fix division return type (#233)

* fix division

* add tests

* more tests; relax hypot types

* fixes

* fix tests

* use oftype; use one(x)

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "0.7.7"
+version = "0.7.8"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/rulesets/Base/base.jl

@@ -138,7 +138,7 @@ end
  ),
  (!(islow | ishigh), islow, ishigh),
 )
-@scalar_rule x \ y (-((y / x) / x), inv(x))
+@scalar_rule x \ y (-(Ω / x), one(y) / x)
 
 function frule((_, ẏ), ::typeof(identity), x)
  return (x, ẏ)

src/rulesets/Base/fastmath_able.jl

@@ -133,15 +133,15 @@ let
 
  @scalar_rule x + y (One(), One())
  @scalar_rule x - y (One(), -1)
- @scalar_rule x / y (inv(y), -((x / y) / y))
+ @scalar_rule x / y (one(x) / y, -(Ω / y))
  #log(complex(x)) is required so it gives correct complex answer for x<0
  @scalar_rule(x ^ y,
  (ifelse(iszero(x), zero(Ω), y * Ω / x), Ω * log(complex(x))),
  )
  # x^y for x < 0 errors when y is not an integer, but then derivative wrt y
  # is undefined, so we adopt subgradient convention and set derivative to 0.
  @scalar_rule(x::Real ^ y::Real,
- (ifelse(iszero(x), zero(Ω), y * Ω / x), Ω * log(ifelse(x ≤ 0, one(x), x))),
+ (ifelse(iszero(x), zero(Ω), y * Ω / x), Ω * log(oftype(Ω, ifelse(x ≤ 0, one(x), x)))),
  )
  @scalar_rule(
  rem(x, y),

test/rulesets/Base/fastmath_able.jl

@@ -137,7 +137,29 @@ const FASTABLE_AST = quote
  Δz = randn(typeof(f(x, y)))
 
  frule_test(f, (x, Δx), (y, Δy))
- rrule_test(f, Δz, (x, x̄), (y, ȳ))
+ rrule_test(f, Δz, (x, x̄), (y, ȳ)) 
+ end
+
+ @testset "$f(x::$T, y::$T) type check" for f in (/, +, -,\, hypot, ^), T in (Float32, Float64)
+ x, Δx, x̄ = 10rand(T, 3)
+ y, Δy, ȳ = rand(T, 3)
+ @assert T == typeof(f(x, y))
+ Δz = randn(typeof(f(x, y)))
+
+ @test frule((Zero(), Δx, Δy), f, x, y) isa Tuple{T, T}
+ _, ∂x, ∂y = rrule(f, x, y)[2](Δz)
+ @test extern.((∂x, ∂y)) isa Tuple{T, T}
+
+ if f != hypot
+ # Issue #233 
+ @test frule((Zero(), Δx, Δy), f, x, 2) isa Tuple{T, T}
+ _, ∂x, ∂y = rrule(f, x, 2)[2](Δz)
+ @test extern.((∂x, ∂y)) isa Tuple{T, T}
+
+ @test frule((Zero(), Δx, Δy), f, 2, y) isa Tuple{T, T}
+ _, ∂x, ∂y = rrule(f, 2, y)[2](Δz)
+ @test extern.((∂x, ∂y)) isa Tuple{T, T}
+ end
  end
 
  @testset "^(x::$T, n::$T)" for T in (Float64, ComplexF64)