doc: Clang 8 or later is required with FORCE_USE_SYSTEM

fanquake commented at 3:04 AM on July 29, 2020: member

The usage of pragmas within the macOS SDK requires LLVM Clang 8. This is the same version as our prebuilt Clang, however the minimum is worth noting here as they may diverge and/or expert users might expect they could use an earlier version.

If you compile depends using FORCE_USE_SYSTEM_CLANG=1 and Clang 7 you'll see output like:

In file included from kernel/qcore_mac_objc.mm:44:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSText.h:9:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSView.h:19:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSResponder.h:10:
/bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSEvent.h:19:1: error:
      expected 'push' or 'pop' after '#pragma clang attribute'
/bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/usr/include/os/availability.h:104:273: note: expanded from macro
      'API_UNAVAILABLE_BEGIN'
  ...__API_UNAVAILABLE_BEGIN5, __API_UNAVAILABLE_BEGIN4, __API_UNAVAILABLE_BEGIN3, __API_UNAVAILABLE_BEGIN2, __API_UNAVAILABLE_BEGIN1, 0)(__VA_A...
                                                                                                             ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.

I've got a godbolt here that contains a demo of the issue (based off the macOS SDK). It will compile with Clang 8 but not with Clang 7.

doc: Clang 8 or later is required with FORCE_USE_SYSTEM_CLANG

The usage of pragmas within the macOS SDK requires LLVM Clang 8. This is
the version as our prebuilt Clang, however the minimum is worth noting here
as they may diverge and/or expert users might expect they could use an
earlier version.

If you compile using Clang 7 you'll see output like:
```bash
In file included from kernel/qcore_mac_objc.mm:44:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSText.h:9:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSView.h:19:
In file included from /bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSResponder.h:10:
/bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/System/Library/Frameworks/AppKit.framework/Headers/NSEvent.h:19:1: error:
      expected 'push' or 'pop' after '#pragma clang attribute'
/bitcoin/depends/SDKs/Xcode-11.3.1-11C505-extracted-SDK-with-libcxx-headers/usr/include/os/availability.h:104:273: note: expanded from macro
      'API_UNAVAILABLE_BEGIN'
  ...__API_UNAVAILABLE_BEGIN5, __API_UNAVAILABLE_BEGIN4, __API_UNAVAILABLE_BEGIN3, __API_UNAVAILABLE_BEGIN2, __API_UNAVAILABLE_BEGIN1, 0)(__VA_A...
                                                                                                             ^
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
```

e60ef21b8a

fanquake added the label Docs on Jul 29, 2020

fanquake requested review from dongcarl on Jul 29, 2020

laanwj commented at 3:02 PM on July 29, 2020: member

ACK e60ef21b8a0f62ebc2e0bdbb5943fa80cc4d98b2

dongcarl commented at 6:09 PM on July 30, 2020: member

Feel free to let me know if you don't want to expand on the scope of this PR @fanquake, but I'd like to document our overall approach to constructing the OSX toolchain, especially picking versions of tools. I don't think it's written down anywhere in the codebase yet.

fanquake commented at 12:23 AM on July 31, 2020: member

@dongcarl I'm going to merge this as-is. We can follow up with some more extensive macOS toolchain docs (although we should probably write some more general docs), either in a separate PR or as part of #17920 🤔.

fanquake merged this on Jul 31, 2020

fanquake closed this on Jul 31, 2020

fanquake deleted the branch on Jul 31, 2020

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doc: Clang 8 or later is required with FORCE_USE_SYSTEM_CLANG #19617