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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 conversions.
package types2
import (
"go/constant"
"unicode"
)
// Conversion type-checks the conversion T(x).
// The result is in x.
func (check *Checker) conversion(x *operand, T Type) {
constArg := x.mode == constant_
var ok bool
switch {
case constArg && isConstType(T):
// constant conversion
switch t := asBasic(T); {
case representableConst(x.val, check, t, &x.val):
ok = true
case isInteger(x.typ) && isString(t):
codepoint := unicode.ReplacementChar
if i, ok := constant.Uint64Val(x.val); ok && i <= unicode.MaxRune {
codepoint = rune(i)
}
x.val = constant.MakeString(string(codepoint))
ok = true
}
case x.convertibleTo(check, T):
// non-constant conversion
x.mode = value
ok = true
}
if !ok {
if x.mode != invalid {
check.errorf(x, "cannot convert %s to %s", x, T)
x.mode = invalid
}
return
}
// The conversion argument types are final. For untyped values the
// conversion provides the type, per the spec: "A constant may be
// given a type explicitly by a constant declaration or conversion,...".
if isUntyped(x.typ) {
final := T
// - For conversions to interfaces, except for untyped nil arguments,
// use the argument's default type.
// - For conversions of untyped constants to non-constant types, also
// use the default type (e.g., []byte("foo") should report string
// not []byte as type for the constant "foo").
// - For integer to string conversions, keep the argument type.
// (See also the TODO below.)
if x.typ == Typ[UntypedNil] {
// ok
} else if IsInterface(T) || constArg && !isConstType(T) {
final = Default(x.typ)
} else if isInteger(x.typ) && isString(T) {
final = x.typ
}
check.updateExprType(x.expr, final, true)
}
x.typ = T
}
// TODO(gri) convertibleTo checks if T(x) is valid. It assumes that the type
// of x is fully known, but that's not the case for say string(1<<s + 1.0):
// Here, the type of 1<<s + 1.0 will be UntypedFloat which will lead to the
// (correct!) refusal of the conversion. But the reported error is essentially
// "cannot convert untyped float value to string", yet the correct error (per
// the spec) is that we cannot shift a floating-point value: 1 in 1<<s should
// be converted to UntypedFloat because of the addition of 1.0. Fixing this
// is tricky because we'd have to run updateExprType on the argument first.
// (Issue #21982.)
// convertibleTo reports whether T(x) is valid.
// The check parameter may be nil if convertibleTo is invoked through an
// exported API call, i.e., when all methods have been type-checked.
func (x *operand) convertibleTo(check *Checker, T Type) bool {
// "x is assignable to T"
if ok, _ := x.assignableTo(check, T, nil); ok {
return true
}
// "x's type and T have identical underlying types if tags are ignored"
V := x.typ
Vu := under(V)
Tu := under(T)
if IdenticalIgnoreTags(Vu, Tu) {
return true
}
// "x's type and T are unnamed pointer types and their pointer base types
// have identical underlying types if tags are ignored"
if V, ok := V.(*Pointer); ok {
if T, ok := T.(*Pointer); ok {
if IdenticalIgnoreTags(under(V.base), under(T.base)) {
return true
}
}
}
// "x's type and T are both integer or floating point types"
if isIntegerOrFloat(V) && isIntegerOrFloat(T) {
return true
}
// "x's type and T are both complex types"
if isComplex(V) && isComplex(T) {
return true
}
// "x is an integer or a slice of bytes or runes and T is a string type"
if (isInteger(V) || isBytesOrRunes(Vu)) && isString(T) {
return true
}
// "x is a string and T is a slice of bytes or runes"
if isString(V) && isBytesOrRunes(Tu) {
return true
}
// package unsafe:
// "any pointer or value of underlying type uintptr can be converted into a unsafe.Pointer"
if (isPointer(Vu) || isUintptr(Vu)) && isUnsafePointer(T) {
return true
}
// "and vice versa"
if isUnsafePointer(V) && (isPointer(Tu) || isUintptr(Tu)) {
return true
}
// "x is a slice, T is a pointer-to-array type,
// and the slice and array types have identical element types."
if s := asSlice(V); s != nil {
if p := asPointer(T); p != nil {
if a := asArray(p.Elem()); a != nil {
if Identical(s.Elem(), a.Elem()) {
if check == nil || check.allowVersion(check.pkg, 1, 17) {
return true
}
// check != nil
if check.conf.CompilerErrorMessages {
check.error(x, "conversion of slices to array pointers only supported as of -lang=go1.17")
} else {
check.error(x, "conversion of slices to array pointers requires go1.17 or later")
}
x.mode = invalid // avoid follow-up error
}
}
}
}
return false
}
func isUintptr(typ Type) bool {
t := asBasic(typ)
return t != nil && t.kind == Uintptr
}
func isUnsafePointer(typ Type) bool {
// TODO(gri): Is this asBasic(typ) instead of typ.(*Basic) correct?
// (The former calls under(), while the latter doesn't.)
// The spec does not say so, but gc claims it is. See also
// issue 6326.
t := asBasic(typ)
return t != nil && t.kind == UnsafePointer
}
func isPointer(typ Type) bool {
return asPointer(typ) != nil
}
func isBytesOrRunes(typ Type) bool {
if s := asSlice(typ); s != nil {
t := asBasic(s.elem)
return t != nil && (t.kind == Byte || t.kind == Rune)
}
return false
}
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