fix collect on stateful iterators

Generalization of #41919
Fixes #42168

Author: vtjnash

base/array.jl

@@ -643,23 +643,38 @@ julia> collect(Float64, 1:2:5)
 """
 collect(::Type{T}, itr) where {T} = _collect(T, itr, IteratorSize(itr))
 
-_collect(::Type{T}, itr, isz::HasLength) where {T} = copyto!(Vector{T}(undef, Int(length(itr)::Integer)), itr)
-_collect(::Type{T}, itr, isz::HasShape) where {T}  = copyto!(similar(Array{T}, axes(itr)), itr)
+_collect(::Type{T}, itr, isz::Union{HasLength,HasShape}) where {T} =
+    copyto!(_array_for(T, isz, _similar_shape(itr, isz)), itr)
 function _collect(::Type{T}, itr, isz::SizeUnknown) where T
     a = Vector{T}()
     for x in itr
-        push!(a,x)
+        push!(a, x)
     end
     return a
 end
 
 # make a collection similar to `c` and appropriate for collecting `itr`
-_similar_for(c::AbstractArray, ::Type{T}, itr, ::SizeUnknown) where {T} = similar(c, T, 0)
-_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasLength) where {T} =
-    similar(c, T, Int(length(itr)::Integer))
-_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasShape) where {T} =
-    similar(c, T, axes(itr))
-_similar_for(c, ::Type{T}, itr, isz) where {T} = similar(c, T)
+_similar_for(c, ::Type{T}, itr, isz, shp) where {T} = similar(c, T)
+
+_similar_shape(itr, ::SizeUnknown) = nothing
+_similar_shape(itr, ::HasLength) = length(itr)::Integer
+_similar_shape(itr, ::HasShape) = axes(itr)
+
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::SizeUnknown, ::Nothing) where {T} =
+    similar(c, T, 0)
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasLength, len::Integer) where {T} =
+    similar(c, T, len)
+_similar_for(c::AbstractArray, ::Type{T}, itr, ::HasShape, axs) where {T} =
+    similar(c, T, axs)
+
+# make a collection appropriate for collecting `itr::Generator`
+_array_for(::Type{T}, ::SizeUnknown, ::Nothing) where {T} = Vector{T}(undef, 0)
+_array_for(::Type{T}, ::HasLength, len::Integer) where {T} = Vector{T}(undef, Int(len))
+_array_for(::Type{T}, ::HasShape{N}, axs) where {T,N} = similar(Array{T,N}, axs)
+
+# used by syntax lowering for simple typed comprehensions
+_array_for(::Type{T}, itr, isz) where {T} = _array_for(T, isz, _similar_shape(itr, isz))
+
 
 """
     collect(collection)
@@ -698,10 +713,10 @@ collect(A::AbstractArray) = _collect_indices(axes(A), A)
 collect_similar(cont, itr) = _collect(cont, itr, IteratorEltype(itr), IteratorSize(itr))
 
 _collect(cont, itr, ::HasEltype, isz::Union{HasLength,HasShape}) =
-    copyto!(_similar_for(cont, eltype(itr), itr, isz), itr)
+    copyto!(_similar_for(cont, eltype(itr), itr, isz, _similar_shape(itr, isz)), itr)
 
 function _collect(cont, itr, ::HasEltype, isz::SizeUnknown)
-    a = _similar_for(cont, eltype(itr), itr, isz)
+    a = _similar_for(cont, eltype(itr), itr, isz, nothing)
     for x in itr
         push!(a,x)
     end
@@ -759,24 +774,19 @@ else
     end
 end
 
-_array_for(::Type{T}, itr, isz::HasLength) where {T} = _array_for(T, itr, isz, length(itr))
-_array_for(::Type{T}, itr, isz::HasShape{N}) where {T,N} = _array_for(T, itr, isz, axes(itr))
-_array_for(::Type{T}, itr, ::HasLength, len) where {T} = Vector{T}(undef, len)
-_array_for(::Type{T}, itr, ::HasShape{N}, axs) where {T,N} = similar(Array{T,N}, axs)
-
 function collect(itr::Generator)
     isz = IteratorSize(itr.iter)
     et = @default_eltype(itr)
     if isa(isz, SizeUnknown)
         return grow_to!(Vector{et}(), itr)
     else
-        shape = isz isa HasLength ? length(itr) : axes(itr)
+        shp = _similar_shape(itr, isz)
         y = iterate(itr)
         if y === nothing
-            return _array_for(et, itr.iter, isz)
+            return _array_for(et, isz, shp)
         end
         v1, st = y
-        dest = _array_for(typeof(v1), itr.iter, isz, shape)
+        dest = _array_for(typeof(v1), isz, shp)
         # The typeassert gives inference a helping hand on the element type and dimensionality
         # (work-around for #28382)
         et′ = et <: Type ? Type : et
@@ -786,15 +796,22 @@ function collect(itr::Generator)
 end
 
 _collect(c, itr, ::EltypeUnknown, isz::SizeUnknown) =
-    grow_to!(_similar_for(c, @default_eltype(itr), itr, isz), itr)
+    grow_to!(_similar_for(c, @default_eltype(itr), itr, isz, nothing), itr)
 
 function _collect(c, itr, ::EltypeUnknown, isz::Union{HasLength,HasShape})
+    et = @default_eltype(itr)
+    shp = _similar_shape(itr, isz)
     y = iterate(itr)
     if y === nothing
-        return _similar_for(c, @default_eltype(itr), itr, isz)
+        return _similar_for(c, et, itr, isz, shp)
     end
     v1, st = y
-    collect_to_with_first!(_similar_for(c, typeof(v1), itr, isz), v1, itr, st)
+    dest = _similar_for(c, typeof(v1), itr, isz, shp)
+    # The typeassert gives inference a helping hand on the element type and dimensionality
+    # (work-around for #28382)
+    et′ = et <: Type ? Type : et
+    RT = dest isa AbstractArray ? AbstractArray{<:et′, ndims(dest)} : Any
+    collect_to_with_first!(dest, v1, itr, st)::RT
 end
 
 function collect_to_with_first!(dest::AbstractArray, v1, itr, st)

base/dict.jl

@@ -826,6 +826,6 @@ length(t::ImmutableDict) = count(Returns(true), t)
 isempty(t::ImmutableDict) = !isdefined(t, :parent)
 empty(::ImmutableDict, ::Type{K}, ::Type{V}) where {K, V} = ImmutableDict{K,V}()
 
-_similar_for(c::Dict, ::Type{Pair{K,V}}, itr, isz) where {K, V} = empty(c, K, V)
-_similar_for(c::AbstractDict, ::Type{T}, itr, isz) where {T} =
+_similar_for(c::AbstractDict, ::Type{Pair{K,V}}, itr, isz, len) where {K, V} = empty(c, K, V)
+_similar_for(c::AbstractDict, ::Type{T}, itr, isz, len) where {T} =
     throw(ArgumentError("for AbstractDicts, similar requires an element type of Pair;\n  if calling map, consider a comprehension instead"))

base/set.jl

@@ -44,7 +44,7 @@ empty(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()
 # by default, a Set is returned
 emptymutable(s::AbstractSet{T}, ::Type{U}=T) where {T,U} = Set{U}()
 
-_similar_for(c::AbstractSet, ::Type{T}, itr, isz) where {T} = empty(c, T)
+_similar_for(c::AbstractSet, ::Type{T}, itr, isz, len) where {T} = empty(c, T)
 
 function show(io::IO, s::Set)
     if isempty(s)

src/julia-syntax.scm

@@ -2734,7 +2734,7 @@
   (check-no-return expr)
   (if (has-break-or-continue? expr)
       (error "break or continue outside loop"))
-  (let ((result    (gensy))
+  (let ((result    (make-ssavalue))
         (idx       (gensy))
         (oneresult (make-ssavalue))
         (prod      (make-ssavalue))
@@ -2758,16 +2758,14 @@
     (let ((overall-itr (if (length= itrs 1) (car iv) prod)))
       `(scope-block
         (block
-         (local ,result) (local ,idx)
+         (local ,idx)
          ,.(map (lambda (v r) `(= ,v ,(caddr r))) iv itrs)
          ,.(if (length= itrs 1)
                '()
                `((= ,prod (call (top product) ,@iv))))
          (= ,isz (call (top IteratorSize) ,overall-itr))
          (= ,szunk (call (core isa) ,isz (top SizeUnknown)))
-         (if ,szunk
-             (= ,result (call (curly (core Array) ,ty 1) (core undef) 0))
-             (= ,result (call (top _array_for) ,ty ,overall-itr ,isz)))
+         (= ,result (call (top _array_for) ,ty ,overall-itr ,isz))
          (= ,idx (call (top first) (call (top LinearIndices) ,result)))
          ,(construct-loops (reverse itrs) (reverse iv))
          ,result)))))

test/iterators.jl

@@ -293,11 +293,14 @@ let (a, b) = (1:3, [4 6;
 end
 
 # collect stateful iterator
-let
-    itr = (i+1 for i in Base.Stateful([1,2,3]))
+let itr
+    itr = Iterators.Stateful(Iterators.map(identity, 1:5))
+    @test collect(itr) == 1:5
+    @test collect(itr) == Int[] # Stateful do not preserve shape
+    itr = (i+1 for i in Base.Stateful([1, 2, 3]))
     @test collect(itr) == [2, 3, 4]
-    A = zeros(Int, 0, 0)
-    itr = (i-1 for i in Base.Stateful(A))
+    @test collect(itr) == Int[] # Stateful do not preserve shape
+    itr = (i-1 for i in Base.Stateful(zeros(Int, 0, 0)))
     @test collect(itr) == Int[] # Stateful do not preserve shape
 end