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

# name and module reflection

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

Get the name of a `Module` as a [`Symbol`](@ref).

# Examples
```jldoctest
julia> nameof(Base.Broadcast)
:Broadcast
```
"""
nameof(m::Module) = ccall(:jl_module_name, Ref{Symbol}, (Any,), m)

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

Get a module's enclosing `Module`. `Main` is its own parent.

See also: [`names`](@ref), [`nameof`](@ref), [`fullname`](@ref), [`@__MODULE__`](@ref).

# Examples
```jldoctest
julia> parentmodule(Main)
Main

julia> parentmodule(Base.Broadcast)
Base
```
"""
parentmodule(m::Module) = ccall(:jl_module_parent, Ref{Module}, (Any,), m)

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

Find the root module of a given module. This is the first module in the chain of
parent modules of `m` which is either a registered root module or which is its
own parent module.
"""
function moduleroot(m::Module)
    while true
        is_root_module(m) && return m
        p = parentmodule(m)
        p === m && return m
        m = p
    end
end

"""
    @__MODULE__ -> Module

Get the `Module` of the toplevel eval,
which is the `Module` code is currently being read from.
"""
macro __MODULE__()
    return __module__
end

"""
    fullname(m::Module)

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

# Examples
```jldoctest
julia> fullname(Base.Iterators)
(:Base, :Iterators)

julia> fullname(Main)
(:Main,)
```
"""
function fullname(m::Module)
    mn = nameof(m)
    if m === Main || m === Base || m === Core
        return (mn,)
    end
    mp = parentmodule(m)
    if mp === m
        return (mn,)
    end
    return (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`.

See also: [`@locals`](@ref Base.@locals), [`@__MODULE__`](@ref).
"""
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

function binding_module(m::Module, s::Symbol)
    p = ccall(:jl_get_module_of_binding, Ptr{Cvoid}, (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

const NamedTuple_typename = NamedTuple.body.body.name

function _fieldnames(@nospecialize t)
    if t.name === NamedTuple_typename
        if t.parameters[1] isa Tuple
            return t.parameters[1]
        else
            throw(ArgumentError("type does not have definite field names"))
        end
    end
    return t.name.names
end

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

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

# Examples
```jldoctest
julia> fieldname(Rational, 1)
:num

julia> fieldname(Rational, 2)
:den
```
"""
function fieldname(t::DataType, i::Integer)
    throw_not_def_field() = throw(ArgumentError("type does not have definite field names"))
    function throw_field_access(t, i, n_fields)
        field_label = n_fields == 1 ? "field" : "fields"
        throw(ArgumentError("Cannot access field $i since type $t only has $n_fields $field_label."))
    end
    throw_need_pos_int(i) = throw(ArgumentError("Field numbers must be positive integers. $i is invalid."))

    isabstracttype(t) && throw_not_def_field()
    names = _fieldnames(t)
    n_fields = length(names)::Int
    i > n_fields && throw_field_access(t, i, n_fields)
    i < 1 && throw_need_pos_int(i)
    return @inbounds names[i]::Symbol
end

fieldname(t::UnionAll, i::Integer) = fieldname(unwrap_unionall(t), i)
fieldname(t::Type{<:Tuple}, i::Integer) =
    i < 1 || i > fieldcount(t) ? throw(BoundsError(t, i)) : Int(i)

"""
    fieldnames(x::DataType)

Get a tuple with the names of the fields of a `DataType`.

See also [`propertynames`](@ref), [`hasfield`](@ref).

# Examples
```jldoctest
julia> fieldnames(Rational)
(:num, :den)

julia> fieldnames(typeof(1+im))
(:re, :im)
```
"""
fieldnames(t::DataType) = (fieldcount(t); # error check to make sure type is specific enough
                           (_fieldnames(t)...,))::Tuple{Vararg{Symbol}}
fieldnames(t::UnionAll) = fieldnames(unwrap_unionall(t))
fieldnames(::Core.TypeofBottom) =
    throw(ArgumentError("The empty type does not have field names since it does not have instances."))
fieldnames(t::Type{<:Tuple}) = ntuple(identity, fieldcount(t))

"""
    hasfield(T::Type, name::Symbol)

Return a boolean indicating whether `T` has `name` as one of its own fields.

!!! compat "Julia 1.2"
     This function requires at least Julia 1.2.
"""
function hasfield(T::Type, name::Symbol)
    @_pure_meta
    return fieldindex(T, name, false) > 0
end

"""
    nameof(t::DataType) -> Symbol

Get the name of a (potentially `UnionAll`-wrapped) `DataType` (without its parent module)
as a symbol.

# Examples
```jldoctest
julia> module Foo
           struct S{T}
           end
       end
Foo

julia> nameof(Foo.S{T} where T)
:S
```
"""
nameof(t::DataType) = t.name.name
nameof(t::UnionAll) = nameof(unwrap_unionall(t))::Symbol

"""
    parentmodule(t::DataType) -> Module

Determine the module containing the definition of a (potentially `UnionAll`-wrapped) `DataType`.

# Examples
```jldoctest
julia> module Foo
           struct Int end
       end
Foo

julia> parentmodule(Int)
Core

julia> parentmodule(Foo.Int)
Foo
```
"""
parentmodule(t::DataType) = t.name.module
parentmodule(t::UnionAll) = parentmodule(unwrap_unionall(t))

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

Determine whether a global is declared `const` in a given `Module`.
"""
isconst(m::Module, s::Symbol) =
    ccall(:jl_is_const, Cint, (Any, Any), m, s) != 0

"""
    @locals()

Construct a dictionary of the names (as symbols) and values of all local
variables defined as of the call site.

!!! compat "Julia 1.1"
    This macro requires at least Julia 1.1.

# Examples
```jldoctest
julia> let x = 1, y = 2
           Base.@locals
       end
Dict{Symbol, Any} with 2 entries:
  :y => 2
  :x => 1

julia> function f(x)
           local y
           show(Base.@locals); println()
           for i = 1:1
               show(Base.@locals); println()
           end
           y = 2
           show(Base.@locals); println()
           nothing
       end;

julia> f(42)
Dict{Symbol, Any}(:x => 42)
Dict{Symbol, Any}(:i => 1, :x => 42)
Dict{Symbol, Any}(:y => 2, :x => 42)
```
"""
macro locals()
    return Expr(:locals)
end

"""
    objectid(x) -> UInt

Get a hash value for `x` based on object identity. `objectid(x)==objectid(y)` if `x === y`.

See also [`hash`](@ref), [`IdDict`](@ref).
"""
objectid(@nospecialize(x)) = ccall(:jl_object_id, UInt, (Any,), x)

# concrete datatype predicates

datatype_fieldtypes(x::DataType) = ccall(:jl_get_fieldtypes, Any, (Any,), x)

struct DataTypeLayout
    nfields::UInt32
    npointers::UInt32
    firstptr::Int32
    alignment::UInt16
    flags::UInt16
    # haspadding : 1;
    # fielddesc_type : 2;
end

"""
    Base.datatype_alignment(dt::DataType) -> Int

Memory allocation minimum alignment for instances of this type.
Can be called on any `isconcretetype`.
"""
function datatype_alignment(dt::DataType)
    @_pure_meta
    dt.layout == C_NULL && throw(UndefRefError())
    alignment = unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).alignment
    return Int(alignment)
end

function uniontype_layout(T::Type)
    sz = RefValue{Csize_t}(0)
    algn = RefValue{Csize_t}(0)
    isinline = ccall(:jl_islayout_inline, Cint, (Any, Ptr{Csize_t}, Ptr{Csize_t}), T, sz, algn) != 0
    (isinline, sz[], algn[])
end

# amount of total space taken by T when stored in a container
function aligned_sizeof(T::Type)
    @_pure_meta
    if isbitsunion(T)
        _, sz, al = uniontype_layout(T)
        return (sz + al - 1) & -al
    elseif allocatedinline(T)
        al = datatype_alignment(T)
        return (Core.sizeof(T) + al - 1) & -al
    else
        return Core.sizeof(Ptr{Cvoid})
    end
end

gc_alignment(sz::Integer) = Int(ccall(:jl_alignment, Cint, (Csize_t,), sz))
gc_alignment(T::Type) = gc_alignment(Core.sizeof(T))

"""
    Base.datatype_haspadding(dt::DataType) -> Bool

Return whether the fields of instances of this type are packed in memory,
with no intervening padding bytes.
Can be called on any `isconcretetype`.
"""
function datatype_haspadding(dt::DataType)
    @_pure_meta
    dt.layout == C_NULL && throw(UndefRefError())
    flags = unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).flags
    return flags & 1 == 1
end

"""
    Base.datatype_nfields(dt::DataType) -> Bool

Return the number of fields known to this datatype's layout.
Can be called on any `isconcretetype`.
"""
function datatype_nfields(dt::DataType)
    @_pure_meta
    dt.layout == C_NULL && throw(UndefRefError())
    return unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).nfields
end

"""
    Base.datatype_pointerfree(dt::DataType) -> Bool

Return whether instances of this type can contain references to gc-managed memory.
Can be called on any `isconcretetype`.
"""
function datatype_pointerfree(dt::DataType)
    @_pure_meta
    dt.layout == C_NULL && throw(UndefRefError())
    npointers = unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).npointers
    return npointers == 0
end

"""
    Base.datatype_fielddesc_type(dt::DataType) -> Int

Return the size in bytes of each field-description entry in the layout array,
located at `(dt.layout + sizeof(DataTypeLayout))`.
Can be called on any `isconcretetype`.

See also [`fieldoffset`](@ref).
"""
function datatype_fielddesc_type(dt::DataType)
    @_pure_meta
    dt.layout == C_NULL && throw(UndefRefError())
    flags = unsafe_load(convert(Ptr{DataTypeLayout}, dt.layout)).flags
    return (flags >> 1) & 3
end

# For type stability, we only expose a single struct that describes everything
struct FieldDesc
    isforeign::Bool
    isptr::Bool
    size::UInt32
    offset::UInt32
end

struct FieldDescStorage{T}
    ptrsize::T
    offset::T
end
FieldDesc(fd::FieldDescStorage{T}) where {T} =
    FieldDesc(false, fd.ptrsize & 1 != 0,
              fd.ptrsize >> 1, fd.offset)

struct DataTypeFieldDesc
    dt::DataType
    function DataTypeFieldDesc(dt::DataType)
        dt.layout == C_NULL && throw(UndefRefError())
        new(dt)
    end
end

function getindex(dtfd::DataTypeFieldDesc, i::Int)
    layout_ptr = convert(Ptr{DataTypeLayout}, dtfd.dt.layout)
    fd_ptr = layout_ptr + sizeof(DataTypeLayout)
    layout = unsafe_load(layout_ptr)
    fielddesc_type = (layout.flags >> 1) & 3
    nfields = layout.nfields
    @boundscheck ((1 <= i <= nfields) || throw(BoundsError(dtfd, i)))
    if fielddesc_type == 0
        return FieldDesc(unsafe_load(Ptr{FieldDescStorage{UInt8}}(fd_ptr), i))
    elseif fielddesc_type == 1
        return FieldDesc(unsafe_load(Ptr{FieldDescStorage{UInt16}}(fd_ptr), i))
    elseif fielddesc_type == 2
        return FieldDesc(unsafe_load(Ptr{FieldDescStorage{UInt32}}(fd_ptr), i))
    else
        # fielddesc_type == 3
        return FieldDesc(true, true, 0, 0)
    end
end

"""
    ismutable(v) -> Bool

Return `true` iff value `v` is mutable.  See [Mutable 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.

See also [`isbits`](@ref), [`isstructtype`](@ref).

# Examples
```jldoctest
julia> ismutable(1)
false

julia> ismutable([1,2])
true
```

!!! compat "Julia 1.5"
    This function requires at least Julia 1.5.
"""
ismutable(@nospecialize(x)) = (@_pure_meta; typeof(x).name.flags & 0x2 == 0x2)


"""
    ismutabletype(T) -> Bool

Determine whether type `T` was declared as a mutable type
(i.e. using `mutable struct` keyword).

!!! compat "Julia 1.7"
    This function requires at least Julia 1.7.
"""
function ismutabletype(@nospecialize(t::Type))
    t = unwrap_unionall(t)
    # TODO: what to do for `Union`?
    return isa(t, DataType) && t.name.flags & 0x2 == 0x2
end


"""
    isstructtype(T) -> Bool

Determine whether type `T` was declared as a struct type
(i.e. using the `struct` or `mutable struct` keyword).
"""
function isstructtype(@nospecialize(t::Type))
    @_pure_meta
    t = unwrap_unionall(t)
    # TODO: what to do for `Union`?
    isa(t, DataType) || return false
    hasfield = !isdefined(t, :types) || !isempty(t.types)
    return hasfield || (t.size == 0 && !isabstracttype(t))
end

"""
    isprimitivetype(T) -> Bool

Determine whether type `T` was declared as a primitive type
(i.e. using the `primitive` keyword).
"""
function isprimitivetype(@nospecialize(t::Type))
    @_pure_meta
    t = unwrap_unionall(t)
    # TODO: what to do for `Union`?
    isa(t, DataType) || return false
    hasfield = !isdefined(t, :types) || !isempty(t.types)
    return !hasfield && t.size != 0 && !isabstracttype(t)
end

"""
    isbitstype(T)

Return `true` if type `T` is a "plain data" type,
meaning it is immutable and contains no references to other values,
only `primitive` types and other `isbitstype` types.
Typical examples are numeric types such as [`UInt8`](@ref),
[`Float64`](@ref), and [`Complex{Float64}`](@ref).
This category of types is significant since they are valid as type parameters,
may not track [`isdefined`](@ref) / [`isassigned`](@ref) status,
and have a defined layout that is compatible with C.

See also [`isbits`](@ref), [`isprimitivetype`](@ref), [`ismutable`](@ref).

# Examples
```jldoctest
julia> isbitstype(Complex{Float64})
true

julia> isbitstype(Complex)
false
```
"""
isbitstype(@nospecialize(t::Type)) = (@_pure_meta; isa(t, DataType) && (t.flags & 0x8) == 0x8)

"""
    isbits(x)

Return `true` if `x` is an instance of an [`isbitstype`](@ref) type.
"""
isbits(@nospecialize x) = (@_pure_meta; typeof(x).flags & 0x8 == 0x8)

"""
    isdispatchtuple(T)

Determine whether type `T` is a tuple "leaf type",
meaning it could appear as a type signature in dispatch
and has no subtypes (or supertypes) which could appear in a call.
"""
isdispatchtuple(@nospecialize(t)) = (@_pure_meta; isa(t, DataType) && (t.flags & 0x4) == 0x4)

iskindtype(@nospecialize t) = (t === DataType || t === UnionAll || t === Union || t === typeof(Bottom))
isconcretedispatch(@nospecialize t) = isconcretetype(t) && !iskindtype(t)
has_free_typevars(@nospecialize(t)) = ccall(:jl_has_free_typevars, Cint, (Any,), t) != 0

# equivalent to isa(v, Type) && isdispatchtuple(Tuple{v}) || v === Union{}
# and is thus perhaps most similar to the old (pre-1.0) `isleaftype` query
const _TYPE_NAME = Type.body.name
function isdispatchelem(@nospecialize v)
    return (v === Bottom) || (v === typeof(Bottom)) || isconcretedispatch(v) ||
        (isa(v, DataType) && v.name === _TYPE_NAME && !has_free_typevars(v)) # isType(v)
end

"""
    isconcretetype(T)

Determine whether type `T` is a concrete type, meaning it could have direct instances
(values `x` such that `typeof(x) === T`).

See also: [`isbits`](@ref), [`isabstracttype`](@ref), [`issingletontype`](@ref).

# Examples
```jldoctest
julia> isconcretetype(Complex)
false

julia> isconcretetype(Complex{Float32})
true

julia> isconcretetype(Vector{Complex})
true

julia> isconcretetype(Vector{Complex{Float32}})
true

julia> isconcretetype(Union{})
false

julia> isconcretetype(Union{Int,String})
false
```
"""
isconcretetype(@nospecialize(t)) = (@_pure_meta; isa(t, DataType) && (t.flags & 0x2) == 0x2)

"""
    isabstracttype(T)

Determine whether type `T` was declared as an abstract type
(i.e. using the `abstract` keyword).

# Examples
```jldoctest
julia> isabstracttype(AbstractArray)
true

julia> isabstracttype(Vector)
false
```
"""
function isabstracttype(@nospecialize(t))
    @_pure_meta
    t = unwrap_unionall(t)
    # TODO: what to do for `Union`?
    return isa(t, DataType) && (t.name.flags & 0x1) == 0x1
end

"""
    Base.issingletontype(T)

Determine whether type `T` has exactly one possible instance; for example, a
struct type with no fields.
"""
issingletontype(@nospecialize(t)) = (@_pure_meta; isa(t, DataType) && isdefined(t, :instance))

"""
    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(@nospecialize(a), @nospecialize(b)) = (@_pure_meta; ccall(:jl_type_intersection, Any, (Any, Any), a, b))

morespecific(@nospecialize(a), @nospecialize(b)) = ccall(:jl_type_morespecific, Cint, (Any, Any), a, b) != 0

"""
    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:

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

julia> structinfo(Base.Filesystem.StatStruct)
13-element Vector{Tuple{UInt64, Symbol, Type}}:
 (0x0000000000000000, :desc, Union{RawFD, String})
 (0x0000000000000008, :device, UInt64)
 (0x0000000000000010, :inode, UInt64)
 (0x0000000000000018, :mode, UInt64)
 (0x0000000000000020, :nlink, Int64)
 (0x0000000000000028, :uid, UInt64)
 (0x0000000000000030, :gid, UInt64)
 (0x0000000000000038, :rdev, UInt64)
 (0x0000000000000040, :size, Int64)
 (0x0000000000000048, :blksize, Int64)
 (0x0000000000000050, :blocks, Int64)
 (0x0000000000000058, :mtime, Float64)
 (0x0000000000000060, :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`.

# Examples
```jldoctest
julia> struct Foo
           x::Int64
           y::String
       end

julia> fieldtype(Foo, :x)
Int64

julia> fieldtype(Foo, 2)
String
```
"""
fieldtype

"""
    Base.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).

# Examples
```jldoctest
julia> struct Foo
           x::Int64
           y::String
       end

julia> Base.fieldindex(Foo, :z)
ERROR: type Foo has no field z
Stacktrace:
[...]

julia> Base.fieldindex(Foo, :z, false)
0
```
"""
function fieldindex(T::DataType, name::Symbol, err::Bool=true)
    return Int(ccall(:jl_field_index, Cint, (Any, Any, Cint), T, name, err)+1)
end

function fieldindex(t::UnionAll, name::Symbol, err::Bool=true)
    t = argument_datatype(t)
    if t === nothing
        throw(ArgumentError("type does not have definite fields"))
    end
    return fieldindex(t, name, err)
end

argument_datatype(@nospecialize t) = ccall(:jl_argument_datatype, Any, (Any,), t)

"""
    fieldcount(t::Type)

Get the number of fields that an instance of the given type would have.
An error is thrown if the type is too abstract to determine this.
"""
function fieldcount(@nospecialize t)
    if t isa UnionAll || t isa Union
        t = argument_datatype(t)
        if t === nothing
            throw(ArgumentError("type does not have a definite number of fields"))
        end
        t = t::DataType
    elseif t == Union{}
        throw(ArgumentError("The empty type does not have a well-defined number of fields since it does not have instances."))
    end
    if !(t isa DataType)
        throw(TypeError(:fieldcount, DataType, t))
    end
    if t.name === NamedTuple_typename
        names, types = t.parameters[1], t.parameters[2]
        if names isa Tuple
            return length(names)
        end
        if types isa DataType && types <: Tuple
            return fieldcount(types)
        end
        abstr = true
    else
        abstr = isabstracttype(t) || (t.name === Tuple.name && isvatuple(t))
    end
    if abstr
        throw(ArgumentError("type does not have a definite number of fields"))
    end
    if isdefined(t, :types)
        return length(t.types)
    end
    return length(t.name.names)
end

"""
    fieldtypes(T::Type)

The declared types of all fields in a composite DataType `T` as a tuple.

!!! compat "Julia 1.1"
    This function requires at least Julia 1.1.

# Examples
```jldoctest
julia> struct Foo
           x::Int64
           y::String
       end

julia> fieldtypes(Foo)
(Int64, String)
```
"""
fieldtypes(T::Type) = ntupleany(i -> fieldtype(T, i), fieldcount(T))

# 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`).

# Example
```jldoctest
julia> @enum Color red blue green

julia> instances(Color)
(red, blue, green)
```
"""
function instances end

function to_tuple_type(@nospecialize(t))
    if isa(t, Tuple) || isa(t, AbstractArray) || isa(t, SimpleVector)
        t = Tuple{t...}
    end
    if isa(t, Type) && t <: Tuple
        for p in unwrap_unionall(t).parameters
            if isa(p, Core.TypeofVararg)
                p = p.T
            end
            if !(isa(p, Type) || isa(p, TypeVar))
                error("argument tuple type must contain only types")
            end
        end
    else
        error("expected tuple type")
    end
    t
end

function signature_type(@nospecialize(f), @nospecialize(args))
    f_type = isa(f, Type) ? Type{f} : typeof(f)
    if isa(args, Type)
        u = unwrap_unionall(args)
        return rewrap_unionall(Tuple{f_type, u.parameters...}, args)
    else
        return Tuple{f_type, args...}
    end
end

"""
    code_lowered(f, types; generated=true, debuginfo=:default)

Return an array of the lowered forms (IR) for the methods matching the given generic function
and type signature.

If `generated` is `false`, the returned `CodeInfo` instances will correspond to fallback
implementations. An error is thrown if no fallback implementation exists.
If `generated` is `true`, these `CodeInfo` instances will correspond to the method bodies
yielded by expanding the generators.

The keyword `debuginfo` controls the amount of code metadata present in the output.

Note that an error will be thrown if `types` are not leaf types when `generated` is
`true` and any of the corresponding methods are an `@generated` method.
"""
function code_lowered(@nospecialize(f), @nospecialize(t=Tuple); generated::Bool=true, debuginfo::Symbol=:default)
    if @isdefined(IRShow)
        debuginfo = IRShow.debuginfo(debuginfo)
    elseif debuginfo === :default
        debuginfo = :source
    end
    if debuginfo !== :source && debuginfo !== :none
        throw(ArgumentError("'debuginfo' must be either :source or :none"))
    end
    return map(method_instances(f, t)) do m
        if generated && hasgenerator(m)
            if may_invoke_generator(m)
                return ccall(:jl_code_for_staged, Any, (Any,), m)::CodeInfo
            else
                error("Could not expand generator for `@generated` method ", m, ". ",
                      "This can happen if the provided argument types (", t, ") are ",
                      "not leaf types, but the `generated` argument is `true`.")
            end
        end
        code = uncompressed_ir(m.def::Method)
        debuginfo === :none && remove_linenums!(code)
        return code
    end
end

hasgenerator(m::Method) = isdefined(m, :generator)
hasgenerator(m::Core.MethodInstance) = hasgenerator(m.def::Method)

# low-level method lookup functions used by the compiler

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

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

function _methods(@nospecialize(f), @nospecialize(t), lim::Int, world::UInt)
    tt = signature_type(f, t)
    return _methods_by_ftype(tt, lim, world)
end

function _methods_by_ftype(@nospecialize(t), lim::Int, world::UInt)
    return _methods_by_ftype(t, nothing, lim, world)
end
function _methods_by_ftype(@nospecialize(t), mt::Union{Core.MethodTable, Nothing}, lim::Int, world::UInt)
    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::Array{UInt,1}, max::Array{UInt,1}, has_ambig::Array{Int32,1})
    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}
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}
end

function _method_by_ftype(args...)
    matches = _methods_by_ftype(args...)
    if length(matches) != 1
        error("no unique matching method found for the specified argument types")
    end
    return matches[1]
end

# high-level, more convenient method lookup functions

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

size(m::MethodList) = size(m.ms)
getindex(m::MethodList, i) = m.ms[i]

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

"""
    methods(f, [types], [module])

Return the method table for `f`.

If `types` is specified, return an array of methods whose types match.
If `module` is specified, return an array of methods defined in that module.
A list of modules can also be specified as an array.

!!! compat "Julia 1.4"
    At least Julia 1.4 is required for specifying a module.

See also: [`which`](@ref) and `@which`.
"""
function methods(@nospecialize(f), @nospecialize(t),
                 mod::Union{Tuple{Module},AbstractArray{Module},Nothing}=nothing)
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    t = to_tuple_type(t)
    world = typemax(UInt)
    # Lack of specialization => a comprehension triggers too many invalidations via _collect, so collect the methods manually
    ms = Method[]
    for m in _methods(f, t, -1, world)::Vector
        m = m::Core.MethodMatch
        (mod === nothing || m.method.module ∈ mod) && push!(ms, m.method)
    end
    MethodList(ms, typeof(f).name.mt)
end
methods(@nospecialize(f), @nospecialize(t), mod::Module) = methods(f, t, (mod,))

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

function methods_including_ambiguous(@nospecialize(f), @nospecialize(t))
    tt = signature_type(f, t)
    world = typemax(UInt)
    min = RefValue{UInt}(typemin(UInt))
    max = RefValue{UInt}(typemax(UInt))
    ms = _methods_by_ftype(tt, nothing, -1, world, true, min, max, Ptr{Int32}(C_NULL))
    isa(ms, Bool) && return ms
    return MethodList(Method[(m::Core.MethodMatch).method for m in ms], typeof(f).name.mt)
end

function methods(@nospecialize(f),
                 mod::Union{Module,AbstractArray{Module},Nothing}=nothing)
    # return all matches
    return methods(f, Tuple{Vararg{Any}}, mod)
end

function visit(f, mt::Core.MethodTable)
    mt.defs !== nothing && visit(f, mt.defs)
    nothing
end
function visit(f, mc::Core.TypeMapLevel)
    if mc.targ !== nothing
        e = mc.targ::Vector{Any}
        for i in 2:2:length(e)
            isassigned(e, i) && visit(f, e[i])
        end
    end
    if mc.arg1 !== nothing
        e = mc.arg1::Vector{Any}
        for i in 2:2:length(e)
            isassigned(e, i) && visit(f, e[i])
        end
    end
    if mc.tname !== nothing
        e = mc.tname::Vector{Any}
        for i in 2:2:length(e)
            isassigned(e, i) && visit(f, e[i])
        end
    end
    if mc.name1 !== nothing
        e = mc.name1::Vector{Any}
        for i in 2:2: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::Core.TypeMapEntry)
    while d !== nothing
        f(d.func)
        d = d.next
    end
    nothing
end

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

uncompressed_ir(m::Method) = isdefined(m, :source) ? _uncompressed_ir(m, m.source) :
                             isdefined(m, :generator) ? error("Method is @generated; try `code_lowered` instead.") :
                             error("Code for this Method is not available.")
_uncompressed_ir(m::Method, s::CodeInfo) = copy(s)
_uncompressed_ir(m::Method, s::Array{UInt8,1}) = ccall(:jl_uncompress_ir, Any, (Any, Ptr{Cvoid}, Any), m, C_NULL, s)::CodeInfo
_uncompressed_ir(ci::Core.CodeInstance, s::Array{UInt8,1}) = ccall(:jl_uncompress_ir, Any, (Any, Any, Any), ci.def.def::Method, ci, s)::CodeInfo
# for backwards compat
const uncompressed_ast = uncompressed_ir
const _uncompressed_ast = _uncompressed_ir

function method_instances(@nospecialize(f), @nospecialize(t), world::UInt = typemax(UInt))
    tt = signature_type(f, t)
    results = Core.MethodInstance[]
    for match in _methods_by_ftype(tt, -1, world)::Vector
        instance = Core.Compiler.specialize_method(match)
        push!(results, instance)
    end
    return results
end

default_debug_info_kind() = unsafe_load(cglobal(:jl_default_debug_info_kind, Cint))

# this type mirrors jl_cgparams_t (documented in julia.h)
struct CodegenParams
    track_allocations::Cint
    code_coverage::Cint
    prefer_specsig::Cint
    gnu_pubnames::Cint
    debug_info_kind::Cint

    lookup::Ptr{Cvoid}

    generic_context::Any

    function CodegenParams(; track_allocations::Bool=true, code_coverage::Bool=true,
                   prefer_specsig::Bool=false,
                   gnu_pubnames=true, debug_info_kind::Cint = default_debug_info_kind(),
                   lookup::Ptr{Cvoid}=cglobal(:jl_rettype_inferred),
                   generic_context = nothing)
        return new(
            Cint(track_allocations), Cint(code_coverage),
            Cint(prefer_specsig),
            Cint(gnu_pubnames), debug_info_kind,
            lookup, generic_context)
    end
end

const SLOT_USED = 0x8
ast_slotflag(@nospecialize(code), i) = ccall(:jl_ir_slotflag, UInt8, (Any, Csize_t), code, i - 1)

"""
    may_invoke_generator(method, atypes, sparams)

Computes whether or not we may invoke the generator for the given `method` on
the given atypes and sparams. For correctness, all generated function are
required to return monotonic answers. However, since we don't expect users to
be able to successfully implement this criterion, we only call generated
functions on concrete types. The one exception to this is that we allow calling
generators with abstract types if the generator does not use said abstract type
(and thus cannot incorrectly use it to break monotonicity). This function
computes whether we are in either of these cases.

Unlike normal functions, the compilation heuristics still can't generate good dispatch
in some cases, but this may still allow inference not to fall over in some limited cases.
"""
function may_invoke_generator(method::MethodInstance)
    return may_invoke_generator(method.def::Method, method.specTypes, method.sparam_vals)
end
function may_invoke_generator(method::Method, @nospecialize(atypes), sparams::SimpleVector)
    # If we have complete information, we may always call the generator
    isdispatchtuple(atypes) && return true

    # We don't have complete information, but it is possible that the generator
    # syntactically doesn't make use of the information we don't have. Check
    # for that.

    # For now, only handle the (common, generated by the frontend case) that the
    # generator only has one method
    generator = method.generator
    isa(generator, Core.GeneratedFunctionStub) || return false
    gen_mthds = methods(generator.gen)::MethodList
    length(gen_mthds) == 1 || return false

    generator_method = first(gen_mthds)
    nsparams = length(sparams)
    isdefined(generator_method, :source) || return false
    code = generator_method.source
    nslots = ccall(:jl_ir_nslots, Int, (Any,), code)
    at = unwrap_unionall(atypes)::DataType
    (nslots >= 1 + length(sparams) + length(at.parameters)) || return false

    for i = 1:nsparams
        if isa(sparams[i], TypeVar)
            if (ast_slotflag(code, 1 + i) & SLOT_USED) != 0
                return false
            end
        end
    end
    for i = 1:length(at.parameters)
        if !isdispatchelem(at.parameters[i])
            if (ast_slotflag(code, 1 + i + nsparams) & SLOT_USED) != 0
                return false
            end
        end
    end
    return true
end

# give a decent error message if we try to instantiate a staged function on non-leaf types
function func_for_method_checked(m::Method, @nospecialize(types), sparams::SimpleVector)
    if isdefined(m, :generator) && !may_invoke_generator(m, types, sparams)
        error("cannot call @generated function `", m, "` ",
              "with abstract argument types: ", types)
    end
    return m
end

"""
    code_typed(f, types; optimize=true, debuginfo=:default)

Returns an array of type-inferred lowered form (IR) 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.
The keyword `debuginfo` controls the amount of code metadata present in the output,
possible options are `:source` or `:none`.
"""
function code_typed(@nospecialize(f), @nospecialize(types=Tuple);
                    optimize=true,
                    debuginfo::Symbol=:default,
                    world = get_world_counter(),
                    interp = Core.Compiler.NativeInterpreter(world))
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    if isa(f, Core.OpaqueClosure)
        return code_typed_opaque_closure(f, types; optimize, debuginfo, interp)
    end
    ft = Core.Typeof(f)
    if isa(types, Type)
        u = unwrap_unionall(types)
        tt = rewrap_unionall(Tuple{ft, u.parameters...}, types)
    else
        tt = Tuple{ft, types...}
    end
    return code_typed_by_type(tt; optimize, debuginfo, world, interp)
end

"""
    code_typed_by_type(types::Type{<:Tuple}; ...)

Similar to [`code_typed`](@ref), except the argument is a tuple type describing
a full signature to query.
"""
function code_typed_by_type(@nospecialize(tt::Type);
                            optimize=true,
                            debuginfo::Symbol=:default,
                            world = get_world_counter(),
                            interp = Core.Compiler.NativeInterpreter(world))
    ccall(:jl_is_in_pure_context, Bool, ()) && error("code reflection cannot be used from generated functions")
    if @isdefined(IRShow)
        debuginfo = IRShow.debuginfo(debuginfo)
    elseif debuginfo === :default
        debuginfo = :source
    end
    if debuginfo !== :source && debuginfo !== :none
        throw(ArgumentError("'debuginfo' must be either :source or :none"))
    end
    tt = to_tuple_type(tt)
    matches = _methods_by_ftype(tt, -1, world)
    if matches === false
        error("signature does not correspond to a generic function")
    end
    asts = []
    for match in matches::Vector
        match = match::Core.MethodMatch
        meth = func_for_method_checked(match.method, tt, match.sparams)
        (code, ty) = Core.Compiler.typeinf_code(interp, meth, match.spec_types, match.sparams, optimize)
        code === nothing && error("inference not successful") # inference disabled?
        debuginfo === :none && remove_linenums!(code)
        push!(asts, code => ty)
    end
    return asts
end

function code_typed_opaque_closure(@nospecialize(closure::Core.OpaqueClosure), @nospecialize(types=Tuple);
        optimize=true,
        debuginfo::Symbol=:default,
        interp = Core.Compiler.NativeInterpreter(closure.world))
    ccall(:jl_is_in_pure_context, Bool, ()) && error("code reflection cannot be used from generated functions")
    if isa(closure.source, Method)
        code = _uncompressed_ir(closure.source, closure.source.source)
        debuginfo === :none && remove_linenums!(code)
        return Any[Pair{CodeInfo,Any}(code, code.rettype)]
    else
        error("encountered invalid Core.OpaqueClosure object")
    end
end

function return_types(@nospecialize(f), @nospecialize(types=Tuple), interp=Core.Compiler.NativeInterpreter())
    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 = get_world_counter()
    for match in _methods(f, types, -1, world)::Vector
        match = match::Core.MethodMatch
        meth = func_for_method_checked(match.method, types, match.sparams)
        ty = Core.Compiler.typeinf_type(interp, meth, match.spec_types, match.sparams)
        ty === nothing && error("inference not successful") # inference disabled?
        push!(rt, ty)
    end
    return rt
end

"""
    print_statement_costs(io::IO, f, types)

Print type-inferred and optimized code for `f` given argument types `types`,
prepending each line with its cost as estimated by the compiler's inlining engine.
"""
function print_statement_costs(io::IO, @nospecialize(f), @nospecialize(t); kwargs...)
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    tt = signature_type(f, t)
    print_statement_costs(io, tt; kwargs...)
end

function print_statement_costs(io::IO, @nospecialize(tt::Type);
                               world = get_world_counter(),
                               interp = Core.Compiler.NativeInterpreter(world))
    matches = _methods_by_ftype(tt, -1, world)
    if matches === false
        error("signature does not correspond to a generic function")
    end
    params = Core.Compiler.OptimizationParams(interp)
    cst = Int[]
    for match in matches::Vector
        match = match::Core.MethodMatch
        meth = func_for_method_checked(match.method, tt, match.sparams)
        (code, ty) = Core.Compiler.typeinf_code(interp, meth, match.spec_types, match.sparams, true)
        code === nothing && error("inference not successful") # inference disabled?
        empty!(cst)
        resize!(cst, length(code.code))
        maxcost = Core.Compiler.statement_costs!(cst, code.code, code, Any[match.sparams...], false, params)
        nd = ndigits(maxcost)
        println(io, meth)
        irshow_config = IRShow.IRShowConfig() do io, linestart, idx
            print(io, idx > 0 ? lpad(cst[idx], nd+1) : " "^(nd+1), " ")
            return ""
        end
        IRShow.show_ir(io, code, irshow_config)
        println(io)
    end
end

print_statement_costs(args...; kwargs...) = print_statement_costs(stdout, args...; kwargs...)

function _which(@nospecialize(tt::Type), world=get_world_counter())
    min_valid = RefValue{UInt}(typemin(UInt))
    max_valid = RefValue{UInt}(typemax(UInt))
    match = ccall(:jl_gf_invoke_lookup_worlds, Any,
        (Any, UInt, Ptr{Csize_t}, Ptr{Csize_t}),
        tt, world, min_valid, max_valid)
    if match === nothing
        error("no unique matching method found for the specified argument types")
    end
    return match::Core.MethodMatch
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.

See also: [`parentmodule`](@ref), and `@which` and `@edit` in [`InteractiveUtils`](@ref man-interactive-utils).
"""
function which(@nospecialize(f), @nospecialize(t))
    if isa(f, Core.Builtin)
        throw(ArgumentError("argument is not a generic function"))
    end
    t = to_tuple_type(t)
    tt = signature_type(f, t)
    return which(tt)
end

"""
    which(types::Type{<:Tuple})

Returns the method that would be called by the given type signature (as a tuple type).
"""
function which(@nospecialize(tt::Type))
    return _which(tt).method
end

"""
    which(module, symbol)

Return the module in which the binding for the variable referenced by `symbol` in `module` was created.
"""
function which(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

"""
    nameof(f::Function) -> Symbol

Get the name of a generic `Function` as a symbol. For anonymous functions,
this is a compiler-generated name. For explicitly-declared subtypes of
`Function`, it is the name of the function's type.
"""
function nameof(f::Function)
    t = typeof(f)
    mt = t.name.mt
    if mt === Symbol.name.mt
        # uses shared method table, so name is not unique to this function type
        return nameof(t)
    end
    return mt.name
end

function nameof(f::Core.IntrinsicFunction)
    name = ccall(:jl_intrinsic_name, Ptr{UInt8}, (Core.IntrinsicFunction,), f)
    return ccall(:jl_symbol, Ref{Symbol}, (Ptr{UInt8},), name)
end

"""
    parentmodule(f::Function) -> Module

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

"""
    parentmodule(f::Function, types) -> Module

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

"""
    hasmethod(f, t::Type{<:Tuple}[, kwnames]; world=typemax(UInt)) -> Bool

Determine whether the given generic function has a method matching the given
`Tuple` of argument types with the upper bound of world age given by `world`.

If a tuple of keyword argument names `kwnames` is provided, this also checks
whether the method of `f` matching `t` has the given keyword argument names.
If the matching method accepts a variable number of keyword arguments, e.g.
with `kwargs...`, any names given in `kwnames` are considered valid. Otherwise
the provided names must be a subset of the method's keyword arguments.

See also [`applicable`](@ref).

!!! compat "Julia 1.2"
    Providing keyword argument names requires Julia 1.2 or later.

# Examples
```jldoctest
julia> hasmethod(length, Tuple{Array})
true

julia> f(; oranges=0) = oranges;

julia> hasmethod(f, Tuple{}, (:oranges,))
true

julia> hasmethod(f, Tuple{}, (:apples, :bananas))
false

julia> g(; xs...) = 4;

julia> hasmethod(g, Tuple{}, (:a, :b, :c, :d))  # g accepts arbitrary kwargs
true
```
"""
function hasmethod(@nospecialize(f), @nospecialize(t); world=typemax(UInt))
    t = to_tuple_type(t)
    t = signature_type(f, t)
    return ccall(:jl_gf_invoke_lookup, Any, (Any, UInt), t, world) !== nothing
end

function hasmethod(@nospecialize(f), @nospecialize(t), kwnames::Tuple{Vararg{Symbol}}; world=typemax(UInt))
    # TODO: this appears to be doing the wrong queries
    hasmethod(f, t, world=world) || return false
    isempty(kwnames) && return true
    m = which(f, t)
    kws = kwarg_decl(m)
    for kw in kws
        endswith(String(kw), "...") && return true
    end
    return issubset(kwnames, kws)
end

"""
    fbody = bodyfunction(basemethod::Method)

Find the keyword "body function" (the function that contains the body of the method
as written, called after all missing keyword-arguments have been assigned default values).
`basemethod` is the method you obtain via [`which`](@ref) or [`methods`](@ref).
"""
function bodyfunction(basemethod::Method)
    function getsym(arg)
        isa(arg, Symbol) && return arg
        isa(arg, GlobalRef) && return arg.name
        return nothing
    end

    fmod = basemethod.module
    # The lowered code for `basemethod` should look like
    #   %1 = mkw(kwvalues..., #self#, args...)
    #        return %1
    # where `mkw` is the name of the "active" keyword body-function.
    ast = Base.uncompressed_ast(basemethod)
    f = nothing
    if isa(ast, Core.CodeInfo) && length(ast.code) >= 2
        callexpr = ast.code[end-1]
        if isa(callexpr, Expr) && callexpr.head == :call
            fsym = callexpr.args[1]
            if isa(fsym, Symbol)
                f = getfield(fmod, fsym)
            elseif isa(fsym, GlobalRef)
                newsym = nothing
                if fsym.mod === Core && fsym.name === :_apply
                    newsym = getsym(callexpr.args[2])
                elseif fsym.mod === Core && fsym.name === :_apply_iterate
                    newsym = getsym(callexpr.args[3])
                end
                if isa(newsym, Symbol)
                    f = getfield(basemethod.module, newsym)::Function
                else
                    f = getfield(fsym.mod, fsym.name)::Function
                end
            end
        end
    end
    return f
end

"""
    Base.isambiguous(m1, m2; ambiguous_bottom=false) -> Bool

Determine whether two methods `m1` and `m2` may be ambiguous for some call
signature. This test is performed in the context of other methods of the same
function; in isolation, `m1` and `m2` might be ambiguous, but if a third method
resolving the ambiguity has been defined, this returns `false`.
Alternatively, in isolation `m1` and `m2` might be ordered, but if a third
method cannot be sorted with them, they may cause an ambiguity together.

For parametric types, the `ambiguous_bottom` keyword argument controls whether
`Union{}` counts as an ambiguous intersection of type parameters – when `true`,
it is considered ambiguous, when `false` it is not.

# Examples
```jldoctest
julia> foo(x::Complex{<:Integer}) = 1
foo (generic function with 1 method)

julia> foo(x::Complex{<:Rational}) = 2
foo (generic function with 2 methods)

julia> m1, m2 = collect(methods(foo));

julia> typeintersect(m1.sig, m2.sig)
Tuple{typeof(foo), Complex{Union{}}}

julia> Base.isambiguous(m1, m2, ambiguous_bottom=true)
true

julia> Base.isambiguous(m1, m2, ambiguous_bottom=false)
false
```
"""
function isambiguous(m1::Method, m2::Method; ambiguous_bottom::Bool=false)
    m1 === m2 && return false
    ti = typeintersect(m1.sig, m2.sig)
    ti === Bottom && return false
    function inner(ti)
        ti === Bottom && return false
        if !ambiguous_bottom
            has_bottom_parameter(ti) && return false
        end
        min = UInt[typemin(UInt)]
        max = UInt[typemax(UInt)]
        has_ambig = Int32[0]
        ms = _methods_by_ftype(ti, nothing, -1, typemax(UInt), true, min, max, has_ambig)::Vector
        has_ambig[] == 0 && return false
        if !ambiguous_bottom
            filter!(ms) do m::Core.MethodMatch
                return !has_bottom_parameter(m.spec_types)
            end
        end
        # if ml-matches reported the existence of an ambiguity over their
        # intersection, see if both m1 and m2 may be involved in it
        have_m1 = have_m2 = false
        for match in ms
            match = match::Core.MethodMatch
            m = match.method
            m === m1 && (have_m1 = true)
            m === m2 && (have_m2 = true)
        end
        if !have_m1 || !have_m2
            # ml-matches did not need both methods to expose the reported ambiguity
            return false
        end
        if !ambiguous_bottom
            # since we're intentionally ignoring certain ambiguities (via the
            # filter call above), see if we can now declare the intersection fully
            # covered even though it is partially ambiguous over Union{} as a type
            # parameter somewhere
            minmax = nothing
            for match in ms
                m = match.method
                match.fully_covers || continue
                if minmax === nothing || morespecific(m.sig, minmax.sig)
                    minmax = m
                end
            end
            if minmax === nothing
                return true
            end
            for match in ms
                m = match.method
                m === minmax && continue
                if match.fully_covers
                    if !morespecific(minmax.sig, m.sig)
                        return true
                    end
                else
                    if morespecific(m.sig, minmax.sig)
                        return true
                    end
                end
            end
            return false
        end
        return true
    end
    if !(ti <: m1.sig && ti <: m2.sig)
        # When type-intersection fails, it's often also not commutative. Thus
        # checking the reverse may allow detecting ambiguity solutions
        # correctly in more cases (and faster).
        ti2 = typeintersect(m2.sig, m1.sig)
        if ti2 <: m1.sig && ti2 <: m2.sig
            ti = ti2
        elseif ti != ti2
            # TODO: this would be the correct way to handle this case, but
            #       people complained so we don't do it
            # inner(ti2) || return false
            return false # report that the type system failed to decide if it was ambiguous by saying they definitely aren't
        else
            return false # report that the type system failed to decide if it was ambiguous by saying they definitely aren't
        end
    end
    inner(ti) || return false
    # otherwise type-intersection reported an ambiguity we couldn't solve
    return true
end

"""
    delete_method(m::Method)

Make method `m` uncallable and force recompilation of any methods that use(d) it.
"""
function delete_method(m::Method)
    ccall(:jl_method_table_disable, Cvoid, (Any, Any), get_methodtable(m), m)
end

function get_methodtable(m::Method)
    return ccall(:jl_method_table_for, Any, (Any,), m.sig)::Core.MethodTable
end

"""
    has_bottom_parameter(t) -> Bool

Determine whether `t` is a Type for which one or more of its parameters is `Union{}`.
"""
function has_bottom_parameter(t::DataType)
    for p in t.parameters
        has_bottom_parameter(p) && return true
    end
    return false
end
has_bottom_parameter(t::typeof(Bottom)) = true
has_bottom_parameter(t::UnionAll) = has_bottom_parameter(unwrap_unionall(t))
has_bottom_parameter(t::Union) = has_bottom_parameter(t.a) & has_bottom_parameter(t.b)
has_bottom_parameter(t::TypeVar) = has_bottom_parameter(t.ub)
has_bottom_parameter(::Any) = false

min_world(m::Core.CodeInstance) = m.min_world
max_world(m::Core.CodeInstance) = m.max_world
min_world(m::Core.CodeInfo) = m.min_world
max_world(m::Core.CodeInfo) = m.max_world
get_world_counter() = ccall(:jl_get_world_counter, UInt, ())


"""
    propertynames(x, private=false)

Get a tuple or a vector of the properties (`x.property`) of an object `x`.
This is typically the same as [`fieldnames(typeof(x))`](@ref), but types
that overload [`getproperty`](@ref) should generally overload `propertynames`
as well to get the properties of an instance of the type.

`propertynames(x)` may return only "public" property names that are part
of the documented interface of `x`.   If you want it to also return "private"
fieldnames intended for internal use, pass `true` for the optional second argument.
REPL tab completion on `x.` shows only the `private=false` properties.

See also: [`hasproperty`](@ref), [`hasfield`](@ref).
"""
propertynames(x) = fieldnames(typeof(x))
propertynames(m::Module) = names(m)
propertynames(x, private::Bool) = propertynames(x) # ignore private flag by default

"""
    hasproperty(x, s::Symbol)

Return a boolean indicating whether the object `x` has `s` as one of its own properties.

!!! compat "Julia 1.2"
     This function requires at least Julia 1.2.

See also: [`propertynames`](@ref), [`hasfield`](@ref).
"""
hasproperty(x, s::Symbol) = s in propertynames(x)