ml-matches: ensure all methods are included

Some methods were filtered out based simply on visit order, which was
not intentional, with the lim==-1 weak-edges mode.

Fix #55231

Author: vtjnash

src/gf.c

@@ -3669,7 +3669,7 @@ static int sort_mlmatches(jl_array_t *t, size_t idx, arraylist_t *visited, array
         int msp2 = !msp && jl_method_morespecific(m2, m);
         if (!msp) {
             if (subt || !include_ambiguous || (lim != -1 && msp2)) {
-                if (subt2 || jl_subtype((jl_value_t*)ti, m2->sig)) {
+                if (subt2 || ((lim != -1 || (!include_ambiguous && !msp2)) && jl_subtype((jl_value_t*)ti, m2->sig))) {
                     // this may be filtered out as fully intersected, if applicable later
                     mayexclude = 1;
                 }

test/ambiguous.jl

@@ -447,4 +447,20 @@ cc46601(::Type{T}, x::Int) where {T<:AbstractString} = 7
 @test length(methods(cc46601, Tuple{Type{<:Integer}, Integer})) == 2
 @test length(Base.methods_including_ambiguous(cc46601, Tuple{Type{<:Integer}, Integer})) == 7
 
+# Issue #55231
+struct U55231{P} end
+struct V55231{P} end
+U55231(::V55231) = nothing
+(::Type{T})(::V55231) where {T<:U55231} = nothing
+@test length(methods(U55231)) == 2
+U55231(a, b) = nothing
+@test length(methods(U55231)) == 3
+struct S55231{P} end
+struct T55231{P} end
+(::Type{T})(::T55231) where {T<:S55231} = nothing
+S55231(::T55231) = nothing
+@test length(methods(S55231)) == 2
+S55231(a, b) = nothing
+@test length(methods(S55231)) == 3
+
 nothing