reflection.jl

# This file is a part of Julia. License is MIT: http://julialang.org/license

# name and module reflection

"""
    module_name(m::Module) -> Symbol

Get the name of a `Module` as a `Symbol`.

```jldoctest
julia> module_name(Base.LinAlg)
:LinAlg
```
"""
module_name(m::Module) = ccall(:jl_module_name, Ref{Symbol}, (Any,), m)

"""
    module_parent(m::Module) -> Module

Get a module's enclosing `Module`. `Main` is its own parent, as is `LastMain` after `workspace()`.
```jldoctest
julia> module_parent(Main)
Main

julia> module_parent(Base.LinAlg.BLAS)
Base.LinAlg
```
"""
module_parent(m::Module) = ccall(:jl_module_parent, Ref{Module}, (Any,), m)

"""
    current_module() -> Module

Get the *dynamically* current `Module`, which is the `Module` code is currently being read
from. In general, this is not the same as the module containing the call to this function.
"""
current_module() = ccall(:jl_get_current_module, Ref{Module}, ())

"""
    fullname(m::Module)

Get the fully-qualified name of a module as a tuple of symbols. For example,

```jldoctest
julia> fullname(Base.Pkg)
(:Base,:Pkg)

julia> fullname(Main)
()
```
"""
function fullname(m::Module)
    m === Main && return ()
    m === Base && return (:Base,)  # issue #10653
    mn = module_name(m)
    mp = module_parent(m)
    if mp === m
        # not Main, but is its own parent, means a prior Main module
        n = ()
        this = Main
        while this !== m
            if isdefined(this, :LastMain)
                n = tuple(n..., :LastMain)
                this = this.LastMain
            else
                error("no reference to module ", mn)
            end
        end
        return n
    end
    return tuple(fullname(mp)..., mn)
end

"""
    names(x::Module, all::Bool=false, imported::Bool=false)

Get an array of the names exported by a `Module`, excluding deprecated names.
If `all` is true, then the list also includes non-exported names defined in the module,
deprecated names, and compiler-generated names.
If `imported` is true, then names explicitly imported from other modules
are also included.

As a special case, all names defined in `Main` are considered \"exported\",
since it is not idiomatic to explicitly export names from `Main`.
"""
names(m::Module, all::Bool=false, imported::Bool=false) = sort!(ccall(:jl_module_names, Array{Symbol,1}, (Any,Cint,Cint), m, all, imported))

isexported(m::Module, s::Symbol) = ccall(:jl_module_exports_p, Cint, (Any, Any), m, s) != 0
isdeprecated(m::Module, s::Symbol) = ccall(:jl_is_binding_deprecated, Cint, (Any, Any), m, s) != 0
isbindingresolved(m::Module, var::Symbol) = ccall(:jl_binding_resolved_p, Cint, (Any, Any), m, var) != 0

binding_module(s::Symbol) = binding_module(current_module(), s)
function binding_module(m::Module, s::Symbol)
    p = ccall(:jl_get_module_of_binding, Ptr{Void}, (Any, Any), m, s)
    p == C_NULL && return m
    return unsafe_pointer_to_objref(p)::Module
end

function resolve(g::GlobalRef; force::Bool=false)
    if force || isbindingresolved(g.mod, g.name)
        return GlobalRef(binding_module(g.mod, g.name), g.name)
    end
    return g
end

"""
    fieldname(x::DataType, i::Integer)

Get the name of field `i` of a `DataType`.

```jldoctest
julia> fieldname(SparseMatrixCSC,1)
:m

julia> fieldname(SparseMatrixCSC,5)
:nzval
```
"""
fieldname(t::DataType, i::Integer) = t.name.names[i]::Symbol
fieldname(t::UnionAll, i::Integer) = fieldname(unwrap_unionall(t), i)
fieldname{T<:Tuple}(t::Type{T}, i::Integer) = i < 1 || i > nfields(t) ? throw(BoundsError(t, i)) : Int(i)

"""
    fieldnames(x::DataType)

Get an array of the fields of a `DataType`.

```jldoctest
julia> fieldnames(Hermitian)
2-element Array{Symbol,1}:
 :data
 :uplo
```
"""
function fieldnames(v)
    t = typeof(v)
    if !isa(t,DataType)
        throw(ArgumentError("cannot call fieldnames() on a non-composite type"))
    end
    return fieldnames(t)
end
fieldnames(t::DataType) = Symbol[fieldname(t, n) for n in 1:nfields(t)]
fieldnames(t::UnionAll) = fieldnames(unwrap_unionall(t))
fieldnames{T<:Tuple}(t::Type{T}) = Int[n for n in 1:nfields(t)]

"""
    Base.datatype_name(t::DataType) -> Symbol

Get the name of a `DataType` (without its parent module) as a symbol.
"""
datatype_name(t::DataType) = t.name.name

"""
    Base.datatype_module(t::DataType) -> Module

Determine the module containing the definition of a `DataType`.
"""
datatype_module(t::DataType) = t.name.module

isconst(s::Symbol) = ccall(:jl_is_const, Cint, (Ptr{Void}, Any), C_NULL, s) != 0

"""
    isconst([m::Module], s::Symbol) -> Bool

Determine whether a global is declared `const` in a given `Module`. The default `Module`
argument is [`current_module()`](@ref).
"""
isconst(m::Module, s::Symbol) =
    ccall(:jl_is_const, Cint, (Any, Any), m, s) != 0

# return an integer such that object_id(x)==object_id(y) if x===y
object_id(x::ANY) = ccall(:jl_object_id, UInt, (Any,), x)

immutable DataTypeLayout
    nfields::UInt32
    alignment::UInt32
    # alignment : 28;
    # haspadding : 1;
    # pointerfree : 1;
    # fielddesc_type : 2;
end


# type predicates
datatype_alignment(dt::DataType) = dt.layout == C_NULL ? throw(UndefRefError()) :
    Int(unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).alignment & 0x0FFFFFFF)

datatype_haspadding(dt::DataType) = dt.layout == C_NULL ? throw(UndefRefError()) :
    (unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).alignment >> 28) & 1 == 1

datatype_pointerfree(dt::DataType) = dt.layout == C_NULL ? throw(UndefRefError()) :
    (unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).alignment >> 29) & 1 == 1

datatype_fielddesc_type(dt::DataType) = dt.layout == C_NULL ? throw(UndefRefError()) :
    (unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).alignment >> 30) & 3

"""
    isimmutable(v)

Return `true` iff value `v` is immutable.  See [Immutable Composite Types](@ref)
for a discussion of immutability. Note that this function works on values, so if you give it
a type, it will tell you that a value of `DataType` is mutable.
"""
isimmutable(x::ANY) = (@_pure_meta; (isa(x,Tuple) || !typeof(x).mutable))
isstructtype(t::DataType) = (@_pure_meta; nfields(t) != 0 || (t.size==0 && !t.abstract))
isstructtype(x) = (@_pure_meta; false)

"""
    isbits(T)

Return `true` if `T` is a "plain data" type, meaning it is immutable and contains no
references to other values. Typical examples are numeric types such as `UInt8`, `Float64`,
and `Complex{Float64}`.

```jldoctest
julia> isbits(Complex{Float64})
true

julia> isbits(Complex)
false
```
"""
isbits(t::DataType) = (@_pure_meta; !t.mutable & (t.layout != C_NULL) && datatype_pointerfree(t))
isbits(t::Type) = (@_pure_meta; false)
isbits(x) = (@_pure_meta; isbits(typeof(x)))

"""
    isleaftype(T)

Determine whether `T` is a concrete type that can have instances, meaning its only subtypes
are itself and `Union{}` (but `T` itself is not `Union{}`).
"""
isleaftype(t::ANY) = (@_pure_meta; (isa(t, DataType) && t.isleaftype) || t === Union{})

"""
    typeintersect(T, S)

Compute a type that contains the intersection of `T` and `S`. Usually this will be the
smallest such type or one close to it.
"""
typeintersect(a::ANY,b::ANY) = (@_pure_meta; ccall(:jl_type_intersection, Any, (Any,Any), a, b))
typeseq(a::ANY,b::ANY) = (@_pure_meta; a<:b && b<:a)

"""
    fieldoffset(type, i)

The byte offset of field `i` of a type relative to the data start. For example, we could
use it in the following manner to summarize information about a struct type:

```jldoctest
julia> structinfo(T) = [(fieldoffset(T,i), fieldname(T,i), fieldtype(T,i)) for i = 1:nfields(T)];

julia> structinfo(Base.Filesystem.StatStruct)
12-element Array{Tuple{UInt64,Symbol,DataType},1}:
 (0x0000000000000000,:device,UInt64)
 (0x0000000000000008,:inode,UInt64)
 (0x0000000000000010,:mode,UInt64)
 (0x0000000000000018,:nlink,Int64)
 (0x0000000000000020,:uid,UInt64)
 (0x0000000000000028,:gid,UInt64)
 (0x0000000000000030,:rdev,UInt64)
 (0x0000000000000038,:size,Int64)
 (0x0000000000000040,:blksize,Int64)
 (0x0000000000000048,:blocks,Int64)
 (0x0000000000000050,:mtime,Float64)
 (0x0000000000000058,:ctime,Float64)
```
"""
fieldoffset(x::DataType, idx::Integer) = (@_pure_meta; ccall(:jl_get_field_offset, Csize_t, (Any, Cint), x, idx))

"""
    fieldtype(T, name::Symbol | index::Int)

Determine the declared type of a field (specified by name or index) in a composite DataType `T`.
"""
fieldtype

"""
    fieldindex(T, name::Symbol, err:Bool=true)

Get the index of a named field, throwing an error if the field does not exist (when err==true)
or returning 0 (when err==false).
"""
function fieldindex(T::DataType, name::Symbol, err::Bool=true)
    return Int(ccall(:jl_field_index, Cint, (Any, Any, Cint), T, name, err)+1)
end

type_alignment(x::DataType) = (@_pure_meta; ccall(:jl_get_alignment, Csize_t, (Any,), x))

# return all instances, for types that can be enumerated

"""
    instances(T::Type)

Return a collection of all instances of the given type, if applicable. Mostly used for
enumerated types (see `@enum`).
"""
function instances end

# subtypes
function _subtypes(m::Module, x::DataType, sts=Set{DataType}(), visited=Set{Module}())
    push!(visited, m)
    for s in names(m, true)
        if isdefined(m, s) && !isdeprecated(m, s)
            t = getfield(m, s)
            if isa(t, DataType) && t.name.name == s && supertype(t).name == x.name
                ti = typeintersect(t, x)
                ti != Bottom && push!(sts, ti)
            elseif isa(t, Module) && !in(t, visited)
                _subtypes(t, x, sts, visited)
            end
        end
    end
    return sts
end
subtypes(m::Module, x::DataType) = sort(collect(_subtypes(m, x)), by=string)

"""
    subtypes(T::DataType)

Return a list of immediate subtypes of DataType `T`. Note that all currently loaded subtypes
are included, including those not visible in the current module.

```jldoctest
julia> subtypes(Integer)
4-element Array{DataType,1}:
 BigInt
 Bool
 Signed
 Unsigned
```
"""
subtypes(x::DataType) = subtypes(Main, x)

function to_tuple_type(t::ANY)
    @_pure_meta
    if isa(t,Tuple) || isa(t,AbstractArray) || isa(t,SimpleVector)
        t = Tuple{t...}
    end
    if isa(t,Type) && t<:Tuple
        if !all(p->(isa(p,Type)||isa(p,TypeVar)), t.parameters)
            error("argument tuple type must contain only types")
        end
    else
        error("expected tuple type")
    end
    t
end

tt_cons(t::ANY, tup::ANY) = (@_pure_meta; Tuple{t, (isa(tup, Type) ? tup.parameters : tup)...})

"""
    code_lowered(f, types)

Returns an array of lowered ASTs for the methods matching the given generic function and type signature.
"""
function code_lowered(f::ANY, t::ANY=Tuple)
    asts = map(methods(f, t)) do m
        m = m::Method
        return uncompressed_ast(m, m.source)
    end
    return asts
end

# low-level method lookup functions used by the compiler

unionlen(x::Union) = unionlen(x.a) + unionlen(x.b)
unionlen(x::ANY) = 1

_uniontypes(x::Union, ts) = (_uniontypes(x.a,ts); _uniontypes(x.b,ts); ts)
_uniontypes(x::ANY, ts) = (push!(ts, x); ts)
uniontypes(x::ANY) = _uniontypes(x, Any[])

function _methods(f::ANY, t::ANY, lim::Int, world::UInt)
    ft = isa(f,Type) ? Type{f} : typeof(f)
    tt = isa(t,Type) ? Tuple{ft, t.parameters...} : Tuple{ft, t...}
    return _methods_by_ftype(tt, lim, world)
end

function _methods_by_ftype(t::ANY, lim::Int, world::UInt)
    return _methods_by_ftype(t, lim, world, UInt[typemin(UInt)], UInt[typemax(UInt)])
end
function _methods_by_ftype(t::ANY, lim::Int, world::UInt, min::Array{UInt,1}, max::Array{UInt,1})
    tp = unwrap_unionall(t).parameters::SimpleVector
    nu = 1
    for ti in tp
        if isa(ti, Union)
            nu *= unionlen(ti::Union)
        end
    end
    if 1 < nu <= 64
        return _methods_by_ftype(Any[tp...], t, length(tp), lim, [], world, min, max)
    end
    # XXX: the following can return incorrect answers that the above branch would have corrected
    return ccall(:jl_matching_methods, Any, (Any, Cint, Cint, UInt, Ptr{UInt}, Ptr{UInt}), t, lim, 0, world, min, max)
end

function _methods_by_ftype(t::Array, origt::ANY, i, lim::Integer, matching::Array{Any,1},
                           world::UInt, min::Array{UInt,1}, max::Array{UInt,1})
    if i == 0
        world = typemax(UInt)
        new = ccall(:jl_matching_methods, Any, (Any, Cint, Cint, UInt, Ptr{UInt}, Ptr{UInt}),
                    rewrap_unionall(Tuple{t...}, origt), lim, 0, world, min, max)
        new === false && return false
        append!(matching, new::Array{Any,1})
    else
        ti = t[i]
        if isa(ti, Union)
            for ty in uniontypes(ti::Union)
                t[i] = ty
                if _methods_by_ftype(t, origt, i - 1, lim, matching, world, min, max) === false
                    t[i] = ti
                    return false
                end
            end
            t[i] = ti
        else
            return _methods_by_ftype(t, origt, i - 1, lim, matching, world, min, max)
        end
    end
    return matching
end

# high-level, more convenient method lookup functions

# type for reflecting and pretty-printing a subset of methods
type MethodList
    ms::Array{Method,1}
    mt::MethodTable
end

length(m::MethodList) = length(m.ms)
isempty(m::MethodList) = isempty(m.ms)
start(m::MethodList) = start(m.ms)
done(m::MethodList, s) = done(m.ms, s)
next(m::MethodList, s) = next(m.ms, s)

function MethodList(mt::MethodTable)
    ms = Method[]
    visit(mt) do m
        push!(ms, m)
    end
    return MethodList(ms, mt)
end

"""
    methods(f, [types])

Returns the method table for `f`.

If `types` is specified, returns an array of methods whose types match.
"""
function methods(f::ANY, t::ANY)
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    t = to_tuple_type(t)
    world = typemax(UInt)
    return MethodList(Method[m[3] for m in _methods(f, t, -1, world)], typeof(f).name.mt)
end

methods(f::Core.Builtin) = MethodList(Method[], typeof(f).name.mt)

function methods_including_ambiguous(f::ANY, t::ANY)
    ft = isa(f,Type) ? Type{f} : typeof(f)
    tt = isa(t,Type) ? Tuple{ft, t.parameters...} : Tuple{ft, t...}
    world = typemax(UInt)
    min = UInt[typemin(UInt)]
    max = UInt[typemax(UInt)]
    ms = ccall(:jl_matching_methods, Any, (Any, Cint, Cint, UInt, Ptr{UInt}, Ptr{UInt}), tt, -1, 1, world, min, max)::Array{Any,1}
    return MethodList(Method[m[3] for m in ms], typeof(f).name.mt)
end
function methods(f::ANY)
    # return all matches
    return methods(f, Tuple{Vararg{Any}})
end

function visit(f, mt::MethodTable)
    mt.defs !== nothing && visit(f, mt.defs)
    nothing
end
function visit(f, mc::TypeMapLevel)
    if mc.targ !== nothing
        e = mc.targ::Vector{Any}
        for i in 1:length(e)
            isassigned(e, i) && visit(f, e[i])
        end
    end
    if mc.arg1 !== nothing
        e = mc.arg1::Vector{Any}
        for i in 1:length(e)
            isassigned(e, i) && visit(f, e[i])
        end
    end
    mc.list !== nothing && visit(f, mc.list)
    mc.any !== nothing && visit(f, mc.any)
    nothing
end
function visit(f, d::TypeMapEntry)
    while d !== nothing
        f(d.func)
        d = d.next
    end
    nothing
end

function length(mt::MethodTable)
    n = 0
    visit(mt) do m
        n += 1
    end
    return n::Int
end
isempty(mt::MethodTable) = (mt.defs === nothing)

uncompressed_ast(m::Method) = uncompressed_ast(m, m.source)
function uncompressed_ast(m::Method, s::CodeInfo)
    if isa(s.code, Array{UInt8,1})
        s = ccall(:jl_copy_code_info, Ref{CodeInfo}, (Any,), s)
        s.code = ccall(:jl_uncompress_ast, Array{Any,1}, (Any, Any), m, s.code)
    end
    return s
end

# this type mirrors jl_cghooks_t (documented in julia.h)
immutable CodegenHooks
    module_setup::Ptr{Void}
    module_activation::Ptr{Void}
    raise_exception::Ptr{Void}

    CodegenHooks(;module_setup=nothing, module_activation=nothing, raise_exception=nothing) =
        new(pointer_from_objref(module_setup),
            pointer_from_objref(module_activation),
            pointer_from_objref(raise_exception))
end

# this type mirrors jl_cgparams_t (documented in julia.h)
immutable CodegenParams
    cached::Cint

    runtime::Cint
    exceptions::Cint
    track_allocations::Cint
    code_coverage::Cint
    static_alloc::Cint
    dynamic_alloc::Cint

    hooks::CodegenHooks

    CodegenParams(;cached::Bool=true,
                   runtime::Bool=true, exceptions::Bool=true,
                   track_allocations::Bool=true, code_coverage::Bool=true,
                   static_alloc::Bool=true, dynamic_alloc::Bool=true,
                   hooks::CodegenHooks=CodegenHooks()) =
        new(Cint(cached),
            Cint(runtime), Cint(exceptions),
            Cint(track_allocations), Cint(code_coverage),
            Cint(static_alloc), Cint(dynamic_alloc),
            hooks)
end

# Printing code representations in IR and assembly
function _dump_function(f::ANY, t::ANY, native::Bool, wrapper::Bool,
                        strip_ir_metadata::Bool, dump_module::Bool, syntax::Symbol=:att,
                        optimize::Bool=true, params::CodegenParams=CodegenParams())
    ccall(:jl_is_in_pure_context, Bool, ()) && error("code reflection cannot be used from generated functions")
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    # get the MethodInstance for the method match
    world = typemax(UInt)
    meth = which(f, t)
    t = to_tuple_type(t)
    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)
    # get the code for it
    return _dump_function_linfo(linfo, world, native, wrapper, strip_ir_metadata, dump_module, syntax, optimize, params)
end

function _dump_function_linfo(linfo::Core.MethodInstance, world::UInt, native::Bool, wrapper::Bool,
                              strip_ir_metadata::Bool, dump_module::Bool, syntax::Symbol=:att,
                              optimize::Bool=true, params::CodegenParams=CodegenParams())
    if syntax != :att && syntax != :intel
        throw(ArgumentError("'syntax' must be either :intel or :att"))
    end
    if native
        llvmf = ccall(:jl_get_llvmf_decl, Ptr{Void}, (Any, UInt, Bool, CodegenParams), linfo, world, wrapper, params)
    else
        llvmf = ccall(:jl_get_llvmf_defn, Ptr{Void}, (Any, UInt, Bool, Bool, CodegenParams), linfo, world, wrapper, optimize, params)
    end
    if llvmf == C_NULL
        error("could not compile the specified method")
    end

    if native
        str = ccall(:jl_dump_function_asm, Ref{String},
                    (Ptr{Void}, Cint, Cstring), llvmf, 0, syntax)
    else
        str = ccall(:jl_dump_function_ir, Ref{String},
                    (Ptr{Void}, Bool, Bool), llvmf, strip_ir_metadata, dump_module)
    end

    # TODO: use jl_is_cacheable_sig instead of isleaftype
    isleaftype(linfo.specTypes) || (str = "; WARNING: This code may not match what actually runs.\n" * str)
    return str
end

"""
    code_llvm([io], f, types)

Prints the LLVM bitcodes generated for running the method matching the given generic
function and type signature to `io` which defaults to `STDOUT`.

All metadata and dbg.* calls are removed from the printed bitcode. Use code_llvm_raw for the full IR.
"""
code_llvm(io::IO, f::ANY, types::ANY=Tuple, strip_ir_metadata=true, dump_module=false) =
    print(io, _dump_function(f, types, false, false, strip_ir_metadata, dump_module))
code_llvm(f::ANY, types::ANY=Tuple) = code_llvm(STDOUT, f, types)
code_llvm_raw(f::ANY, types::ANY=Tuple) = code_llvm(STDOUT, f, types, false)

"""
    code_native([io], f, types, [syntax])

Prints the native assembly instructions generated for running the method matching the given
generic function and type signature to `io` which defaults to `STDOUT`.
Switch assembly syntax using `syntax` symbol parameter set to `:att` for AT&T syntax or `:intel` for Intel syntax. Output is AT&T syntax by default.
"""
code_native(io::IO, f::ANY, types::ANY=Tuple, syntax::Symbol=:att) =
    print(io, _dump_function(f, types, true, false, false, false, syntax))
code_native(f::ANY, types::ANY=Tuple, syntax::Symbol=:att) = code_native(STDOUT, f, types, syntax)
code_native(::IO, ::ANY, ::Symbol) = error("illegal code_native call") # resolve ambiguous call

# give a decent error message if we try to instantiate a staged function on non-leaf types
function func_for_method_checked(m::Method, types::ANY)
    if m.isstaged && !isleaftype(types)
        error("cannot call @generated function `", m, "` ",
              "with abstract argument types: ", types)
    end
    return m
end


"""
    code_typed(f, types; optimize=true)

Returns an array of lowered and type-inferred ASTs for the methods matching the given
generic function and type signature. The keyword argument `optimize` controls whether
additional optimizations, such as inlining, are also applied.
"""
function code_typed(f::ANY, types::ANY=Tuple; optimize=true)
    ccall(:jl_is_in_pure_context, Bool, ()) && error("code reflection cannot be used from generated functions")
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    types = to_tuple_type(types)
    asts = []
    world = typemax(UInt)
    params = Core.Inference.InferenceParams(world)
    for x in _methods(f, types, -1, world)
        meth = func_for_method_checked(x[3], types)
        (_, code, ty) = Core.Inference.typeinf_code(meth, x[1], x[2], optimize, optimize, params)
        code === nothing && error("inference not successful") # Inference disabled?
        push!(asts, uncompressed_ast(meth, code) => ty)
    end
    return asts
end

function return_types(f::ANY, types::ANY=Tuple)
    ccall(:jl_is_in_pure_context, Bool, ()) && error("code reflection cannot be used from generated functions")
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    types = to_tuple_type(types)
    rt = []
    world = typemax(UInt)
    params = Core.Inference.InferenceParams(world)
    for x in _methods(f, types, -1, world)
        meth = func_for_method_checked(x[3], types)
        ty = Core.Inference.typeinf_type(meth, x[1], x[2], true, params)
        ty === nothing && error("inference not successful") # Inference disabled?
        push!(rt, ty)
    end
    return rt
end

"""
    which(f, types)

Returns the method of `f` (a `Method` object) that would be called for arguments of the given `types`.

If `types` is an abstract type, then the method that would be called by `invoke` is returned.
"""
function which(f::ANY, t::ANY)
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    t = to_tuple_type(t)
    if isleaftype(t)
        ms = methods(f, t)
        isempty(ms) && error("no method found for the specified argument types")
        length(ms)!=1 && error("no unique matching method for the specified argument types")
        return first(ms)
    else
        ft = isa(f,Type) ? Type{f} : typeof(f)
        tt = Tuple{ft, t.parameters...}
        m = ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), tt, typemax(UInt))
        if m === nothing
            error("no method found for the specified argument types")
        end
        meth = m.func::Method
        if ccall(:jl_has_call_ambiguities, Cint, (Any, Any), tt, meth) != 0
            error("method match is ambiguous for the specified argument types")
        end
        return meth
    end
end

"""
    which(symbol)

Return the module in which the binding for the variable referenced by `symbol` was created.
"""
which(s::Symbol) = which_module(current_module(), s)
# TODO: making this a method of which() causes a strange error
function which_module(m::Module, s::Symbol)
    if !isdefined(m, s)
        error("\"$s\" is not defined in module $m")
    end
    return binding_module(m, s)
end

# function reflection
"""
    Base.function_name(f::Function) -> Symbol

Get the name of a generic `Function` as a symbol, or `:anonymous`.
"""
function_name(f::Function) = typeof(f).name.mt.name

functionloc(m::Core.MethodInstance) = functionloc(m.def)

"""
    functionloc(m::Method)

Returns a tuple `(filename,line)` giving the location of a `Method` definition.
"""
function functionloc(m::Method)
    ln = m.line
    if ln <= 0
        error("could not determine location of method definition")
    end
    return (find_source_file(string(m.file)), ln)
end

"""
    functionloc(f::Function, types)

Returns a tuple `(filename,line)` giving the location of a generic `Function` definition.
"""
functionloc(f::ANY, types::ANY) = functionloc(which(f,types))

function functionloc(f::ANY)
    mt = methods(f)
    if isempty(mt)
        if isa(f, Function)
            error("function has no definitions")
        else
            error("object is not callable")
        end
    end
    if length(mt) > 1
        error("function has multiple methods; please specify a type signature")
    end
    return functionloc(first(mt))
end

"""
    Base.function_module(f::Function) -> Module

Determine the module containing the (first) definition of a generic
function.
"""
function_module(f::Function) = datatype_module(typeof(f))

"""
    Base.function_module(f::Function, types) -> Module

Determine the module containing a given definition of a generic function.
"""
function function_module(f::ANY, types::ANY)
    m = methods(f, types)
    if isempty(m)
        error("no matching methods")
    end
    return first(m).module
end

"""
    method_exists(f, Tuple type) -> Bool

Determine whether the given generic function has a method matching the given
`Tuple` of argument types.

```jldoctest
julia> method_exists(length, Tuple{Array})
true
```
"""
function method_exists(f::ANY, t::ANY)
    t = to_tuple_type(t)
    t = Tuple{isa(f,Type) ? Type{f} : typeof(f), t.parameters...}
    return ccall(:jl_method_exists, Cint, (Any, Any, UInt), typeof(f).name.mt, t,
        typemax(UInt)) != 0
end

function isambiguous(m1::Method, m2::Method)
    ti = typeintersect(m1.sig, m2.sig)
    ti === Bottom && return false
    ml = _methods_by_ftype(ti, -1, typemax(UInt))
    isempty(ml) && return true
    for m in ml
        if ti <: m[3].sig
            return false
        end
    end
    return true
end

min_world(m::Method) = reinterpret(UInt, m.min_world)
max_world(m::Method) = reinterpret(UInt, m.max_world)
min_world(m::Core.MethodInstance) = reinterpret(UInt, m.min_world)
max_world(m::Core.MethodInstance) = reinterpret(UInt, m.max_world)