Revert "fix it and remove global check"

This reverts commit 17b4411.

Author: oxinabox

docs/src/index.md

@@ -9,6 +9,12 @@ For information about ChainRules, including how to write rules, refer to the gen
 [![](https://img.shields.io/badge/docs-main-blue.svg)](https://JuliaDiff.github.io/ChainRulesCore.jl/dev)
 [![](https://img.shields.io/badge/docs-stable-blue.svg)](https://JuliaDiff.github.io/ChainRulesCore.jl/stable)
 
+## Testing Method Table Sensibility
+A basic feature of ChainRulesTestUtils is its ability to check that the method tables for `rrule` and `frule` remain sensible.
+This searches the method tables for methods that should not exist and when it fails tells you where they were defined.
+By calling [`test_method_tables`](@ref) ChainRulesTestUtils will check for things such as having attracted a rule to `DataType` rather than attaching it to a constructor.
+Basically all packages using ChainRulesTestUtils can use [`test_method_tables`](@ref), as it is independent of what rules you have written.
+
 ## Canonical example of testing frule and rrule
 
 Let's suppose a custom transformation has been defined

src/ChainRulesTestUtils.jl

@@ -28,10 +28,10 @@ include("iterator.jl")
 
 include("output_control.jl")
 include("check_result.jl")
-include("method_checks.jl")
 
 include("rule_config.jl")
 include("finite_difference_calls.jl")
 include("testers.jl")
 
+include("global_checks.jl")
 end # module

src/method_checks.jl renamed to src/global_checks.jl

@@ -26,8 +26,7 @@ function test_method_signature(::typeof(rrule), method::Method)
         function_type = if method.sig <: Tuple{Any, RuleConfig, Type, Vararg}
             _parameters(method.sig)[3]
         elseif method.sig <: Tuple{Any, Type, Vararg}
-            _parameters(method.sig)[2]
-        else
+            _parameters(method.sig)else
             nothing
         end
 
@@ -54,3 +53,29 @@ function test_method_signature(::typeof(frule), method::Method)
         )
     end
 end
+
+"""
+    test_method_tables()
+
+Checks that the method tables for `rrule` and `frule` are sensible.
+This in future may carry out a number of checks, but presently just checks to make sure that
+no rules have been added to the very general `DataType`, `Union` or `UnionAll` types,
+which is easy to do accidentally when writing rules for constructors.
+It happens if you write e.g. `rrule(::typeof(Foo), x)` rather than `rrule(::Type{<:Foo}, x)`.
+This would then actually define `rrule(::DataType, x)`. (or `UnionAll` if `Foo`
+was parametric, or `Union` if `Foo` was a type alias for a `Union`)
+"""
+function test_method_tables()
+    @testset "Sensible Constructors" begin
+        # if someone wrote e.g. `rrule(::typeof(Foo), x)` rather than
+        # `rrule(::Type{<:Foo}, x)` then that would actually define `rrule(::DataType, x)`
+        # which would be bad. This test checks for that and fails if such a method exists.
+        for method in methods(rrule)
+            test_method_signature(method)
+        end
+        # frule
+        for method in methods(frule)
+            test_method_signature(frule, method)
+        end
+    end
+end

test/global_checks.jl

@@ -0,0 +1,34 @@
+struct BadConstructor
+    x
+end
+
+if VERSION >= v"1.3"
+    @testset "global_checks.jl" begin
+        test_method_tables()
+        ChainRulesCore.rrule(::typeof(BadConstructor), x) = nothing
+        @test fails(test_method_tables)
+        Base.delete_method(Base.which(rrule, (DataType, Any)))
+        test_method_tables()  # make sure delete worked
+
+        ChainRulesCore.rrule(::RuleConfig, ::typeof(BadConstructor), x) = nothing
+        @test fails(test_method_tables)
+        Base.delete_method(Base.which(rrule, (RuleConfig, DataType, Any)))
+        test_method_tables()  # make sure delete worked
+
+
+
+        ChainRulesCore.frule(::Any, ::typeof(BadConstructor), x) = nothing
+        @test fails(test_method_tables)
+        Base.delete_method(Base.which(frule, (Any, DataType, Any)))
+        test_method_tables()  # make sure delete worked
+
+        ChainRulesCore.frule(::RuleConfig, ::Any, ::typeof(BadConstructor), x) = nothing
+        @test fails(test_method_tables)
+        Base.delete_method(Base.which(frule, (RuleConfig, Any, DataType, Any)))
+        test_method_tables()  # make sure delete worked
+    end
+else # pre 1.3, so no `delete_method` so just test happy path
+    @testset "global_checks.jl" begin
+        test_method_tables()
+    end
+end

test/method_checks.jl

@@ -17,5 +17,5 @@ ChainRulesTestUtils.TEST_INFERRED[] = true
     include("data_generation.jl")
     include("rand_tangent.jl")
 
-    include("method_checks.jl")
+    include("global_checks.jl")
 end