retain size for zero length multidimensional arrays in mmap (#59719)

Fixes #44679

Co-authored-by: KristofferC <[email protected]>

Author: KristofferC

stdlib/Mmap/src/Mmap.jl

@@ -199,7 +199,7 @@ function mmap(io::IO,
         overflow && throw(ArgumentError("requested size prod($((len, dims...))) too large, would overflow typeof(size(T)) == $(typeof(len))"))
     end
     len >= 0 || throw(ArgumentError("requested size must be ≥ 0, got $len"))
-    len == 0 && return Array{T}(undef, ntuple(x->0,Val(N)))
+    len == 0 && return Array{T}(undef, dims)
     len < typemax(Int) - PAGESIZE || throw(ArgumentError("requested size must be < $(typemax(Int)-PAGESIZE), got $len"))
 
     offset >= 0 || throw(ArgumentError("requested offset must be ≥ 0, got $offset"))

stdlib/Mmap/test/runtests.jl

@@ -11,12 +11,13 @@ GC.gc(); GC.gc()
 GC.gc(); GC.gc()
 @test mmap(file, Array{UInt8,3}, (1,1,11)) == reshape(t,(1,1,11))
 GC.gc(); GC.gc()
-@test mmap(file, Array{UInt8,3}, (11,0,1)) == Array{UInt8}(undef, (0,0,0))
+@test size(mmap(file, Array{UInt8,3}, (11,0,1))) == (11,0,1)
 @test mmap(file, Vector{UInt8}, (11,)) == t
 GC.gc(); GC.gc()
 @test mmap(file, Array{UInt8,2}, (1,11)) == t'
 GC.gc(); GC.gc()
-@test mmap(file, Array{UInt8,2}, (0,12)) == Array{UInt8}(undef, (0,0))
+@test size(mmap(file, Array{UInt8,2}, (0,12))) == (0,12)
+@test size(mmap(file, Matrix{Float32}, (10,0))) == (10,0)
 m = mmap(file, Array{UInt8,3}, (1,2,1))
 @test m == reshape(b"He",(1,2,1))
 finalize(m); m=nothing; GC.gc()