// assign1to1 typechecks a single assignment of the form lhs = rhs (if rhs != nil), or
// lhs = x (if rhs == nil). If decl is set, the lhs expression must be an identifier;
// if its type is not set, it is deduced from the type of x or set to Typ[Invalid] in
// case of an error.
//
func (check *checker) assign1to1(lhs, rhs ast.Expr, x *operand, decl bool, iota int) {
// Start with rhs so we have an expression type
// for declarations with implicit type.
if x == nil {
x = new(operand)
check.expr(x, rhs, nil, iota)
// don't exit for declarations - we need the lhs first
if x.mode == invalid && !decl {
return
}
}
// x.mode == valid || decl
// lhs may be an identifier
ident, _ := lhs.(*ast.Ident)
// regular assignment; we know x is valid
if !decl {
// anything can be assigned to the blank identifier
if ident != nil && ident.Name == "_" {
// the rhs has its final type
check.updateExprType(rhs, x.typ, true)
return
}
var z operand
check.expr(&z, lhs, nil, -1)
if z.mode == invalid {
return
}
// TODO(gri) verify that all other z.mode values
// that may appear here are legal
if z.mode == constant || !check.assignment(x, z.typ) {
if x.mode != invalid {
check.errorf(x.pos(), "cannot assign %s to %s", x, &z)
}
}
return
}
// declaration with initialization; lhs must be an identifier
if ident == nil {
check.errorf(lhs.Pos(), "cannot declare %s", lhs)
return
}
// Determine typ of lhs: If the object doesn't have a type
// yet, determine it from the type of x; if x is invalid,
// set the object type to Typ[Invalid].
var typ Type
obj := check.lookup(ident)
switch obj := obj.(type) {
default:
unreachable()
case nil:
// TODO(gri) is this really unreachable?
unreachable()
case *Const:
typ = obj.Type // may already be Typ[Invalid]
if typ == nil {
typ = Typ[Invalid]
if x.mode != invalid {
typ = x.typ
}
obj.Type = typ
}
case *Var:
typ = obj.Type // may already be Typ[Invalid]
if typ == nil {
typ = Typ[Invalid]
if x.mode != invalid {
typ = x.typ
if isUntyped(typ) {
// convert untyped types to default types
if typ == Typ[UntypedNil] {
check.errorf(x.pos(), "use of untyped nil")
typ = Typ[Invalid]
} else {
typ = defaultType(typ)
}
}
}
obj.Type = typ
}
}
// nothing else to check if we don't have a valid lhs or rhs
if typ == Typ[Invalid] || x.mode == invalid {
return
}
if !check.assignment(x, typ) {
if x.mode != invalid {
if x.typ != Typ[Invalid] && typ != Typ[Invalid] {
check.errorf(x.pos(), "cannot initialize %s (type %s) with %s", ident.Name, typ, x)
}
}
return
}
// for constants, set their value
if obj, _ := obj.(*Const); obj != nil {
obj.Val = exact.MakeUnknown() // failure case: we don't know the constant value
if x.mode == constant {
if isConstType(x.typ) {
obj.Val = x.val
} else if x.typ != Typ[Invalid] {
check.errorf(x.pos(), "%s has invalid constant type", x)
}
} else if x.mode != invalid {
check.errorf(x.pos(), "%s is not constant", x)
}
}
}
// object typechecks an object by assigning it a type.
//
func (check *checker) object(obj Object, cycleOk bool) {
switch obj := obj.(type) {
case *Package:
// nothing to do
case *Const:
if obj.Type != nil {
return // already checked
}
// The obj.Val field for constants is initialized to its respective
// iota value (type int) by the parser.
// If the object's type is Typ[Invalid], the object value is ignored.
// If the object's type is valid, the object value must be a legal
// constant value; it may be nil to indicate that we don't know the
// value of the constant (e.g., in: "const x = float32("foo")" we
// know that x is a constant and has type float32, but we don't
// have a value due to the error in the conversion).
if obj.visited {
check.errorf(obj.GetPos(), "illegal cycle in initialization of constant %s", obj.Name)
obj.Type = Typ[Invalid]
return
}
obj.visited = true
spec := obj.spec
iota, ok := exact.Int64Val(obj.Val)
assert(ok)
obj.Val = exact.MakeUnknown()
// determine spec for type and initialization expressions
init := spec
if len(init.Values) == 0 {
init = check.initspecs[spec]
}
check.valueSpec(spec.Pos(), obj, spec.Names, init, int(iota))
case *Var:
if obj.Type != nil {
return // already checked
}
if obj.visited {
check.errorf(obj.GetPos(), "illegal cycle in initialization of variable %s", obj.Name)
obj.Type = Typ[Invalid]
return
}
obj.visited = true
switch d := obj.decl.(type) {
case *ast.Field:
unreachable() // function parameters are always typed when collected
case *ast.ValueSpec:
check.valueSpec(d.Pos(), obj, d.Names, d, 0)
case *ast.AssignStmt:
unreachable() // assign1to1 sets the type for failing short var decls
default:
unreachable() // see also function newObj
}
case *TypeName:
if obj.Type != nil {
return // already checked
}
typ := &NamedType{Obj: obj}
obj.Type = typ // "mark" object so recursion terminates
typ.Underlying = underlying(check.typ(obj.spec.Type, cycleOk))
// typecheck associated method signatures
if scope := check.methods[obj]; scope != nil {
switch t := typ.Underlying.(type) {
case *Struct:
// struct fields must not conflict with methods
for _, f := range t.Fields {
if m := scope.Lookup(f.Name); m != nil {
check.errorf(m.GetPos(), "type %s has both field and method named %s", obj.Name, f.Name)
// ok to continue
}
}
case *Interface:
// methods cannot be associated with an interface type
for _, m := range scope.Entries {
recv := m.(*Func).decl.Recv.List[0].Type
check.errorf(recv.Pos(), "invalid receiver type %s (%s is an interface type)", obj.Name, obj.Name)
// ok to continue
}
}
// typecheck method signatures
var methods []*Method
for _, obj := range scope.Entries {
m := obj.(*Func)
sig := check.typ(m.decl.Type, cycleOk).(*Signature)
params, _ := check.collectParams(m.decl.Recv, false)
sig.Recv = params[0] // the parser/assocMethod ensure there is exactly one parameter
m.Type = sig
methods = append(methods, &Method{QualifiedName{check.pkg, m.Name}, sig})
check.later(m, sig, m.decl.Body)
}
typ.Methods = methods
delete(check.methods, obj) // we don't need this scope anymore
}
case *Func:
if obj.Type != nil {
return // already checked
}
fdecl := obj.decl
// methods are typechecked when their receivers are typechecked
if fdecl.Recv == nil {
sig := check.typ(fdecl.Type, cycleOk).(*Signature)
if obj.Name == "init" && (len(sig.Params) != 0 || len(sig.Results) != 0) {
check.errorf(fdecl.Pos(), "func init must have no arguments and no return values")
// ok to continue
}
obj.Type = sig
check.later(obj, sig, fdecl.Body)
}
default:
unreachable()
}
}