Eagerly do boundscheck when indexing CartesianIndices with CartesianIndices (JuliaLang#42235)

Author: johnnychen94

base/multidimensional.jl

@@ -355,14 +355,19 @@ module IteratorsMD
     # CartesianIndices act as a multidimensional range, so cartesian indexing of CartesianIndices
     # with compatible dimensions may be seen as indexing into the component ranges.
     # This may use the special indexing behavior implemented for ranges to return another CartesianIndices
-    @propagate_inbounds function Base.getindex(iter::CartesianIndices{N,R},
+    @inline function Base.getindex(iter::CartesianIndices{N,R},
         I::Vararg{Union{OrdinalRange{<:Integer, <:Integer}, Colon}, N}) where {N,R}
-        CartesianIndices(getindex.(iter.indices, I))
+        @boundscheck checkbounds(iter, I...)
+        indices = map(iter.indices, I) do r, i
+            @inbounds getindex(r, i)
+        end
+        CartesianIndices(indices)
     end
     @propagate_inbounds function Base.getindex(iter::CartesianIndices{N},
         C::CartesianIndices{N}) where {N}
-        CartesianIndices(getindex.(iter.indices, C.indices))
+        getindex(iter, C.indices...)
     end
+    @inline Base.getindex(iter::CartesianIndices{0}, ::CartesianIndices{0}) = iter
 
     # If dimensions permit, we may index into a CartesianIndices directly instead of constructing a SubArray wrapper
     @propagate_inbounds function Base.view(c::CartesianIndices{N}, r::Vararg{Union{OrdinalRange{<:Integer, <:Integer}, Colon},N}) where {N}

test/boundscheck_exec.jl

@@ -260,6 +260,7 @@ if bc_opt == bc_default || bc_opt == bc_off
 end
 
 @testset "pass inbounds meta to getindex on CartesianIndices (#42115)" begin
+    @inline getindex_42115(r, i) = @inbounds getindex(r, i)
     @inline getindex_42115(r, i, j) = @inbounds getindex(r, i, j)
 
     R = CartesianIndices((5, 5))
@@ -270,6 +271,14 @@ end
         @test getindex_42115(R, -1, -1) == CartesianIndex(-1, -1)
         @test getindex_42115(R, 1, -1) == CartesianIndex(1, -1)
     end
+
+    if bc_opt == bc_on
+        @test_throws BoundsError getindex_42115(R, CartesianIndices((6, 6)))
+        @test_throws BoundsError getindex_42115(R, -1:3, :)
+    else
+        @test getindex_42115(R, CartesianIndices((6, 6))) == CartesianIndices((6, 6))
+        @test getindex_42115(R, -1:3, :) == CartesianIndices((-1:3, 1:5))
+    end
 end