properly support offset indices

src/array-lib.jl

@@ -22,12 +22,12 @@ function Base.getindex(x::SymArray, idx...)
     meta = metadata(unwrap(x))
     if shape(x) !== Unknown() && all(i -> i isa Integer, idx)
         II = CartesianIndices(axes(x))
+        ii = CartesianIndex(idx)
         @boundscheck begin
-            if !checkbounds(Bool, II, idx...)
+            if !in(ii, II)
                 throw(BoundsError(x, idx))
             end
         end
-        ii = II[idx...]
         res = Term{eltype(symtype(x))}(getindex, [x, Tuple(ii)...]; metadata = meta)
     elseif all(i -> symtype(i) <: Integer, idx)
         shape(x) !== Unknown() && @boundscheck begin

src/arrays.jl

@@ -526,7 +526,7 @@ end
 function axes(A::Union{Arr, SymArray})
     s = shape(unwrap(A))
     s === Unknown() && error("axes of $A not known")
-    return map(x->1:length(x), s)
+    return s
 end
 
 

test/arrays.jl

@@ -393,3 +393,19 @@ end
     @test !isequal(a, b) && !isequal(b, c) && !isequal(a, c)
     @test hash(a) != hash(b) && hash(b) != hash(c) && hash(a) != hash(c)
 end
+
+@testset "Offset Indices" begin
+    @variables k[0:3]
+
+    @testset "i = $i" for i in 0:3
+        sym = unwrap(k[i])
+        @test operation(sym) === getindex
+        args = arguments(sym)
+        @test length(args) == 2
+        @test args[1] === unwrap(k)
+        @test args[2] === i
+    end
+
+    @test_throws BoundsError k[-1]
+    @test_throws BoundsError k[4]
+end