// constValue returns the value of the constant with the
// dynamic type tag appropriate for c.Type().
func constValue(c *ssa.Const) value {
if c.IsNil() {
return zero(c.Type()) // typed nil
}
if t, ok := c.Type().Underlying().(*types.Basic); ok {
// TODO(adonovan): eliminate untyped constants from SSA form.
switch t.Kind() {
case types.Bool, types.UntypedBool:
return exact.BoolVal(c.Value)
case types.Int, types.UntypedInt:
// Assume sizeof(int) is same on host and target.
return int(c.Int64())
case types.Int8:
return int8(c.Int64())
case types.Int16:
return int16(c.Int64())
case types.Int32, types.UntypedRune:
return int32(c.Int64())
case types.Int64:
return c.Int64()
case types.Uint:
// Assume sizeof(uint) is same on host and target.
return uint(c.Uint64())
case types.Uint8:
return uint8(c.Uint64())
case types.Uint16:
return uint16(c.Uint64())
case types.Uint32:
return uint32(c.Uint64())
case types.Uint64:
return c.Uint64()
case types.Uintptr:
// Assume sizeof(uintptr) is same on host and target.
return uintptr(c.Uint64())
case types.Float32:
return float32(c.Float64())
case types.Float64, types.UntypedFloat:
return c.Float64()
case types.Complex64:
return complex64(c.Complex128())
case types.Complex128, types.UntypedComplex:
return c.Complex128()
case types.String, types.UntypedString:
if c.Value.Kind() == exact.String {
return exact.StringVal(c.Value)
}
return string(rune(c.Int64()))
}
}
panic(fmt.Sprintf("constValue: %s", c))
}
func (c *Const) RelString(from *types.Package) string {
var s string
if c.Value == nil {
s = "nil"
} else if c.Value.Kind() == exact.String {
s = exact.StringVal(c.Value)
const max = 20
// TODO(adonovan): don't cut a rune in half.
if len(s) > max {
s = s[:max-3] + "..." // abbreviate
}
s = strconv.Quote(s)
} else {
s = c.Value.String()
}
return s + ":" + relType(c.Type(), from)
}
// 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.expr(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)) {
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 exact.Value
switch typ = implicitArrayDeref(x.typ.Underlying()); t := typ.(type) {
case *Basic:
if isString(t) && id == _Len {
if x.mode == constant {
mode = constant
val = exact.MakeInt64(int64(len(exact.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 = exact.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 realT) complexT
if !check.complexArg(x) {
return
}
var y operand
arg(&y, 1)
if y.mode == invalid {
return
}
if !check.complexArg(&y) {
return
}
check.convertUntyped(x, y.typ)
if x.mode == invalid {
return
}
check.convertUntyped(&y, x.typ)
if y.mode == invalid {
return
}
if !Identical(x.typ, y.typ) {
check.invalidArg(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
return
}
if x.mode == constant && y.mode == constant {
x.val = exact.BinaryOp(x.val, token.ADD, exact.MakeImag(y.val))
} else {
x.mode = value
}
realT := x.typ
complexT := Typ[Invalid]
switch realT.Underlying().(*Basic).kind {
case Float32:
complexT = Typ[Complex64]
case Float64:
complexT = Typ[Complex128]
case UntypedInt, UntypedRune, UntypedFloat:
if x.mode == constant {
realT = defaultType(realT).(*Basic)
complexT = Typ[UntypedComplex]
} else {
// untyped but not constant; probably because one
// operand is a non-constant shift of untyped lhs
realT = Typ[Float64]
complexT = Typ[Complex128]
}
default:
check.invalidArg(x.pos(), "float32 or float64 arguments expected")
return
}
x.typ = complexT
if check.Types != nil && x.mode != constant {
check.recordBuiltinType(call.Fun, makeSig(complexT, realT, realT))
}
if x.mode != constant {
// The arguments have now their final types, which at run-
// time will be materialized. Update the expression trees.
// If the current types are untyped, the materialized type
// is the respective default type.
// (If the result is constant, the arguments are never
// materialized and there is nothing to do.)
check.updateExprType(x.expr, realT, true)
check.updateExprType(y.expr, realT, true)
}
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) {
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) realT
// real(complexT) realT
if !isComplex(x.typ) {
check.invalidArg(x.pos(), "%s must be a complex number", x)
return
}
if x.mode == constant {
if id == _Real {
x.val = exact.Real(x.val)
} else {
x.val = exact.Imag(x.val)
}
} else {
x.mode = value
}
var k BasicKind
switch x.typ.Underlying().(*Basic).kind {
case Complex64:
k = Float32
case Complex128:
k = Float64
case UntypedComplex:
k = UntypedFloat
default:
unreachable()
}
if check.Types != nil && x.mode != constant {
check.recordBuiltinType(call.Fun, makeSig(Typ[k], x.typ))
}
x.typ = Typ[k]
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)
if !check.assignment(x, T) {
assert(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
}
if !check.assignment(x, nil) {
assert(x.mode == invalid)
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 = new(Interface)
if check.Types != nil {
check.recordBuiltinType(call.Fun, makeSig(x.typ))
}
case _Alignof:
// unsafe.Alignof(x T) uintptr
if !check.assignment(x, nil) {
assert(x.mode == invalid)
return
}
x.mode = constant
x.val = exact.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: http://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 = exact.MakeInt64(offs)
x.typ = Typ[Uintptr]
// result is constant - no need to record signature
case _Sizeof:
// unsafe.Sizeof(x T) uintptr
if !check.assignment(x, nil) {
assert(x.mode == invalid)
return
}
x.mode = constant
x.val = exact.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() != exact.Bool {
check.errorf(x.pos(), "internal error: value of %s should be a boolean constant", x)
return
}
if !exact.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
}
// exprInternal contains the core of type checking of expressions.
// Must only be called by rawExpr.
//
func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
// make sure x has a valid state in case of bailout
// (was issue 5770)
x.mode = invalid
x.typ = Typ[Invalid]
switch e := e.(type) {
case *ast.BadExpr:
goto Error // error was reported before
case *ast.Ident:
check.ident(x, e, nil, nil)
case *ast.Ellipsis:
// ellipses are handled explicitly where they are legal
// (array composite literals and parameter lists)
check.error(e.Pos(), "invalid use of '...'")
goto Error
case *ast.BasicLit:
x.setConst(e.Kind, e.Value)
if x.mode == invalid {
check.invalidAST(e.Pos(), "invalid literal %v", e.Value)
goto Error
}
case *ast.FuncLit:
if sig, ok := check.typ(e.Type).(*Signature); ok {
// Anonymous functions are considered part of the
// init expression/func declaration which contains
// them: use existing package-level declaration info.
check.funcBody(check.decl, "", sig, e.Body)
x.mode = value
x.typ = sig
} else {
check.invalidAST(e.Pos(), "invalid function literal %s", e)
goto Error
}
case *ast.CompositeLit:
typ := hint
openArray := false
if e.Type != nil {
// [...]T array types may only appear with composite literals.
// Check for them here so we don't have to handle ... in general.
typ = nil
if atyp, _ := e.Type.(*ast.ArrayType); atyp != nil && atyp.Len != nil {
if ellip, _ := atyp.Len.(*ast.Ellipsis); ellip != nil && ellip.Elt == nil {
// We have an "open" [...]T array type.
// Create a new ArrayType with unknown length (-1)
// and finish setting it up after analyzing the literal.
typ = &Array{len: -1, elem: check.typ(atyp.Elt)}
openArray = true
}
}
if typ == nil {
typ = check.typ(e.Type)
}
}
if typ == nil {
// TODO(gri) provide better error messages depending on context
check.error(e.Pos(), "missing type in composite literal")
goto Error
}
switch typ, _ := deref(typ); utyp := typ.Underlying().(type) {
case *Struct:
if len(e.Elts) == 0 {
break
}
fields := utyp.fields
if _, ok := e.Elts[0].(*ast.KeyValueExpr); ok {
// all elements must have keys
visited := make([]bool, len(fields))
for _, e := range e.Elts {
kv, _ := e.(*ast.KeyValueExpr)
if kv == nil {
check.error(e.Pos(), "mixture of field:value and value elements in struct literal")
continue
}
key, _ := kv.Key.(*ast.Ident)
if key == nil {
check.errorf(kv.Pos(), "invalid field name %s in struct literal", kv.Key)
continue
}
i := fieldIndex(utyp.fields, check.pkg, key.Name)
if i < 0 {
check.errorf(kv.Pos(), "unknown field %s in struct literal", key.Name)
continue
}
fld := fields[i]
check.recordUse(key, fld)
// 0 <= i < len(fields)
if visited[i] {
check.errorf(kv.Pos(), "duplicate field name %s in struct literal", key.Name)
continue
}
visited[i] = true
check.expr(x, kv.Value)
etyp := fld.typ
if !check.assignment(x, etyp) {
if x.mode != invalid {
check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
}
continue
}
}
} else {
// no element must have a key
for i, e := range e.Elts {
if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
check.error(kv.Pos(), "mixture of field:value and value elements in struct literal")
continue
}
check.expr(x, e)
if i >= len(fields) {
check.error(x.pos(), "too many values in struct literal")
break // cannot continue
}
// i < len(fields)
fld := fields[i]
if !fld.Exported() && fld.pkg != check.pkg {
check.errorf(x.pos(), "implicit assignment to unexported field %s in %s literal", fld.name, typ)
continue
}
etyp := fld.typ
if !check.assignment(x, etyp) {
if x.mode != invalid {
check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
}
continue
}
}
if len(e.Elts) < len(fields) {
check.error(e.Rbrace, "too few values in struct literal")
// ok to continue
}
}
case *Array:
n := check.indexedElts(e.Elts, utyp.elem, utyp.len)
// if we have an "open" [...]T array, set the length now that we know it
if openArray {
utyp.len = n
}
case *Slice:
check.indexedElts(e.Elts, utyp.elem, -1)
case *Map:
visited := make(map[interface{}][]Type, len(e.Elts))
for _, e := range e.Elts {
kv, _ := e.(*ast.KeyValueExpr)
if kv == nil {
check.error(e.Pos(), "missing key in map literal")
continue
}
check.exprWithHint(x, kv.Key, utyp.key)
if !check.assignment(x, utyp.key) {
if x.mode != invalid {
check.errorf(x.pos(), "cannot use %s as %s key in map literal", x, utyp.key)
}
continue
}
if x.mode == constant {
duplicate := false
// if the key is of interface type, the type is also significant when checking for duplicates
if _, ok := utyp.key.Underlying().(*Interface); ok {
for _, vtyp := range visited[x.val] {
if Identical(vtyp, x.typ) {
duplicate = true
break
}
}
visited[x.val] = append(visited[x.val], x.typ)
} else {
_, duplicate = visited[x.val]
visited[x.val] = nil
}
if duplicate {
check.errorf(x.pos(), "duplicate key %s in map literal", x.val)
continue
}
}
check.exprWithHint(x, kv.Value, utyp.elem)
if !check.assignment(x, utyp.elem) {
if x.mode != invalid {
check.errorf(x.pos(), "cannot use %s as %s value in map literal", x, utyp.elem)
}
continue
}
}
default:
// if utyp is invalid, an error was reported before
if utyp != Typ[Invalid] {
check.errorf(e.Pos(), "invalid composite literal type %s", typ)
goto Error
}
}
x.mode = value
x.typ = typ
case *ast.ParenExpr:
kind := check.rawExpr(x, e.X, nil)
x.expr = e
return kind
case *ast.SelectorExpr:
check.selector(x, e)
case *ast.IndexExpr:
check.expr(x, e.X)
if x.mode == invalid {
goto Error
}
valid := false
length := int64(-1) // valid if >= 0
switch typ := x.typ.Underlying().(type) {
case *Basic:
if isString(typ) {
valid = true
if x.mode == constant {
length = int64(len(exact.StringVal(x.val)))
}
// an indexed string always yields a byte value
// (not a constant) even if the string and the
// index are constant
x.mode = value
x.typ = universeByte // use 'byte' name
}
case *Array:
valid = true
length = typ.len
if x.mode != variable {
x.mode = value
}
x.typ = typ.elem
case *Pointer:
if typ, _ := typ.base.Underlying().(*Array); typ != nil {
valid = true
length = typ.len
x.mode = variable
x.typ = typ.elem
}
case *Slice:
valid = true
x.mode = variable
x.typ = typ.elem
case *Map:
var key operand
check.expr(&key, e.Index)
if !check.assignment(&key, typ.key) {
if key.mode != invalid {
check.invalidOp(key.pos(), "cannot use %s as map index of type %s", &key, typ.key)
}
goto Error
}
x.mode = mapindex
x.typ = typ.elem
x.expr = e
return expression
}
if !valid {
check.invalidOp(x.pos(), "cannot index %s", x)
goto Error
}
if e.Index == nil {
check.invalidAST(e.Pos(), "missing index for %s", x)
goto Error
}
check.index(e.Index, length)
// ok to continue
case *ast.SliceExpr:
check.expr(x, e.X)
if x.mode == invalid {
goto Error
}
valid := false
length := int64(-1) // valid if >= 0
switch typ := x.typ.Underlying().(type) {
case *Basic:
if isString(typ) {
if e.Slice3 {
check.invalidOp(x.pos(), "3-index slice of string")
goto Error
}
valid = true
if x.mode == constant {
length = int64(len(exact.StringVal(x.val)))
}
// spec: "For untyped string operands the result
// is a non-constant value of type string."
if typ.kind == UntypedString {
x.typ = Typ[String]
}
}
case *Array:
valid = true
length = typ.len
if x.mode != variable {
check.invalidOp(x.pos(), "cannot slice %s (value not addressable)", x)
goto Error
}
x.typ = &Slice{elem: typ.elem}
case *Pointer:
if typ, _ := typ.base.Underlying().(*Array); typ != nil {
valid = true
length = typ.len
x.typ = &Slice{elem: typ.elem}
}
case *Slice:
valid = true
// x.typ doesn't change
}
if !valid {
check.invalidOp(x.pos(), "cannot slice %s", x)
goto Error
}
x.mode = value
// spec: "Only the first index may be omitted; it defaults to 0."
if e.Slice3 && (e.High == nil || e.Max == nil) {
check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")
goto Error
}
// check indices
var ind [3]int64
for i, expr := range []ast.Expr{e.Low, e.High, e.Max} {
x := int64(-1)
switch {
case expr != nil:
// The "capacity" is only known statically for strings, arrays,
// and pointers to arrays, and it is the same as the length for
// those types.
max := int64(-1)
if length >= 0 {
max = length + 1
}
if t, ok := check.index(expr, max); ok && t >= 0 {
x = t
}
case i == 0:
// default is 0 for the first index
x = 0
case length >= 0:
// default is length (== capacity) otherwise
x = length
}
ind[i] = x
}
// constant indices must be in range
// (check.index already checks that existing indices >= 0)
L:
for i, x := range ind[:len(ind)-1] {
if x > 0 {
for _, y := range ind[i+1:] {
if y >= 0 && x > y {
check.errorf(e.Rbrack, "invalid slice indices: %d > %d", x, y)
break L // only report one error, ok to continue
}
}
}
}
case *ast.TypeAssertExpr:
check.expr(x, e.X)
if x.mode == invalid {
goto Error
}
xtyp, _ := x.typ.Underlying().(*Interface)
if xtyp == nil {
check.invalidOp(x.pos(), "%s is not an interface", x)
goto Error
}
// x.(type) expressions are handled explicitly in type switches
if e.Type == nil {
check.invalidAST(e.Pos(), "use of .(type) outside type switch")
goto Error
}
T := check.typ(e.Type)
if T == Typ[Invalid] {
goto Error
}
check.typeAssertion(x.pos(), x, xtyp, T)
x.mode = commaok
x.typ = T
case *ast.CallExpr:
return check.call(x, e)
case *ast.StarExpr:
check.exprOrType(x, e.X)
switch x.mode {
case invalid:
goto Error
case typexpr:
x.typ = &Pointer{base: x.typ}
default:
if typ, ok := x.typ.Underlying().(*Pointer); ok {
x.mode = variable
x.typ = typ.base
} else {
check.invalidOp(x.pos(), "cannot indirect %s", x)
goto Error
}
}
case *ast.UnaryExpr:
check.expr(x, e.X)
if x.mode == invalid {
goto Error
}
check.unary(x, e, e.Op)
if x.mode == invalid {
goto Error
}
if e.Op == token.ARROW {
x.expr = e
return statement // receive operations may appear in statement context
}
case *ast.BinaryExpr:
check.binary(x, e, e.X, e.Y, e.Op)
if x.mode == invalid {
goto Error
}
case *ast.KeyValueExpr:
// key:value expressions are handled in composite literals
check.invalidAST(e.Pos(), "no key:value expected")
goto Error
case *ast.ArrayType, *ast.StructType, *ast.FuncType,
*ast.InterfaceType, *ast.MapType, *ast.ChanType:
x.mode = typexpr
x.typ = check.typ(e)
// Note: rawExpr (caller of exprInternal) will call check.recordTypeAndValue
// even though check.typ has already called it. This is fine as both
// times the same expression and type are recorded. It is also not a
// performance issue because we only reach here for composite literal
// types, which are comparatively rare.
default:
panic(fmt.Sprintf("%s: unknown expression type %T", check.fset.Position(e.Pos()), e))
}
// everything went well
x.expr = e
return expression
Error:
x.mode = invalid
x.expr = e
return statement // avoid follow-up errors
}