I'm not sure why this happens sometimes, but I sometimes get a failing language build which fails somewhere in the ESV. The next build always succeeds, so it doesn't block me. I've been working in a guest Eclipse for a while though, so I'm not sure if it's related to that or perhaps to not updating to the latest nightly.

First the standard bug report info, then the stacktrace:

Eclipse: org.eclipse.platform.ide 4.6.3.M20170301-0400
Spoofax: org.metaborg.spoofax.eclipse 2.3.0.qualifier
System: Mac OS X x86_64 10.12.5

15:06 | ERROR | o.m.c.build.Builder            - Transformation failed unexpectedly for eclipse:///meta.flowspec.lang/editor/Main.esv
org.metaborg.core.transform.TransformException: Invoking Stratego strategy pack-main-descriptor-file failed unexpectedly
Stratego trace:
	pack_main_descriptor_file_0_0
	pack_main_descriptor_file_0_0
	with_1_1
	create_packed_descriptor_1_0
	Module_3_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_definitions_0_0
	with_1_1
	map_1_0
	read_descriptor_file_0_0
	with_1_1
	parse_file_with_current_lang_0_0
org.spoofax.interpreter.core.InterpreterException: Exception during evaluation: Exception in execution of primitive 'parse'
	at org.metaborg.spoofax.core.transform.StrategoTransformer.transform(StrategoTransformer.java:144) ~[org.metaborg.spoofax.core/:na]
	at org.metaborg.spoofax.core.transform.StrategoTransformer.transform(StrategoTransformer.java:80) ~[org.metaborg.spoofax.core/:na]
	at org.metaborg.spoofax.core.transform.StrategoTransformer.transform(StrategoTransformer.java:1) ~[org.metaborg.spoofax.core/:na]
	at org.metaborg.core.transform.TransformService.transform(TransformService.java:76) ~[org.metaborg.core/:na]
	at org.metaborg.core.transform.ITransformService.transform(ITransformService.java:135) ~[org.metaborg.core/:na]
	at org.metaborg.core.build.Builder.transform(Builder.java:472) [org.metaborg.core/:na]
	at org.metaborg.core.build.Builder.updateLanguageResources(Builder.java:284) [org.metaborg.core/:na]
	at org.metaborg.core.build.Builder.build(Builder.java:167) [org.metaborg.core/:na]
	at org.metaborg.spoofax.core.build.SpoofaxBuilder.build(SpoofaxBuilder.java:48) [org.metaborg.spoofax.core/:na]
	at org.metaborg.spoofax.core.build.SpoofaxBuilder.build(SpoofaxBuilder.java:1) [org.metaborg.spoofax.core/:na]
	at org.metaborg.spoofax.eclipse.build.BuildRunnable.run(BuildRunnable.java:60) [org.metaborg.spoofax.eclipse/:na]
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2240) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2267) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.metaborg.spoofax.eclipse.processing.RunnableTask.schedule(RunnableTask.java:45) [org.metaborg.spoofax.eclipse/:na]
	at org.metaborg.spoofax.meta.core.build.LanguageSpecBuilder.compile(LanguageSpecBuilder.java:164) [org.metaborg.spoofax.meta.core/:na]
	at org.metaborg.spoofax.eclipse.meta.build.CompileBuilder$1.run(CompileBuilder.java:49) [org.metaborg.spoofax.eclipse.meta/:na]
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2240) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2267) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.metaborg.spoofax.eclipse.meta.build.CompileBuilder.build(CompileBuilder.java:69) [org.metaborg.spoofax.eclipse.meta/:na]
	at org.metaborg.spoofax.eclipse.meta.build.Builder.build(Builder.java:53) [org.metaborg.spoofax.eclipse.meta/:na]
	at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:735) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42) [org.eclipse.equinox.common_3.8.0.v20160509-1230.jar:na]
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:246) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:301) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42) [org.eclipse.equinox.common_3.8.0.v20160509-1230.jar:na]
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:304) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:360) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:383) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.resources.Workspace.buildInternal(Workspace.java:487) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.resources.Workspace.build(Workspace.java:406) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.ui.actions.BuildAction$1.runInWorkspace(BuildAction.java:285) [org.eclipse.ui.ide_3.12.3.v20170119-0935.jar:na]
	at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:39) [org.eclipse.core.resources_3.11.1.v20161107-2032.jar:na]
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55) [org.eclipse.core.jobs_3.8.0.v20160509-0411.jar:na]
Submitted by Jeff Smits on 30 May 2017 at 15:13

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