delete_method: remove method from any pre-existing ambiguities (fixes #…

…28899)

base/reflection.jl

@@ -1076,6 +1076,15 @@ Make method `m` uncallable and force recompilation of any methods that use(d) it
 """
 function delete_method(m::Method)
     ccall(:jl_method_table_disable, Cvoid, (Any, Any), get_methodtable(m), m)
+    if m.ambig !== nothing
+        for m2 in m.ambig
+            if m2.ambig !== nothing
+                i = findfirst(isequal(m), m2.ambig)
+                i === nothing || deleteat!(m2.ambig, i)
+            end
+        end
+    end
+    nothing
 end
 
 function get_methodtable(m::Method)

test/reflection.jl

@@ -764,6 +764,18 @@ Base.delete_method(first(methods(foo)))
 @test_throws MethodError foo(1, 1)
 @test map(g->g.ambig==nothing, methods(foo)) == [false, false]
 
+# pre-existing ambiguities (#28899)
+uambig(::Union{Nothing,Int}) = 1
+uambig(::Union{Nothing,Float64}) = 2
+@test uambig(1) == 1
+@test uambig(1.0) == 2
+@test_throws MethodError uambig(nothing)
+m = which(uambig, Tuple{Int})
+Base.delete_method(m)
+@test_throws MethodError uambig(1)
+@test uambig(1.0) == 2
+@test uambig(nothing) == 2
+
 # multiple deletions and ambiguities
 typeparam(::Type{T}, a::Array{T}) where T<:AbstractFloat = 1
 typeparam(::Type{T}, a::Array{T}) where T = 2