fix setindex(::ReinterpretArray,...) for zero-d arrays (#58868)

by copying the way getindex works.

Found in
#58814 (comment)

---------

Co-authored-by: Andy Dienes <[email protected]>

Author: mbauman

base/reinterpretarray.jl

@@ -412,7 +412,7 @@ end
     # Convert to full indices here, to avoid needing multiple conversions in
     # the loop in _getindex_ra
     inds = _to_subscript_indices(a, i)
-    isempty(inds) ? _getindex_ra(a, 1, ()) : _getindex_ra(a, inds[1], tail(inds))
+    isempty(inds) ? _getindex_ra(a, firstindex(a), ()) : _getindex_ra(a, inds[1], tail(inds))
 end
 
 @propagate_inbounds function getindex(a::ReshapedReinterpretArray{T,N,S}, ind::SCartesianIndex2) where {T,N,S}
@@ -556,7 +556,7 @@ end
         return _setindex_ra!(a, v, i, ())
     end
     inds = _to_subscript_indices(a, i)
-    _setindex_ra!(a, v, inds[1], tail(inds))
+    isempty(inds) ? _setindex_ra!(a, v, firstindex(a), ()) : _setindex_ra!(a, v, inds[1], tail(inds))
 end
 
 @propagate_inbounds function setindex!(a::ReshapedReinterpretArray{T,N,S}, v, ind::SCartesianIndex2) where {T,N,S}

test/reinterpretarray.jl

@@ -160,6 +160,16 @@ test_many_wrappers(A3) do A3_
     @test A3[2,1,2] == 400
 end
 
+test_many_wrappers(C) do Cr
+    r = reinterpret(reshape, Tuple{Int, Int}, Cr)
+    r[] = (2,2)
+    @test r[] === (2,2)
+    r[1] = (3,3)
+    @test r[1] === (3,3)
+    r[1,1] = (4,4)
+    @test r[1,1] === (4,4)
+end
+
 # same-size reinterpret where one of the types is non-primitive
 let a = NTuple{4,UInt8}[(0x01,0x02,0x03,0x04)]
     test_many_wrappers(a, (identity, wrapper, fcviews)) do a_