I interrupted a build of master recently, and this was the result when I tried to resume it:

----------------- snip -----------------
ERROR: util-macros-1_1.19.0-r0 do_prepare_recipe_sysroot: Error executing a python function in exec_python_func() autogenerated:

The stack trace of python calls that resulted in this exception/failure was:
File: 'exec_python_func() autogenerated', lineno: 2, function: <module>
     0001:
 *** 0002:extend_recipe_sysroot(d)
     0003:
File: '/home/paul/poky/poky/meta/classes/staging.bbclass', lineno: 577, function: extend_recipe_sysroot
     0573:                        continue
     0574:                    if native:
     0575:                        dest = staging_copyfile(l, recipesysrootnative, fixme['native'], postinsts, stagingdir)
     0576:                    else:
 *** 0577:                        dest = staging_copyfile(l, destsysroot, fixme[''], postinsts, stagingdir)
     0578:                    if dest:
     0579:                        m.write(dest.replace(workdir + "/", "") + "\n")
     0580:
     0581:    for f in fixme:
File: '/home/paul/poky/poky/meta/classes/staging.bbclass', lineno: 273, function: staging_copyfile
     0269:        os.symlink(linkto, dest)
     0270:        #bb.warn(c)
     0271:    else:
     0272:        try:
 *** 0273:            os.link(c, dest)
     0274:        except OSError as err:
     0275:            if err.errno == errno.EXDEV:
     0276:                bb.utils.copyfile(c, dest)
     0277:            else:
Exception: FileExistsError: [Errno 17] File exists: '/home/paul/poky/poky/build/tmp/sysroots-components/core2-64/gcc-runtime/usr/include/c++/6.3.0/experimental/memory' -> '/home/paul/poky/poky/build/tmp/work/core2-64-poky-linux/util-macros/1_1.19.0-r0/recipe-sysroot/usr/include/c++/6.3.0/experimental/memory'

ERROR: util-macros-1_1.19.0-r0 do_prepare_recipe_sysroot: Function failed: extend_recipe_sysroot
ERROR: Logfile of failure stored in: /home/paul/poky/poky/build/tmp/work/core2-64-poky-linux/util-macros/1_1.19.0-r0/temp/log.do_prepare_recipe_sysroot.20600
ERROR: Task (/home/paul/poky/poky/meta/recipes-graphics/xorg-util/util-macros_1.19.0.bb:do_prepare_recipe_sysroot) failed with exit code '1'
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I'm not sure if we want to extend this to handle FileExistsError (or OSError with errno.EEXIST, same thing), or whether we should alternatively be doing something to avoid this scenario occurring.