Build Error from compile commands generator on MBS projects with build location outside workspace

[Kummallinen]

Describe the bug
When building an MBS project that has the build location set to outside of the workspace the build errors with an NPE in CompilationDatabaseGenerator.

!ENTRY org.eclipse.core.resources 4 2 2025-01-20 18:31:28.848
!MESSAGE Problems occurred when invoking code from plug-in: "org.eclipse.core.resources".
!STACK 0
java.lang.NullPointerException: Cannot invoke "org.eclipse.core.runtime.IPath.append(String)" because "buildDirectory" is null
	at org.eclipse.cdt.managedbuilder.internal.core.jsoncdb.generator.CompilationDatabaseGenerator.generate(CompilationDatabaseGenerator.java:93)
	at org.eclipse.cdt.managedbuilder.internal.core.CommonBuilder.build(CommonBuilder.java:515)
	at org.eclipse.cdt.managedbuilder.internal.core.CommonBuilder.build(CommonBuilder.java:471)
	at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:1077)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:296)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:352)
	at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:441)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:47)
	at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:444)
	at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:555)
	at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:503)
	at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:585)
	at org.eclipse.core.internal.resources.Workspace.buildInternal(Workspace.java:595)
	at org.eclipse.core.internal.resources.Workspace.build(Workspace.java:491)
	at org.eclipse.ui.actions.BuildAction$1.runInWorkspace(BuildAction.java:288)
	at org.eclipse.core.internal.resources.InternalWorkspaceJob.run(InternalWorkspaceJob.java:43)
	at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)

To Reproduce
Steps to reproduce the behavior:

1. Create a managed build project
2. Disable Makefile generation & move the build location to a folder outside of the workspace (C/C++Build -> Builder Settings)
3. Run a build

Expected behavior
Should disable compile-commands.json generation when makefile generation is disabled, as the invoked build may not match the MBS settings

[jonahgraham]

AFAICT this only happens if compile_commands.json generation is enabled, so the workaround for anyone affected is to disable the generation manually in preferences:

or in the project properties

@Kummallinen I see you self-assigned, lmk if you want any help with this.

[Kummallinen]

Thanks @jonahgraham, I've asked @alicetrifu to look at this so we can get a fix into CDT 12. Not sure why but I can't assign it to her