These are the packages that would be merged, in reverse order:

Calculating dependencies  ... done!
[nomerge       ] app-editors/vim-8.0.1298::gentoo  USE="lua python -X -acl -cscope -debug -gpm (-luajit) -minimal -nls -perl (-racket) -ruby (-selinux) -tcl -terminal -vim-pager" PYTHON_SINGLE_TARGET="python3_5 -python2_7 -python3_4 -python3_6" PYTHON_TARGETS="python2_7 python3_5 python3_6 -python3_4" 
[nomerge       ]  app-editors/vim-core-8.0.1298::gentoo  USE="-acl -minimal -nls" 
[ebuild  N     ]   app-vim/gentoo-syntax-20170225::gentoo  USE="-ignore-glep31" 19 KiB
[ebuild  N     ]    app-editors/vim-8.0.1298::gentoo  USE="lua python -X -acl -cscope -debug -gpm (-luajit) -minimal -nls -perl (-racket) -ruby (-selinux) -tcl -terminal -vim-pager" PYTHON_SINGLE_TARGET="python3_5 -python2_7 -python3_4 -python3_6" PYTHON_TARGETS="python2_7 python3_5 python3_6 -python3_4" 13084 KiB
[ebuild  N     ]     app-editors/vim-core-8.0.1298::gentoo  USE="-acl -minimal -nls" 0 KiB
[ebuild  N     ]     dev-util/ctags-20161028::gentoo  USE="xml -json -yaml" 833 KiB
[ebuild  NS    ]     dev-lang/lua-5.1.5-r4:0::gentoo [5.2.3-r2:5.2::gentoo, 5.3.3-r1:5.3::gentoo] USE="deprecated emacs readline -static" 217 KiB
[ebuild  N     ]     app-eselect/eselect-vi-1.1.9::gentoo  7 KiB
[blocks B      ] dev-lang/lua:0 ("dev-lang/lua:0" is blocking dev-lang/lua-5.3.3-r1, dev-lang/lua-5.2.3-r2)

Total: 6 packages (5 new, 1 in new slot), Size of downloads: 14157 KiB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (dev-lang/lua-5.1.5-r4:0/0::gentoo, ebuild scheduled for merge) pulled in by
    dev-lang/lua:0[deprecated] required by (app-editors/vim-8.0.1298:0/0::gentoo, ebuild scheduled for merge)

  (dev-lang/lua-5.2.3-r2:5.2/5.2::gentoo, installed) pulled in by
    dev-lang/lua:5.2/5.2= required by (dev-lua/luaposix-33.4.0:0/0::walrus, installed)
    dev-lang/lua:5.2 required by @selected
    dev-lang/lua:= required by (dev-lua/luaposix-33.4.0:0/0::walrus, installed)

  (dev-lang/lua-5.3.3-r1:5.3/5.3::gentoo, installed) pulled in by
    dev-lang/lua:5.3 required by @selected


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages


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