os/mac/sdk: parse version from SDKSettings.json

[carlocab]

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This implements feedback from #10072.

We try to use a more sensible version check for the SDK, by querying, in order of priority:

1. sdk_prefix/MacOSX.sdk/SDKSettings.json
2. sdk_prefix/MacOSX.sdk/SDKSettings.plist
3. OS::Mac.sdk_version

[BrewTestBot]

Review period will end on 2020-12-24 at 13:35:46 UTC.

[carlocab]

@Bo98 Not sure if the last fallback to OS::Mac.sdk_version is necessary or even desired. Let me know your thoughts.

[MikeMcQuaid]

Great work so far! Any thoughts on removing the existing :big_sur logic you mentioned given this too? Interested in @Bo98's thoughts on that too if they have a chance.

[MikeMcQuaid]

Suggested change

	version = JSON.parse(File.read(sdk_settings_json))["Version"]
	version = JSON.parse(File.read(sdk_settings_json))["Version"].presence

and then I'd suggest using version ||= on the other cases below so it gets set to something even if this version is missing in the JSON.

[MikeMcQuaid]

Can skip this too once it's only the JSON stuff.

[Bo98]

Not sure if the last fallback to OS::Mac.sdk_version is necessary or even desired.

Probably not. I'd much rather reject a SDK if SDKSettings is missing (which should never really happen).

[carlocab]

Thanks, @Bo98. Did you have thoughts regarding this

brew/Library/Homebrew/os/mac/sdk.rb

Lines 57 to 64 in d6692d2

	# Accept an SDK for another OS version if it shares a major version
	# with the current OS - for example, the 11.0 SDK on 11.1,
	# or vice versa.
	# Note that this only applies on macOS 11
	# or greater, given the way the versioning has changed.
	# This shortcuts the below check, since we *do* accept an older version
	# on macOS 11 or greater if the major version matches.
	return sdk if OS::Mac.version >= :big_sur && sdk.version.major == OS::Mac.version.major

in light of the last PR?

[Bo98]

I believe that will still be necessary if the user has, for example, macOS 11.1 installed but hasn't updated Xcode and so still has the 11.0 SDK.

[MikeMcQuaid]

I believe that will still be necessary if the user has, for example, macOS 11.1 installed but hasn't updated Xcode and so still has the 11.0 SDK.

Thanks @Bo98 👍🏻

[Bo98]

Just to copy over the point from the other PR:

Only extra thing to remember is that the 10.15 SDK might(?) have 3 components in the version so might need to strip that off to be just 2. I know a 10.15.4 SDK was released at some point.

Is this something we want to handle or just assume it won't happen again with the Big Sur versioning system? I reckon it won't happen again so I'm fine with this pull request as-is.

[BrewTestBot]

Review period ended.

[MikeMcQuaid]

Is this something we want to handle or just assume it won't happen again with the Big Sur versioning system? I reckon it won't happen again so I'm fine with this pull request as-is.

Me too. Thanks @carlocab and thanks @Bo98 for all the review.