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A general description is here.
Jumps to outer contexts, for example in error recovery, now make intermediate jumps to contexts where ‘on.exit’ actions are established instead of trying to run all ‘on.exit’ actions before jumping to the final target. This unwinds the stack gradually, releases resources held on the stack, and significantly reduces the chance of a segfault when running out of C stack space. Error handlers established using ‘withCallingHandlers()’ and ‘options("error")’ specifications are ignored when handling a C stack overflow error as attempting one of these would trigger a cascade of C stack overflow errors. These changes resolve PR#16753.