Fix Julia v1.0

Base.popat! requires Julia v1.5. So define and export it only if it's
not defined already. We should consider not exporting it or instead
defining Compat.popat!, as simply exporting it may be breaking.

JuliaLang/julia#42080

Author: jonas-schulze

src/DataStructures.jl

@@ -5,6 +5,10 @@ module DataStructures
                 isbitsunion, isiterable, dict_with_eltype, KeySet, Callable, _tablesz,
                 findnextnot, unsafe_getindex, unsafe_setindex!, peek
 
+    if !isdefined(Base, :popat!)
+        export popat!
+    end
+
 
     using Compat # Provides Base.Order.ReverseOrdering(). May remove this line with julia 1.4
     using OrderedCollections

src/deprecations.jl

@@ -13,6 +13,6 @@ Base.@deprecate_binding IntDisjointSets IntDisjointSet
 @deprecate enqueue!(q::PriorityQueue, k, v) Base.push!(q, k=>v)
 @deprecate dequeue!(q::Queue) Base.popfirst!(q)
 @deprecate dequeue!(q::PriorityQueue) Base.popfirst!(q).first # maybe better: `val, _ = popfirst!(pq)`
-@deprecate dequeue!(q::PriorityQueue, x) Base.popat!(q, x).first
+@deprecate dequeue!(q::PriorityQueue, x) popat!(q, x).first
 @deprecate dequeue_pair!(q::PriorityQueue) Base.popfirst!(q)
-@deprecate dequeue_pair!(q::PriorityQueue, key) Base.popat!(q, key)
+@deprecate dequeue_pair!(q::PriorityQueue, key) popat!(q, key)

src/priorityqueue.jl

@@ -274,7 +274,13 @@ function Base.popfirst!(pq::PriorityQueue)
     return x
 end
 
-function Base.popat!(pq::PriorityQueue, key)
+if isdefined(Base, :popat!)
+    Base.popat!(pq::PriorityQueue, key) = _popat!(pq, key)
+else
+    popat!(pq::PriorityQueue, key) = _popat!(pq, key)
+end
+
+function _popat!(pq::PriorityQueue, key)
     idx = pq.index[key]
     force_up!(pq, idx)
     popfirst!(pq)