[KristofferC]

When a stepping command finishes the debugged call, execute_command read the result with get_return(root(state.frame)). By then JuliaInterpreter has put the finished frames back in its reuse pool (junk_frames), and the object in state.frame may already have been reused.

Frames reused inside the debugged call still walk up to the right root, so ordinary code is not affected. It breaks when, during the command, a frame is created outside the debugged call tree, e.g. when the debugged code itself uses JuliaInterpreter (@interpret, or a package such as Revise that uses it internally). The recycled leaf then becomes the root of that other call, and @run returns its result:

@noinline f(x) = x * 10
function g(x)
    a = f(x)
    b = JuliaInterpreter.@interpret identity(42)
    return a + b
end
breakpoint(f); @run g(1)   # c  →  returned 42, should be 52

The root is now looked up before calling debug_command. This also makes Debugger independent of when JuliaInterpreter reuses frames.

The added test fails without the fix (42 == 52).

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