go builtins 源码
golang builtins 代码
文件路径：/src/cmd/compile/internal/types2/builtins.go
// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements typechecking of builtin function calls.
package types2
import (
"cmd/compile/internal/syntax"
"go/constant"
"go/token"
)
// builtin type-checks a call to the built-in specified by id and
// reports whether the call is valid, with *x holding the result;
// but x.expr is not set. If the call is invalid, the result is
// false, and *x is undefined.
func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (_ bool) {
// append is the only built-in that permits the use of ... for the last argument
bin := predeclaredFuncs[id]
if call.HasDots && id != _Append {
//check.errorf(call.Ellipsis, invalidOp + "invalid use of ... with built-in %s", bin.name)
check.errorf(call, invalidOp+"invalid use of ... with built-in %s", bin.name)
check.use(call.ArgList...)
return
}
// For len(x) and cap(x) we need to know if x contains any function calls or
// receive operations. Save/restore current setting and set hasCallOrRecv to
// false for the evaluation of x so that we can check it afterwards.
// Note: We must do this _before_ calling exprList because exprList evaluates
// all arguments.
if id == _Len || id == _Cap {
defer func(b bool) {
check.hasCallOrRecv = b
}(check.hasCallOrRecv)
check.hasCallOrRecv = false
}
// determine actual arguments
var arg func(*operand, int) // TODO(gri) remove use of arg getter in favor of using xlist directly
nargs := len(call.ArgList)
switch id {
default:
// make argument getter
xlist, _ := check.exprList(call.ArgList, false)
arg = func(x *operand, i int) { *x = *xlist[i] }
nargs = len(xlist)
// evaluate first argument, if present
if nargs > 0 {
arg(x, 0)
if x.mode == invalid {
return
}
}
case _Make, _New, _Offsetof, _Trace:
// arguments require special handling
}
// check argument count
{
msg := ""
if nargs < bin.nargs {
msg = "not enough"
} else if !bin.variadic && nargs > bin.nargs {
msg = "too many"
}
if msg != "" {
check.errorf(call, invalidOp+"%s arguments for %v (expected %d, found %d)", msg, call, bin.nargs, nargs)
return
}
}
switch id {
case _Append:
// append(s S, x ...T) S, where T is the element type of S
// spec: "The variadic function append appends zero or more values x to s of type
// S, which must be a slice type, and returns the resulting slice, also of type S.
// The values x are passed to a parameter of type ...T where T is the element type
// of S and the respective parameter passing rules apply."
S := x.typ
var T Type
if s, _ := coreType(S).(*Slice); s != nil {
T = s.elem
} else {
var cause string
switch {
case x.isNil():
cause = "have untyped nil"
case isTypeParam(S):
if u := coreType(S); u != nil {
cause = check.sprintf("%s has core type %s", x, u)
} else {
cause = check.sprintf("%s has no core type", x)
}
default:
cause = check.sprintf("have %s", x)
}
// don't use invalidArg prefix here as it would repeat "argument" in the error message
check.errorf(x, "first argument to append must be a slice; %s", cause)
return
}
// remember arguments that have been evaluated already
alist := []operand{*x}
// spec: "As a special case, append also accepts a first argument assignable
// to type []byte with a second argument of string type followed by ... .
// This form appends the bytes of the string.
if nargs == 2 && call.HasDots {
if ok, _ := x.assignableTo(check, NewSlice(universeByte), nil); ok {
arg(x, 1)
if x.mode == invalid {
return
}
if t := coreString(x.typ); t != nil && isString(t) {
if check.Types != nil {
sig := makeSig(S, S, x.typ)
sig.variadic = true
check.recordBuiltinType(call.Fun, sig)
}
x.mode = value
x.typ = S
break
}
alist = append(alist, *x)
// fallthrough
}
}
// check general case by creating custom signature
sig := makeSig(S, S, NewSlice(T)) // []T required for variadic signature
sig.variadic = true
var xlist []*operand
// convert []operand to []*operand
for i := range alist {
xlist = append(xlist, &alist[i])
}
for i := len(alist); i < nargs; i++ {
var x operand
arg(&x, i)
xlist = append(xlist, &x)
}
check.arguments(call, sig, nil, xlist, nil) // discard result (we know the result type)
// ok to continue even if check.arguments reported errors
x.mode = value
x.typ = S
if check.Types != nil {
check.recordBuiltinType(call.Fun, sig)
}
case _Cap, _Len:
// cap(x)
// len(x)
mode := invalid
var val constant.Value
switch t := arrayPtrDeref(under(x.typ)).(type) {
case *Basic:
if isString(t) && id == _Len {
if x.mode == constant_ {
mode = constant_
val = constant.MakeInt64(int64(len(constant.StringVal(x.val))))
} else {
mode = value
}
}
case *Array:
mode = value
// spec: "The expressions len(s) and cap(s) are constants
// if the type of s is an array or pointer to an array and
// the expression s does not contain channel receives or
// function calls; in this case s is not evaluated."
if !check.hasCallOrRecv {
mode = constant_
if t.len >= 0 {
val = constant.MakeInt64(t.len)
} else {
val = constant.MakeUnknown()
}
}
case *Slice, *Chan:
mode = value
case *Map:
if id == _Len {
mode = value
}
case *Interface:
if !isTypeParam(x.typ) {
break
}
if t.typeSet().underIs(func(t Type) bool {
switch t := arrayPtrDeref(t).(type) {
case *Basic:
if isString(t) && id == _Len {
return true
}
case *Array, *Slice, *Chan:
return true
case *Map:
if id == _Len {
return true
}
}
return false
}) {
mode = value
}
}
if mode == invalid && under(x.typ) != Typ[Invalid] {
check.errorf(x, invalidArg+"%s for %s", x, bin.name)
return
}
// record the signature before changing x.typ
if check.Types != nil && mode != constant_ {
check.recordBuiltinType(call.Fun, makeSig(Typ[Int], x.typ))
}
x.mode = mode
x.typ = Typ[Int]
x.val = val
case _Close:
// close(c)
if !underIs(x.typ, func(u Type) bool {
uch, _ := u.(*Chan)
if uch == nil {
check.errorf(x, invalidOp+"cannot close non-channel %s", x)
return false
}
if uch.dir == RecvOnly {
check.errorf(x, invalidOp+"cannot close receive-only channel %s", x)
return false
}
return true
}) {
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, x.typ))
}
case _Complex:
// complex(x, y floatT) complexT
var y operand
arg(&y, 1)
if y.mode == invalid {
return
}
// convert or check untyped arguments
d := 0
if isUntyped(x.typ) {
d |= 1
}
if isUntyped(y.typ) {
d |= 2
}
switch d {
case 0:
// x and y are typed => nothing to do
case 1:
// only x is untyped => convert to type of y
check.convertUntyped(x, y.typ)
case 2:
// only y is untyped => convert to type of x
check.convertUntyped(&y, x.typ)
case 3:
// x and y are untyped =>
// 1) if both are constants, convert them to untyped
// floating-point numbers if possible,
// 2) if one of them is not constant (possible because
// it contains a shift that is yet untyped), convert
// both of them to float64 since they must have the
// same type to succeed (this will result in an error
// because shifts of floats are not permitted)
if x.mode == constant_ && y.mode == constant_ {
toFloat := func(x *operand) {
if isNumeric(x.typ) && constant.Sign(constant.Imag(x.val)) == 0 {
x.typ = Typ[UntypedFloat]
}
}
toFloat(x)
toFloat(&y)
} else {
check.convertUntyped(x, Typ[Float64])
check.convertUntyped(&y, Typ[Float64])
// x and y should be invalid now, but be conservative
// and check below
}
}
if x.mode == invalid || y.mode == invalid {
return
}
// both argument types must be identical
if !Identical(x.typ, y.typ) {
check.errorf(x, invalidOp+"%v (mismatched types %s and %s)", call, x.typ, y.typ)
return
}
// the argument types must be of floating-point type
// (applyTypeFunc never calls f with a type parameter)
f := func(typ Type) Type {
assert(!isTypeParam(typ))
if t, _ := under(typ).(*Basic); t != nil {
switch t.kind {
case Float32:
return Typ[Complex64]
case Float64:
return Typ[Complex128]
case UntypedFloat:
return Typ[UntypedComplex]
}
}
return nil
}
resTyp := check.applyTypeFunc(f, x, id)
if resTyp == nil {
check.errorf(x, invalidArg+"arguments have type %s, expected floating-point", x.typ)
return
}
// if both arguments are constants, the result is a constant
if x.mode == constant_ && y.mode == constant_ {
x.val = constant.BinaryOp(constant.ToFloat(x.val), token.ADD, constant.MakeImag(constant.ToFloat(y.val)))
} else {
x.mode = value
}
if check.Types != nil && x.mode != constant_ {
check.recordBuiltinType(call.Fun, makeSig(resTyp, x.typ, x.typ))
}
x.typ = resTyp
case _Copy:
// copy(x, y []T) int
dst, _ := coreType(x.typ).(*Slice)
var y operand
arg(&y, 1)
if y.mode == invalid {
return
}
src0 := coreString(y.typ)
if src0 != nil && isString(src0) {
src0 = NewSlice(universeByte)
}
src, _ := src0.(*Slice)
if dst == nil || src == nil {
check.errorf(x, invalidArg+"copy expects slice arguments; found %s and %s", x, &y)
return
}
if !Identical(dst.elem, src.elem) {
check.errorf(x, invalidArg+"arguments to copy %s and %s have different element types %s and %s", x, &y, dst.elem, src.elem)
return
}
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(Typ[Int], x.typ, y.typ))
}
x.mode = value
x.typ = Typ[Int]
case _Delete:
// delete(map_, key)
// map_ must be a map type or a type parameter describing map types.
// The key cannot be a type parameter for now.
map_ := x.typ
var key Type
if !underIs(map_, func(u Type) bool {
map_, _ := u.(*Map)
if map_ == nil {
check.errorf(x, invalidArg+"%s is not a map", x)
return false
}
if key != nil && !Identical(map_.key, key) {
check.errorf(x, invalidArg+"maps of %s must have identical key types", x)
return false
}
key = map_.key
return true
}) {
return
}
arg(x, 1) // k
if x.mode == invalid {
return
}
check.assignment(x, key, "argument to delete")
if x.mode == invalid {
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, map_, key))
}
case _Imag, _Real:
// imag(complexT) floatT
// real(complexT) floatT
// convert or check untyped argument
if isUntyped(x.typ) {
if x.mode == constant_ {
// an untyped constant number can always be considered
// as a complex constant
if isNumeric(x.typ) {
x.typ = Typ[UntypedComplex]
}
} else {
// an untyped non-constant argument may appear if
// it contains a (yet untyped non-constant) shift
// expression: convert it to complex128 which will
// result in an error (shift of complex value)
check.convertUntyped(x, Typ[Complex128])
// x should be invalid now, but be conservative and check
if x.mode == invalid {
return
}
}
}
// the argument must be of complex type
// (applyTypeFunc never calls f with a type parameter)
f := func(typ Type) Type {
assert(!isTypeParam(typ))
if t, _ := under(typ).(*Basic); t != nil {
switch t.kind {
case Complex64:
return Typ[Float32]
case Complex128:
return Typ[Float64]
case UntypedComplex:
return Typ[UntypedFloat]
}
}
return nil
}
resTyp := check.applyTypeFunc(f, x, id)
if resTyp == nil {
check.errorf(x, invalidArg+"argument has type %s, expected complex type", x.typ)
return
}
// if the argument is a constant, the result is a constant
if x.mode == constant_ {
if id == _Real {
x.val = constant.Real(x.val)
} else {
x.val = constant.Imag(x.val)
}
} else {
x.mode = value
}
if check.Types != nil && x.mode != constant_ {
check.recordBuiltinType(call.Fun, makeSig(resTyp, x.typ))
}
x.typ = resTyp
case _Make:
// make(T, n)
// make(T, n, m)
// (no argument evaluated yet)
arg0 := call.ArgList[0]
T := check.varType(arg0)
if T == Typ[Invalid] {
return
}
var min int // minimum number of arguments
switch coreType(T).(type) {
case *Slice:
min = 2
case *Map, *Chan:
min = 1
case nil:
check.errorf(arg0, invalidArg+"cannot make %s: no core type", arg0)
return
default:
check.errorf(arg0, invalidArg+"cannot make %s; type must be slice, map, or channel", arg0)
return
}
if nargs < min || min+1 < nargs {
check.errorf(call, invalidOp+"%v expects %d or %d arguments; found %d", call, min, min+1, nargs)
return
}
types := []Type{T}
var sizes []int64 // constant integer arguments, if any
for _, arg := range call.ArgList[1:] {
typ, size := check.index(arg, -1) // ok to continue with typ == Typ[Invalid]
types = append(types, typ)
if size >= 0 {
sizes = append(sizes, size)
}
}
if len(sizes) == 2 && sizes[0] > sizes[1] {
check.error(call.ArgList[1], invalidArg+"length and capacity swapped")
// safe to continue
}
x.mode = value
x.typ = T
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ, types...))
}
case _New:
// new(T)
// (no argument evaluated yet)
T := check.varType(call.ArgList[0])
if T == Typ[Invalid] {
return
}
x.mode = value
x.typ = &Pointer{base: T}
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ, T))
}
case _Panic:
// panic(x)
// record panic call if inside a function with result parameters
// (for use in Checker.isTerminating)
if check.sig != nil && check.sig.results.Len() > 0 {
// function has result parameters
p := check.isPanic
if p == nil {
// allocate lazily
p = make(map[*syntax.CallExpr]bool)
check.isPanic = p
}
p[call] = true
}
check.assignment(x, &emptyInterface, "argument to panic")
if x.mode == invalid {
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, &emptyInterface))
}
case _Print, _Println:
// print(x, y, ...)
// println(x, y, ...)
var params []Type
if nargs > 0 {
params = make([]Type, nargs)
for i := 0; i < nargs; i++ {
if i > 0 {
arg(x, i) // first argument already evaluated
}
check.assignment(x, nil, "argument to "+predeclaredFuncs[id].name)
if x.mode == invalid {
// TODO(gri) "use" all arguments?
return
}
params[i] = x.typ
}
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, params...))
}
case _Recover:
// recover() interface{}
x.mode = value
x.typ = &emptyInterface
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ))
}
case _Add:
// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
if !check.allowVersion(check.pkg, 1, 17) {
check.versionErrorf(call.Fun, "go1.17", "unsafe.Add")
return
}
check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
if x.mode == invalid {
return
}
var y operand
arg(&y, 1)
if !check.isValidIndex(&y, "length", true) {
return
}
x.mode = value
x.typ = Typ[UnsafePointer]
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ, x.typ, y.typ))
}
case _Alignof:
// unsafe.Alignof(x T) uintptr
check.assignment(x, nil, "argument to unsafe.Alignof")
if x.mode == invalid {
return
}
if hasVarSize(x.typ, nil) {
x.mode = value
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(Typ[Uintptr], x.typ))
}
} else {
x.mode = constant_
x.val = constant.MakeInt64(check.conf.alignof(x.typ))
// result is constant - no need to record signature
}
x.typ = Typ[Uintptr]
case _Offsetof:
// unsafe.Offsetof(x T) uintptr, where x must be a selector
// (no argument evaluated yet)
arg0 := call.ArgList[0]
selx, _ := unparen(arg0).(*syntax.SelectorExpr)
if selx == nil {
check.errorf(arg0, invalidArg+"%s is not a selector expression", arg0)
check.use(arg0)
return
}
check.expr(x, selx.X)
if x.mode == invalid {
return
}
base := derefStructPtr(x.typ)
sel := selx.Sel.Value
obj, index, indirect := LookupFieldOrMethod(base, false, check.pkg, sel)
switch obj.(type) {
case nil:
check.errorf(x, invalidArg+"%s has no single field %s", base, sel)
return
case *Func:
// TODO(gri) Using derefStructPtr may result in methods being found
// that don't actually exist. An error either way, but the error
// message is confusing. See: https://play.golang.org/p/al75v23kUy ,
// but go/types reports: "invalid argument: x.m is a method value".
check.errorf(arg0, invalidArg+"%s is a method value", arg0)
return
}
if indirect {
check.errorf(x, invalidArg+"field %s is embedded via a pointer in %s", sel, base)
return
}
// TODO(gri) Should we pass x.typ instead of base (and have indirect report if derefStructPtr indirected)?
check.recordSelection(selx, FieldVal, base, obj, index, false)
// record the selector expression (was bug - issue #47895)
{
mode := value
if x.mode == variable || indirect {
mode = variable
}
check.record(&operand{mode, selx, obj.Type(), nil, 0})
}
// The field offset is considered a variable even if the field is declared before
// the part of the struct which is variable-sized. This makes both the rules
// simpler and also permits (or at least doesn't prevent) a compiler from re-
// arranging struct fields if it wanted to.
if hasVarSize(base, nil) {
x.mode = value
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(Typ[Uintptr], obj.Type()))
}
} else {
x.mode = constant_
x.val = constant.MakeInt64(check.conf.offsetof(base, index))
// result is constant - no need to record signature
}
x.typ = Typ[Uintptr]
case _Sizeof:
// unsafe.Sizeof(x T) uintptr
check.assignment(x, nil, "argument to unsafe.Sizeof")
if x.mode == invalid {
return
}
if hasVarSize(x.typ, nil) {
x.mode = value
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(Typ[Uintptr], x.typ))
}
} else {
x.mode = constant_
x.val = constant.MakeInt64(check.conf.sizeof(x.typ))
// result is constant - no need to record signature
}
x.typ = Typ[Uintptr]
case _Slice:
// unsafe.Slice(ptr *T, len IntegerType) []T
if !check.allowVersion(check.pkg, 1, 17) {
check.versionErrorf(call.Fun, "go1.17", "unsafe.Slice")
return
}
typ, _ := under(x.typ).(*Pointer)
if typ == nil {
check.errorf(x, invalidArg+"%s is not a pointer", x)
return
}
var y operand
arg(&y, 1)
if !check.isValidIndex(&y, "length", false) {
return
}
x.mode = value
x.typ = NewSlice(typ.base)
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ, typ, y.typ))
}
case _Assert:
// assert(pred) causes a typechecker error if pred is false.
// The result of assert is the value of pred if there is no error.
// Note: assert is only available in self-test mode.
if x.mode != constant_ || !isBoolean(x.typ) {
check.errorf(x, invalidArg+"%s is not a boolean constant", x)
return
}
if x.val.Kind() != constant.Bool {
check.errorf(x, "internal error: value of %s should be a boolean constant", x)
return
}
if !constant.BoolVal(x.val) {
check.errorf(call, "%v failed", call)
// compile-time assertion failure - safe to continue
}
// result is constant - no need to record signature
case _Trace:
// trace(x, y, z, ...) dumps the positions, expressions, and
// values of its arguments. The result of trace is the value
// of the first argument.
// Note: trace is only available in self-test mode.
// (no argument evaluated yet)
if nargs == 0 {
check.dump("%v: trace() without arguments", posFor(call))
x.mode = novalue
break
}
var t operand
x1 := x
for _, arg := range call.ArgList {
check.rawExpr(x1, arg, nil, false) // permit trace for types, e.g.: new(trace(T))
check.dump("%v: %s", posFor(x1), x1)
x1 = &t // use incoming x only for first argument
}
// trace is only available in test mode - no need to record signature
default:
unreachable()
}
return true
}
// hasVarSize reports if the size of type t is variable due to type parameters
// or if the type is infinitely-sized due to a cycle for which the type has not
// yet been checked.
func hasVarSize(t Type, seen map[*Named]bool) (varSized bool) {
// Cycles are only possible through *Named types.
// The seen map is used to detect cycles and track
// the results of previously seen types.
if named, _ := t.(*Named); named != nil {
if v, ok := seen[named]; ok {
return v
}
if seen == nil {
seen = make(map[*Named]bool)
}
seen[named] = true // possibly cyclic until proven otherwise
defer func() {
seen[named] = varSized // record final determination for named
}()
}
switch u := under(t).(type) {
case *Array:
return hasVarSize(u.elem, seen)
case *Struct:
for _, f := range u.fields {
if hasVarSize(f.typ, seen) {
return true
}
}
case *Interface:
return isTypeParam(t)
case *Named, *Union:
unreachable()
}
return false
}
// applyTypeFunc applies f to x. If x is a type parameter,
// the result is a type parameter constrained by an new
// interface bound. The type bounds for that interface
// are computed by applying f to each of the type bounds
// of x. If any of these applications of f return nil,
// applyTypeFunc returns nil.
// If x is not a type parameter, the result is f(x).
func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId) Type {
if tp, _ := x.typ.(*TypeParam); tp != nil {
// Test if t satisfies the requirements for the argument
// type and collect possible result types at the same time.
var terms []*Term
if !tp.is(func(t *term) bool {
if t == nil {
return false
}
if r := f(t.typ); r != nil {
terms = append(terms, NewTerm(t.tilde, r))
return true
}
return false
}) {
return nil
}
// We can type-check this fine but we're introducing a synthetic
// type parameter for the result. It's not clear what the API
// implications are here. Report an error for 1.18 but continue
// type-checking.
check.softErrorf(x, "%s not supported as argument to %s for go1.18 (see issue #50937)", x, predeclaredFuncs[id].name)
// Construct a suitable new type parameter for the result type.
// The type parameter is placed in the current package so export/import
// works as expected.
tpar := NewTypeName(nopos, check.pkg, tp.obj.name, nil)
ptyp := check.newTypeParam(tpar, NewInterfaceType(nil, []Type{NewUnion(terms)})) // assigns type to tpar as a side-effect
ptyp.index = tp.index
return ptyp
}
return f(x.typ)
}
// makeSig makes a signature for the given argument and result types.
// Default types are used for untyped arguments, and res may be nil.
func makeSig(res Type, args ...Type) *Signature {
list := make([]*Var, len(args))
for i, param := range args {
list[i] = NewVar(nopos, nil, "", Default(param))
}
params := NewTuple(list...)
var result *Tuple
if res != nil {
assert(!isUntyped(res))
result = NewTuple(NewVar(nopos, nil, "", res))
}
return &Signature{params: params, results: result}
}
// arrayPtrDeref returns A if typ is of the form *A and A is an array;
// otherwise it returns typ.
func arrayPtrDeref(typ Type) Type {
if p, ok := typ.(*Pointer); ok {
if a, _ := under(p.base).(*Array); a != nil {
return a
}
}
return typ
}
// unparen returns e with any enclosing parentheses stripped.
func unparen(e syntax.Expr) syntax.Expr {
for {
p, ok := e.(*syntax.ParenExpr)
if !ok {
return e
}
e = p.X
}
}
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