// index checks an index expression for validity.
// If max >= 0, it is the upper bound for index.
// If index is valid and the result i >= 0, then i is the constant value of index.
func (check *Checker) index(index ast.Expr, max int64) (i int64, valid bool) {
var x operand
check.expr(&x, index)
if x.mode == invalid {
return
}
// an untyped constant must be representable as Int
check.convertUntyped(&x, Typ[Int])
if x.mode == invalid {
return
}
// the index must be of integer type
if !isInteger(x.typ) {
check.invalidArg(x.pos(), "index %s must be integer", &x)
return
}
// a constant index i must be in bounds
if x.mode == constant_ {
if constant.Sign(x.val) < 0 {
check.invalidArg(x.pos(), "index %s must not be negative", &x)
return
}
i, valid = constant.Int64Val(constant.ToInt(x.val))
if !valid || max >= 0 && i >= max {
check.errorf(x.pos(), "index %s is out of bounds", &x)
return i, false
}
// 0 <= i [ && i < max ]
return i, true
}
return -1, true
}
// The binary expression e may be nil. It's passed in for better error messages only.
func (check *Checker) binary(x *operand, e *ast.BinaryExpr, lhs, rhs ast.Expr, op token.Token) {
var y operand
check.expr(x, lhs)
check.expr(&y, rhs)
if x.mode == invalid {
return
}
if y.mode == invalid {
x.mode = invalid
x.expr = y.expr
return
}
if isShift(op) {
check.shift(x, &y, e, op)
return
}
check.convertUntyped(x, y.typ)
if x.mode == invalid {
return
}
check.convertUntyped(&y, x.typ)
if y.mode == invalid {
x.mode = invalid
return
}
if isComparison(op) {
check.comparison(x, &y, op)
return
}
if !Identical(x.typ, y.typ) {
// only report an error if we have valid types
// (otherwise we had an error reported elsewhere already)
if x.typ != Typ[Invalid] && y.typ != Typ[Invalid] {
check.invalidOp(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
}
x.mode = invalid
return
}
if !check.op(binaryOpPredicates, x, op) {
x.mode = invalid
return
}
if (op == token.QUO || op == token.REM) && (x.mode == constant_ || isInteger(x.typ)) && y.mode == constant_ && constant.Sign(y.val) == 0 {
check.invalidOp(y.pos(), "division by zero")
x.mode = invalid
return
}
if x.mode == constant_ && y.mode == constant_ {
xval := x.val
yval := y.val
typ := x.typ.Underlying().(*Basic)
// force integer division of integer operands
if op == token.QUO && isInteger(typ) {
op = token.QUO_ASSIGN
}
x.val = constant.BinaryOp(xval, op, yval)
// Typed constants must be representable in
// their type after each constant operation.
if isTyped(typ) {
if e != nil {
x.expr = e // for better error message
}
check.representable(x, typ)
}
return
}
x.mode = value
// x.typ is unchanged
}
// representableConst reports whether x can be represented as
// value of the given basic type and for the configuration
// provided (only needed for int/uint sizes).
//
// If rounded != nil, *rounded is set to the rounded value of x for
// representable floating-point and complex values, and to an Int
// value for integer values; it is left alone otherwise.
// It is ok to provide the addressof the first argument for rounded.
func representableConst(x constant.Value, conf *Config, typ *Basic, rounded *constant.Value) bool {
if x.Kind() == constant.Unknown {
return true // avoid follow-up errors
}
switch {
case isInteger(typ):
x := constant.ToInt(x)
if x.Kind() != constant.Int {
return false
}
if rounded != nil {
*rounded = x
}
if x, ok := constant.Int64Val(x); ok {
switch typ.kind {
case Int:
var s = uint(conf.sizeof(typ)) * 8
return int64(-1)<<(s-1) <= x && x <= int64(1)<<(s-1)-1
case Int8:
const s = 8
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int16:
const s = 16
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int32:
const s = 32
return -1<<(s-1) <= x && x <= 1<<(s-1)-1
case Int64, UntypedInt:
return true
case Uint, Uintptr:
if s := uint(conf.sizeof(typ)) * 8; s < 64 {
return 0 <= x && x <= int64(1)<<s-1
}
return 0 <= x
case Uint8:
const s = 8
return 0 <= x && x <= 1<<s-1
case Uint16:
const s = 16
return 0 <= x && x <= 1<<s-1
case Uint32:
const s = 32
return 0 <= x && x <= 1<<s-1
case Uint64:
return 0 <= x
default:
unreachable()
}
}
// x does not fit into int64
switch n := constant.BitLen(x); typ.kind {
case Uint, Uintptr:
var s = uint(conf.sizeof(typ)) * 8
return constant.Sign(x) >= 0 && n <= int(s)
case Uint64:
return constant.Sign(x) >= 0 && n <= 64
case UntypedInt:
return true
}
case isFloat(typ):
x := constant.ToFloat(x)
if x.Kind() != constant.Float {
return false
}
switch typ.kind {
case Float32:
if rounded == nil {
return fitsFloat32(x)
}
r := roundFloat32(x)
if r != nil {
*rounded = r
return true
}
case Float64:
if rounded == nil {
return fitsFloat64(x)
}
r := roundFloat64(x)
if r != nil {
*rounded = r
return true
}
case UntypedFloat:
return true
default:
unreachable()
}
case isComplex(typ):
x := constant.ToComplex(x)
if x.Kind() != constant.Complex {
return false
}
switch typ.kind {
case Complex64:
if rounded == nil {
return fitsFloat32(constant.Real(x)) && fitsFloat32(constant.Imag(x))
}
re := roundFloat32(constant.Real(x))
im := roundFloat32(constant.Imag(x))
if re != nil && im != nil {
*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
return true
}
case Complex128:
if rounded == nil {
return fitsFloat64(constant.Real(x)) && fitsFloat64(constant.Imag(x))
}
re := roundFloat64(constant.Real(x))
im := roundFloat64(constant.Imag(x))
if re != nil && im != nil {
*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
return true
}
case UntypedComplex:
return true
default:
unreachable()
}
case isString(typ):
return x.Kind() == constant.String
case isBoolean(typ):
return x.Kind() == constant.Bool
}
return false
}
func (check *Checker) shift(x, y *operand, e *ast.BinaryExpr, op token.Token) {
untypedx := isUntyped(x.typ)
var xval constant.Value
if x.mode == constant_ {
xval = constant.ToInt(x.val)
}
if isInteger(x.typ) || untypedx && xval != nil && xval.Kind() == constant.Int {
// The lhs is of integer type or an untyped constant representable
// as an integer. Nothing to do.
} else {
// shift has no chance
check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
x.mode = invalid
return
}
// spec: "The right operand in a shift expression must have unsigned
// integer type or be an untyped constant that can be converted to
// unsigned integer type."
switch {
case isUnsigned(y.typ):
// nothing to do
case isUntyped(y.typ):
check.convertUntyped(y, Typ[UntypedInt])
if y.mode == invalid {
x.mode = invalid
return
}
default:
check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
x.mode = invalid
return
}
if x.mode == constant_ {
if y.mode == constant_ {
// rhs must be an integer value
yval := constant.ToInt(y.val)
if yval.Kind() != constant.Int {
check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
x.mode = invalid
return
}
// rhs must be within reasonable bounds
const shiftBound = 1023 - 1 + 52 // so we can express smallestFloat64
s, ok := constant.Uint64Val(yval)
if !ok || s > shiftBound {
check.invalidOp(y.pos(), "invalid shift count %s", y)
x.mode = invalid
return
}
// The lhs is representable as an integer but may not be an integer
// (e.g., 2.0, an untyped float) - this can only happen for untyped
// non-integer numeric constants. Correct the type so that the shift
// result is of integer type.
if !isInteger(x.typ) {
x.typ = Typ[UntypedInt]
}
// x is a constant so xval != nil and it must be of Int kind.
x.val = constant.Shift(xval, op, uint(s))
// Typed constants must be representable in
// their type after each constant operation.
if isTyped(x.typ) {
if e != nil {
x.expr = e // for better error message
}
check.representable(x, x.typ.Underlying().(*Basic))
}
return
}
// non-constant shift with constant lhs
if untypedx {
// spec: "If the left operand of a non-constant shift
// expression is an untyped constant, the type of the
// constant is what it would be if the shift expression
// were replaced by its left operand alone.".
//
// Delay operand checking until we know the final type
// by marking the lhs expression as lhs shift operand.
//
// Usually (in correct programs), the lhs expression
// is in the untyped map. However, it is possible to
// create incorrect programs where the same expression
// is evaluated twice (via a declaration cycle) such
// that the lhs expression type is determined in the
// first round and thus deleted from the map, and then
// not found in the second round (double insertion of
// the same expr node still just leads to one entry for
// that node, and it can only be deleted once).
// Be cautious and check for presence of entry.
// Example: var e, f = int(1<<""[f]) // issue 11347
if info, found := check.untyped[x.expr]; found {
info.isLhs = true
check.untyped[x.expr] = info
}
// keep x's type
x.mode = value
return
}
}
// constant rhs must be >= 0
if y.mode == constant_ && constant.Sign(y.val) < 0 {
check.invalidOp(y.pos(), "shift count %s must not be negative", y)
}
// non-constant shift - lhs must be an integer
if !isInteger(x.typ) {
check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
x.mode = invalid
return
}
x.mode = value
}
// builtin type-checks a call to the built-in specified by id and
// returns true if 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 *ast.CallExpr, id builtinId) (_ bool) {
// append is the only built-in that permits the use of ... for the last argument
bin := predeclaredFuncs[id]
if call.Ellipsis.IsValid() && id != _Append {
check.invalidOp(call.Ellipsis, "invalid use of ... with built-in %s", bin.name)
check.use(call.Args...)
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 unpack because unpack evaluates the
// first argument before we even call arg(x, 0)!
if id == _Len || id == _Cap {
defer func(b bool) {
check.hasCallOrRecv = b
}(check.hasCallOrRecv)
check.hasCallOrRecv = false
}
// determine actual arguments
var arg getter
nargs := len(call.Args)
switch id {
default:
// make argument getter
arg, nargs, _ = unpack(func(x *operand, i int) { check.multiExpr(x, call.Args[i]) }, nargs, false)
if arg == nil {
return
}
// 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.invalidOp(call.Rparen, "%s arguments for %s (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, _ := S.Underlying().(*Slice); s != nil {
T = s.elem
} else {
check.invalidArg(x.pos(), "%s is not a slice", x)
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.Ellipsis.IsValid() && x.assignableTo(check.conf, NewSlice(universeByte), nil) {
arg(x, 1)
if x.mode == invalid {
return
}
if isString(x.typ) {
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
check.arguments(x, call, sig, func(x *operand, i int) {
// only evaluate arguments that have not been evaluated before
if i < len(alist) {
*x = alist[i]
return
}
arg(x, i)
}, nargs)
// 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 typ Type
var val constant.Value
switch typ = implicitArrayDeref(x.typ.Underlying()); t := 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_
val = constant.MakeInt64(t.len)
}
case *Slice, *Chan:
mode = value
case *Map:
if id == _Len {
mode = value
}
}
if mode == invalid {
check.invalidArg(x.pos(), "%s for %s", x, bin.name)
return
}
x.mode = mode
x.typ = Typ[Int]
x.val = val
if check.Types != nil && mode != constant_ {
check.recordBuiltinType(call.Fun, makeSig(x.typ, typ))
}
case _Close:
// close(c)
c, _ := x.typ.Underlying().(*Chan)
if c == nil {
check.invalidArg(x.pos(), "%s is not a channel", x)
return
}
if c.dir == RecvOnly {
check.invalidArg(x.pos(), "%s must not be a receive-only channel", x)
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, c))
}
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.invalidArg(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
return
}
// the argument types must be of floating-point type
if !isFloat(x.typ) {
check.invalidArg(x.pos(), "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
}
// determine result type
var res BasicKind
switch x.typ.Underlying().(*Basic).kind {
case Float32:
res = Complex64
case Float64:
res = Complex128
case UntypedFloat:
res = UntypedComplex
default:
unreachable()
}
resTyp := Typ[res]
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
var dst Type
if t, _ := x.typ.Underlying().(*Slice); t != nil {
dst = t.elem
}
var y operand
arg(&y, 1)
if y.mode == invalid {
return
}
var src Type
switch t := y.typ.Underlying().(type) {
case *Basic:
if isString(y.typ) {
src = universeByte
}
case *Slice:
src = t.elem
}
if dst == nil || src == nil {
check.invalidArg(x.pos(), "copy expects slice arguments; found %s and %s", x, &y)
return
}
if !Identical(dst, src) {
check.invalidArg(x.pos(), "arguments to copy %s and %s have different element types %s and %s", x, &y, dst, src)
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(m, k)
m, _ := x.typ.Underlying().(*Map)
if m == nil {
check.invalidArg(x.pos(), "%s is not a map", x)
return
}
arg(x, 1) // k
if x.mode == invalid {
return
}
if !x.assignableTo(check.conf, m.key, nil) {
check.invalidArg(x.pos(), "%s is not assignable to %s", x, m.key)
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, m, m.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 alway 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
if !isComplex(x.typ) {
check.invalidArg(x.pos(), "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
}
// determine result type
var res BasicKind
switch x.typ.Underlying().(*Basic).kind {
case Complex64:
res = Float32
case Complex128:
res = Float64
case UntypedComplex:
res = UntypedFloat
default:
unreachable()
}
resTyp := Typ[res]
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.Args[0]
T := check.typ(arg0)
if T == Typ[Invalid] {
return
}
var min int // minimum number of arguments
switch T.Underlying().(type) {
case *Slice:
min = 2
case *Map, *Chan:
min = 1
default:
check.invalidArg(arg0.Pos(), "cannot make %s; type must be slice, map, or channel", arg0)
return
}
if nargs < min || min+1 < nargs {
check.errorf(call.Pos(), "%s expects %d or %d arguments; found %d", call, min, min+1, nargs)
return
}
var sizes []int64 // constant integer arguments, if any
for _, arg := range call.Args[1:] {
if s, ok := check.index(arg, -1); ok && s >= 0 {
sizes = append(sizes, s)
}
}
if len(sizes) == 2 && sizes[0] > sizes[1] {
check.invalidArg(call.Args[1].Pos(), "length and capacity swapped")
// safe to continue
}
x.mode = value
x.typ = T
if check.Types != nil {
params := [...]Type{T, Typ[Int], Typ[Int]}
check.recordBuiltinType(call.Fun, makeSig(x.typ, params[:1+len(sizes)]...))
}
case _New:
// new(T)
// (no argument evaluated yet)
T := check.typ(call.Args[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)
T := new(Interface)
check.assignment(x, T, "argument to panic")
if x.mode == invalid {
return
}
x.mode = novalue
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(nil, T))
}
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 = NewOptional(new(Interface))
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ))
}
case _Alignof:
// unsafe.Alignof(x T) uintptr
check.assignment(x, nil, "argument to unsafe.Alignof")
if x.mode == invalid {
return
}
x.mode = constant_
x.val = constant.MakeInt64(check.conf.alignof(x.typ))
x.typ = Typ[Uintptr]
// result is constant - no need to record signature
case _Offsetof:
// unsafe.Offsetof(x T) uintptr, where x must be a selector
// (no argument evaluated yet)
arg0 := call.Args[0]
selx, _ := unparen(arg0).(*ast.SelectorExpr)
if selx == nil {
check.invalidArg(arg0.Pos(), "%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.Name
obj, index, indirect := LookupFieldOrMethod(base, false, check.pkg, sel)
switch obj.(type) {
case nil:
check.invalidArg(x.pos(), "%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.invalidArg(arg0.Pos(), "%s is a method value", arg0)
return
}
if indirect {
check.invalidArg(x.pos(), "field %s is embedded via a pointer in %s", sel, base)
return
}
// TODO(gri) Should we pass x.typ instead of base (and indirect report if derefStructPtr indirected)?
check.recordSelection(selx, FieldVal, base, obj, index, false)
offs := check.conf.offsetof(base, index)
x.mode = constant_
x.val = constant.MakeInt64(offs)
x.typ = Typ[Uintptr]
// result is constant - no need to record signature
case _Sizeof:
// unsafe.Sizeof(x T) uintptr
check.assignment(x, nil, "argument to unsafe.Sizeof")
if x.mode == invalid {
return
}
x.mode = constant_
x.val = constant.MakeInt64(check.conf.sizeof(x.typ))
x.typ = Typ[Uintptr]
// result is constant - no need to record signature
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.invalidArg(x.pos(), "%s is not a boolean constant", x)
return
}
if x.val.Kind() != constant.Bool {
check.errorf(x.pos(), "internal error: value of %s should be a boolean constant", x)
return
}
if !constant.BoolVal(x.val) {
check.errorf(call.Pos(), "%s 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("%s: trace() without arguments", call.Pos())
x.mode = novalue
break
}
var t operand
x1 := x
for _, arg := range call.Args {
check.rawExpr(x1, arg, nil) // permit trace for types, e.g.: new(trace(T))
check.dump("%s: %s", x1.pos(), 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
}