mmaietta There, the tests passed on my computer, so it should theoretically pass on the CI. However, it may not pass as it still uses the old Xcode SDK and not Xcode 26. In that case, we might have to change the CI runner from macos-latest to macos-26, but it may not be ideal.

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Edit:

Huh, it seems like the macIconTest file isn't being ran in CI. I wonder if that's intentional?

I've added a commit that runs the macIconTests on macos-26 in the CI, but let me know if you want me to revert that.

[mmaietta]

I took a look at dmg-builder and it does seem to indeed rely on an icns file., but it's in its own config param dmg.icon and does not inherit from mac.icon, so we should be good there!

Thank you for your great work on this PR and I appreciate your flexibility in working through these iterations

[mmaietta]

FYI, this LGTM, but I need to fix the core test-updater test suite before I can merge this. Working on this currently and hope to resolve asap