packages appear in constraints list twice with different versions

[domdere]

not sure how this happens yet:

Process failed: cabal install --ghc-options=-j1 --max-backjumps=0 lens-4.15.4 --constraint adjunctions == 4.4 --constraint base-orphans == 0.7 --constraint bifunctors == 5.5.2 --constraint Cabal == 2.2.0.0 --constraint cabal-doctest == 1.0.5 --constraint cabal-doctest == 1.0.6 --constraint call-stack == 0.1.0 --constraint comonad == 5.0.3 --constraint contravariant == 1.4.1 --constraint directory == 1.2.7.1 --constraint distributive == 0.5.3 --constraint exceptions == 0.8.3 --constraint fail == 4.9.0.0 --constraint free == 4.12.4 --constraint hashable == 1.2.7.0 --constraint kan-extensions == 5.1 --constraint lens == 4.15.4 --constraint mtl == 2.2.2 --constraint parallel == 3.2.1.1 --constraint parsec == 3.1.13.0 --constraint prelude-extras == 0.4.0.3 --constraint primitive == 0.6.3.0 --constraint process == 1.6.3.0 --constraint profunctors == 5.2.2 --constraint reflection == 2.1.3 --constraint semigroupoids == 5.2.2 --constraint semigroups == 0.18.4 --constraint StateVar == 1.1.0.4 --constraint stm == 2.4.5.0 --constraint tagged == 0.8.5 --constraint text == 1.2.3.0 --constraint th-abstraction == 0.2.6.0 --constraint transformers-compat == 0.5.1.4 --constraint unordered-containers == 0.2.9.0 --constraint vector == 0.12.0.1 --constraint void == 0.7.2

In particular:

--constraint cabal-doctest == 1.0.5 --constraint cabal-doctest == 1.0.6

[domdere]

no lock files were involved

[erikd]

Cabal file that caused this? Or better yet the git repo?