Exemplo n.º 1
0
// rawExpr typechecks expression e and initializes x with the expression
// value or type. If an error occurred, x.mode is set to invalid.
// If hint != nil, it is the type of a composite literal element.
// iota >= 0 indicates that the expression is part of a constant declaration.
// cycleOk indicates whether it is ok for a type expression to refer to itself.
//
func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycleOk bool) {
	if trace {
		c := ""
		if cycleOk {
			c = " тиБ"
		}
		check.trace(e.Pos(), "%s%s", e, c)
		defer check.untrace("=> %s", x)
	}

	// record final type of x if untyped, notify clients of type otherwise
	defer check.callExpr(x)

	switch e := e.(type) {
	case *ast.BadExpr:
		goto Error // error was reported before

	case *ast.Ident:
		if e.Name == "_" {
			check.invalidOp(e.Pos(), "cannot use _ as value or type")
			goto Error
		}
		obj := check.lookup(e)
		if obj == nil {
			goto Error // error was reported before
		}
		check.object(obj, cycleOk)
		switch obj := obj.(type) {
		case *Package:
			check.errorf(e.Pos(), "use of package %s not in selector", obj.Name)
			goto Error
		case *Const:
			if obj.typ == Typ[Invalid] {
				goto Error
			}
			x.mode = constant
			if obj == universeIota {
				if iota < 0 {
					check.invalidAST(e.Pos(), "cannot use iota outside constant declaration")
					goto Error
				}
				x.val = exact.MakeInt64(int64(iota))
			} else {
				x.val = obj.val // may be nil if we don't know the constant value
			}
		case *TypeName:
			x.mode = typexpr
			if !cycleOk && obj.typ.Underlying() == nil {
				check.errorf(obj.spec.Pos(), "illegal cycle in declaration of %s", obj.Name)
				x.expr = e
				x.typ = Typ[Invalid]
				return // don't goto Error - need x.mode == typexpr
			}
		case *Var:
			x.mode = variable
		case *Func:
			x.mode = value
		default:
			unreachable()
		}
		x.typ = obj.Type()

	case *ast.Ellipsis:
		// ellipses are handled explicitly where they are legal
		// (array composite literals and parameter lists)
		check.errorf(e.Pos(), "invalid use of '...'")
		goto Error

	case *ast.BasicLit:
		x.setConst(e.Kind, e.Value)
		if x.mode == invalid {
			check.invalidAST(e.Pos(), "invalid literal %v", e.Value)
			goto Error
		}

	case *ast.FuncLit:
		if sig, ok := check.typ(e.Type, false).(*Signature); ok {
			x.mode = value
			x.typ = sig
			check.later(nil, sig, e.Body)
		} else {
			check.invalidAST(e.Pos(), "invalid function literal %s", e)
			goto Error
		}

	case *ast.CompositeLit:
		typ := hint
		openArray := false
		if e.Type != nil {
			// [...]T array types may only appear with composite literals.
			// Check for them here so we don't have to handle ... in general.
			typ = nil
			if atyp, _ := e.Type.(*ast.ArrayType); atyp != nil && atyp.Len != nil {
				if ellip, _ := atyp.Len.(*ast.Ellipsis); ellip != nil && ellip.Elt == nil {
					// We have an "open" [...]T array type.
					// Create a new ArrayType with unknown length (-1)
					// and finish setting it up after analyzing the literal.
					typ = &Array{len: -1, elt: check.typ(atyp.Elt, cycleOk)}
					openArray = true
				}
			}
			if typ == nil {
				typ = check.typ(e.Type, false)
			}
		}
		if typ == nil {
			check.errorf(e.Pos(), "missing type in composite literal")
			goto Error
		}

		switch utyp := typ.Deref().Underlying().(type) {
		case *Struct:
			if len(e.Elts) == 0 {
				break
			}
			fields := utyp.fields
			if _, ok := e.Elts[0].(*ast.KeyValueExpr); ok {
				// all elements must have keys
				visited := make([]bool, len(fields))
				for _, e := range e.Elts {
					kv, _ := e.(*ast.KeyValueExpr)
					if kv == nil {
						check.errorf(e.Pos(), "mixture of field:value and value elements in struct literal")
						continue
					}
					key, _ := kv.Key.(*ast.Ident)
					if key == nil {
						check.errorf(kv.Pos(), "invalid field name %s in struct literal", kv.Key)
						continue
					}
					i := utyp.fieldIndex(check.pkg, key.Name)
					if i < 0 {
						check.errorf(kv.Pos(), "unknown field %s in struct literal", key.Name)
						continue
					}
					// 0 <= i < len(fields)
					if visited[i] {
						check.errorf(kv.Pos(), "duplicate field name %s in struct literal", key.Name)
						continue
					}
					visited[i] = true
					check.expr(x, kv.Value, nil, iota)
					check.register(key, fields[i])
					etyp := fields[i].typ
					if !check.assignment(x, etyp) {
						if x.mode != invalid {
							check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
						}
						continue
					}
				}
			} else {
				// no element must have a key
				for i, e := range e.Elts {
					if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
						check.errorf(kv.Pos(), "mixture of field:value and value elements in struct literal")
						continue
					}
					check.expr(x, e, nil, iota)
					if i >= len(fields) {
						check.errorf(x.pos(), "too many values in struct literal")
						break // cannot continue
					}
					// i < len(fields)
					etyp := fields[i].typ
					if !check.assignment(x, etyp) {
						if x.mode != invalid {
							check.errorf(x.pos(), "cannot use %s as %s value in struct literal", x, etyp)
						}
						continue
					}
				}
				if len(e.Elts) < len(fields) {
					check.errorf(e.Rbrace, "too few values in struct literal")
					// ok to continue
				}
			}

		case *Array:
			n := check.indexedElts(e.Elts, utyp.elt, utyp.len, iota)
			// if we have an "open" [...]T array, set the length now that we know it
			if openArray {
				utyp.len = n
			}

		case *Slice:
			check.indexedElts(e.Elts, utyp.elt, -1, iota)

		case *Map:
			visited := make(map[interface{}]bool, len(e.Elts))
			for _, e := range e.Elts {
				kv, _ := e.(*ast.KeyValueExpr)
				if kv == nil {
					check.errorf(e.Pos(), "missing key in map literal")
					continue
				}
				check.compositeLitKey(kv.Key)
				check.expr(x, kv.Key, nil, iota)
				if !check.assignment(x, utyp.key) {
					if x.mode != invalid {
						check.errorf(x.pos(), "cannot use %s as %s key in map literal", x, utyp.key)
					}
					continue
				}
				if x.mode == constant {
					if visited[x.val] {
						check.errorf(x.pos(), "duplicate key %s in map literal", x.val)
						continue
					}
					visited[x.val] = true
				}
				check.expr(x, kv.Value, utyp.elt, iota)
				if !check.assignment(x, utyp.elt) {
					if x.mode != invalid {
						check.errorf(x.pos(), "cannot use %s as %s value in map literal", x, utyp.elt)
					}
					continue
				}
			}

		default:
			check.errorf(e.Pos(), "%s is not a valid composite literal type", typ)
			goto Error
		}

		x.mode = value
		x.typ = typ

	case *ast.ParenExpr:
		check.rawExpr(x, e.X, nil, iota, cycleOk)

	case *ast.SelectorExpr:
		sel := e.Sel.Name
		// If the identifier refers to a package, handle everything here
		// so we don't need a "package" mode for operands: package names
		// can only appear in qualified identifiers which are mapped to
		// selector expressions.
		if ident, ok := e.X.(*ast.Ident); ok {
			if pkg, ok := check.lookup(ident).(*Package); ok {
				exp := pkg.scope.Lookup(sel)
				if exp == nil {
					check.errorf(e.Pos(), "%s not declared by package %s", sel, ident)
					goto Error
				} else if !ast.IsExported(exp.Name()) {
					// gcimported package scopes contain non-exported
					// objects such as types used in partially exported
					// objects - do not accept them
					check.errorf(e.Pos(), "%s not exported by package %s", sel, ident)
					goto Error
				}
				check.register(e.Sel, exp)
				// Simplified version of the code for *ast.Idents:
				// - imported packages use types.Scope and types.Objects
				// - imported objects are always fully initialized
				switch exp := exp.(type) {
				case *Const:
					assert(exp.Val != nil)
					x.mode = constant
					x.typ = exp.typ
					x.val = exp.val
				case *TypeName:
					x.mode = typexpr
					x.typ = exp.typ
				case *Var:
					x.mode = variable
					x.typ = exp.typ
				case *Func:
					x.mode = value
					x.typ = exp.typ
				default:
					unreachable()
				}
				x.expr = e
				return
			}
		}

		check.exprOrType(x, e.X, iota, false)
		if x.mode == invalid {
			goto Error
		}
		res := lookupField(x.typ, check.pkg, sel)
		utyp := x.typ.Underlying()
		if res.mode == invalid {
			check.invalidOp(e.Pos(), "%s has no single field or method %s", x, sel)
			goto Error
		}
		if x.mode == typexpr {
			// method expression
			sig, ok := res.typ.(*Signature)
			if !ok {
				check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
				goto Error
			}
			// the receiver type becomes the type of the first function
			// argument of the method expression's function type
			// TODO(gri) at the moment, method sets don't correctly track
			// pointer vs non-pointer receivers => typechecker is too lenient
			var params []*Var
			if sig.params != nil {
				params = sig.params.vars
			}
			x.mode = value
			m := x.typ.Deref().(*Named).methods.Lookup(check.pkg, sel)
			check.register(e.Sel, m)
			x.typ = &Signature{
				params:     NewTuple(append([]*Var{{typ: x.typ}}, params...)...),
				results:    sig.results,
				isVariadic: sig.isVariadic,
			}
		} else {
			// regular selector
			x.mode = res.mode
			if res.index == nil {
				// method
				var method Object
				if t, ok := x.typ.Deref().(*Named); ok {
					method = t.methods.Lookup(check.pkg, sel)
				}
				if method == nil {
					if t, ok := utyp.Deref().(*Interface); ok {
						method = t.methods.Lookup(check.pkg, sel)
					}
				}
				if method != nil {
					check.register(e.Sel, method)
				} else if false {
					// TODO(sqs): fix this - it occurs when we aren't propagating the methods of an embedded interface.
					fmt.Printf("nil method: %s", e.Sel)
				}
			} else {
				// field
				if s, ok := utyp.Deref().(*Struct); ok {
					check.register(e.Sel, s.Field(res.index[0]))
				}
			}
			x.typ = res.typ
		}

	case *ast.IndexExpr:
		check.expr(x, e.X, nil, iota)
		if x.mode == invalid {
			goto Error
		}

		valid := false
		length := int64(-1) // valid if >= 0
		switch typ := x.typ.Underlying().(type) {
		case *Basic:
			if isString(typ) {
				valid = true
				if x.mode == constant {
					length = int64(len(exact.StringVal(x.val)))
				}
				// an indexed string always yields a byte value
				// (not a constant) even if the string and the
				// index are constant
				x.mode = value
				x.typ = Typ[Byte]
			}

		case *Array:
			valid = true
			length = typ.len
			if x.mode != variable {
				x.mode = value
			}
			x.typ = typ.elt

		case *Pointer:
			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
				valid = true
				length = typ.len
				x.mode = variable
				x.typ = typ.elt
			}

		case *Slice:
			valid = true
			x.mode = variable
			x.typ = typ.elt

		case *Map:
			var key operand
			check.expr(&key, e.Index, nil, iota)
			if !check.assignment(&key, typ.key) {
				if key.mode != invalid {
					check.invalidOp(key.pos(), "cannot use %s as map index of type %s", &key, typ.key)
				}
				goto Error
			}
			x.mode = valueok
			x.typ = typ.elt
			x.expr = e
			return
		}

		if !valid {
			check.invalidOp(x.pos(), "cannot index %s", x)
			goto Error
		}

		if e.Index == nil {
			check.invalidAST(e.Pos(), "missing index expression for %s", x)
			return
		}

		check.index(e.Index, length, iota)
		// ok to continue

	case *ast.SliceExpr:
		check.expr(x, e.X, nil, iota)
		if x.mode == invalid {
			goto Error
		}

		valid := false
		length := int64(-1) // valid if >= 0
		switch typ := x.typ.Underlying().(type) {
		case *Basic:
			if isString(typ) {
				valid = true
				if x.mode == constant {
					length = int64(len(exact.StringVal(x.val))) + 1 // +1 for slice
				}
				// a sliced string always yields a string value
				// of the same type as the original string (not
				// a constant) even if the string and the indices
				// are constant
				x.mode = value
				// x.typ doesn't change, but if it is an untyped
				// string it becomes string (see also issue 4913).
				if typ.kind == UntypedString {
					x.typ = Typ[String]
				}
			}

		case *Array:
			valid = true
			length = typ.len + 1 // +1 for slice
			if x.mode != variable {
				check.invalidOp(x.pos(), "cannot slice %s (value not addressable)", x)
				goto Error
			}
			x.typ = &Slice{elt: typ.elt}

		case *Pointer:
			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
				valid = true
				length = typ.len + 1 // +1 for slice
				x.mode = variable
				x.typ = &Slice{elt: typ.elt}
			}

		case *Slice:
			valid = true
			x.mode = variable
			// x.typ doesn't change
		}

		if !valid {
			check.invalidOp(x.pos(), "cannot slice %s", x)
			goto Error
		}

		lo := int64(0)
		if e.Low != nil {
			if i, ok := check.index(e.Low, length, iota); ok && i >= 0 {
				lo = i
			}
		}

		hi := int64(-1)
		if e.High != nil {
			if i, ok := check.index(e.High, length, iota); ok && i >= 0 {
				hi = i
			}
		} else if length >= 0 {
			hi = length
		}

		if lo >= 0 && hi >= 0 && lo > hi {
			check.errorf(e.Low.Pos(), "inverted slice range: %d > %d", lo, hi)
			// ok to continue
		}

	case *ast.TypeAssertExpr:
		check.expr(x, e.X, nil, iota)
		if x.mode == invalid {
			goto Error
		}
		var T *Interface
		if T, _ = x.typ.Underlying().(*Interface); T == nil {
			check.invalidOp(x.pos(), "%s is not an interface", x)
			goto Error
		}
		// x.(type) expressions are handled explicitly in type switches
		if e.Type == nil {
			check.errorf(e.Pos(), "use of .(type) outside type switch")
			goto Error
		}
		typ := check.typ(e.Type, false)
		if typ == Typ[Invalid] {
			goto Error
		}
		if method, wrongType := missingMethod(typ, T); method != nil {
			var msg string
			if wrongType {
				msg = "%s cannot have dynamic type %s (wrong type for method %s)"
			} else {
				msg = "%s cannot have dynamic type %s (missing method %s)"
			}
			check.errorf(e.Type.Pos(), msg, x, typ, method.name)
			// ok to continue
		}
		x.mode = valueok
		x.expr = e
		x.typ = typ

	case *ast.CallExpr:
		check.exprOrType(x, e.Fun, iota, false)
		if x.mode == invalid {
			goto Error
		} else if x.mode == typexpr {
			check.conversion(x, e, x.typ, iota)
		} else if sig, ok := x.typ.Underlying().(*Signature); ok {
			// check parameters

			// If we have a trailing ... at the end of the parameter
			// list, the last argument must match the parameter type
			// []T of a variadic function parameter x ...T.
			passSlice := false
			if e.Ellipsis.IsValid() {
				if sig.isVariadic {
					passSlice = true
				} else {
					check.errorf(e.Ellipsis, "cannot use ... in call to %s", e.Fun)
					// ok to continue
				}
			}

			// If we have a single argument that is a function call
			// we need to handle it separately. Determine if this
			// is the case without checking the argument.
			var call *ast.CallExpr
			if len(e.Args) == 1 {
				call, _ = unparen(e.Args[0]).(*ast.CallExpr)
			}

			n := 0 // parameter count
			if call != nil {
				// We have a single argument that is a function call.
				check.expr(x, call, nil, -1)
				if x.mode == invalid {
					goto Error // TODO(gri): we can do better
				}
				if t, ok := x.typ.(*Tuple); ok {
					// multiple result values
					n = t.Len()
					for i := 0; i < n; i++ {
						obj := t.At(i)
						x.mode = value
						x.expr = nil // TODO(gri) can we do better here? (for good error messages)
						x.typ = obj.typ
						check.argument(sig, i, nil, x, passSlice && i+1 == n)
					}
				} else {
					// single result value
					n = 1
					check.argument(sig, 0, nil, x, passSlice)
				}

			} else {
				// We don't have a single argument or it is not a function call.
				n = len(e.Args)
				for i, arg := range e.Args {
					check.argument(sig, i, arg, x, passSlice && i+1 == n)
				}
			}

			// determine if we have enough arguments
			if sig.isVariadic {
				// a variadic function accepts an "empty"
				// last argument: count one extra
				n++
			}
			if n < sig.params.Len() {
				check.errorf(e.Fun.Pos(), "too few arguments in call to %s", e.Fun)
				// ok to continue
			}

			// determine result
			switch sig.results.Len() {
			case 0:
				x.mode = novalue
			case 1:
				x.mode = value
				x.typ = sig.results.vars[0].typ
			default:
				x.mode = value
				x.typ = sig.results
			}

		} else if bin, ok := x.typ.(*Builtin); ok {
			check.builtin(x, e, bin, iota)

		} else {
			check.invalidOp(x.pos(), "cannot call non-function %s", x)
			goto Error
		}

	case *ast.StarExpr:
		check.exprOrType(x, e.X, iota, true)
		switch x.mode {
		case invalid:
			goto Error
		case typexpr:
			x.typ = &Pointer{base: x.typ}
		default:
			if typ, ok := x.typ.Underlying().(*Pointer); ok {
				x.mode = variable
				x.typ = typ.base
			} else {
				check.invalidOp(x.pos(), "cannot indirect %s", x)
				goto Error
			}
		}

	case *ast.UnaryExpr:
		check.expr(x, e.X, nil, iota)
		if x.mode == invalid {
			goto Error
		}
		check.unary(x, e.Op)
		if x.mode == invalid {
			goto Error
		}

	case *ast.BinaryExpr:
		check.binary(x, e.X, e.Y, e.Op, iota)
		if x.mode == invalid {
			goto Error
		}

	case *ast.KeyValueExpr:
		// key:value expressions are handled in composite literals
		check.invalidAST(e.Pos(), "no key:value expected")
		goto Error

	case *ast.ArrayType:
		if e.Len != nil {
			check.expr(x, e.Len, nil, iota)
			if x.mode == invalid {
				goto Error
			}
			if x.mode != constant {
				if x.mode != invalid {
					check.errorf(x.pos(), "array length %s must be constant", x)
				}
				goto Error
			}
			if !x.isInteger() {
				check.errorf(x.pos(), "array length %s must be integer", x)
				goto Error
			}
			n, ok := exact.Int64Val(x.val)
			if !ok || n < 0 {
				check.errorf(x.pos(), "invalid array length %s", x)
				goto Error
			}
			x.typ = &Array{len: n, elt: check.typ(e.Elt, cycleOk)}
		} else {
			x.typ = &Slice{elt: check.typ(e.Elt, true)}
		}
		x.mode = typexpr

	case *ast.StructType:
		x.mode = typexpr
		fields, tags := check.collectFields(e.Fields, cycleOk)
		x.typ = &Struct{fields: fields, tags: tags}

	case *ast.FuncType:
		params, isVariadic := check.collectParams(e.Params, true)
		results, _ := check.collectParams(e.Results, false)
		x.mode = typexpr
		x.typ = &Signature{recv: nil, params: NewTuple(params...), results: NewTuple(results...), isVariadic: isVariadic}

	case *ast.InterfaceType:
		x.mode = typexpr
		x.typ = &Interface{methods: check.collectMethods(e.Methods)}

	case *ast.MapType:
		x.mode = typexpr
		x.typ = &Map{key: check.typ(e.Key, true), elt: check.typ(e.Value, true)}

	case *ast.ChanType:
		x.mode = typexpr
		x.typ = &Chan{dir: e.Dir, elt: check.typ(e.Value, true)}

	default:
		if debug {
			check.dump("expr = %v (%T)", e, e)
		}
		unreachable()
	}

	// everything went well
	x.expr = e
	return

Error:
	x.mode = invalid
	x.expr = e
}
Exemplo n.º 2
0
// builtin typechecks a built-in call. The built-in type is bin, and iota is the current
// value of iota or -1 if iota doesn't have a value in the current context. The result
// of the call is returned via x. If the call has type errors, the returned x is marked
// as invalid (x.mode == invalid).
//
func (check *checker) builtin(x *operand, call *ast.CallExpr, bin *Builtin, iota int) {
	args := call.Args
	id := bin.id

	// declare before goto's
	var arg0 ast.Expr // first argument, if present

	// check argument count
	n := len(args)
	msg := ""
	if n < bin.nargs {
		msg = "not enough"
	} else if !bin.isVariadic && n > bin.nargs {
		msg = "too many"
	}
	if msg != "" {
		check.invalidOp(call.Pos(), msg+" arguments for %s (expected %d, found %d)", call, bin.nargs, n)
		goto Error
	}

	// common case: evaluate first argument if present;
	// if it is an expression, x has the expression value
	if n > 0 {
		arg0 = args[0]
		switch id {
		case _Make, _New, _Print, _Println, _Offsetof, _Trace:
			// respective cases below do the work
		default:
			// argument must be an expression
			check.expr(x, arg0, nil, iota)
			if x.mode == invalid {
				goto Error
			}
		}
	}

	switch id {
	case _Append:
		if _, ok := x.typ.Underlying().(*Slice); !ok {
			check.invalidArg(x.pos(), "%s is not a typed slice", x)
			goto Error
		}
		resultTyp := x.typ
		for _, arg := range args[1:] {
			check.expr(x, arg, nil, iota)
			if x.mode == invalid {
				goto Error
			}
			// TODO(gri) check assignability
		}
		x.mode = value
		x.typ = resultTyp

	case _Cap, _Len:
		mode := invalid
		var val exact.Value
		switch typ := implicitArrayDeref(x.typ.Underlying()).(type) {
		case *Basic:
			if isString(typ) && id == _Len {
				if x.mode == constant {
					mode = constant
					val = exact.MakeInt64(int64(len(exact.StringVal(x.val))))
				} else {
					mode = value
				}
			}

		case *Array:
			mode = value
			// spec: "The expressions len(s) and cap(s) are constants
			// if the type of s is an array or pointer to an array and
			// the expression s does not contain channel receives or
			// function calls; in this case s is not evaluated."
			if !check.containsCallsOrReceives(arg0) {
				mode = constant
				val = exact.MakeInt64(typ.len)
			}

		case *Slice, *Chan:
			mode = value

		case *Map:
			if id == _Len {
				mode = value
			}
		}

		if mode == invalid {
			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
			goto Error
		}
		x.mode = mode
		x.typ = Typ[Int]
		x.val = val

	case _Close:
		ch, ok := x.typ.Underlying().(*Chan)
		if !ok {
			check.invalidArg(x.pos(), "%s is not a channel", x)
			goto Error
		}
		if ch.dir&ast.SEND == 0 {
			check.invalidArg(x.pos(), "%s must not be a receive-only channel", x)
			goto Error
		}
		x.mode = novalue

	case _Complex:
		if !check.complexArg(x) {
			goto Error
		}

		var y operand
		check.expr(&y, args[1], nil, iota)
		if y.mode == invalid {
			goto Error
		}
		if !check.complexArg(&y) {
			goto Error
		}

		check.convertUntyped(x, y.typ)
		if x.mode == invalid {
			goto Error
		}
		check.convertUntyped(&y, x.typ)
		if y.mode == invalid {
			goto Error
		}

		if !IsIdentical(x.typ, y.typ) {
			check.invalidArg(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
			goto Error
		}

		typ := x.typ.Underlying().(*Basic)
		if x.mode == constant && y.mode == constant {
			x.val = exact.BinaryOp(x.val, token.ADD, exact.MakeImag(y.val))
		} else {
			x.mode = value
		}

		switch typ.kind {
		case Float32:
			x.typ = Typ[Complex64]
		case Float64:
			x.typ = Typ[Complex128]
		case UntypedInt, UntypedRune, UntypedFloat:
			if x.mode == constant {
				typ = defaultType(typ).(*Basic)
				x.typ = Typ[UntypedComplex]
			} else {
				// untyped but not constant; probably because one
				// operand is a non-constant shift of untyped lhs
				typ = Typ[Float64]
				x.typ = Typ[Complex128]
			}
		default:
			check.invalidArg(x.pos(), "float32 or float64 arguments expected")
			goto Error
		}

		if x.mode != constant {
			// The arguments 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.
			// (If the result is constant, the arguments are never
			// materialized and there is nothing to do.)
			check.updateExprType(args[0], typ, true)
			check.updateExprType(args[1], typ, true)
		}

	case _Copy:
		var y operand
		check.expr(&y, args[1], nil, iota)
		if y.mode == invalid {
			goto Error
		}

		var dst, src Type
		if t, ok := x.typ.Underlying().(*Slice); ok {
			dst = t.elt
		}
		switch t := y.typ.Underlying().(type) {
		case *Basic:
			if isString(y.typ) {
				src = Typ[Byte]
			}
		case *Slice:
			src = t.elt
		}

		if dst == nil || src == nil {
			check.invalidArg(x.pos(), "copy expects slice arguments; found %s and %s", x, &y)
			goto Error
		}

		if !IsIdentical(dst, src) {
			check.invalidArg(x.pos(), "arguments to copy %s and %s have different element types %s and %s", x, &y, dst, src)
			goto Error
		}

		x.mode = value
		x.typ = Typ[Int]

	case _Delete:
		m, ok := x.typ.Underlying().(*Map)
		if !ok {
			check.invalidArg(x.pos(), "%s is not a map", x)
			goto Error
		}
		check.expr(x, args[1], nil, iota)
		if x.mode == invalid {
			goto Error
		}
		if !x.isAssignable(check.ctxt, m.key) {
			check.invalidArg(x.pos(), "%s is not assignable to %s", x, m.key)
			goto Error
		}
		x.mode = novalue

	case _Imag, _Real:
		if !isComplex(x.typ) {
			check.invalidArg(x.pos(), "%s must be a complex number", x)
			goto Error
		}
		if x.mode == constant {
			if id == _Real {
				x.val = exact.Real(x.val)
			} else {
				x.val = exact.Imag(x.val)
			}
		} else {
			x.mode = value
		}
		k := Invalid
		switch x.typ.Underlying().(*Basic).kind {
		case Complex64:
			k = Float32
		case Complex128:
			k = Float64
		case UntypedComplex:
			k = UntypedFloat
		default:
			unreachable()
		}
		x.typ = Typ[k]

	case _Make:
		resultTyp := check.typ(arg0, false)
		if resultTyp == Typ[Invalid] {
			goto Error
		}
		var min int // minimum number of arguments
		switch resultTyp.Underlying().(type) {
		case *Slice:
			min = 2
		case *Map, *Chan:
			min = 1
		default:
			check.invalidArg(arg0.Pos(), "cannot make %s; type must be slice, map, or channel", arg0)
			goto Error
		}
		if n := len(args); n < min || min+1 < n {
			check.errorf(call.Pos(), "%s expects %d or %d arguments; found %d", call, min, min+1, n)
			goto Error
		}
		var sizes []int64 // constant integer arguments, if any
		for _, arg := range args[1:] {
			if s, ok := check.index(arg, -1, iota); ok && s >= 0 {
				sizes = append(sizes, s)
			}
		}
		if len(sizes) == 2 && sizes[0] > sizes[1] {
			check.invalidArg(args[1].Pos(), "length and capacity swapped")
			// safe to continue
		}
		x.mode = variable
		x.typ = resultTyp

	case _New:
		resultTyp := check.typ(arg0, false)
		if resultTyp == Typ[Invalid] {
			goto Error
		}
		x.mode = variable
		x.typ = &Pointer{base: resultTyp}

	case _Panic:
		x.mode = novalue

	case _Print, _Println:
		for _, arg := range args {
			check.expr(x, arg, nil, -1)
			if x.mode == invalid {
				goto Error
			}
		}
		x.mode = novalue

	case _Recover:
		x.mode = value
		x.typ = new(Interface)

	case _Alignof:
		x.mode = constant
		x.val = exact.MakeInt64(check.ctxt.alignof(x.typ))
		x.typ = Typ[Uintptr]

	case _Offsetof:
		arg, ok := unparen(arg0).(*ast.SelectorExpr)
		if !ok {
			check.invalidArg(arg0.Pos(), "%s is not a selector expression", arg0)
			goto Error
		}
		check.expr(x, arg.X, nil, -1)
		if x.mode == invalid {
			goto Error
		}
		sel := arg.Sel.Name
		res := lookupField(x.typ, check.pkg, arg.Sel.Name)
		if res.index == nil {
			check.invalidArg(x.pos(), "%s has no single field %s", x, sel)
			goto Error
		}
		offs := check.ctxt.offsetof(x.typ.Deref(), res.index)
		if offs < 0 {
			check.invalidArg(x.pos(), "field %s is embedded via a pointer in %s", sel, x)
			goto Error
		}
		x.mode = constant
		x.val = exact.MakeInt64(offs)
		x.typ = Typ[Uintptr]

	case _Sizeof:
		x.mode = constant
		x.val = exact.MakeInt64(check.ctxt.sizeof(x.typ))
		x.typ = Typ[Uintptr]

	case _Assert:
		// assert(pred) causes a typechecker error if pred is false.
		// The result of assert is the value of pred if there is no error.
		// Note: assert is only available in self-test mode.
		if x.mode != constant || !isBoolean(x.typ) {
			check.invalidArg(x.pos(), "%s is not a boolean constant", x)
			goto Error
		}
		if x.val.Kind() != exact.Bool {
			check.errorf(x.pos(), "internal error: value of %s should be a boolean constant", x)
			goto Error
		}
		if !exact.BoolVal(x.val) {
			check.errorf(call.Pos(), "%s failed", call)
			// compile-time assertion failure - safe to continue
		}

	case _Trace:
		// trace(x, y, z, ...) dumps the positions, expressions, and
		// values of its arguments. The result of trace is the value
		// of the first argument.
		// Note: trace is only available in self-test mode.
		if len(args) == 0 {
			check.dump("%s: trace() without arguments", call.Pos())
			x.mode = novalue
			x.expr = call
			return
		}
		var t operand
		x1 := x
		for _, arg := range args {
			check.rawExpr(x1, arg, nil, iota, true) // permit trace for types, e.g.: new(trace(T))
			check.dump("%s: %s", x1.pos(), x1)
			x1 = &t // use incoming x only for first argument
		}

	default:
		check.invalidAST(call.Pos(), "unknown builtin id %d", id)
		goto Error
	}

	x.expr = call
	return

Error:
	x.mode = invalid
	x.expr = call
}