ml-matches: using relaxed sorting when unlimited

If we're attempting to apply limits to the results, then it is generally better and faster to use more accurate sorting. Otherwise, approximate sorting should be sufficient and much faster.
JuliaLang · Oct 19, 2020 · 12328e2 · 12328e2
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commit 12328e2
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diff --git a/doc/src/manual/methods.md b/doc/src/manual/methods.md
@@ -252,8 +252,8 @@ julia> g(2, 3.0)
 
 julia> g(2.0, 3.0)
 ERROR: MethodError: g(::Float64, ::Float64) is ambiguous. Candidates:
-  g(x, y::Float64) in Main at none:1
   g(x::Float64, y) in Main at none:1
+  g(x, y::Float64) in Main at none:1
 Possible fix, define
   g(::Float64, ::Float64)
 ```

diff --git a/src/gf.c b/src/gf.c
@@ -2815,10 +2815,20 @@ static jl_value_t *ml_matches(jl_methtable_t *mt, int offs,
                 int subt2 = matc2->fully_covers != NOT_FULLY_COVERS;
                 if (!subt2 && subt)
                     break;
-                if (subt == subt2)
-                    if (subt || !jl_has_empty_intersection(m->sig, m2->sig))
-                        if (!jl_type_morespecific((jl_value_t*)m->sig, (jl_value_t*)m2->sig))
+                if (subt == subt2) {
+                    if (lim >= 0) {
+                        if (subt || !jl_has_empty_intersection(m->sig, m2->sig))
+                            if (!jl_type_morespecific((jl_value_t*)m->sig, (jl_value_t*)m2->sig))
+                                break;
+                    }
+                    else {
+                        // if unlimited, use approximate sorting, with the only
+                        // main downside being that it may be overly-
+                        // conservative at reporting existence of ambiguities
+                        if (jl_type_morespecific((jl_value_t*)m2->sig, (jl_value_t*)m->sig))
                             break;
+                    }
+                }
                 jl_array_ptr_set(env.t, i - j, matc2);
             }
             jl_array_ptr_set(env.t, i - j, env.matc);

diff --git a/test/errorshow.jl b/test/errorshow.jl
@@ -86,7 +86,7 @@ method_c2(x::Int32, y::Int32, z::Int32) = true
 method_c2(x::T, y::T, z::T) where {T<:Real} = true
 
 Base.show_method_candidates(buf, Base.MethodError(method_c2,(1., 1., 2)))
-@test String(take!(buf)) ==  "\nClosest candidates are:\n  method_c2(!Matched::Int32, ::Float64, ::Any...)$cfile$(c2line+2)\n  method_c2(::T, ::T, !Matched::T) where T<:Real$cfile$(c2line+5)\n  method_c2(!Matched::Int32, ::Any...)$cfile$(c2line+1)\n  ..."
+@test String(take!(buf)) ==  "\nClosest candidates are:\n  method_c2(!Matched::Int32, ::Float64, ::Any...)$cfile$(c2line+2)\n  method_c2(!Matched::Int32, ::Any...)$cfile$(c2line+1)\n  method_c2(::T, ::T, !Matched::T) where T<:Real$cfile$(c2line+5)\n  ..."
 
 c3line = @__LINE__() + 1
 method_c3(x::Float64, y::Float64) = true
@@ -124,7 +124,7 @@ PR16155line2 = @__LINE__() + 1
 (::Type{T})(arg::Any) where {T<:PR16155} = "replace call-to-convert method from sysimg"
 
 Base.show_method_candidates(buf, MethodError(PR16155,(1.0, 2.0, Int64(3))))
-@test String(take!(buf)) == "\nClosest candidates are:\n  $(curmod_prefix)PR16155(::Any, ::Any)$cfile$PR16155line\n  (::Type{T})(::Any) where T<:$(curmod_prefix)PR16155$cfile$PR16155line2\n  $(curmod_prefix)PR16155(!Matched::Int64, ::Any)$cfile$PR16155line"
+@test String(take!(buf)) == "\nClosest candidates are:\n  $(curmod_prefix)PR16155(::Any, ::Any)$cfile$PR16155line\n  $(curmod_prefix)PR16155(!Matched::Int64, ::Any)$cfile$PR16155line\n  (::Type{T})(::Any) where T<:$(curmod_prefix)PR16155$cfile$PR16155line2"
 
 Base.show_method_candidates(buf, MethodError(PR16155,(Int64(3), 2.0, Int64(3))))
 @test String(take!(buf)) == "\nClosest candidates are:\n  $(curmod_prefix)PR16155(::Int64, ::Any)$cfile$PR16155line\n  $(curmod_prefix)PR16155(::Any, ::Any)$cfile$PR16155line\n  (::Type{T})(::Any) where T<:$(curmod_prefix)PR16155$cfile$PR16155line2"