Merge pull request #13695 from JuliaLang/jq/mmap_0_len

Allow 0-length arrays to be returned from Mmap.mmap. Fixes #10516

base/mmap.jl

@@ -99,7 +99,8 @@ function mmap{T,N}(io::IO,
     isbits(T)  || throw(ArgumentError("unable to mmap $T; must satisfy isbits(T) == true"))
 
     len = prod(dims) * sizeof(T)
-    len > 0 || throw(ArgumentError("requested size must be > 0, got $len"))
+    len >= 0 || throw(ArgumentError("requested size must be ≥ 0, got $len"))
+    len == 0 && return Array(T,ntuple(x->0,N))
     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"))

test/mmap.jl

@@ -11,12 +11,12 @@ gc(); gc()
 gc(); gc()
 @test Mmap.mmap(file, Array{UInt8,3}, (1,1,11)) == reshape(t,(1,1,11))
 gc(); gc()
-@test_throws ArgumentError Mmap.mmap(file, Array{UInt8,3}, (11,0,1)) # 0-dimension results in len=0
+@test Mmap.mmap(file, Array{UInt8,3}, (11,0,1)) == Array(UInt8,(0,0,0))
 @test Mmap.mmap(file, Vector{UInt8}, (11,)) == t
 gc(); gc()
 @test Mmap.mmap(file, Array{UInt8,2}, (1,11)) == t'
 gc(); gc()
-@test_throws ArgumentError Mmap.mmap(file, Array{UInt8,2}, (0,12))
+@test Mmap.mmap(file, Array{UInt8,2}, (0,12)) == Array(UInt8,(0,0))
 m = Mmap.mmap(file, Array{UInt8,3}, (1,2,1))
 @test m == reshape("He".data,(1,2,1))
 finalize(m); m=nothing; gc()
@@ -48,8 +48,8 @@ close(s)
 gc(); gc()
 
 s = open(f->f,file,"w")
-@test_throws ArgumentError Mmap.mmap(file) # requested len=0 on empty file
-@test_throws ArgumentError Mmap.mmap(file,Vector{UInt8},0)
+@test Mmap.mmap(file) == Array(UInt8, 0) # requested len=0 on empty file
+@test Mmap.mmap(file,Vector{UInt8},0) == Array(UInt8, 0)
 m = Mmap.mmap(file,Vector{UInt8},12)
 m[:] = "Hello World\n".data
 Mmap.sync!(m)
@@ -284,4 +284,4 @@ n = similar(m, (2,2))
 n = similar(m, 12)
 @test length(n) == 12
 @test size(n) == (12,)
-finalize(m); m = nothing; gc()
+finalize(m); m = nothing; gc()