remove additional rule that parameters must match for dispath

matching a method signature is a simple subtyping test,
with no additional rule to ensure that all parameters have a value

and adds a Test for possibly unbound parameters,
which allows detecting methods definitions that this change affects

NEWS.md

@@ -32,6 +32,16 @@ Language changes
   * `{ }` expressions now use `braces` and `bracescat` as expression heads instead
     of `cell1d` and `cell2d`, and parse similarly to `vect` and `vcat` ([#8470]).
 
+  * Dispatch rules have been simplified:
+    matching methods is now determined exclusively by subtyping;
+    the rule that method type parameters must be also be captured has been removed.
+    Instead, attempting to access the uncontrained parameters will throw an `UndefVarError`.
+    Linting in package tests is recommended to confirm that the set of methods
+    which might throw `UndefVarError` when accessing the static parameters
+    (`need_to_handle_undef_sparam = Set{Any}(m.sig for m in Test.detect_unbound_args(Base, recursive=true))`)
+    is equal (`==`) to some known set (`expected = Set()`). ([#TBD])
+
+
 Breaking changes
 ----------------
 

base/essentials.jl

@@ -64,12 +64,6 @@ end
 convert(::Type{Any}, @nospecialize(x)) = x
 convert(::Type{T}, x::T) where {T} = x
 
-convert(::Type{Tuple{}}, ::Tuple{}) = ()
-convert(::Type{Tuple}, x::Tuple) = x
-convert(::Type{Tuple{Vararg{T}}}, x::Tuple) where {T} = cnvt_all(T, x...)
-cnvt_all(T) = ()
-cnvt_all(T, x, rest...) = tuple(convert(T,x), cnvt_all(T, rest...)...)
-
 """
     @eval [mod,] ex
 
@@ -86,13 +80,24 @@ end
 argtail(x, rest...) = rest
 tail(x::Tuple) = argtail(x...)
 
+# TODO: a better / more infer-able definition would pehaps be
+#   tuple_type_head(T::Type) = fieldtype(T::Type{<:Tuple}, 1)
 tuple_type_head(T::UnionAll) = (@_pure_meta; UnionAll(T.var, tuple_type_head(T.body)))
+function tuple_type_head(T::Union)
+    @_pure_meta
+    return Union{tuple_type_head(T.a), tuple_type_head(T.b)}
+end
 function tuple_type_head(T::DataType)
     @_pure_meta
     T.name === Tuple.name || throw(MethodError(tuple_type_head, (T,)))
     return unwrapva(T.parameters[1])
 end
+
 tuple_type_tail(T::UnionAll) = (@_pure_meta; UnionAll(T.var, tuple_type_tail(T.body)))
+function tuple_type_tail(T::Union)
+    @_pure_meta
+    return Union{tuple_type_tail(T.a), tuple_type_tail(T.b)}
+end
 function tuple_type_tail(T::DataType)
     @_pure_meta
     T.name === Tuple.name || throw(MethodError(tuple_type_tail, (T,)))
@@ -159,11 +164,44 @@ function typename(a::Union)
 end
 typename(union::UnionAll) = typename(union.body)
 
-convert(::Type{T}, x::Tuple{Any,Vararg{Any}}) where {T<:Tuple{Any,Vararg{Any}}} =
-    tuple(convert(tuple_type_head(T),x[1]), convert(tuple_type_tail(T), tail(x))...)
-convert(::Type{T}, x::T) where {T<:Tuple{Any,Vararg{Any}}} = x
-
-oftype(x,c) = convert(typeof(x),c)
+convert(::Type{T}, x::T) where {T<:Tuple{Any, Vararg{Any}}} = x
+convert(::Type{T}, x::Tuple{Any, Vararg{Any}}) where {T<:Tuple} =
+    (convert(tuple_type_head(T), x[1]), convert(tuple_type_tail(T), tail(x))...)
+
+# TODO: the following definitions are equivalent (behaviorally) to the above method
+# I think they may be faster / more efficient for inference,
+# if we could enable them, but are they?
+# TODO: These currently can't be used (#21026) since with
+#     z(::Type{Tuple{Val{T}} where T}) = T
+#   calling
+#     z(Tuple{Val})
+#   fails, even though `Type{Tuple{Val}} == Type{Tuple{Val{S}} where S}`
+#   and so T should be Val{S} where S
+#convert(_::Type{Tuple{S}}, x::Tuple{S}) where {S} = x
+#convert(_::Type{Tuple{S}}, x::Tuple{Any}) where {S} = (convert(S, x[1]),)
+#convert(_::Type{T}, x::T) where {S, N, T<:Tuple{S, Vararg{S, N}}} = x
+#convert(_::Type{Tuple{S, Vararg{S, N}}},
+#        x::Tuple{Any, Vararg{Any, N}}) where
+#       {S, N} = cnvt_all(S, x...)
+#convert(_::Type{Tuple{Vararg{S, N}}},
+#        x::Tuple{Vararg{Any, N}}) where
+#       {S, N} = cnvt_all(S, x...)
+# TODO: These currently can't be used since
+#   Type{NTuple} <: (Type{Tuple{Vararg{S}}} where S) is true
+#   even though the value S doesn't exist
+#convert(_::Type{Tuple{Vararg{S}}},
+#        x::Tuple{Any, Vararg{Any}}) where
+#       {S} = cnvt_all(S, x...)
+#convert(_::Type{Tuple{Vararg{S}}},
+#        x::Tuple{Vararg{Any}}) where
+#       {S} = cnvt_all(S, x...)
+#cnvt_all(T) = ()
+#cnvt_all(T, x, rest...) = (convert(T, x), cnvt_all(T, rest...)...)
+# TODO: These may be necessary if the above are enabled
+#convert(::Type{Tuple{}}, ::Tuple{}) = ()
+#convert(::Type{Tuple{Vararg{S}}} where S, ::Tuple{}) = ()
+
+oftype(x, c) = convert(typeof(x), c)
 
 unsigned(x::Int) = reinterpret(UInt, x)
 signed(x::UInt) = reinterpret(Int, x)

base/inference.jl

@@ -1448,8 +1448,7 @@ function invoke_tfunc(@nospecialize(f), @nospecialize(types), @nospecialize(argt
         return Any
     end
     meth = entry.func
-    (ti, env) = ccall(:jl_match_method, Ref{SimpleVector}, (Any, Any),
-                      argtype, meth.sig)
+    (ti, env) = ccall(:jl_env_from_type_intersection, Any, (Any, Any), argtype, meth.sig)::SimpleVector
     rt, edge = typeinf_edge(meth::Method, ti, env, sv)
     edge !== nothing && add_backedge!(edge::MethodInstance, sv)
     return rt
@@ -1826,7 +1825,7 @@ function abstract_call_method(method::Method, @nospecialize(f), @nospecialize(si
 
     # if sig changed, may need to recompute the sparams environment
     if isa(method.sig, UnionAll) && isempty(sparams)
-        recomputed = ccall(:jl_env_from_type_intersection, Ref{SimpleVector}, (Any, Any), sig, method.sig)
+        recomputed = ccall(:jl_match_method, Any, (Any, Any), sig, method.sig)::SimpleVector
         sig = recomputed[1]
         if !isa(unwrap_unionall(sig), DataType) # probably Union{}
             return Any
@@ -2448,7 +2447,9 @@ function abstract_eval(@nospecialize(e), vtypes::VarTable, sv::InferenceState)
             n = sym.args[1]
             if 1 <= n <= length(sv.sp)
                 val = sv.sp[n]
-                t = Const(true)
+                if !isa(val, TypeVar)
+                    t = Const(true)
+                end
             end
         end
     else
@@ -3837,9 +3838,13 @@ function effect_free(@nospecialize(e), src::CodeInfo, mod::Module, allow_volatil
     elseif isa(e, Expr)
         e = e::Expr
         head = e.head
-        if head === :static_parameter || is_meta_expr_head(head)
+        if is_meta_expr_head(head)
             return true
         end
+        if head === :static_parameter
+            # if we aren't certain about the type, it might be an UndefVarError at runtime
+            return isa(e.typ, DataType) && isleaftype(e.typ)
+        end
         if e.typ === Bottom
             return false
         end
@@ -4248,8 +4253,8 @@ function inlineable(@nospecialize(f), @nospecialize(ft), e::Expr, atypes::Vector
     else
         invoke_data = invoke_data::InvokeData
         method = invoke_data.entry.func
-        (metharg, methsp) = ccall(:jl_match_method, Ref{SimpleVector}, (Any, Any),
-                                  atype_unlimited, method.sig)
+        (metharg, methsp) = ccall(:jl_match_method, Any, (Any, Any),
+                                  atype_unlimited, method.sig)::SimpleVector
         methsp = methsp::SimpleVector
     end
 
@@ -4983,20 +4988,21 @@ function inlining_pass(e::Expr, sv::InferenceState, stmts, ins)
                 aarg = e.args[i]
                 argt = exprtype(aarg, sv.src, sv.mod)
                 t = widenconst(argt)
-                if isa(aarg,Expr) && (is_known_call(aarg, tuple, sv.src, sv.mod) || is_known_call(aarg, svec, sv.src, sv.mod))
-                    # apply(f,tuple(x,y,...)) => f(x,y,...)
-                    newargs[i-2] = aarg.args[2:end]
-                elseif isa(argt,Const) && (isa(argt.val, Tuple) || isa(argt.val, SimpleVector)) &&
+                if isa(aarg, Expr) && (is_known_call(aarg, tuple, sv.src, sv.mod) || is_known_call(aarg, svec, sv.src, sv.mod))
+                    # apply(f, tuple(x, y, ...)) => f(x, y, ...)
+                    newargs[i - 2] = aarg.args[2:end]
+                elseif isa(argt, Const) && (isa(argt.val, Tuple) || isa(argt.val, SimpleVector)) &&
                         effect_free(aarg, sv.src, sv.mod, true)
-                    newargs[i-2] = Any[ QuoteNode(x) for x in argt.val ]
+                    val = argt.val
+                    newargs[i - 2] = Any[ QuoteNode(val[i]) for i in 1:(length(val)::Int) ] # avoid making a tuple Generator here!
                 elseif isa(aarg, Tuple) || (isa(aarg, QuoteNode) && (isa(aarg.value, Tuple) || isa(aarg.value, SimpleVector)))
                     if isa(aarg, QuoteNode)
                         aarg = aarg.value
                     end
-                    newargs[i-2] = Any[ QuoteNode(x) for x in aarg ]
+                    newargs[i - 2] = Any[ QuoteNode(aarg[i]) for i in 1:(length(aarg)::Int) ] # avoid making a tuple Generator here!
                 elseif isa(t, DataType) && t.name === Tuple.name && !isvatuple(t) &&
                          length(t.parameters) <= sv.params.MAX_TUPLE_SPLAT
-                    for k = (effect_free_upto+1):(i-3)
+                    for k = (effect_free_upto + 1):(i - 3)
                         as = newargs[k]
                         for kk = 1:length(as)
                             ak = as[kk]
@@ -5007,7 +5013,7 @@ function inlining_pass(e::Expr, sv::InferenceState, stmts, ins)
                             end
                         end
                     end
-                    effect_free_upto = i-3
+                    effect_free_upto = i - 3
                     if effect_free(aarg, sv.src, sv.mod, true)
                         # apply(f,t::(x,y)) => f(t[1],t[2])
                         tmpv = aarg
@@ -5021,13 +5027,13 @@ function inlining_pass(e::Expr, sv::InferenceState, stmts, ins)
                     else
                         tp = t.parameters
                     end
-                    newargs[i-2] = Any[ mk_getfield(tmpv,j,tp[j]) for j=1:length(tp) ]
+                    newargs[i - 2] = Any[ mk_getfield(tmpv, j, tp[j]) for j in 1:(length(tp)::Int) ]
                 else
                     # not all args expandable
                     return e
                 end
             end
-            splice!(stmts, ins:ins-1, newstmts)
+            splice!(stmts, ins:(ins - 1), newstmts)
             ins += length(newstmts)
             e.args = [Any[e.args[2]]; newargs...]
 
@@ -5155,11 +5161,17 @@ normvar(@nospecialize(s)) = s
 
 # given a single-assigned var and its initializer `init`, return what we can
 # replace `var` with, or `var` itself if we shouldn't replace it
-function get_replacement(table, var::Union{SlotNumber, SSAValue}, @nospecialize(init), nargs, slottypes, ssavaluetypes)
+function get_replacement(table::ObjectIdDict, var::Union{SlotNumber, SSAValue}, @nospecialize(init),
+                         nargs::Int, slottypes::Vector{Any}, ssavaluetypes::Vector{Any})
     #if isa(init, QuoteNode)  # this can cause slight code size increases
     #    return init
-    if (isa(init, Expr) && init.head === :static_parameter) || isa(init, corenumtype) ||
-        init === () || init === nothing
+    if isa(init, Expr) && init.head === :static_parameter
+        # if we aren't certain about the type, it might be an UndefVarError at runtime (!effect_free)
+        # so we need to preserve the original point of assignment
+        if isa(init.typ, DataType) && isleaftype(init.typ)
+            return init
+        end
+    elseif isa(init, corenumtype) || init === () || init === nothing
         return init
     elseif isa(init, Slot) && is_argument(nargs, init::Slot)
         # the transformation is not ideal if the assignment
@@ -5206,7 +5218,7 @@ function remove_redundant_temp_vars!(src::CodeInfo, nargs::Int, sa::ObjectIdDict
     repls = ObjectIdDict()
     for (v, init) in sa
         repl = get_replacement(sa, v, init, nargs, slottypes, ssavaluetypes)
-        compare = isa(repl,TypedSlot) ? normslot(repl) : repl
+        compare = isa(repl, TypedSlot) ? normslot(repl) : repl
         if compare !== v
             repls[v] = repl
         end

base/reflection.jl

@@ -738,8 +738,8 @@ function _dump_function(@nospecialize(f), @nospecialize(t), native::Bool, wrappe
     ft = isa(f, Type) ? Type{f} : typeof(f)
     tt = Tuple{ft, t.parameters...}
     (ti, env) = ccall(:jl_match_method, Any, (Any, Any), tt, meth.sig)::SimpleVector
-    meth = func_for_method_checked(meth, tt)
-    linfo = ccall(:jl_specializations_get_linfo, Ref{Core.MethodInstance}, (Any, Any, Any, UInt), meth, tt, env, world)
+    meth = func_for_method_checked(meth, ti)
+    linfo = ccall(:jl_specializations_get_linfo, Ref{Core.MethodInstance}, (Any, Any, Any, UInt), meth, ti, env, world)
     # get the code for it
     return _dump_function_linfo(linfo, world, native, wrapper, strip_ir_metadata, dump_module, syntax, optimize, params)
 end

base/test.jl

@@ -19,7 +19,7 @@ export @test, @test_throws, @test_broken, @test_skip, @test_warn, @test_nowarn
 export @testset
 # Legacy approximate testing functions, yet to be included
 export @inferred
-export detect_ambiguities
+export detect_ambiguities, detect_unbound_args
 export GenericString, GenericSet, GenericDict, GenericArray
 
 #-----------------------------------------------------------------------
@@ -1257,6 +1257,107 @@ function detect_ambiguities(mods...;
     return collect(ambs)
 end
 
+"""
+    detect_unbound_args(mod1, mod2...; imported=false)
+
+Returns a vector of `Method`s which may have unbound type parameters.
+Use `imported=true` if you wish to also test functions that were
+imported into these modules from elsewhere.
+Use `recursive=true` to test in all submodules.
+"""
+function detect_unbound_args(mods...;
+                             imported::Bool = false,
+                             recursive::Bool = false)
+    ambs = Set{Method}()
+    for mod in mods
+        for n in names(mod, true, imported)
+            Base.isdeprecated(mod, n) && continue
+            if !isdefined(mod, n)
+                println("Skipping ", mod, '.', n)  # typically stale exports
+                continue
+            end
+            f = Base.unwrap_unionall(getfield(mod, n))
+            if recursive && isa(f, Module) && module_parent(f) === mod && module_name(f) === n
+                subambs = detect_unbound_args(f, imported=imported, recursive=recursive)
+                union!(ambs, subambs)
+            elseif isa(f, DataType) && isdefined(f.name, :mt)
+                mt = Base.MethodList(f.name.mt)
+                for m in mt
+                    if has_unbound_vars(m.sig)
+                        tuple_sig = Base.unwrap_unionall(m.sig)::DataType
+                        if Base.isvatuple(tuple_sig)
+                            params = tuple_sig.parameters[1:(end - 1)]
+                            tuple_sig = Base.rewrap_unionall(Tuple{params...}, m.sig)
+                            mf = ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), tuple_sig, typemax(UInt))
+                            if mf != nothing && mf.func !== m && mf.func.sig <: tuple_sig
+                                continue
+                            end
+                        end
+                        push!(ambs, m)
+                    end
+                end
+            end
+        end
+    end
+    return collect(ambs)
+end
+
+# find if var will be constrained to have a definite value
+# in any concrete leaftype subtype of typ
+function constrains_param(var::TypeVar, @nospecialize(typ), cov::Bool)
+    typ === var && return true
+    while typ isa UnionAll
+        cov && constrains_param(var, typ.var.ub, cov) && return true
+        # typ.var.lb doesn't constrain var
+        typ = typ.body
+    end
+    if typ isa Union
+        # for unions, verify that both options would constrain var
+        ba = constrains_param(var, typ.a, cov)
+        bb = constrains_param(var, typ.b, cov)
+        (ba && bb) && return true
+    elseif typ isa DataType
+        # return true if any param constrains var
+        fc = length(typ.parameters)
+        if fc > 0
+            if typ.name === Tuple.name
+                # vararg tuple needs special handling
+                for i in 1:(fc - 1)
+                    p = typ.parameters[i]
+                    constrains_param(var, p, cov) && return true
+                end
+                lastp = typ.parameters[fc]
+                vararg = Base.unwrap_unionall(lastp)
+                if vararg isa DataType && vararg.name === Base._va_typename
+                    N = vararg.parameters[2]
+                    constrains_param(var, N, cov) && return true
+                    # T = vararg.parameters[1] doesn't constrain var
+                else
+                    constrains_param(var, lastp, cov) && return true
+                end
+            else
+                for i in 1:fc
+                    p = typ.parameters[i]
+                    constrains_param(var, p, false) && return true
+                end
+            end
+        end
+    end
+    return false
+end
+
+function has_unbound_vars(@nospecialize sig)
+    while sig isa UnionAll
+        var = sig.var
+        sig = sig.body
+        if !constrains_param(var, sig, true)
+            return true
+        end
+    end
+    return false
+end
+
+
 """
 The `GenericString` can be used to test generic string APIs that program to
 the `AbstractString` interface, in order to ensure that functions can work

base/tuple.jl

@@ -63,6 +63,7 @@ first(t::Tuple) = t[1]
 # eltype
 
 eltype(::Type{Tuple{}}) = Bottom
+#eltype(::Type{Tuple{Vararg{E}}}) where {E} = E
 eltype(::Type{<:Tuple{Vararg{E}}}) where {E} = E
 function eltype(t::Type{<:Tuple})
     @_pure_meta

src/ast.c

@@ -897,7 +897,8 @@ jl_value_t *jl_parse_eval_all(const char *fname,
             jl_get_ptls_states()->world_age = jl_world_counter;
             form = scm_to_julia(fl_ctx, expansion, 0);
             jl_sym_t *head = NULL;
-            if (jl_is_expr(form)) head = ((jl_expr_t*)form)->head;
+            if (jl_is_expr(form))
+                head = ((jl_expr_t*)form)->head;
             JL_SIGATOMIC_END();
             jl_get_ptls_states()->world_age = jl_world_counter;
             if (head == jl_incomplete_sym)