Add test

Author: pxl-th

test/rulesets/Base/indexing.jl

@@ -261,4 +261,17 @@ end
         Val(3);
         check_inferred=(VERSION >= v"1.7"),
     )
+
+    # eachslice: Make sure pulling back an array of thunks unthunks them and does not return all zeros.
+    x = ones(Float32, 3)
+    Δ = ones(Float32, 1)
+    _, norm_back = ChainRules.rrule(norm, x)
+    dx = norm_back(Δ)[2]
+    @test dx isa AbstractThunk
+
+    x = ones(Float32, 3, 1)
+    _, eachcol_back = ChainRules.rrule(eachcol, x)
+    Δ2 = [dx]
+    dx2 = eachcol_back(Δ2)[2]
+    @test all(dx2 .≉ 0f0)
 end