bug#30015: WebKitGTK nondeterministic build failures

[Mark H Weaver]

I recently wrote on guix-devel:

> I just followed this up with a Spectre mitigation for WebKitGTK+
> backported from upstream WebKit:
>
>   
> https://git.savannah.gnu.org/cgit/guix.git/commit/?id=56804398a94bea941183ae4ed29d2a9f82069a6f

Unfortunately, this seems to have introduced non-deterministic build
failures on Hydra.  On the first attempt, WebKitGTK+ failed to build on
both x86_64 and i686.  On the second attempt, it succeeded on x86_64 but
failed again on i686.  Hydra is currently working on the third build
attempt on i686.

I find it very unlikely that this problem is related to the content of
the patch itself.  My best guess is that it's caused by the fact that
our 'patch-and-repack' mechanism, which generates the patched tarball,
resets all the timestamps to 0, whereas previously we built the upstream
tarball directly with non-zero timestamps.

I guess that the build system contains a race condition that is much
more likely to occur when the timestamps are 0.  It did happen once in
December 2015 on i686, but the other three failures happened today.

I suppose the issue could be solved by disabling parallelism in the
build, but that would be a shame given that WebKitGTK+ already takes a
very long time to build: almost 5 hours on my X200 and about 2 hours on
hydra.gnunet.org.

It's also inconvenient that the build log is so large (around 70 MB)
that Hydra's web interface refuses to display it.

The failure is always the same:

--8<---------------cut here---------------start------------->8---
Traceback (most recent call last):
  File 
"/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py",
 line 28, in <module>
    import webkit.messages
EOFError: EOF read where object expected
--8<---------------cut here---------------end--------------->8---

although the specific target being built when this error occurs varies.
The targets that I've seen fail are:

1. make[2]: *** [Source/WebKit/CMakeFiles/WebKit2.dir/build.make:745: 
DerivedSources/WebKit2/WebRTCSocketMessageReceiver.cpp] Error 1
2. make[2]: *** [Source/WebKit/CMakeFiles/WebKit2.dir/build.make:722: 
DerivedSources/WebKit2/WebRTCMonitorMessageReceiver.cpp] Error 1
3. make[2]: *** [Source/WebKit/CMakeFiles/WebKit2.dir/build.make:457: 
DerivedSources/WebKit2/WebFullScreenManagerProxyMessageReceiver.cpp] Error 1
4. GNUmakefile:82826: recipe for target 
'DerivedSources/WebKit2/CustomProtocolManagerProxyMessages.h' failed

That last one (4) occurred with webkitgtk-2.4.9 on i686-linux in
December 2015.

Here's a longer tail of the failed build log from today on x86_64:

--8<---------------cut here---------------start------------->8---
[ 83%] Generating 
../../DerivedSources/WebKit2/WebResourceLoadStatisticsStoreMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebResourceLoadStatisticsStoreMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/WebResourceLoadStatisticsStore.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebResourceLoadStatisticsStoreMessageReceiver.cpp
[ 83%] Generating 
../../DerivedSources/WebKit2/WebAutomationSessionMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebAutomationSessionMessages.h
[ 83%] Generating 
../../DerivedSources/WebKit2/DownloadProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/DownloadProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/WebResourceLoadStatisticsStore.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebResourceLoadStatisticsStoreMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Automation/WebAutomationSession.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebAutomationSessionMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Downloads/DownloadProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/DownloadProxyMessageReceiver.cpp
[ 83%] Generating 
../../DerivedSources/WebKit2/NetworkProcessProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/NetworkProcessProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Network/NetworkProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/NetworkProcessProxyMessageReceiver.cpp
[ 83%] Generating 
../../DerivedSources/WebKit2/LegacyCustomProtocolManagerProxyMessageReceiver.cpp,
 ../../DerivedSources/WebKit2/LegacyCustomProtocolManagerProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Network/CustomProtocols/LegacyCustomProtocolManagerProxy.messages.in 
> 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/LegacyCustomProtocolManagerProxyMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Network/NetworkProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/NetworkProcessProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Downloads/DownloadProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/DownloadProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Automation/WebAutomationSession.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebAutomationSessionMessages.h
[ 83%] Generating 
../../DerivedSources/WebKit2/PluginProcessProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/PluginProcessProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Plugins/PluginProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/PluginProcessProxyMessageReceiver.cpp
[ 84%] Generating 
../../DerivedSources/WebKit2/StorageProcessProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/StorageProcessProxyMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/WebUserContentControllerProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebUserContentControllerProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/Storage/StorageProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/StorageProcessProxyMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/UserContent/WebUserContentControllerProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebUserContentControllerProxyMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Network/CustomProtocols/LegacyCustomProtocolManagerProxy.messages.in 
> 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/LegacyCustomProtocolManagerProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Plugins/PluginProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/PluginProcessProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/Storage/StorageProcessProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/StorageProcessProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/UserContent/WebUserContentControllerProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebUserContentControllerProxyMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/StorageManagerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/StorageManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 UIProcess/WebStorage/StorageManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/StorageManagerMessageReceiver.cpp
[ 84%] Generating ../../DerivedSources/WebKit2/WebProcessMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebProcessMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/WebProcess.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebProcessMessageReceiver.cpp
[ 84%] Generating 
../../DerivedSources/WebKit2/WebAutomationSessionProxyMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebAutomationSessionProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Automation/WebAutomationSessionProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebAutomationSessionProxyMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 UIProcess/WebStorage/StorageManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/StorageManagerMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/WebCookieManagerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebCookieManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Cookies/WebCookieManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebCookieManagerMessageReceiver.cpp
[ 84%] Generating 
../../DerivedSources/WebKit2/WebIDBConnectionToServerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebIDBConnectionToServerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/WebProcess.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebProcessMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Automation/WebAutomationSessionProxy.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebAutomationSessionProxyMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Cookies/WebCookieManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebCookieManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Databases/IndexedDB/WebIDBConnectionToServer.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebIDBConnectionToServerMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Databases/IndexedDB/WebIDBConnectionToServer.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebIDBConnectionToServerMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/WebFullScreenManagerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebFullScreenManagerMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/WebGeolocationManagerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebGeolocationManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/FullScreen/WebFullScreenManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebFullScreenManagerMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Geolocation/WebGeolocationManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebGeolocationManagerMessageReceiver.cpp
[ 84%] Generating 
../../DerivedSources/WebKit2/WebRTCMonitorMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebRTCMonitorMessages.h
[ 84%] Generating 
../../DerivedSources/WebKit2/WebRTCResolverMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebRTCResolverMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Network/webrtc/WebRTCMonitor.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCMonitorMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Network/webrtc/WebRTCResolver.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCResolverMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/FullScreen/WebFullScreenManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebFullScreenManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Geolocation/WebGeolocationManager.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebGeolocationManagerMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Network/webrtc/WebRTCMonitor.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCMonitorMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Network/webrtc/WebRTCResolver.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCResolverMessages.h
[ 84%] Generating ../../DerivedSources/WebKit2/WebRTCSocketMessageReceiver.cpp, 
../../DerivedSources/WebKit2/WebRTCSocketMessages.h
Traceback (most recent call last):
  File 
"/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py",
 line 28, in <module>
    import webkit.messages
EOFError: EOF read where object expected
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Network/webrtc/WebRTCSocket.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCSocketMessageReceiver.cpp
make[2]: *** [Source/WebKit/CMakeFiles/WebKit2.dir/build.make:722: 
DerivedSources/WebKit2/WebRTCMonitorMessageReceiver.cpp] Error 1
make[2]: *** Deleting file 
'DerivedSources/WebKit2/WebRTCMonitorMessageReceiver.cpp'
make[2]: *** Waiting for unfinished jobs....
[ 84%] Generating 
../../DerivedSources/WebKit2/NetworkProcessConnectionMessageReceiver.cpp, 
../../DerivedSources/WebKit2/NetworkProcessConnectionMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-message-receiver.py
 WebProcess/Network/NetworkProcessConnection.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/NetworkProcessConnectionMessageReceiver.cpp
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Network/webrtc/WebRTCSocket.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/WebRTCSocketMessages.h
cd /tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit && 
/gnu/store/zlbbayv8rv6z7gnhz435gjq8pzjm06v6-python-2.7.13/bin/python2.7 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/webkitgtk-2.18.4/Source/WebKit/Scripts/generate-messages-header.py
 WebProcess/Network/NetworkProcessConnection.messages.in > 
/tmp/guix-build-webkitgtk-2.18.4.drv-0/build/DerivedSources/WebKit2/NetworkProcessConnectionMessages.h
make[2]: Leaving directory '/tmp/guix-build-webkitgtk-2.18.4.drv-0/build'
make[1]: *** [CMakeFiles/Makefile2:1581: 
Source/WebKit/CMakeFiles/WebKit2.dir/all] Error 2
make[1]: Leaving directory '/tmp/guix-build-webkitgtk-2.18.4.drv-0/build'
make: *** [Makefile:153: all] Error 2
phase `build' failed after 5645.4 seconds
builder for `/gnu/store/hp17k74lrlbm62gg5321dqf2r99m5d3q-webkitgtk-2.18.4.drv' 
failed with exit code 1
@ build-failed /gnu/store/hp17k74lrlbm62gg5321dqf2r99m5d3q-webkitgtk-2.18.4.drv 
- 1 builder for 
`/gnu/store/hp17k74lrlbm62gg5321dqf2r99m5d3q-webkitgtk-2.18.4.drv' failed with 
exit code 1
--8<---------------cut here---------------end--------------->8---

On my X200, the build succeeded on my first try.

Would someone like to investigate further?

       Mark