go typexpr 源码
golang typexpr 代码
文件路径：/src/go/types/typexpr.go
// Copyright 2013 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 type-checking of identifiers and type expressions.
package types
import (
"fmt"
"go/ast"
"go/constant"
"go/internal/typeparams"
"strings"
)
// ident type-checks identifier e and initializes x with the value or type of e.
// If an error occurred, x.mode is set to invalid.
// For the meaning of def, see Checker.definedType, below.
// If wantType is set, the identifier e is expected to denote a type.
func (check *Checker) ident(x *operand, e *ast.Ident, def *Named, wantType bool) {
x.mode = invalid
x.expr = e
// Note that we cannot use check.lookup here because the returned scope
// may be different from obj.Parent(). See also Scope.LookupParent doc.
scope, obj := check.scope.LookupParent(e.Name, check.pos)
switch obj {
case nil:
if e.Name == "_" {
// Blank identifiers are never declared, but the current identifier may
// be a placeholder for a receiver type parameter. In this case we can
// resolve its type and object from Checker.recvTParamMap.
if tpar := check.recvTParamMap[e]; tpar != nil {
x.mode = typexpr
x.typ = tpar
} else {
check.error(e, _InvalidBlank, "cannot use _ as value or type")
}
} else {
check.errorf(e, _UndeclaredName, "undeclared name: %s", e.Name)
}
return
case universeAny, universeComparable:
if !check.allowVersion(check.pkg, 1, 18) {
check.versionErrorf(e, _UndeclaredName, "go1.18", "predeclared %s", e.Name)
return // avoid follow-on errors
}
}
check.recordUse(e, obj)
// Type-check the object.
// Only call Checker.objDecl if the object doesn't have a type yet
// (in which case we must actually determine it) or the object is a
// TypeName and we also want a type (in which case we might detect
// a cycle which needs to be reported). Otherwise we can skip the
// call and avoid a possible cycle error in favor of the more
// informative "not a type/value" error that this function's caller
// will issue (see issue #25790).
typ := obj.Type()
if _, gotType := obj.(*TypeName); typ == nil || gotType && wantType {
check.objDecl(obj, def)
typ = obj.Type() // type must have been assigned by Checker.objDecl
}
assert(typ != nil)
// The object may have been dot-imported.
// If so, mark the respective package as used.
// (This code is only needed for dot-imports. Without them,
// we only have to mark variables, see *Var case below).
if pkgName := check.dotImportMap[dotImportKey{scope, obj.Name()}]; pkgName != nil {
pkgName.used = true
}
switch obj := obj.(type) {
case *PkgName:
check.errorf(e, _InvalidPkgUse, "use of package %s not in selector", obj.name)
return
case *Const:
check.addDeclDep(obj)
if typ == Typ[Invalid] {
return
}
if obj == universeIota {
if check.iota == nil {
check.errorf(e, _InvalidIota, "cannot use iota outside constant declaration")
return
}
x.val = check.iota
} else {
x.val = obj.val
}
assert(x.val != nil)
x.mode = constant_
case *TypeName:
if check.isBrokenAlias(obj) {
check.errorf(e, _InvalidDeclCycle, "invalid use of type alias %s in recursive type (see issue #50729)", obj.name)
return
}
x.mode = typexpr
case *Var:
// It's ok to mark non-local variables, but ignore variables
// from other packages to avoid potential race conditions with
// dot-imported variables.
if obj.pkg == check.pkg {
obj.used = true
}
check.addDeclDep(obj)
if typ == Typ[Invalid] {
return
}
x.mode = variable
case *Func:
check.addDeclDep(obj)
x.mode = value
case *Builtin:
x.id = obj.id
x.mode = builtin
case *Nil:
x.mode = value
default:
unreachable()
}
x.typ = typ
}
// typ type-checks the type expression e and returns its type, or Typ[Invalid].
// The type must not be an (uninstantiated) generic type.
func (check *Checker) typ(e ast.Expr) Type {
return check.definedType(e, nil)
}
// varType type-checks the type expression e and returns its type, or Typ[Invalid].
// The type must not be an (uninstantiated) generic type and it must not be a
// constraint interface.
func (check *Checker) varType(e ast.Expr) Type {
typ := check.definedType(e, nil)
check.validVarType(e, typ)
return typ
}
// validVarType reports an error if typ is a constraint interface.
// The expression e is used for error reporting, if any.
func (check *Checker) validVarType(e ast.Expr, typ Type) {
// If we have a type parameter there's nothing to do.
if isTypeParam(typ) {
return
}
// We don't want to call under() or complete interfaces while we are in
// the middle of type-checking parameter declarations that might belong
// to interface methods. Delay this check to the end of type-checking.
check.later(func() {
if t, _ := under(typ).(*Interface); t != nil {
tset := computeInterfaceTypeSet(check, e.Pos(), t) // TODO(gri) is this the correct position?
if !tset.IsMethodSet() {
if tset.comparable {
check.softErrorf(e, _MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface is (or embeds) comparable", typ)
} else {
check.softErrorf(e, _MisplacedConstraintIface, "cannot use type %s outside a type constraint: interface contains type constraints", typ)
}
}
}
}).describef(e, "check var type %s", typ)
}
// definedType is like typ but also accepts a type name def.
// If def != nil, e is the type specification for the defined type def, declared
// in a type declaration, and def.underlying will be set to the type of e before
// any components of e are type-checked.
func (check *Checker) definedType(e ast.Expr, def *Named) Type {
typ := check.typInternal(e, def)
assert(isTyped(typ))
if isGeneric(typ) {
check.errorf(e, _WrongTypeArgCount, "cannot use generic type %s without instantiation", typ)
typ = Typ[Invalid]
}
check.recordTypeAndValue(e, typexpr, typ, nil)
return typ
}
// genericType is like typ but the type must be an (uninstantiated) generic
// type. If reason is non-nil and the type expression was a valid type but not
// generic, reason will be populated with a message describing the error.
func (check *Checker) genericType(e ast.Expr, reason *string) Type {
typ := check.typInternal(e, nil)
assert(isTyped(typ))
if typ != Typ[Invalid] && !isGeneric(typ) {
if reason != nil {
*reason = check.sprintf("%s is not a generic type", typ)
}
typ = Typ[Invalid]
}
// TODO(gri) what is the correct call below?
check.recordTypeAndValue(e, typexpr, typ, nil)
return typ
}
// goTypeName returns the Go type name for typ and
// removes any occurrences of "types." from that name.
func goTypeName(typ Type) string {
return strings.ReplaceAll(fmt.Sprintf("%T", typ), "types.", "")
}
// typInternal drives type checking of types.
// Must only be called by definedType or genericType.
func (check *Checker) typInternal(e0 ast.Expr, def *Named) (T Type) {
if trace {
check.trace(e0.Pos(), "-- type %s", e0)
check.indent++
defer func() {
check.indent--
var under Type
if T != nil {
// Calling under() here may lead to endless instantiations.
// Test case: type T[P any] *T[P]
under = safeUnderlying(T)
}
if T == under {
check.trace(e0.Pos(), "=> %s // %s", T, goTypeName(T))
} else {
check.trace(e0.Pos(), "=> %s (under = %s) // %s", T, under, goTypeName(T))
}
}()
}
switch e := e0.(type) {
case *ast.BadExpr:
// ignore - error reported before
case *ast.Ident:
var x operand
check.ident(&x, e, def, true)
switch x.mode {
case typexpr:
typ := x.typ
def.setUnderlying(typ)
return typ
case invalid:
// ignore - error reported before
case novalue:
check.errorf(&x, _NotAType, "%s used as type", &x)
default:
check.errorf(&x, _NotAType, "%s is not a type", &x)
}
case *ast.SelectorExpr:
var x operand
check.selector(&x, e, def)
switch x.mode {
case typexpr:
typ := x.typ
def.setUnderlying(typ)
return typ
case invalid:
// ignore - error reported before
case novalue:
check.errorf(&x, _NotAType, "%s used as type", &x)
default:
check.errorf(&x, _NotAType, "%s is not a type", &x)
}
case *ast.IndexExpr, *ast.IndexListExpr:
ix := typeparams.UnpackIndexExpr(e)
if !check.allowVersion(check.pkg, 1, 18) {
check.softErrorf(inNode(e, ix.Lbrack), _UnsupportedFeature, "type instantiation requires go1.18 or later")
}
return check.instantiatedType(ix, def)
case *ast.ParenExpr:
// Generic types must be instantiated before they can be used in any form.
// Consequently, generic types cannot be parenthesized.
return check.definedType(e.X, def)
case *ast.ArrayType:
if e.Len == nil {
typ := new(Slice)
def.setUnderlying(typ)
typ.elem = check.varType(e.Elt)
return typ
}
typ := new(Array)
def.setUnderlying(typ)
typ.len = check.arrayLength(e.Len)
typ.elem = check.varType(e.Elt)
if typ.len >= 0 {
return typ
}
case *ast.Ellipsis:
// dots are handled explicitly where they are legal
// (array composite literals and parameter lists)
check.error(e, _InvalidDotDotDot, "invalid use of '...'")
check.use(e.Elt)
case *ast.StructType:
typ := new(Struct)
def.setUnderlying(typ)
check.structType(typ, e)
return typ
case *ast.StarExpr:
typ := new(Pointer)
typ.base = Typ[Invalid] // avoid nil base in invalid recursive type declaration
def.setUnderlying(typ)
typ.base = check.varType(e.X)
return typ
case *ast.FuncType:
typ := new(Signature)
def.setUnderlying(typ)
check.funcType(typ, nil, e)
return typ
case *ast.InterfaceType:
typ := check.newInterface()
def.setUnderlying(typ)
check.interfaceType(typ, e, def)
return typ
case *ast.MapType:
typ := new(Map)
def.setUnderlying(typ)
typ.key = check.varType(e.Key)
typ.elem = check.varType(e.Value)
// spec: "The comparison operators == and != must be fully defined
// for operands of the key type; thus the key type must not be a
// function, map, or slice."
//
// Delay this check because it requires fully setup types;
// it is safe to continue in any case (was issue 6667).
check.later(func() {
if !Comparable(typ.key) {
var why string
if isTypeParam(typ.key) {
why = " (missing comparable constraint)"
}
check.errorf(e.Key, _IncomparableMapKey, "incomparable map key type %s%s", typ.key, why)
}
}).describef(e.Key, "check map key %s", typ.key)
return typ
case *ast.ChanType:
typ := new(Chan)
def.setUnderlying(typ)
dir := SendRecv
switch e.Dir {
case ast.SEND | ast.RECV:
// nothing to do
case ast.SEND:
dir = SendOnly
case ast.RECV:
dir = RecvOnly
default:
check.invalidAST(e, "unknown channel direction %d", e.Dir)
// ok to continue
}
typ.dir = dir
typ.elem = check.varType(e.Value)
return typ
default:
check.errorf(e0, _NotAType, "%s is not a type", e0)
}
typ := Typ[Invalid]
def.setUnderlying(typ)
return typ
}
func (check *Checker) instantiatedType(ix *typeparams.IndexExpr, def *Named) (res Type) {
if trace {
check.trace(ix.Pos(), "-- instantiating type %s with %s", ix.X, ix.Indices)
check.indent++
defer func() {
check.indent--
// Don't format the underlying here. It will always be nil.
check.trace(ix.Pos(), "=> %s", res)
}()
}
var reason string
gtyp := check.genericType(ix.X, &reason)
if reason != "" {
check.invalidOp(ix.Orig, _NotAGenericType, "%s (%s)", ix.Orig, reason)
}
if gtyp == Typ[Invalid] {
return gtyp // error already reported
}
orig, _ := gtyp.(*Named)
if orig == nil {
panic(fmt.Sprintf("%v: cannot instantiate %v", ix.Pos(), gtyp))
}
// evaluate arguments
targs := check.typeList(ix.Indices)
if targs == nil {
def.setUnderlying(Typ[Invalid]) // avoid errors later due to lazy instantiation
return Typ[Invalid]
}
// create the instance
inst := check.instance(ix.Pos(), orig, targs, nil, check.context()).(*Named)
def.setUnderlying(inst)
// orig.tparams may not be set up, so we need to do expansion later.
check.later(func() {
// This is an instance from the source, not from recursive substitution,
// and so it must be resolved during type-checking so that we can report
// errors.
check.recordInstance(ix.Orig, inst.TypeArgs().list(), inst)
if check.validateTArgLen(ix.Pos(), inst.TypeParams().Len(), inst.TypeArgs().Len()) {
if i, err := check.verify(ix.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), check.context()); err != nil {
// best position for error reporting
pos := ix.Pos()
if i < len(ix.Indices) {
pos = ix.Indices[i].Pos()
}
check.softErrorf(atPos(pos), _InvalidTypeArg, err.Error())
} else {
check.mono.recordInstance(check.pkg, ix.Pos(), inst.TypeParams().list(), inst.TypeArgs().list(), ix.Indices)
}
}
// TODO(rfindley): remove this call: we don't need to call validType here,
// as cycles can only occur for types used inside a Named type declaration,
// and so it suffices to call validType from declared types.
check.validType(inst)
}).describef(ix, "resolve instance %s", inst)
return inst
}
// arrayLength type-checks the array length expression e
// and returns the constant length >= 0, or a value < 0
// to indicate an error (and thus an unknown length).
func (check *Checker) arrayLength(e ast.Expr) int64 {
// If e is an identifier, the array declaration might be an
// attempt at a parameterized type declaration with missing
// constraint. Provide an error message that mentions array
// length.
if name, _ := e.(*ast.Ident); name != nil {
obj := check.lookup(name.Name)
if obj == nil {
check.errorf(name, _InvalidArrayLen, "undeclared name %s for array length", name.Name)
return -1
}
if _, ok := obj.(*Const); !ok {
check.errorf(name, _InvalidArrayLen, "invalid array length %s", name.Name)
return -1
}
}
var x operand
check.expr(&x, e)
if x.mode != constant_ {
if x.mode != invalid {
check.errorf(&x, _InvalidArrayLen, "array length %s must be constant", &x)
}
return -1
}
if isUntyped(x.typ) || isInteger(x.typ) {
if val := constant.ToInt(x.val); val.Kind() == constant.Int {
if representableConst(val, check, Typ[Int], nil) {
if n, ok := constant.Int64Val(val); ok && n >= 0 {
return n
}
check.errorf(&x, _InvalidArrayLen, "invalid array length %s", &x)
return -1
}
}
}
check.errorf(&x, _InvalidArrayLen, "array length %s must be integer", &x)
return -1
}
// typeList provides the list of types corresponding to the incoming expression list.
// If an error occurred, the result is nil, but all list elements were type-checked.
func (check *Checker) typeList(list []ast.Expr) []Type {
res := make([]Type, len(list)) // res != nil even if len(list) == 0
for i, x := range list {
t := check.varType(x)
if t == Typ[Invalid] {
res = nil
}
if res != nil {
res[i] = t
}
}
return res
}
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