go_agent/src/code.google.com/p/go.tools/go/types/expr.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 expressions.
package types
import (
"go/ast"
"go/token"
"math"
"code.google.com/p/go.tools/go/exact"
)
/*
Basic algorithm:
Expressions are checked recursively, top down. Expression checker functions
are generally of the form:
func f(x *operand, e *ast.Expr, ...)
where e is the expression to be checked, and x is the result of the check.
The check performed by f may fail in which case x.mode == invalid, and
related error messages will have been issued by f.
If a hint argument is present, it is the composite literal element type
of an outer composite literal; it is used to type-check composite literal
elements that have no explicit type specification in the source
(e.g.: []T{{...}, {...}}, the hint is the type T in this case).
All expressions are checked via rawExpr, which dispatches according
to expression kind. Upon returning, rawExpr is recording the types and
constant values for all expressions that have an untyped type (those types
may change on the way up in the expression tree). Usually these are constants,
but the results of comparisons or non-constant shifts of untyped constants
may also be untyped, but not constant.
Untyped expressions may eventually become fully typed (i.e., not untyped),
typically when the value is assigned to a variable, or is used otherwise.
The updateExprType method is used to record this final type and update
the recorded types: the type-checked expression tree is again traversed down,
and the new type is propagated as needed. Untyped constant expression values
that become fully typed must now be representable by the full type (constant
sub-expression trees are left alone except for their roots). This mechanism
ensures that a client sees the actual (run-time) type an untyped value would
have. It also permits type-checking of lhs shift operands "as if the shift
were not present": when updateExprType visits an untyped lhs shift operand
and assigns it it's final type, that type must be an integer type, and a
constant lhs must be representable as an integer.
When an expression gets its final type, either on the way out from rawExpr,
on the way down in updateExprType, or at the end of the type checker run,
the type (and constant value, if any) is recorded via Info.Types and Values,
if present.
*/
type opPredicates map[token.Token]func(Type) bool
var unaryOpPredicates = opPredicates{
token.ADD: isNumeric,
token.SUB: isNumeric,
token.XOR: isInteger,
token.NOT: isBoolean,
}
func (check *checker) op(m opPredicates, x *operand, op token.Token) bool {
if pred := m[op]; pred != nil {
if !pred(x.typ) {
check.invalidOp(x.pos(), "operator %s not defined for %s", op, x)
return false
}
} else {
check.invalidAST(x.pos(), "unknown operator %s", op)
return false
}
return true
}
func (check *checker) unary(x *operand, op token.Token) {
switch op {
case token.AND:
// spec: "As an exception to the addressability
// requirement x may also be a composite literal."
if _, ok := unparen(x.expr).(*ast.CompositeLit); ok {
x.mode = variable
}
if x.mode != variable {
check.invalidOp(x.pos(), "cannot take address of %s", x)
x.mode = invalid
return
}
x.typ = &Pointer{base: x.typ}
return
case token.ARROW:
typ, ok := x.typ.Underlying().(*Chan)
if !ok {
check.invalidOp(x.pos(), "cannot receive from non-channel %s", x)
x.mode = invalid
return
}
if typ.dir&ast.RECV == 0 {
check.invalidOp(x.pos(), "cannot receive from send-only channel %s", x)
x.mode = invalid
return
}
x.mode = commaok
x.typ = typ.elem
return
}
if !check.op(unaryOpPredicates, x, op) {
x.mode = invalid
return
}
if x.mode == constant {
typ := x.typ.Underlying().(*Basic)
size := -1
if isUnsigned(typ) {
size = int(check.conf.sizeof(typ))
}
x.val = exact.UnaryOp(op, x.val, size)
// Typed constants must be representable in
// their type after each constant operation.
if isTyped(typ) {
check.isRepresentableAs(x, typ)
}
return
}
x.mode = value
// x.typ remains unchanged
}
func isShift(op token.Token) bool {
return op == token.SHL || op == token.SHR
}
func isComparison(op token.Token) bool {
// Note: tokens are not ordered well to make this much easier
switch op {
case token.EQL, token.NEQ, token.LSS, token.LEQ, token.GTR, token.GEQ:
return true
}
return false
}
func fitsFloat32(x exact.Value) bool {
f, _ := exact.Float64Val(x)
// spec: "In all non-constant conversions involving floating-point
// or complex values, if the result type cannot represent the value
// the conversion succeeds but the result value is implementation-
// dependent."
//
// We assume that float32(f) returns an Inf if f is too large for
// a float32, or if f is an Inf; and that it returns 0 for values
// with too small a magnitude.
return !math.IsInf(float64(float32(f)), 0)
}
func roundFloat32(x exact.Value) exact.Value {
f, _ := exact.Float64Val(x)
f = float64(float32(f))
if !math.IsInf(f, 0) {
return exact.MakeFloat64(f)
}
return nil
}
func fitsFloat64(x exact.Value) bool {
f, _ := exact.Float64Val(x)
return !math.IsInf(f, 0)
}
func roundFloat64(x exact.Value) exact.Value {
f, _ := exact.Float64Val(x)
if !math.IsInf(f, 0) {
return exact.MakeFloat64(f)
}
return nil
}
// isRepresentableConst reports whether x can be represented as
// value of the given basic type kind 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 values; it is left alone otherwise.
// It is ok to provide the addressof the first argument for rounded.
func isRepresentableConst(x exact.Value, conf *Config, as BasicKind, rounded *exact.Value) bool {
switch x.Kind() {
case exact.Unknown:
return true
case exact.Bool:
return as == Bool || as == UntypedBool
case exact.Int:
if x, ok := exact.Int64Val(x); ok {
switch as {
case Int:
var s = uint(conf.sizeof(Typ[as])) * 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:
return true
case Uint, Uintptr:
if s := uint(conf.sizeof(Typ[as])) * 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
case Float32, Float64, Complex64, Complex128,
UntypedInt, UntypedFloat, UntypedComplex:
return true
}
}
n := exact.BitLen(x)
switch as {
case Uint, Uintptr:
var s = uint(conf.sizeof(Typ[as])) * 8
return exact.Sign(x) >= 0 && n <= int(s)
case Uint64:
return exact.Sign(x) >= 0 && n <= 64
case Float32, Complex64:
if rounded == nil {
return fitsFloat32(x)
}
r := roundFloat32(x)
if r != nil {
*rounded = r
return true
}
case Float64, Complex128:
if rounded == nil {
return fitsFloat64(x)
}
r := roundFloat64(x)
if r != nil {
*rounded = r
return true
}
case UntypedInt, UntypedFloat, UntypedComplex:
return true
}
case exact.Float:
switch as {
case Float32, Complex64:
if rounded == nil {
return fitsFloat32(x)
}
r := roundFloat32(x)
if r != nil {
*rounded = r
return true
}
case Float64, Complex128:
if rounded == nil {
return fitsFloat64(x)
}
r := roundFloat64(x)
if r != nil {
*rounded = r
return true
}
case UntypedFloat, UntypedComplex:
return true
}
case exact.Complex:
switch as {
case Complex64:
if rounded == nil {
return fitsFloat32(exact.Real(x)) && fitsFloat32(exact.Imag(x))
}
re := roundFloat32(exact.Real(x))
im := roundFloat32(exact.Imag(x))
if re != nil && im != nil {
*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
return true
}
case Complex128:
if rounded == nil {
return fitsFloat64(exact.Real(x)) && fitsFloat64(exact.Imag(x))
}
re := roundFloat64(exact.Real(x))
im := roundFloat64(exact.Imag(x))
if re != nil && im != nil {
*rounded = exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
return true
}
case UntypedComplex:
return true
}
case exact.String:
return as == String || as == UntypedString
default:
unreachable()
}
return false
}
// isRepresentableAs checks that a constant operand is representable in the given basic type.
func (check *checker) isRepresentableAs(x *operand, typ *Basic) {
assert(x.mode == constant)
if !isRepresentableConst(x.val, check.conf, typ.kind, &x.val) {
var msg string
if isNumeric(x.typ) && isNumeric(typ) {
// numeric conversion : error msg
//
// integer -> integer : overflows
// integer -> float : overflows (actually not possible)
// float -> integer : truncated
// float -> float : overflows
//
if !isInteger(x.typ) && isInteger(typ) {
msg = "%s truncated to %s"
} else {
msg = "%s overflows %s"
}
} else {
msg = "cannot convert %s to %s"
}
check.errorf(x.pos(), msg, x, typ)
x.mode = invalid
}
}
// updateExprType updates the type of x to typ and invokes itself
// recursively for the operands of x, depending on expression kind.
// If typ is still an untyped and not the final type, updateExprType
// only updates the recorded untyped type for x and possibly its
// operands. Otherwise (i.e., typ is not an untyped type anymore,
// or it is the final type for x), the type and value are recorded.
// Also, if x is a constant, it must be representable as a value of typ,
// and if x is the (formerly untyped) lhs operand of a non-constant
// shift, it must be an integer value.
//
func (check *checker) updateExprType(x ast.Expr, typ Type, final bool) {
old, found := check.untyped[x]
if !found {
return // nothing to do
}
// update operands of x if necessary
switch x := x.(type) {
case *ast.BadExpr,
*ast.FuncLit,
*ast.CompositeLit,
*ast.IndexExpr,
*ast.SliceExpr,
*ast.TypeAssertExpr,
*ast.StarExpr,
*ast.KeyValueExpr,
*ast.ArrayType,
*ast.StructType,
*ast.FuncType,
*ast.InterfaceType,
*ast.MapType,
*ast.ChanType:
// These expression are never untyped - nothing to do.
// The respective sub-expressions got their final types
// upon assignment or use.
if debug {
check.dump("%s: found old type(%s): %s (new: %s)", x.Pos(), x, old.typ, typ)
unreachable()
}
return
case *ast.CallExpr:
// Resulting in an untyped constant (e.g., built-in complex).
// The respective calls take care of calling updateExprType
// for the arguments if necessary.
case *ast.Ident, *ast.BasicLit, *ast.SelectorExpr:
// An identifier denoting a constant, a constant literal,
// or a qualified identifier (imported untyped constant).
// No operands to take care of.
case *ast.ParenExpr:
check.updateExprType(x.X, typ, final)
case *ast.UnaryExpr:
// If x is a constant, the operands were constants.
// They don't need to be updated since they never
// get "materialized" into a typed value; and they
// will be processed at the end of the type check.
if old.val != nil {
break
}
check.updateExprType(x.X, typ, final)
case *ast.BinaryExpr:
if old.val != nil {
break // see comment for unary expressions
}
if isComparison(x.Op) {
// The result type is independent of operand types
// and the operand types must have final types.
} else if isShift(x.Op) {
// The result type depends only on lhs operand.
// The rhs type was updated when checking the shift.
check.updateExprType(x.X, typ, final)
} else {
// The operand types match the result type.
check.updateExprType(x.X, typ, final)
check.updateExprType(x.Y, typ, final)
}
default:
unreachable()
}
// If the new type is not final and still untyped, just
// update the recorded type.
if !final && isUntyped(typ) {
old.typ = typ.Underlying().(*Basic)
check.untyped[x] = old
return
}
// Otherwise we have the final (typed or untyped type).
// Remove it from the map.
delete(check.untyped, x)
// If x is the lhs of a shift, its final type must be integer.
// We already know from the shift check that it is representable
// as an integer if it is a constant.
if old.isLhs && !isInteger(typ) {
check.invalidOp(x.Pos(), "shifted operand %s (type %s) must be integer", x, typ)
return
}
// Everything's fine, record final type and value for x.
check.recordTypeAndValue(x, typ, old.val)
}
// convertUntyped attempts to set the type of an untyped value to the target type.
func (check *checker) convertUntyped(x *operand, target Type) {
if x.mode == invalid || isTyped(x.typ) {
return
}
// TODO(gri) Sloppy code - clean up. This function is central
// to assignment and expression checking.
if isUntyped(target) {
// both x and target are untyped
xkind := x.typ.(*Basic).kind
tkind := target.(*Basic).kind
if isNumeric(x.typ) && isNumeric(target) {
if xkind < tkind {
x.typ = target
check.updateExprType(x.expr, target, false)
}
} else if xkind != tkind {
goto Error
}
return
}
// typed target
switch t := target.Underlying().(type) {
case *Basic:
if x.mode == constant {
check.isRepresentableAs(x, t)
if x.mode == invalid {
return
}
} else {
// Non-constant untyped values may appear as the
// result of comparisons (untyped bool), intermediate
// (delayed-checked) rhs operands of shifts, and as
// the value nil.
switch x.typ.(*Basic).kind {
case UntypedBool:
if !isBoolean(target) {
goto Error
}
case UntypedInt, UntypedRune, UntypedFloat, UntypedComplex:
if !isNumeric(target) {
goto Error
}
case UntypedString:
// Non-constant untyped string values are not
// permitted by the spec and should not occur.
unreachable()
case UntypedNil:
// Unsafe.Pointer is a basic type that includes nil.
if !hasNil(target) {
goto Error
}
default:
goto Error
}
}
case *Interface:
if !x.isNil() && t.NumMethods() > 0 /* empty interfaces are ok */ {
goto Error
}
// Update operand types to the default type rather then
// the target (interface) type: values must have concrete
// dynamic types. If the value is nil, keep it untyped
// (this is important for tools such as go vet which need
// the dynamic type for argument checking of say, print
// functions)
if x.isNil() {
target = Typ[UntypedNil]
} else {
// cannot assign untyped values to non-empty interfaces
if t.NumMethods() > 0 {
goto Error
}
target = defaultType(x.typ)
}
case *Pointer, *Signature, *Slice, *Map, *Chan:
if !x.isNil() {
goto Error
}
// keep nil untyped - see comment for interfaces, above
target = Typ[UntypedNil]
default:
goto Error
}
x.typ = target
check.updateExprType(x.expr, target, true) // UntypedNils are final
return
Error:
check.errorf(x.pos(), "cannot convert %s to %s", x, target)
x.mode = invalid
}
func (check *checker) comparison(x, y *operand, op token.Token) {
// spec: "In any comparison, the first operand must be assignable
// to the type of the second operand, or vice versa."
err := ""
if x.isAssignableTo(check.conf, y.typ) || y.isAssignableTo(check.conf, x.typ) {
defined := false
switch op {
case token.EQL, token.NEQ:
// spec: "The equality operators == and != apply to operands that are comparable."
defined = isComparable(x.typ) || x.isNil() && hasNil(y.typ) || y.isNil() && hasNil(x.typ)
case token.LSS, token.LEQ, token.GTR, token.GEQ:
// spec: The ordering operators <, <=, >, and >= apply to operands that are ordered."
defined = isOrdered(x.typ)
default:
unreachable()
}
if !defined {
typ := x.typ
if x.isNil() {
typ = y.typ
}
err = check.sprintf("operator %s not defined for %s", op, typ)
}
} else {
err = check.sprintf("mismatched types %s and %s", x.typ, y.typ)
}
if err != "" {
check.errorf(x.pos(), "cannot compare %s %s %s (%s)", x.expr, op, y.expr, err)
x.mode = invalid
return
}
if x.mode == constant && y.mode == constant {
x.val = exact.MakeBool(exact.Compare(x.val, op, y.val))
// The operands are never materialized; no need to update
// their types.
} else {
x.mode = value
// The operands 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.
check.updateExprType(x.expr, defaultType(x.typ), true)
check.updateExprType(y.expr, defaultType(y.typ), true)
}
// spec: "Comparison operators compare two operands and yield
// an untyped boolean value."
x.typ = Typ[UntypedBool]
}
func (check *checker) shift(x, y *operand, op token.Token) {
untypedx := isUntyped(x.typ)
// The lhs must be of integer type or be representable
// as an integer; otherwise the shift has no chance.
if !isInteger(x.typ) && (!untypedx || !isRepresentableConst(x.val, nil, UntypedInt, nil)) {
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 isInteger(y.typ) && 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 within reasonable bounds
const stupidShift = 1023 - 1 + 52 // so we can express smallestFloat64
s, ok := exact.Uint64Val(y.val)
if !ok || s > stupidShift {
check.invalidOp(y.pos(), "stupid 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.val = exact.Shift(x.val, op, uint(s))
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:
// The lhs expression must be in the untyped map, mark
// the entry as lhs shift operand.
info, found := check.untyped[x.expr]
assert(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 && exact.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
}
var binaryOpPredicates = opPredicates{
token.ADD: func(typ Type) bool { return isNumeric(typ) || isString(typ) },
token.SUB: isNumeric,
token.MUL: isNumeric,
token.QUO: isNumeric,
token.REM: isInteger,
token.AND: isInteger,
token.OR: isInteger,
token.XOR: isInteger,
token.AND_NOT: isInteger,
token.LAND: isBoolean,
token.LOR: isBoolean,
}
func (check *checker) binary(x *operand, 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, 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 !IsIdentical(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 && exact.Sign(y.val) == 0 {
check.invalidOp(y.pos(), "division by zero")
x.mode = invalid
return
}
if x.mode == constant && y.mode == constant {
typ := x.typ.Underlying().(*Basic)
// force integer division of integer operands
if op == token.QUO && isInteger(typ) {
op = token.QUO_ASSIGN
}
x.val = exact.BinaryOp(x.val, op, y.val)
// Typed constants must be representable in
// their type after each constant operation.
if isTyped(typ) {
check.isRepresentableAs(x, typ)
}
return
}
x.mode = value
// x.typ is unchanged
}
// 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 exact.Sign(x.val) < 0 {
check.invalidArg(x.pos(), "index %s must not be negative", &x)
return
}
i, valid = exact.Int64Val(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
}
// indexElts checks the elements (elts) of an array or slice composite literal
// against the literal's element type (typ), and the element indices against
// the literal length if known (length >= 0). It returns the length of the
// literal (maximum index value + 1).
//
func (check *checker) indexedElts(elts []ast.Expr, typ Type, length int64) int64 {
visited := make(map[int64]bool, len(elts))
var index, max int64
for _, e := range elts {
// determine and check index
validIndex := false
eval := e
if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
if i, ok := check.index(kv.Key, length); ok {
if i >= 0 {
index = i
validIndex = true
} else {
check.errorf(e.Pos(), "index %s must be integer constant", kv.Key)
}
}
eval = kv.Value
} else if length >= 0 && index >= length {
check.errorf(e.Pos(), "index %d is out of bounds (>= %d)", index, length)
} else {
validIndex = true
}
// if we have a valid index, check for duplicate entries
if validIndex {
if visited[index] {
check.errorf(e.Pos(), "duplicate index %d in array or slice literal", index)
}
visited[index] = true
}
index++
if index > max {
max = index
}
// check element against composite literal element type
var x operand
check.exprWithHint(&x, eval, typ)
if !check.assignment(&x, typ) && x.mode != invalid {
check.errorf(x.pos(), "cannot use %s as %s value in array or slice literal", &x, typ)
}
}
return max
}
// exprKind describes the kind of an expression; the kind
// determines if an expression is valid in 'statement context'.
type exprKind int
const (
conversion exprKind = iota
expression
statement
)
// rawExpr typechecks expression e and initializes x with the expression
// value or type. If an error occurred, x.mode is set to invalid.
// If hint != nil, it is the type of a composite literal element.
//
func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
if trace {
check.trace(e.Pos(), "%s", e)
check.indent++
}
kind := check.exprInternal(x, e, hint)
// convert x into a user-friendly set of values
record := true
var typ Type
var val exact.Value
switch x.mode {
case invalid:
typ = Typ[Invalid]
record = false // nothing to do
case novalue:
typ = (*Tuple)(nil)
case constant:
typ = x.typ
val = x.val
default:
typ = x.typ
}
assert(x.expr != nil && typ != nil)
if isUntyped(typ) {
// delay notification until it becomes typed
// or until the end of type checking
check.untyped[x.expr] = exprInfo{false, typ.(*Basic), val}
} else if record {
// TODO(gri) ensure that literals always report
// their dynamic (never interface) type.
// This is not the case yet.
check.recordTypeAndValue(e, typ, val)
}
if trace {
check.indent--
check.trace(e.Pos(), "=> %s", x)
}
return kind
}
// 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, false)
case *ast.Ellipsis:
// ellipses are handled explicitly where they are legal
// (array composite literals and parameter lists)
check.errorf(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, nil, false).(*Signature); ok {
x.mode = value
x.typ = sig
// Anonymous functions are considered part of the
// init expression/func declaration which contains
// them: use the current package-level declaration
// info.
check.later(nil, check.decl, sig, e.Body)
} 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, nil, false)}
openArray = true
}
}
if typ == nil {
typ = check.typ(e.Type, nil, false)
}
}
if typ == nil {
check.errorf(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.errorf(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.recordObject(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.errorf(kv.Pos(), "mixture of field:value and value elements in struct literal")
continue
}
check.expr(x, e)
if i >= len(fields) {
check.errorf(x.pos(), "too many values in struct literal")
break // cannot continue
}
// i < len(fields)
etyp := fields[i].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.errorf(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{}]bool, len(e.Elts))
for _, e := range e.Elts {
kv, _ := e.(*ast.KeyValueExpr)
if kv == nil {
check.errorf(e.Pos(), "missing key in map literal")
continue
}
check.expr(x, kv.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 {
if visited[x.val] {
check.errorf(x.pos(), "duplicate key %s in map literal", x.val)
continue
}
visited[x.val] = true
}
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:
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 = Typ[Byte]
}
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 slice3(e) {
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."
x.mode = value
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.mode = variable
x.typ = &Slice{elem: typ.elem}
}
case *Slice:
valid = true
x.mode = variable
// x.typ doesn't change
}
if !valid {
check.invalidOp(x.pos(), "cannot slice %s", x)
goto Error
}
// spec: "Only the first index may be omitted; it defaults to 0."
if slice3(e) && (e.High == nil || sliceMax(e) == nil) {
check.errorf(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, sliceMax(e)} {
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, nil, false)
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.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.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, nil, false)
// 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:
if debug {
check.dump("expr = %v (%T)", e, e)
}
unreachable()
}
// everything went well
x.expr = e
return expression
Error:
x.mode = invalid
x.expr = e
return statement // avoid follow-up errors
}
// typeAssertion checks that x.(T) is legal; xtyp must be the type of x.
func (check *checker) typeAssertion(pos token.Pos, x *operand, xtyp *Interface, T Type) {
method, wrongType := MissingMethod(T, xtyp, false)
if method == nil {
return
}
var msg string
if wrongType {
msg = "wrong type for method"
} else {
msg = "missing method"
}
check.errorf(pos, "%s cannot have dynamic type %s (%s %s)", x, T, msg, method.name)
}
// expr typechecks expression e and initializes x with the expression value.
// If an error occurred, x.mode is set to invalid.
//
func (check *checker) expr(x *operand, e ast.Expr) {
check.rawExpr(x, e, nil)
var msg string
switch x.mode {
default:
return
case novalue:
msg = "used as value"
case builtin:
msg = "must be called"
case typexpr:
msg = "is not an expression"
}
check.errorf(x.pos(), "%s %s", x, msg)
x.mode = invalid
}
// exprWithHint typechecks expression e and initializes x with the expression value.
// If an error occurred, x.mode is set to invalid.
// If hint != nil, it is the type of a composite literal element.
//
func (check *checker) exprWithHint(x *operand, e ast.Expr, hint Type) {
assert(hint != nil)
check.rawExpr(x, e, hint)
var msg string
switch x.mode {
default:
return
case novalue:
msg = "used as value"
case builtin:
msg = "must be called"
case typexpr:
msg = "is not an expression"
}
check.errorf(x.pos(), "%s %s", x, msg)
x.mode = invalid
}
// exprOrType typechecks expression or type e and initializes x with the expression value or type.
// If an error occurred, x.mode is set to invalid.
//
func (check *checker) exprOrType(x *operand, e ast.Expr) {
check.rawExpr(x, e, nil)
if x.mode == novalue {
check.errorf(x.pos(), "%s used as value or type", x)
x.mode = invalid
}
}