Merge pull request #3713 from lethosor/fix-removejob-gcc-optimization

Hack to force GCC to invoke cancel_job() through DF's vtable

library/modules/Job.cpp

@@ -387,7 +387,14 @@ bool DFHack::Job::removeJob(df::job* job) {
     // call the job cancel vmethod graciously provided by The Toady One.
     // job_handler::cancel_job calls job::~job, and then deletes job (this has
     // been confirmed by disassembly).
-    world->jobs.cancel_job(job);
+
+    // HACK: GCC (starting around GCC 10 targeting C++20 as of v50.09) optimizes
+    // out the vmethod call here regardless of optimization level, so we need to
+    // invoke the vmethod manually through a pointer, as the Lua wrapper does.
+    // `volatile` does not seem to be necessary but is included for good
+    // measure.
+    volatile auto cancel_job_method = &df::job_handler::cancel_job;
+    (world->jobs.*cancel_job_method)(job);
 
     return true;
 }

test/modules/job.lua

@@ -0,0 +1,19 @@
+config.target = 'core'
+config.mode = 'title' -- alters world state, not safe when a world is loaded
+
+function test.removeJob()
+    -- removeJob() calls DF code, so ensure that that DF code is actually running
+
+    -- for an explanation of why this is necessary to check,
+    -- see https://github.com/DFHack/dfhack/pull/3713 and Job.cpp:removeJob()
+
+    expect.nil_(df.global.world.jobs.list.next, 'job list is not empty')
+
+    local job = df.job:new()  -- will be deleted by removeJob() if the test passes
+    dfhack.job.linkIntoWorld(job)
+    expect.true_(df.global.world.jobs.list.next, 'job list is empty')
+    expect.eq(df.global.world.jobs.list.next.item, job, 'expected job not found in list')
+
+    expect.true_(dfhack.job.removeJob(job))
+    expect.nil_(df.global.world.jobs.list.next, 'job list is not empty after removeJob()')
+end