Cover all implementations of getindex(::AbstractRange,...)

Author: mbauman

base/subarray.jl

@@ -164,7 +164,7 @@ function view(A::AbstractArray, I::Vararg{Any,N}) where {N}
     unsafe_view(_maybe_reshape_parent(A, index_ndims(J...)), J...)
 end
 
-# Ranges tend to be compact & immutable
+# Ranges implement getindex to return recomputed ranges; use that for views, too (when possible)
 function view(r1::OneTo, r2::OneTo)
     @_propagate_inbounds_meta
     getindex(r1, r2)
@@ -181,6 +181,14 @@ function view(r1::StepRange, r2::AbstractRange{<:Integer})
     @_propagate_inbounds_meta
     getindex(r1, r2)
 end
+function view(r1::StepRangeLen, r2::OrdinalRange{<:Integer})
+    @_propagate_inbounds_meta
+    getindex(r1, r2)
+end
+function view(r1::LinRange, r2::OrdinalRange{<:Integer})
+    @_propagate_inbounds_meta
+    getindex(r1, r2)
+end
 
 function unsafe_view(A::AbstractArray, I::Vararg{ViewIndex,N}) where {N}
     @_inline_meta

test/ranges.jl

@@ -1368,6 +1368,15 @@ end
     @test view(1:10, 1:5) === 1:5
     @test view(1:10, 1:2:5) === 1:2:5
     @test view(1:2:9, 1:5) === 1:2:9
+
+    # Ensure we don't hit a fallback `view` if there's a better `getindex` implementation
+    vmt = collect(methods(view, Tuple{AbstractRange, AbstractRange}))
+    for m in methods(getindex, Tuple{AbstractRange, AbstractRange})
+        tt = Base.tuple_type_tail(m.sig)
+        tt == Tuple{AbstractArray,Vararg{Any,N}} where N && continue
+        vm = findfirst(sig->tt <: Base.tuple_type_tail(sig.sig), vmt)
+        @test vmt[vm].sig != Tuple{typeof(view),AbstractArray,Vararg{Any,N}} where N
+    end
 end
 
 @testset "Issue #26608" begin