Dart's package manager (Pub) uses an SAT solver to find possible solutions, and even more impressively, to describe why a dependency can't be fulfilled:
Because dropdown >=2.0.0 depends on icons >=2.0.0 and root depends
on icons <2.0.0, dropdown >=2.0.0 is forbidden.
And because menu >=1.1.0 depends on dropdown >=2.0.0, menu >=1.1.0
is forbidden.
And because menu <1.1.0 depends on dropdown >=1.0.0 <2.0.0 which
depends on intl <4.0.0, every version of menu requires intl
<4.0.0.
So, because root depends on both menu >=1.0.0 and intl >=5.0.0,
version solving failed.
