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expr.go
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1782 lines (1630 loc) · 51.3 KB
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// 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 (
"fmt"
"go/ast"
"go/constant"
"go/internal/typeparams"
"go/token"
"math"
)
/*
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, if present.
*/
type opPredicates map[token.Token]func(Type) bool
var unaryOpPredicates opPredicates
func init() {
// Setting unaryOpPredicates in init avoids declaration cycles.
unaryOpPredicates = opPredicates{
token.ADD: allNumeric,
token.SUB: allNumeric,
token.XOR: allInteger,
token.NOT: allBoolean,
}
}
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, _UndefinedOp, "operator %s not defined on %s", op, x)
return false
}
} else {
check.invalidAST(x, "unknown operator %s", op)
return false
}
return true
}
// overflow checks that the constant x is representable by its type.
// For untyped constants, it checks that the value doesn't become
// arbitrarily large.
func (check *Checker) overflow(x *operand, opPos token.Pos) {
assert(x.mode == constant_)
if x.val.Kind() == constant.Unknown {
// TODO(gri) We should report exactly what went wrong. At the
// moment we don't have the (go/constant) API for that.
// See also TODO in go/constant/value.go.
check.errorf(atPos(opPos), _InvalidConstVal, "constant result is not representable")
return
}
// Typed constants must be representable in
// their type after each constant operation.
// x.typ cannot be a type parameter (type
// parameters cannot be constant types).
if isTyped(x.typ) {
check.representable(x, under(x.typ).(*Basic))
return
}
// Untyped integer values must not grow arbitrarily.
const prec = 512 // 512 is the constant precision
if x.val.Kind() == constant.Int && constant.BitLen(x.val) > prec {
check.errorf(atPos(opPos), _InvalidConstVal, "constant %s overflow", opName(x.expr))
x.val = constant.MakeUnknown()
}
}
// opName returns the name of the operation if x is an operation
// that might overflow; otherwise it returns the empty string.
func opName(e ast.Expr) string {
switch e := e.(type) {
case *ast.BinaryExpr:
if int(e.Op) < len(op2str2) {
return op2str2[e.Op]
}
case *ast.UnaryExpr:
if int(e.Op) < len(op2str1) {
return op2str1[e.Op]
}
}
return ""
}
var op2str1 = [...]string{
token.XOR: "bitwise complement",
}
// This is only used for operations that may cause overflow.
var op2str2 = [...]string{
token.ADD: "addition",
token.SUB: "subtraction",
token.XOR: "bitwise XOR",
token.MUL: "multiplication",
token.SHL: "shift",
}
// If typ is a type parameter, underIs returns the result of typ.underIs(f).
// Otherwise, underIs returns the result of f(under(typ)).
func underIs(typ Type, f func(Type) bool) bool {
if tpar, _ := typ.(*TypeParam); tpar != nil {
return tpar.underIs(f)
}
return f(under(typ))
}
// The unary expression e may be nil. It's passed in for better error messages only.
func (check *Checker) unary(x *operand, e *ast.UnaryExpr) {
check.expr(x, e.X)
if x.mode == invalid {
return
}
switch e.Op {
case token.AND:
// spec: "As an exception to the addressability
// requirement x may also be a composite literal."
if _, ok := unparen(e.X).(*ast.CompositeLit); !ok && x.mode != variable {
check.invalidOp(x, _UnaddressableOperand, "cannot take address of %s", x)
x.mode = invalid
return
}
x.mode = value
x.typ = &Pointer{base: x.typ}
return
case token.ARROW:
u := coreType(x.typ)
if u == nil {
check.invalidOp(x, _InvalidReceive, "cannot receive from %s: no core type", x)
x.mode = invalid
return
}
ch, _ := u.(*Chan)
if ch == nil {
check.invalidOp(x, _InvalidReceive, "cannot receive from non-channel %s", x)
x.mode = invalid
return
}
if ch.dir == SendOnly {
check.invalidOp(x, _InvalidReceive, "cannot receive from send-only channel %s", x)
x.mode = invalid
return
}
x.mode = commaok
x.typ = ch.elem
check.hasCallOrRecv = true
return
}
if !check.op(unaryOpPredicates, x, e.Op) {
x.mode = invalid
return
}
if x.mode == constant_ {
if x.val.Kind() == constant.Unknown {
// nothing to do (and don't cause an error below in the overflow check)
return
}
var prec uint
if isUnsigned(x.typ) {
prec = uint(check.conf.sizeof(x.typ) * 8)
}
x.val = constant.UnaryOp(e.Op, x.val, prec)
x.expr = e
check.overflow(x, x.Pos())
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 constant.Value) bool {
f32, _ := constant.Float32Val(x)
f := float64(f32)
return !math.IsInf(f, 0)
}
func roundFloat32(x constant.Value) constant.Value {
f32, _ := constant.Float32Val(x)
f := float64(f32)
if !math.IsInf(f, 0) {
return constant.MakeFloat64(f)
}
return nil
}
func fitsFloat64(x constant.Value) bool {
f, _ := constant.Float64Val(x)
return !math.IsInf(f, 0)
}
func roundFloat64(x constant.Value) constant.Value {
f, _ := constant.Float64Val(x)
if !math.IsInf(f, 0) {
return constant.MakeFloat64(f)
}
return nil
}
// 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.
//
// The check parameter may be nil if representableConst is invoked
// (indirectly) through an exported API call (AssignableTo, ConvertibleTo)
// because we don't need the Checker's config for those calls.
func representableConst(x constant.Value, check *Checker, typ *Basic, rounded *constant.Value) bool {
if x.Kind() == constant.Unknown {
return true // avoid follow-up errors
}
var conf *Config
if check != nil {
conf = check.conf
}
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
}
// representable checks that a constant operand is representable in the given
// basic type.
func (check *Checker) representable(x *operand, typ *Basic) {
v, code := check.representation(x, typ)
if code != 0 {
check.invalidConversion(code, x, typ)
x.mode = invalid
return
}
assert(v != nil)
x.val = v
}
// representation returns the representation of the constant operand x as the
// basic type typ.
//
// If no such representation is possible, it returns a non-zero error code.
func (check *Checker) representation(x *operand, typ *Basic) (constant.Value, errorCode) {
assert(x.mode == constant_)
v := x.val
if !representableConst(x.val, check, typ, &v) {
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) {
return nil, _TruncatedFloat
} else {
return nil, _NumericOverflow
}
}
return nil, _InvalidConstVal
}
return v, 0
}
func (check *Checker) invalidConversion(code errorCode, x *operand, target Type) {
msg := "cannot convert %s to %s"
switch code {
case _TruncatedFloat:
msg = "%s truncated to %s"
case _NumericOverflow:
msg = "%s overflows %s"
}
check.errorf(x, code, msg, x, target)
}
// 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) {
check.updateExprType0(nil, x, typ, final)
}
func (check *Checker) updateExprType0(parent, 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("%v: 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.updateExprType0(x, x.X, typ, final)
case *ast.UnaryExpr:
// If x is a constant, the operands were constants.
// The operands don't need to be updated since they
// never get "materialized" into a typed value. If
// left in the untyped map, they will be processed
// at the end of the type check.
if old.val != nil {
break
}
check.updateExprType0(x, 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.updateExprType0(x, x.X, typ, final)
} else {
// The operand types match the result type.
check.updateExprType0(x, x.X, typ, final)
check.updateExprType0(x, 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 = under(typ).(*Basic)
check.untyped[x] = old
return
}
// Otherwise we have the final (typed or untyped type).
// Remove it from the map of yet untyped expressions.
delete(check.untyped, x)
if old.isLhs {
// 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 !allInteger(typ) {
if compilerErrorMessages {
check.invalidOp(x, _InvalidShiftOperand, "%s (shift of type %s)", parent, typ)
} else {
check.invalidOp(x, _InvalidShiftOperand, "shifted operand %s (type %s) must be integer", x, typ)
}
return
}
// Even if we have an integer, if the value is a constant we
// still must check that it is representable as the specific
// int type requested (was issue #22969). Fall through here.
}
if old.val != nil {
// If x is a constant, it must be representable as a value of typ.
c := operand{old.mode, x, old.typ, old.val, 0}
check.convertUntyped(&c, typ)
if c.mode == invalid {
return
}
}
// Everything's fine, record final type and value for x.
check.recordTypeAndValue(x, old.mode, typ, old.val)
}
// updateExprVal updates the value of x to val.
func (check *Checker) updateExprVal(x ast.Expr, val constant.Value) {
if info, ok := check.untyped[x]; ok {
info.val = val
check.untyped[x] = info
}
}
// convertUntyped attempts to set the type of an untyped value to the target type.
func (check *Checker) convertUntyped(x *operand, target Type) {
newType, val, code := check.implicitTypeAndValue(x, target)
if code != 0 {
t := target
if !isTypeParam(target) {
t = safeUnderlying(target)
}
check.invalidConversion(code, x, t)
x.mode = invalid
return
}
if val != nil {
x.val = val
check.updateExprVal(x.expr, val)
}
if newType != x.typ {
x.typ = newType
check.updateExprType(x.expr, newType, false)
}
}
// implicitTypeAndValue returns the implicit type of x when used in a context
// where the target type is expected. If no such implicit conversion is
// possible, it returns a nil Type and non-zero error code.
//
// If x is a constant operand, the returned constant.Value will be the
// representation of x in this context.
func (check *Checker) implicitTypeAndValue(x *operand, target Type) (Type, constant.Value, errorCode) {
if x.mode == invalid || isTyped(x.typ) || target == Typ[Invalid] {
return x.typ, nil, 0
}
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 {
return target, nil, 0
}
} else if xkind != tkind {
return nil, nil, _InvalidUntypedConversion
}
return x.typ, nil, 0
}
switch u := under(target).(type) {
case *Basic:
if x.mode == constant_ {
v, code := check.representation(x, u)
if code != 0 {
return nil, nil, code
}
return target, v, code
}
// 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) {
return nil, nil, _InvalidUntypedConversion
}
case UntypedInt, UntypedRune, UntypedFloat, UntypedComplex:
if !isNumeric(target) {
return nil, nil, _InvalidUntypedConversion
}
case UntypedString:
// Non-constant untyped string values are not permitted by the spec and
// should not occur during normal typechecking passes, but this path is
// reachable via the AssignableTo API.
if !isString(target) {
return nil, nil, _InvalidUntypedConversion
}
case UntypedNil:
// Unsafe.Pointer is a basic type that includes nil.
if !hasNil(target) {
return nil, nil, _InvalidUntypedConversion
}
// Preserve the type of nil as UntypedNil: see #13061.
return Typ[UntypedNil], nil, 0
default:
return nil, nil, _InvalidUntypedConversion
}
case *Interface:
if isTypeParam(target) {
if !u.typeSet().underIs(func(u Type) bool {
if u == nil {
return false
}
t, _, _ := check.implicitTypeAndValue(x, u)
return t != nil
}) {
return nil, nil, _InvalidUntypedConversion
}
// keep nil untyped (was bug #39755)
if x.isNil() {
return Typ[UntypedNil], nil, 0
}
break
}
// 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() {
return Typ[UntypedNil], nil, 0
}
// cannot assign untyped values to non-empty interfaces
if !u.Empty() {
return nil, nil, _InvalidUntypedConversion
}
return Default(x.typ), nil, 0
case *Pointer, *Signature, *Slice, *Map, *Chan:
if !x.isNil() {
return nil, nil, _InvalidUntypedConversion
}
// Keep nil untyped - see comment for interfaces, above.
return Typ[UntypedNil], nil, 0
default:
return nil, nil, _InvalidUntypedConversion
}
return target, nil, 0
}
// If switchCase is true, the operator op is ignored.
func (check *Checker) comparison(x, y *operand, op token.Token, switchCase bool) {
if switchCase {
op = token.EQL
}
errOp := x // operand for which error is reported, if any
cause := "" // specific error cause, if any
// spec: "In any comparison, the first operand must be assignable
// to the type of the second operand, or vice versa."
code := _MismatchedTypes
ok, _ := x.assignableTo(check, y.typ, nil)
if !ok {
ok, _ = y.assignableTo(check, x.typ, nil)
}
if !ok {
// Report the error on the 2nd operand since we only
// know after seeing the 2nd operand whether we have
// a type mismatch.
errOp = y
// For now, if we're not running the compiler, use the
// position of x to minimize changes to existing tests.
if !compilerErrorMessages {
errOp = x
}
cause = check.sprintf("mismatched types %s and %s", x.typ, y.typ)
goto Error
}
// check if comparison is defined for operands
code = _UndefinedOp
switch op {
case token.EQL, token.NEQ:
// spec: "The equality operators == and != apply to operands that are comparable."
switch {
case x.isNil() || y.isNil():
// Comparison against nil requires that the other operand type has nil.
typ := x.typ
if x.isNil() {
typ = y.typ
}
if !hasNil(typ) {
// This case should only be possible for "nil == nil".
// Report the error on the 2nd operand since we only
// know after seeing the 2nd operand whether we have
// an invalid comparison.
errOp = y
goto Error
}
case !Comparable(x.typ):
errOp = x
cause = check.incomparableCause(x.typ)
goto Error
case !Comparable(y.typ):
errOp = y
cause = check.incomparableCause(y.typ)
goto Error
}
case token.LSS, token.LEQ, token.GTR, token.GEQ:
// spec: The ordering operators <, <=, >, and >= apply to operands that are ordered."
switch {
case !allOrdered(x.typ):
errOp = x
goto Error
case !allOrdered(y.typ):
errOp = y
goto Error
}
default:
unreachable()
}
// comparison is ok
if x.mode == constant_ && y.mode == constant_ {
x.val = constant.MakeBool(constant.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, Default(x.typ), true)
check.updateExprType(y.expr, Default(y.typ), true)
}
// spec: "Comparison operators compare two operands and yield
// an untyped boolean value."
x.typ = Typ[UntypedBool]
return
Error:
// We have an offending operand errOp and possibly an error cause.
if cause == "" {
if isTypeParam(x.typ) || isTypeParam(y.typ) {
// TODO(gri) should report the specific type causing the problem, if any
if !isTypeParam(x.typ) {
errOp = y
}
cause = check.sprintf("type parameter %s is not comparable with %s", errOp.typ, op)
} else {
cause = check.sprintf("operator %s not defined on %s", op, check.kindString(errOp.typ)) // catch-all
}
}
if switchCase {
check.errorf(x, code, "invalid case %s in switch on %s (%s)", x.expr, y.expr, cause) // error position always at 1st operand
} else {
if compilerErrorMessages {
check.invalidOp(errOp, code, "%s %s %s (%s)", x.expr, op, y.expr, cause)
} else {
check.invalidOp(errOp, code, "cannot compare %s %s %s (%s)", x.expr, op, y.expr, cause)
}
}
x.mode = invalid
}
// incomparableCause returns a more specific cause why typ is not comparable.
// If there is no more specific cause, the result is "".
func (check *Checker) incomparableCause(typ Type) string {
switch under(typ).(type) {
case *Slice, *Signature, *Map:
return check.kindString(typ) + " can only be compared to nil"
}
// see if we can extract a more specific error
var cause string
comparable(typ, true, nil, func(format string, args ...interface{}) {
cause = check.sprintf(format, args...)
})
return cause
}
// kindString returns the type kind as a string.
func (check *Checker) kindString(typ Type) string {
switch under(typ).(type) {
case *Array:
return "array"
case *Slice:
return "slice"
case *Struct:
return "struct"
case *Pointer:
return "pointer"
case *Signature:
return "func"
case *Interface:
if isTypeParam(typ) {
return check.sprintf("type parameter %s", typ)
}
return "interface"
case *Map:
return "map"
case *Chan:
return "chan"
default:
return check.sprintf("%s", typ) // catch-all
}
}
// If e != nil, it must be the shift expression; it may be nil for non-constant shifts.
func (check *Checker) shift(x, y *operand, e ast.Expr, op token.Token) {
// TODO(gri) This function seems overly complex. Revisit.
var xval constant.Value
if x.mode == constant_ {
xval = constant.ToInt(x.val)
}
if allInteger(x.typ) || isUntyped(x.typ) && 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, _InvalidShiftOperand, "shifted operand %s must be integer", x)
x.mode = invalid
return
}
// spec: "The right operand in a shift expression must have integer type
// or be an untyped constant representable by a value of type uint."
// Check that constants are representable by uint, but do not convert them
// (see also issue #47243).
if y.mode == constant_ {
// Provide a good error message for negative shift counts.
yval := constant.ToInt(y.val) // consider -1, 1.0, but not -1.1
if yval.Kind() == constant.Int && constant.Sign(yval) < 0 {
check.invalidOp(y, _InvalidShiftCount, "negative shift count %s", y)
x.mode = invalid
return
}
if isUntyped(y.typ) {
// Caution: Check for representability here, rather than in the switch
// below, because isInteger includes untyped integers (was bug #43697).
check.representable(y, Typ[Uint])
if y.mode == invalid {
x.mode = invalid
return
}
}
} else {
// Check that RHS is otherwise at least of integer type.
switch {
case allInteger(y.typ):
if !allUnsigned(y.typ) && !check.allowVersion(check.pkg, 1, 13) {
check.invalidOp(y, _InvalidShiftCount, "signed shift count %s requires go1.13 or later", y)
x.mode = invalid
return
}
case isUntyped(y.typ):
// This is incorrect, but preserves pre-existing behavior.
// See also bug #47410.
check.convertUntyped(y, Typ[Uint])
if y.mode == invalid {
x.mode = invalid
return
}
default:
check.invalidOp(y, _InvalidShiftCount, "shift count %s must be integer", y)
x.mode = invalid
return
}
}
if x.mode == constant_ {
if y.mode == constant_ {
// if either x or y has an unknown value, the result is unknown
if x.val.Kind() == constant.Unknown || y.val.Kind() == constant.Unknown {
x.val = constant.MakeUnknown()
// ensure the correct type - see comment below
if !isInteger(x.typ) {
x.typ = Typ[UntypedInt]
}
return
}
// rhs must be within reasonable bounds in constant shifts
const shiftBound = 1023 - 1 + 52 // so we can express smallestFloat64 (see issue #44057)
s, ok := constant.Uint64Val(y.val)
if !ok || s > shiftBound {
check.invalidOp(y, _InvalidShiftCount, "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))
x.expr = e
opPos := x.Pos()
if b, _ := e.(*ast.BinaryExpr); b != nil {
opPos = b.OpPos
}
check.overflow(x, opPos)
return
}
// non-constant shift with constant lhs
if isUntyped(x.typ) {
// spec: "If the left operand of a non-constant shift