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// 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 (
"go/ast"
"go/constant"
"go/token"
"sort"
"strconv"
)
// 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)
if obj == nil {
if e.Name == "_" {
check.errorf(e, _InvalidBlank, "cannot use _ as value or type")
} else {
check.errorf(e, _UndeclaredName, "undeclared name: %s", e.Name)
}
return
}
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 be dot-imported: If so, remove its package from
// the map of unused dot imports for the respective file scope.
// (This code is only needed for dot-imports. Without them,
// we only have to mark variables, see *Var case below).
if pkg := obj.Pkg(); pkg != check.pkg && pkg != nil {
delete(check.unusedDotImports[scope], pkg)
}
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:
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].
func (check *Checker) typ(e ast.Expr) Type {
return check.definedType(e, nil)
}
// 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) (T Type) {
if trace {
check.trace(e.Pos(), "%s", e)
check.indent++
defer func() {
check.indent--
check.trace(e.Pos(), "=> %s", T)
}()
}
T = check.typInternal(e, def)
assert(isTyped(T))
check.recordTypeAndValue(e, typexpr, T, nil)
return
}
// funcType type-checks a function or method type.
func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) {
scope := NewScope(check.scope, token.NoPos, token.NoPos, "function")
scope.isFunc = true
check.recordScope(ftyp, scope)
recvList, _ := check.collectParams(scope, recvPar, false)
params, variadic := check.collectParams(scope, ftyp.Params, true)
results, _ := check.collectParams(scope, ftyp.Results, false)
if recvPar != nil {
// recv parameter list present (may be empty)
// spec: "The receiver is specified via an extra parameter section preceding the
// method name. That parameter section must declare a single parameter, the receiver."
var recv *Var
switch len(recvList) {
case 0:
check.error(recvPar, _BadRecv, "method is missing receiver")
recv = NewParam(0, nil, "", Typ[Invalid]) // ignore recv below
default:
// more than one receiver
check.error(recvList[len(recvList)-1], _BadRecv, "method must have exactly one receiver")
fallthrough // continue with first receiver
case 1:
recv = recvList[0]
}
// spec: "The receiver type must be of the form T or *T where T is a type name."
// (ignore invalid types - error was reported before)
if t, _ := deref(recv.typ); t != Typ[Invalid] {
var err string
if T, _ := t.(*Named); T != nil {
// spec: "The type denoted by T is called the receiver base type; it must not
// be a pointer or interface type and it must be declared in the same package
// as the method."
if T.obj.pkg != check.pkg {
err = "type not defined in this package"
} else {
// TODO(gri) This is not correct if the underlying type is unknown yet.
switch u := T.underlying.(type) {
case *Basic:
// unsafe.Pointer is treated like a regular pointer
if u.kind == UnsafePointer {
err = "unsafe.Pointer"
}
case *Pointer, *Interface:
err = "pointer or interface type"
}
}
} else {
err = "basic or unnamed type"
}
if err != "" {
check.errorf(recv, _InvalidRecv, "invalid receiver %s (%s)", recv.typ, err)
// ok to continue
}
}
sig.recv = recv
}
sig.scope = scope
sig.params = NewTuple(params...)
sig.results = NewTuple(results...)
sig.variadic = variadic
}
// typInternal drives type checking of types.
// Must only be called by definedType.
//
func (check *Checker) typInternal(e ast.Expr, def *Named) Type {
switch e := e.(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)
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.ParenExpr:
return check.definedType(e.X, def)
case *ast.ArrayType:
if e.Len != nil {
typ := new(Array)
def.setUnderlying(typ)
typ.len = check.arrayLength(e.Len)
typ.elem = check.typ(e.Elt)
return typ
} else {
typ := new(Slice)
def.setUnderlying(typ)
typ.elem = check.typ(e.Elt)
return typ
}
case *ast.StructType:
typ := new(Struct)
def.setUnderlying(typ)
check.structType(typ, e)
return typ
case *ast.StarExpr:
typ := new(Pointer)
def.setUnderlying(typ)
typ.base = check.typ(e.X)
return typ
case *ast.FuncType:
typ := new(Signature)
def.setUnderlying(typ)
check.funcType(typ, nil, e)
return typ
case *ast.InterfaceType:
typ := new(Interface)
def.setUnderlying(typ)
check.interfaceType(typ, e, def)
return typ
case *ast.MapType:
typ := new(Map)
def.setUnderlying(typ)
typ.key = check.typ(e.Key)
typ.elem = check.typ(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.atEnd(func() {
if !Comparable(typ.key) {
check.errorf(e.Key, _IncomparableMapKey, "incomparable map key type %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.typ(e.Value)
return typ
default:
check.errorf(e, _NotAType, "%s is not a type", e)
}
typ := Typ[Invalid]
def.setUnderlying(typ)
return typ
}
// typeOrNil type-checks the type expression (or nil value) e
// and returns the typ of e, or nil.
// If e is neither a type nor nil, typOrNil returns Typ[Invalid].
//
func (check *Checker) typOrNil(e ast.Expr) Type {
var x operand
check.rawExpr(&x, e, nil)
switch x.mode {
case invalid:
// ignore - error reported before
case novalue:
check.errorf(&x, _NotAType, "%s used as type", &x)
case typexpr:
return x.typ
case value:
if x.isNil() {
return nil
}
fallthrough
default:
check.errorf(&x, _NotAType, "%s is not a type", &x)
}
return Typ[Invalid]
}
// 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 {
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
}
func (check *Checker) collectParams(scope *Scope, list *ast.FieldList, variadicOk bool) (params []*Var, variadic bool) {
if list == nil {
return
}
var named, anonymous bool
for i, field := range list.List {
ftype := field.Type
if t, _ := ftype.(*ast.Ellipsis); t != nil {
ftype = t.Elt
if variadicOk && i == len(list.List)-1 && len(field.Names) <= 1 {
variadic = true
} else {
check.softErrorf(t, _MisplacedDotDotDot, "can only use ... with final parameter in list")
// ignore ... and continue
}
}
typ := check.typ(ftype)
// The parser ensures that f.Tag is nil and we don't
// care if a constructed AST contains a non-nil tag.
if len(field.Names) > 0 {
// named parameter
for _, name := range field.Names {
if name.Name == "" {
check.invalidAST(name, "anonymous parameter")
// ok to continue
}
par := NewParam(name.Pos(), check.pkg, name.Name, typ)
check.declare(scope, name, par, scope.pos)
params = append(params, par)
}
named = true
} else {
// anonymous parameter
par := NewParam(ftype.Pos(), check.pkg, "", typ)
check.recordImplicit(field, par)
params = append(params, par)
anonymous = true
}
}
if named && anonymous {
check.invalidAST(list, "list contains both named and anonymous parameters")
// ok to continue
}
// For a variadic function, change the last parameter's type from T to []T.
// Since we type-checked T rather than ...T, we also need to retro-actively
// record the type for ...T.
if variadic {
last := params[len(params)-1]
last.typ = &Slice{elem: last.typ}
check.recordTypeAndValue(list.List[len(list.List)-1].Type, typexpr, last.typ, nil)
}
return
}
func (check *Checker) declareInSet(oset *objset, pos token.Pos, obj Object) bool {
if alt := oset.insert(obj); alt != nil {
check.errorf(atPos(pos), _DuplicateDecl, "%s redeclared", obj.Name())
check.reportAltDecl(alt)
return false
}
return true
}
func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, def *Named) {
for _, f := range iface.Methods.List {
if len(f.Names) > 0 {
// We have a method with name f.Names[0].
// (The parser ensures that there's only one method
// and we don't care if a constructed AST has more.)
name := f.Names[0]
if name.Name == "_" {
check.errorf(name, _BlankIfaceMethod, "invalid method name _")
continue // ignore
}
typ := check.typ(f.Type)
sig, _ := typ.(*Signature)
if sig == nil {
if typ != Typ[Invalid] {
check.invalidAST(f.Type, "%s is not a method signature", typ)
}
continue // ignore
}
// use named receiver type if available (for better error messages)
var recvTyp Type = ityp
if def != nil {
recvTyp = def
}
sig.recv = NewVar(name.Pos(), check.pkg, "", recvTyp)
m := NewFunc(name.Pos(), check.pkg, name.Name, sig)
check.recordDef(name, m)
ityp.methods = append(ityp.methods, m)
} else {
// We have an embedded interface and f.Type is its
// (possibly qualified) embedded type name. Collect
// it if it's a valid interface.
typ := check.typ(f.Type)
utyp := check.underlying(typ)
if _, ok := utyp.(*Interface); !ok {
if utyp != Typ[Invalid] {
check.errorf(f.Type, _InvalidIfaceEmbed, "%s is not an interface", typ)
}
continue
}
ityp.embeddeds = append(ityp.embeddeds, typ)
check.posMap[ityp] = append(check.posMap[ityp], f.Type.Pos())
}
}
if len(ityp.methods) == 0 && len(ityp.embeddeds) == 0 {
// empty interface
ityp.allMethods = markComplete
return
}
// sort for API stability
sort.Sort(byUniqueMethodName(ityp.methods))
sort.Stable(byUniqueTypeName(ityp.embeddeds))
check.later(func() { check.completeInterface(ityp) })
}
func (check *Checker) completeInterface(ityp *Interface) {
if ityp.allMethods != nil {
return
}
// completeInterface may be called via the LookupFieldOrMethod,
// MissingMethod, Identical, or IdenticalIgnoreTags external API
// in which case check will be nil. In this case, type-checking
// must be finished and all interfaces should have been completed.
if check == nil {
panic("internal error: incomplete interface")
}
if trace {
check.trace(token.NoPos, "complete %s", ityp)
check.indent++
defer func() {
check.indent--
check.trace(token.NoPos, "=> %s", ityp)
}()
}
// An infinitely expanding interface (due to a cycle) is detected
// elsewhere (Checker.validType), so here we simply assume we only
// have valid interfaces. Mark the interface as complete to avoid
// infinite recursion if the validType check occurs later for some
// reason.
ityp.allMethods = markComplete
// Methods of embedded interfaces are collected unchanged; i.e., the identity
// of a method I.m's Func Object of an interface I is the same as that of
// the method m in an interface that embeds interface I. On the other hand,
// if a method is embedded via multiple overlapping embedded interfaces, we
// don't provide a guarantee which "original m" got chosen for the embedding
// interface. See also issue #34421.
//
// If we don't care to provide this identity guarantee anymore, instead of
// reusing the original method in embeddings, we can clone the method's Func
// Object and give it the position of a corresponding embedded interface. Then
// we can get rid of the mpos map below and simply use the cloned method's
// position.
var seen objset
var methods []*Func
mpos := make(map[*Func]token.Pos) // method specification or method embedding position, for good error messages
addMethod := func(pos token.Pos, m *Func, explicit bool) {
switch other := seen.insert(m); {
case other == nil:
methods = append(methods, m)
mpos[m] = pos
case explicit:
check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
default:
// check method signatures after all types are computed (issue #33656)
check.atEnd(func() {
if !check.identical(m.typ, other.Type()) {
check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
}
})
}
}
for _, m := range ityp.methods {
addMethod(m.pos, m, true)
}
posList := check.posMap[ityp]
for i, typ := range ityp.embeddeds {
pos := posList[i] // embedding position
typ, ok := check.underlying(typ).(*Interface)
if !ok {
// An error was reported when collecting the embedded types.
// Ignore it.
continue
}
check.completeInterface(typ)
for _, m := range typ.allMethods {
addMethod(pos, m, false) // use embedding position pos rather than m.pos
}
}
if methods != nil {
sort.Sort(byUniqueMethodName(methods))
ityp.allMethods = methods
}
}
// byUniqueTypeName named type lists can be sorted by their unique type names.
type byUniqueTypeName []Type
func (a byUniqueTypeName) Len() int { return len(a) }
func (a byUniqueTypeName) Less(i, j int) bool { return sortName(a[i]) < sortName(a[j]) }
func (a byUniqueTypeName) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func sortName(t Type) string {
if named, _ := t.(*Named); named != nil {
return named.obj.Id()
}
return ""
}
// byUniqueMethodName method lists can be sorted by their unique method names.
type byUniqueMethodName []*Func
func (a byUniqueMethodName) Len() int { return len(a) }
func (a byUniqueMethodName) Less(i, j int) bool { return a[i].Id() < a[j].Id() }
func (a byUniqueMethodName) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (check *Checker) tag(t *ast.BasicLit) string {
if t != nil {
if t.Kind == token.STRING {
if val, err := strconv.Unquote(t.Value); err == nil {
return val
}
}
check.invalidAST(t, "incorrect tag syntax: %q", t.Value)
}
return ""
}
func (check *Checker) structType(styp *Struct, e *ast.StructType) {
list := e.Fields
if list == nil {
return
}
// struct fields and tags
var fields []*Var
var tags []string
// for double-declaration checks
var fset objset
// current field typ and tag
var typ Type
var tag string
add := func(ident *ast.Ident, embedded bool, pos token.Pos) {
if tag != "" && tags == nil {
tags = make([]string, len(fields))
}
if tags != nil {
tags = append(tags, tag)
}
name := ident.Name
fld := NewField(pos, check.pkg, name, typ, embedded)
// spec: "Within a struct, non-blank field names must be unique."
if name == "_" || check.declareInSet(&fset, pos, fld) {
fields = append(fields, fld)
check.recordDef(ident, fld)
}
}
// addInvalid adds an embedded field of invalid type to the struct for
// fields with errors; this keeps the number of struct fields in sync
// with the source as long as the fields are _ or have different names
// (issue #25627).
addInvalid := func(ident *ast.Ident, pos token.Pos) {
typ = Typ[Invalid]
tag = ""
add(ident, true, pos)
}
for _, f := range list.List {
typ = check.typ(f.Type)
tag = check.tag(f.Tag)
if len(f.Names) > 0 {
// named fields
for _, name := range f.Names {
add(name, false, name.Pos())
}
} else {
// embedded field
// spec: "An embedded type must be specified as a type name T or as a pointer
// to a non-interface type name *T, and T itself may not be a pointer type."
pos := f.Type.Pos()
name := embeddedFieldIdent(f.Type)
if name == nil {
check.invalidAST(f.Type, "embedded field type %s has no name", f.Type)
name = ast.NewIdent("_")
name.NamePos = pos
addInvalid(name, pos)
continue
}
t, isPtr := deref(typ)
// Because we have a name, typ must be of the form T or *T, where T is the name
// of a (named or alias) type, and t (= deref(typ)) must be the type of T.
switch t := t.Underlying().(type) {
case *Basic:
if t == Typ[Invalid] {
// error was reported before
addInvalid(name, pos)
continue
}
// unsafe.Pointer is treated like a regular pointer
if t.kind == UnsafePointer {
check.errorf(f.Type, _InvalidPtrEmbed, "embedded field type cannot be unsafe.Pointer")
addInvalid(name, pos)
continue
}
case *Pointer:
check.errorf(f.Type, _InvalidPtrEmbed, "embedded field type cannot be a pointer")
addInvalid(name, pos)
continue
case *Interface:
if isPtr {
check.errorf(f.Type, _InvalidPtrEmbed, "embedded field type cannot be a pointer to an interface")
addInvalid(name, pos)
continue
}
}
add(name, true, pos)
}
}
styp.fields = fields
styp.tags = tags
}
func embeddedFieldIdent(e ast.Expr) *ast.Ident {
switch e := e.(type) {
case *ast.Ident:
return e
case *ast.StarExpr:
// *T is valid, but **T is not
if _, ok := e.X.(*ast.StarExpr); !ok {
return embeddedFieldIdent(e.X)
}
case *ast.SelectorExpr:
return e.Sel
}
return nil // invalid embedded field
}