Support views on empty UnsafeArrays

.github/workflows/CompatHelper.yml

@@ -15,7 +15,7 @@ jobs:
         run: which julia
         continue-on-error: true
       - name: Install Julia, but only if it is not already available in the PATH
-        uses: julia-actions/setup-julia@v1
+        uses: julia-actions/setup-julia@v2
         with:
           version: '1'
           arch: ${{ runner.arch }}

.github/workflows/ci.yml

@@ -43,19 +43,21 @@ jobs:
             os: windows-latest
             arch: x64
     steps:
-      - uses: actions/checkout@v3
-      - uses: julia-actions/setup-julia@v1
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}
           arch: ${{ matrix.arch }}
-      - uses: julia-actions/cache@v1
+      - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
         with:
           coverage: ${{ matrix.version == '1' && matrix.os == 'ubuntu-latest' && matrix.arch == 'x64' }}
       - uses: julia-actions/julia-processcoverage@v1
         if: matrix.version == '1' && matrix.os == 'ubuntu-latest' && matrix.arch == 'x64'
-      - uses: codecov/codecov-action@v3
+      - uses: codecov/codecov-action@v4
         if: matrix.version == '1' && matrix.os == 'ubuntu-latest' && matrix.arch == 'x64'
         with:
+          fail_ci_if_error: true
+          token: ${{ secrets.CODECOV_TOKEN }}
           file: lcov.info

src/unsafe_array.jl

@@ -87,12 +87,20 @@ Base.@propagate_inbounds _unsafe_view_impl(IFwd::NTuple{M,Base.ViewIndex}, A::Un
     _unsafe_view_impl((IFwd..., i), A, I...)
 
 @inline function _unsafe_view_impl(IFwd::NTuple{M,Base.Slice}, A::UnsafeArray{T,N}, i::DenseIdx, I::Integer...) where {T,M,N}
+    ax_A = axes(A)
     @assert IFwd == ntuple(i -> axes(A)[i], Val{M}())
     I_all = (IFwd..., i, I...)
     @boundscheck checkbounds(A, I_all...)
     startidxs = map(first, (IFwd..., i, I...))
+    firstidxs = map(first, ax_A)
     sub_s = _sub_size(I_all...)
-    p = pointer(A, LinearIndices(size(A))[startidxs...])
+    A_isempty = length(A) == 0
+    view_isempty = prod(sub_s) == 0
+    # getindex on LinearIndices fails with startidxs if A is empty, so use pseudo-size in that case:
+    sz = size(A)
+    pseudo_sz = ntuple(_ -> 1, Val(N))
+    mod_size, mod_startidxs = ifelse(A_isempty && view_isempty, (pseudo_sz, firstidxs), (sz, startidxs))
+    p = pointer(A, LinearIndices(mod_size)[mod_startidxs...])
     UnsafeArray(p, sub_s)
 end
 

src/uview.jl

@@ -154,16 +154,23 @@ function Base.mightalias(A::UnsafeArray, B::AbstractArray)
         if typeof(B) <: UnsafeArray
             Base.mightalias(A, B)
         else
+            # Don't know if A and B might alias:
             false
         end
     end
 end
 
 Base.mightalias(A::AbstractArray, B::UnsafeArray) = Base.mightalias(B, A)
 
+# Need to specialize mightalias SubArrays of UnsafeArrays since the
+# default mightalias implementation returns false for all isbits types:
+
 Base.mightalias(A::SubArray{T,N,<:UnsafeArray}, B::AbstractArray) where {T,N} =
     Base.mightalias(parent(A), B)
 
+Base.mightalias(A::SubArray{T,N,<:UnsafeArray}, B::SubArray) where {T,N} =
+    Base.mightalias(parent(A), B)
+
 Base.mightalias(A::SubArray{T1,N1,<:UnsafeArray}, B::SubArray{T2,N2,<:UnsafeArray}) where {T1,N1,T2,N2} =
     Base.mightalias(parent(A), parent(B))
 
@@ -173,5 +180,8 @@ Base.mightalias(A::SubArray{T,N,<:UnsafeArray}, B::UnsafeArray) where {T,N} =
 Base.mightalias(A::AbstractArray, B::SubArray{T,N,<:UnsafeArray}) where {T,N} =
     Base.mightalias(B, A)
 
+Base.mightalias(A::SubArray, B::SubArray{T,N,<:UnsafeArray}) where {T,N} =
+    Base.mightalias(B, A)
+
 Base.mightalias(A::UnsafeArray, B::SubArray{T,N,<:UnsafeArray}) where {T,N} =
     Base.mightalias(B, A)

test/unsafe_array.jl

@@ -34,6 +34,13 @@ using Random
     end
 
 
+    function test_empty_A_UA(test_code::Function, ::Type{T}, Val_N::Val{N}) where {T, N}
+        A = rand(T, 0, fill(4, N-1)...)
+        UA = UnsafeArray(pointer(A), size(A))
+        UnsafeArrays.@gc_preserve A test_code(A, UA)
+    end
+
+
     @testset "ctors" begin
         test_A(Float64, Val(0)) do A
             ptr = pointer(A)
@@ -146,6 +153,11 @@ using Random
             @test isbits(view(UA, :, :, :)) == true
             @test isbits(view(UA, :, 3, :)) == true
         end
+
+        test_empty_A_UA(Float32, Val(2)) do A, UA
+            @test @inferred(view(UA, :, 2:3)) isa UnsafeArray
+            @test size(@inferred(view(UA, :, 2:3))) == (0, 2)
+        end
     end