Make @opt_out rrule(...) automatically qualify rrule namespace as…

… `ChainRulesCore.rrule` (#546)

src/rule_definition_tools.jl

@@ -490,34 +490,45 @@ Similar applies for [`frule`](@ref) and [`ChainRulesCore.no_frule`](@ref)
 For more information see the [documentation on opting out of rules](@ref opt_out).
 """
 macro opt_out(expr)
-    no_rule_target = _no_rule_target_rewrite!(deepcopy(expr))
+    no_rule_target = _target_rewrite!(deepcopy(expr), true)
+    rule_target = _target_rewrite!(deepcopy(expr), false)
 
     return @strip_linenos quote
         $(esc(no_rule_target)) = nothing
-        $(esc(expr)) = nothing
+        $(esc(rule_target)) = nothing
     end
 end
 
-"Rewrite method sig Expr for `rrule` to be for `no_rrule`, and `frule` to be `no_frule`."
-function _no_rule_target_rewrite!(expr::Expr)
+"""
+    _target_rewrite!(expr::Expr, no_rule)
+
+Rewrite method sig `expr` for `rrule` to be for `no_rrule` or `ChainRulesCore.rrule`
+(with the CRC namespace qualification), depending on the `no_rule` argument.
+Does the equivalent for `frule`.
+"""
+function _target_rewrite!(expr::Expr, no_rule)
     length(expr.args) === 0 && error("Malformed method expression. $expr")
     if expr.head === :call || expr.head === :where
-        expr.args[1] = _no_rule_target_rewrite!(expr.args[1])
+        expr.args[1] = _target_rewrite!(expr.args[1], no_rule)
     elseif expr.head == :(.) && expr.args[1] == :ChainRulesCore
-        expr = _no_rule_target_rewrite!(expr.args[end])
+        expr = _target_rewrite!(expr.args[end], no_rule)
     else
         error("Malformed method expression. $(expr)")
     end
     return expr
 end
-_no_rule_target_rewrite!(qt::QuoteNode) = _no_rule_target_rewrite!(qt.value)
-function _no_rule_target_rewrite!(call_target::Symbol)
-    return if call_target == :rrule
-        :(ChainRulesCore.no_rrule)
-    elseif call_target == :frule
-        :(ChainRulesCore.no_frule)
+_target_rewrite!(qt::QuoteNode, no_rule) = _target_rewrite!(qt.value, no_rule)
+function _target_rewrite!(call_target::Symbol, no_rule)
+    return if call_target == :rrule && no_rule
+        :($ChainRulesCore.no_rrule)
+    elseif call_target == :rrule && !no_rule
+        :($ChainRulesCore.rrule)
+    elseif call_target == :frule && no_rule
+        :($ChainRulesCore.no_frule)
+    elseif call_target == :frule && !no_rule
+        :($ChainRulesCore.frule)
     else
-        error("Unexpected opt-out target. Exprected frule or rrule, got: $call_target")
+        error("Unexpected opt-out target. Expected frule or rrule, got: $call_target")
     end
 end
 

test/rule_definition_tools.jl

@@ -285,7 +285,7 @@ end
 # workaround for https://github.com/domluna/JuliaFormatter.jl/issues/484
 module IsolatedModuleForTestingScoping
     # check that rules can be defined by macros without any additional imports
-    using ChainRulesCore: @scalar_rule, @non_differentiable
+    using ChainRulesCore: @scalar_rule, @non_differentiable, @opt_out
 
     # ensure that functions, types etc. in module `ChainRulesCore` can't be resolved
     const ChainRulesCore = nothing
@@ -303,11 +303,20 @@ module IsolatedModuleForTestingScoping
     my_id(x) = x
     @scalar_rule(my_id(x), 1.0)
 
+    # @opt_out
+    first_oa(x, y) = x
+    @scalar_rule(first_oa(x, y), (1, 0))
+    # Declared without using the ChainRulesCore namespace qualification
+    # see https://github.com/JuliaDiff/ChainRulesCore.jl/issues/545
+    @opt_out rrule(::typeof(first_oa), x::T, y::T) where {T<:Float16}
+    @opt_out frule(::Any, ::typeof(first_oa), x::T, y::T) where {T<:Float16}
+
     module IsolatedSubmodule
         # check that rules defined in isolated module without imports can be called
         # without errors
         using ChainRulesCore: frule, rrule, ZeroTangent, NoTangent, derivatives_given_output
-        using ..IsolatedModuleForTestingScoping: fixed, fixed_kwargs, my_id
+        using ChainRulesCore: no_rrule, no_frule
+        using ..IsolatedModuleForTestingScoping: fixed, fixed_kwargs, my_id, first_oa
         using Test
 
         @testset "@non_differentiable" begin
@@ -339,6 +348,25 @@ module IsolatedModuleForTestingScoping
 
             @test derivatives_given_output(y, my_id, x) == ((1.0,),)
         end
+
+        @testset "@optout" begin
+            # rrule
+            @test rrule(first_oa, Float16(3.0), Float16(4.0)) === nothing
+            @test !isempty(
+                Iterators.filter(methods(no_rrule)) do m
+                    m.sig <: Tuple{Any,typeof(first_oa),T,T} where {T<:Float16}
+                end,
+            )
+
+            # frule
+            @test frule((NoTangent(), 1, 0), first_oa, Float16(3.0), Float16(4.0)) ===
+                nothing
+            @test !isempty(
+                Iterators.filter(methods(no_frule)) do m
+                    m.sig <: Tuple{Any,Any,typeof(first_oa),T,T} where {T<:Float16}
+                end,
+            )
+        end
     end
 end
 #! format: on