go_agent/src/code.google.com/p/go.tools/go/types/call.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 typechecking of call and selector expressions.
package types
import (
"go/ast"
"go/token"
)
func (check *checker) call(x *operand, e *ast.CallExpr) exprKind {
check.exprOrType(x, e.Fun)
switch x.mode {
case invalid:
check.use(e.Args)
x.mode = invalid
x.expr = e
return statement
case typexpr:
// conversion
T := x.typ
x.mode = invalid
switch n := len(e.Args); n {
case 0:
check.errorf(e.Rparen, "missing argument in conversion to %s", T)
case 1:
check.expr(x, e.Args[0])
if x.mode != invalid {
check.conversion(x, T)
if x.mode != invalid {
check.conversions[e] = true // for cap/len checking
}
}
default:
check.errorf(e.Args[n-1].Pos(), "too many arguments in conversion to %s", T)
}
x.expr = e
return conversion
case builtin:
id := x.id
if !check.builtin(x, e, id) {
x.mode = invalid
}
x.expr = e
return predeclaredFuncs[id].kind
default:
// function/method call
sig, _ := x.typ.Underlying().(*Signature)
if sig == nil {
check.invalidOp(x.pos(), "cannot call non-function %s", x)
x.mode = invalid
x.expr = e
return statement
}
arg, n, _ := unpack(func(x *operand, i int) { check.expr(x, e.Args[i]) }, len(e.Args), false)
check.arguments(x, e, sig, arg, n)
// determine result
switch sig.results.Len() {
case 0:
x.mode = novalue
case 1:
x.mode = value
x.typ = sig.results.vars[0].typ // unpack tuple
default:
x.mode = value
x.typ = sig.results
}
x.expr = e
return statement
}
}
// use type-checks each list element.
// Useful to make sure a list of expressions is evaluated
// (and variables are "used") in the presence of other errors.
func (check *checker) use(list []ast.Expr) {
var x operand
for _, e := range list {
check.rawExpr(&x, e, nil)
}
}
// A getter sets x as the i'th operand, where 0 <= i < n and n is the total
// number of operands (context-specific, and maintained elsewhere). A getter
// type-checks the i'th operand; the details of the actual check are getter-
// specific.
type getter func(x *operand, i int)
// unpack takes a getter get and a number of operands n. If n == 1 and the
// first operand is a function call, or a comma,ok expression and allowCommaOk
// is set, the result is a new getter and operand count providing access to the
// function results, or comma,ok values, respectively. The third result value
// reports if it is indeed the comma,ok case. In all other cases, the incoming
// getter and operand count are returned unchanged, and the third result value
// is false.
//
// In other words, if there's exactly one operand that - after type-checking by
// calling get - stands for multiple operands, the resulting getter provides access
// to those operands instead.
//
// Note that unpack may call get(..., 0); but if the result getter is called
// at most once for a given operand index i (including i == 0), that operand
// is guaranteed to cause only one call of the incoming getter with that i.
//
func unpack(get getter, n int, allowCommaOk bool) (getter, int, bool) {
if n == 1 {
// possibly result of an n-valued function call or comma,ok value
var x0 operand
get(&x0, 0)
if x0.mode == invalid {
return func(x *operand, i int) {
if i != 0 {
unreachable()
}
x.mode = invalid
}, 1, false
}
if t, ok := x0.typ.(*Tuple); ok {
// result of an n-valued function call
return func(x *operand, i int) {
x.mode = value
x.expr = x0.expr
x.typ = t.At(i).typ
}, t.Len(), false
}
if x0.mode == mapindex || x0.mode == commaok {
// comma-ok value
if allowCommaOk {
a := [2]Type{x0.typ, Typ[UntypedBool]}
return func(x *operand, i int) {
x.mode = value
x.expr = x0.expr
x.typ = a[i]
}, 2, true
}
x0.mode = value
}
// single value
return func(x *operand, i int) {
if i != 0 {
unreachable()
}
*x = x0
}, 1, false
}
// zero or multiple values
return get, n, false
}
// arguments checks argument passing for the call with the given signature.
// The arg function provides the operand for the i'th argument.
func (check *checker) arguments(x *operand, call *ast.CallExpr, sig *Signature, arg getter, n int) {
passSlice := false
if call.Ellipsis.IsValid() {
// last argument is of the form x...
if sig.isVariadic {
passSlice = true
} else {
check.errorf(call.Ellipsis, "cannot use ... in call to non-variadic %s", call.Fun)
// ok to continue
}
}
// evaluate arguments
for i := 0; i < n; i++ {
arg(x, i)
if x.mode != invalid {
check.argument(sig, i, x, passSlice && i == n-1)
}
}
// check argument count
if sig.isVariadic {
// a variadic function accepts an "empty"
// last argument: count one extra
n++
}
if n < sig.params.Len() {
check.errorf(call.Rparen, "too few arguments in call to %s", call.Fun)
// ok to continue
}
}
// argument checks passing of argument x to the i'th parameter of the given signature.
// If passSlice is set, the argument is followed by ... in the call.
func (check *checker) argument(sig *Signature, i int, x *operand, passSlice bool) {
n := sig.params.Len()
// determine parameter type
var typ Type
switch {
case i < n:
typ = sig.params.vars[i].typ
case sig.isVariadic:
typ = sig.params.vars[n-1].typ
if debug {
if _, ok := typ.(*Slice); !ok {
check.dump("%s: expected unnamed slice type, got %s", sig.params.vars[n-1].Pos(), typ)
}
}
default:
check.errorf(x.pos(), "too many arguments")
return
}
if passSlice {
// argument is of the form x...
if i != n-1 {
check.errorf(x.pos(), "can only use ... with matching parameter")
return
}
if _, ok := x.typ.Underlying().(*Slice); !ok {
check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
return
}
} else if sig.isVariadic && i >= n-1 {
// use the variadic parameter slice's element type
typ = typ.(*Slice).elem
}
if !check.assignment(x, typ) && x.mode != invalid {
check.errorf(x.pos(), "cannot pass argument %s to parameter of type %s", x, typ)
}
}
func (check *checker) selector(x *operand, e *ast.SelectorExpr) {
// these must be declared before the "goto Error" statements
var (
obj Object
index []int
indirect bool
)
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, _ := check.topScope.LookupParent(ident.Name).(*PkgName); pkg != nil {
check.recordObject(ident, pkg)
pkg.used = true
exp := pkg.pkg.scope.Lookup(sel)
if exp == nil {
if !pkg.pkg.fake {
check.errorf(e.Pos(), "%s not declared by package %s", sel, ident)
}
goto Error
}
if !exp.IsExported() {
check.errorf(e.Pos(), "%s not exported by package %s", sel, ident)
// ok to continue
}
check.recordSelection(e, PackageObj, nil, exp, nil, false)
// 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
case *Builtin:
x.mode = builtin
x.typ = exp.typ
x.id = exp.id
default:
unreachable()
}
x.expr = e
return
}
}
check.exprOrType(x, e.X)
if x.mode == invalid {
goto Error
}
obj, index, indirect = LookupFieldOrMethod(x.typ, check.pkg, sel)
if obj == nil {
if index != nil {
// TODO(gri) should provide actual type where the conflict happens
check.invalidOp(e.Pos(), "ambiguous selector %s", sel)
} else {
check.invalidOp(e.Pos(), "%s has no field or method %s", x, sel)
}
goto Error
}
if x.mode == typexpr {
// method expression
m, _ := obj.(*Func)
if m == nil {
check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
goto Error
}
// verify that m is in the method set of x.typ
if !indirect && ptrRecv(m) {
check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x.typ)
goto Error
}
check.recordSelection(e, MethodExpr, x.typ, m, index, indirect)
// the receiver type becomes the type of the first function
// argument of the method expression's function type
var params []*Var
sig := m.typ.(*Signature)
if sig.params != nil {
params = sig.params.vars
}
x.mode = value
x.typ = &Signature{
params: NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "", x.typ)}, params...)...),
results: sig.results,
isVariadic: sig.isVariadic,
}
check.addDeclDep(m)
} else {
// regular selector
switch obj := obj.(type) {
case *Var:
check.recordSelection(e, FieldVal, x.typ, obj, index, indirect)
if x.mode == variable || indirect {
x.mode = variable
} else {
x.mode = value
}
x.typ = obj.typ
case *Func:
// TODO(gri) This code appears elsewhere, too. Factor!
// verify that obj is in the method set of x.typ (or &(x.typ) if x is addressable)
//
// spec: "A method call x.m() is valid if the method set of (the type of) x
// contains m and the argument list can be assigned to the parameter
// list of m. If x is addressable and &x's method set contains m, x.m()
// is shorthand for (&x).m()".
if !indirect && x.mode != variable && ptrRecv(obj) {
check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x)
goto Error
}
check.recordSelection(e, MethodVal, x.typ, obj, index, indirect)
if debug {
// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
typ := x.typ
if x.mode == variable {
// If typ is not an (unnamed) pointer or an interface,
// use *typ instead, because the method set of *typ
// includes the methods of typ.
// Variables are addressable, so we can always take their
// address.
if _, ok := typ.(*Pointer); !ok && !isInterface(typ) {
typ = &Pointer{base: typ}
}
}
// If we created a synthetic pointer type above, we will throw
// away the method set computed here after use.
// TODO(gri) Method set computation should probably always compute
// both, the value and the pointer receiver method set and represent
// them in a single structure.
// TODO(gri) Consider also using a method set cache for the lifetime
// of checker once we rely on MethodSet lookup instead of individual
// lookup.
mset := typ.MethodSet()
if m := mset.Lookup(check.pkg, sel); m == nil || m.obj != obj {
check.dump("%s: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
check.dump("%s\n", mset)
panic("method sets and lookup don't agree")
}
}
x.mode = value
// remove receiver
sig := *obj.typ.(*Signature)
sig.recv = nil
x.typ = &sig
default:
unreachable()
}
}
// everything went well
x.expr = e
return
Error:
x.mode = invalid
x.expr = e
}