macdeploy: alternative info to download the macOS SDK #22516

The previous link wasn't accessible for me, this adds some instructions given to me by Hebasto on #bitcoin-core-builds as well as a shasum for the archive to quickly check the downloaded one is the right one before processing with the entire Guix build.

Concept ACK.

It seems https://developer.apple.com just requires that one is logged in before following the https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip link.

Concept ACK. I always get a "403 Forbidden", also after being logged in. Searching for "12.1" on https://developer.apple.com/download/all/ works. I checked the sha256sum of my Xcode_12.1.xip file and got a match. 612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f

While touching this file, maybe update these lines as well https://github.com/bitcoin/bitcoin/blob/5bbb2edf6960798eee6998181fa78f0bbe07740e/contrib/macdeploy/README.md#L79-L81 ?

Or just drop them?

I think it would be useful to mention that cookies for https://download.developer.apple.com/ need to be allowed in order for the actual download link to work. Otherwise you could still login and click the download link and still get a 403.

Concept ACK

It's a bit tricky to accurately convey my suggestions using the online github tools, so below is a diff and here is a branch with my suggestions:

diff --git a/contrib/macdeploy/README.md b/contrib/macdeploy/README.md
index ad52f7d20..6b8de576e 100644
--- a/contrib/macdeploy/README.md
+++ b/contrib/macdeploy/README.md
@@ -15,10 +15,11 @@ When complete, it will have produced `Bitcoin-Core.dmg`.
 Our current macOS SDK
 (`Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz`) can be
 extracted from
-[Xcode_12.1.xip](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip)
-(alternatively, after login to your account go to "Downloads", then "More" and look for [`Xcode_12.1`](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip)).
-An Apple ID is needed to download this.
-The `sha256sum` of the archive should be `612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f`.
+[Xcode_12.1.xip](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip). An Apple ID is needed to download this.
+
+Alternatively, after logging in to your Apple Developer account, go to 'Downloads' -> 'More' and look for [`Xcode_12.1`](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
+
+The `sha256sum` of the SDK archive file should be `612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f`.
 
 After Xcode version 7.x, Apple started shipping the `Xcode.app` in a `.xip`
 archive. This makes the SDK less-trivial to extract on non-macOS machines. One

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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #21851 by fanquake

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

While touching this file, maybe update these lines as well Or just drop them?

As mentioned afterward by Achow the link isn't dead, but needs cookies to be enabled. Edited to reflect that.

I think it would be useful to mention that cookies for https://download.developer.apple.com/ need to be allowed in order for the actual download link to work. Otherwise you could still login and click the download link and still get a 403.

Done.

so below is a diff and here is a branch with my suggestions

Thanks, took part of it for the english and formatting part.

Diff:

diff --git a/contrib/macdeploy/README.md b/contrib/macdeploy/README.md
index ad52f7d20e..cdf2b6609f 100644
--- a/contrib/macdeploy/README.md
+++ b/contrib/macdeploy/README.md
@@ -15,8 +15,10 @@ When complete, it will have produced `Bitcoin-Core.dmg`.
 Our current macOS SDK
 (`Xcode-12.1-12A7403-extracted-SDK-with-libcxx-headers.tar.gz`) can be
 extracted from
-[Xcode_12.1.xip](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip)
-(alternatively, after login to your account go to "Downloads", then "More" and look for [`Xcode_12.1`](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip)).
+[Xcode_12.1.xip](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
+Cookies must be enabled for this link to work after logging in.
+Alternatively, after logging in to your account go to 'Downloads', then 'More'
+and look for [`Xcode_12.1`](https://download.developer.apple.com/Developer_Tools/Xcode_12.1/Xcode_12.1.xip).
 An Apple ID is needed to download this.
 The `sha256sum` of the archive should be `612443b1894b39368a596ea1607f30cbb0481ad44d5e29c75edb71a6d2cf050f`.

While touching this file, maybe update these lines as well Or just drop them?

As mentioned afterward by Achow the link isn't dead, but needs cookies to be enabled. Edited to reflect that.

Another link points at Xcode_11.3.1 but we use Xcode_12.1 for now.

Do we really need to link to the same xip from 3 different places in this README? Given that half the time the links don't even seem to work (they don't work for me now even when logged in), why not just remove them, or just have one.

As mentioned above, can you also update the instance of Xcode_11.3.1 further down, and remove the link there as well. There is some duplication of information in this file, but that doesn't have to be fixed here.

Do we really need to link to the same xip from 3 different places in this README?

No, i don't think so. I figured adding another link was helpful since it's what worked for me but i definitely don't have any opinion on how to rework this doc. This PR was just meant as a quick tiny link fix as i got through the process..

ACK f8f772dc495f7d3ee02d75d42ee22ceb90c3a693