make ml_matches return nothing when there are too many matches

Continuation from <#44448 (comment)>.
Previously `ml_matches` (and its dependent utilities like `_methods_by_ftype`)
returned `false` for cases when there are too many matching method, but
its consumer like `findall(::Type, ::InternalMethodTable)` usually handles
such case as `missing`. This commit does a refactor so that they all use
the more consistent value `nothing` for representing that case.

base/compiler/abstractinterpretation.jl

@@ -287,7 +287,7 @@ function find_matching_methods(argtypes::Vector{Any}, @nospecialize(atype), meth
             mt === nothing && return FailedMethodMatch("Could not identify method table for call")
             mt = mt::Core.MethodTable
             result = findall(sig_n, method_table; limit = max_methods)
-            if result === missing
+            if result === nothing
                 return FailedMethodMatch("For one of the union split cases, too many methods matched")
             end
             matches, overlayedᵢ = result
@@ -326,7 +326,7 @@ function find_matching_methods(argtypes::Vector{Any}, @nospecialize(atype), meth
         end
         mt = mt::Core.MethodTable
         result = findall(atype, method_table; limit = max_methods)
-        if result === missing
+        if result === nothing
             # this means too many methods matched
             # (assume this will always be true, so we don't compute / update valid age in this case)
             return FailedMethodMatch("Too many methods matched")

base/compiler/bootstrap.jl

@@ -38,8 +38,9 @@ let
         else
             tt = Tuple{typeof(f), Vararg{Any}}
         end
-        for m in _methods_by_ftype(tt, 10, typemax(UInt))
+        for m in _methods_by_ftype(tt, 10, typemax(UInt))::Vector
             # remove any TypeVars from the intersection
+            m = m::MethodMatch
             typ = Any[m.spec_types.parameters...]
             for i = 1:length(typ)
                 typ[i] = unwraptv(typ[i])

base/compiler/methodtable.jl

@@ -41,11 +41,11 @@ getindex(result::MethodLookupResult, idx::Int) = getindex(result.matches, idx)::
 
 """
     findall(sig::Type, view::MethodTableView; limit::Int=typemax(Int)) ->
-        (matches::MethodLookupResult, overlayed::Bool) or missing
+        (matches::MethodLookupResult, overlayed::Bool) or nothing
 
 Find all methods in the given method table `view` that are applicable to the given signature `sig`.
 If no applicable methods are found, an empty result is returned.
-If the number of applicable methods exceeded the specified limit, `missing` is returned.
+If the number of applicable methods exceeded the specified limit, `nothing` is returned.
 `overlayed` indicates if any matching method is defined in an overlayed method table.
 """
 function findall(@nospecialize(sig::Type), table::InternalMethodTable; limit::Int=Int(typemax(Int32)))
@@ -56,15 +56,15 @@ end
 
 function findall(@nospecialize(sig::Type), table::OverlayMethodTable; limit::Int=Int(typemax(Int32)))
     result = _findall(sig, table.mt, table.world, limit)
-    result === missing && return missing
+    result === nothing && return nothing
     nr = length(result)
     if nr ≥ 1 && result[nr].fully_covers
         # no need to fall back to the internal method table
         return result, true
     end
     # fall back to the internal method table
     fallback_result = _findall(sig, nothing, table.world, limit)
-    fallback_result === missing && return missing
+    fallback_result === nothing && return nothing
     # merge the fallback match results with the internal method table
     return MethodLookupResult(
         vcat(result.matches, fallback_result.matches),
@@ -79,10 +79,8 @@ function _findall(@nospecialize(sig::Type), mt::Union{Nothing,Core.MethodTable},
     _max_val = RefValue{UInt}(typemax(UInt))
     _ambig = RefValue{Int32}(0)
     ms = _methods_by_ftype(sig, mt, limit, world, false, _min_val, _max_val, _ambig)
-    if ms === false
-        return missing
-    end
-    return MethodLookupResult(ms::Vector{Any}, WorldRange(_min_val[], _max_val[]), _ambig[] != 0)
+    isa(ms, Vector) || return nothing
+    return MethodLookupResult(ms, WorldRange(_min_val[], _max_val[]), _ambig[] != 0)
 end
 
 """

base/reflection.jl

@@ -942,7 +942,7 @@ function _methods_by_ftype(@nospecialize(t), mt::Union{Core.MethodTable, Nothing
     return _methods_by_ftype(t, mt, lim, world, false, RefValue{UInt}(typemin(UInt)), RefValue{UInt}(typemax(UInt)), Ptr{Int32}(C_NULL))
 end
 function _methods_by_ftype(@nospecialize(t), mt::Union{Core.MethodTable, Nothing}, lim::Int, world::UInt, ambig::Bool, min::Ref{UInt}, max::Ref{UInt}, has_ambig::Ref{Int32})
-    return ccall(:jl_matching_methods, Any, (Any, Any, Cint, Cint, UInt, Ptr{UInt}, Ptr{UInt}, Ptr{Int32}), t, mt, lim, ambig, world, min, max, has_ambig)::Union{Array{Any,1}, Bool}
+    return ccall(:jl_matching_methods, Any, (Any, Any, Cint, Cint, UInt, Ptr{UInt}, Ptr{UInt}, Ptr{Int32}), t, mt, lim, ambig, world, min, max, has_ambig)::Union{Vector{Any},Nothing}
 end
 
 # high-level, more convenient method lookup functions

src/dump.c

@@ -1258,7 +1258,7 @@ static void jl_collect_backedges( /* edges */ jl_array_t *s, /* ext_targets */ j
                         size_t max_valid = ~(size_t)0;
                         int ambig = 0;
                         jl_value_t *matches = jl_matching_methods((jl_tupletype_t*)sig, jl_nothing, -1, 0, jl_atomic_load_acquire(&jl_world_counter), &min_valid, &max_valid, &ambig);
-                        if (matches == jl_false) {
+                        if (matches == jl_nothing) {
                             valid = 0;
                             break;
                         }
@@ -2339,7 +2339,7 @@ static void jl_verify_edges(jl_array_t *targets, jl_array_t **pvalids)
         int ambig = 0;
         // TODO: possibly need to included ambiguities too (for the optimizer correctness)?
         jl_value_t *matches = jl_matching_methods((jl_tupletype_t*)sig, jl_nothing, -1, 0, jl_atomic_load_acquire(&jl_world_counter), &min_valid, &max_valid, &ambig);
-        if (matches == jl_false || jl_array_len(matches) != jl_array_len(expected)) {
+        if (matches == jl_nothing || jl_array_len(matches) != jl_array_len(expected)) {
             valid = 0;
         }
         else {

src/gf.c

@@ -1089,7 +1089,7 @@ static jl_method_instance_t *cache_method(
         size_t max_valid2 = ~(size_t)0;
         temp = ml_matches(mt, compilationsig, MAX_UNSPECIALIZED_CONFLICTS, 1, 1, world, 0, &min_valid2, &max_valid2, NULL);
         int guards = 0;
-        if (temp == jl_false) {
+        if (temp == jl_nothing) {
             cache_with_orig = 1;
         }
         else {
@@ -2559,7 +2559,7 @@ static jl_method_match_t *_gf_invoke_lookup(jl_value_t *types JL_PROPAGATES_ROOT
     if (mt == jl_nothing)
         mt = NULL;
     jl_value_t *matches = ml_matches((jl_methtable_t*)mt, (jl_tupletype_t*)types, 1, 0, 0, world, 1, min_valid, max_valid, NULL);
-    if (matches == jl_false || jl_array_len(matches) != 1)
+    if (matches == jl_nothing || jl_array_len(matches) != 1)
         return NULL;
     jl_method_match_t *matc = (jl_method_match_t*)jl_array_ptr_ref(matches, 0);
     return matc;
@@ -2887,14 +2887,14 @@ static jl_value_t *ml_matches(jl_methtable_t *mt,
         }
         if (!jl_typemap_intersection_visitor(mt->defs, 0, &env.match)) {
             JL_GC_POP();
-            return jl_false;
+            return jl_nothing;
         }
     }
     else {
         // else: scan everything
         if (!jl_foreach_reachable_mtable(ml_mtable_visitor, &env.match)) {
             JL_GC_POP();
-            return jl_false;
+            return jl_nothing;
         }
     }
     *min_valid = env.min_valid;
@@ -2976,7 +2976,7 @@ static jl_value_t *ml_matches(jl_methtable_t *mt,
                 }
                 else if (lim == 1) {
                     JL_GC_POP();
-                    return jl_false;
+                    return jl_nothing;
                 }
             }
             else {
@@ -3120,7 +3120,7 @@ static jl_value_t *ml_matches(jl_methtable_t *mt,
                     ndisjoint += 1;
                     if (ndisjoint > lim) {
                         JL_GC_POP();
-                        return jl_false;
+                        return jl_nothing;
                     }
                 }
             }
@@ -3271,7 +3271,7 @@ static jl_value_t *ml_matches(jl_methtable_t *mt,
         *ambig = has_ambiguity;
     JL_GC_POP();
     if (lim >= 0 && len > lim)
-        return jl_false;
+        return jl_nothing;
     return env.t;
 }
 

stdlib/REPL/src/REPLCompletions.jl

@@ -613,10 +613,10 @@ function complete_methods!(out::Vector{Completion}, @nospecialize(funct), args_e
     t_in = Tuple{funct, args_ex...}
     m = Base._methods_by_ftype(t_in, nothing, max_method_completions, Base.get_world_counter(),
         #=ambig=# true, Ref(typemin(UInt)), Ref(typemax(UInt)), Ptr{Int32}(C_NULL))
-    if m === false
+    if !isa(m, Vector)
         push!(out, TextCompletion(sprint(Base.show_signature_function, funct) * "( too many methods to show )"))
+        return
     end
-    m isa Vector || return
     for match in m
         # TODO: if kwargs_ex, filter out methods without kwargs?
         push!(out, MethodCompletion(match.spec_types, match.method))