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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 typechecking of call and selector expressions.
package types
import (
"go/ast"
"go/internal/typeparams"
"go/token"
"strings"
"unicode"
)
// funcInst type-checks a function instantiation inst and returns the result in x.
// The operand x must be the evaluation of inst.X and its type must be a signature.
func (check *Checker) funcInst(x *operand, inst *ast.IndexExpr) {
xlist := typeparams.UnpackExpr(inst.Index)
targs := check.typeList(xlist)
if targs == nil {
x.mode = invalid
x.expr = inst
return
}
assert(len(targs) == len(xlist))
// check number of type arguments (got) vs number of type parameters (want)
sig := x.typ.(*Signature)
got, want := len(targs), len(sig.tparams)
if got > want {
check.errorf(xlist[got-1], _Todo, "got %d type arguments but want %d", got, want)
x.mode = invalid
x.expr = inst
return
}
// if we don't have enough type arguments, try type inference
inferred := false
if got < want {
targs = check.infer(inst, sig.tparams, targs, nil, nil, true)
if targs == nil {
// error was already reported
x.mode = invalid
x.expr = inst
return
}
got = len(targs)
inferred = true
}
assert(got == want)
// determine argument positions (for error reporting)
// TODO(rFindley) use a positioner here? instantiate would need to be
// updated accordingly.
poslist := make([]token.Pos, len(xlist))
for i, x := range xlist {
poslist[i] = x.Pos()
}
// instantiate function signature
res := check.instantiate(x.Pos(), sig, targs, poslist).(*Signature)
assert(res.tparams == nil) // signature is not generic anymore
if inferred {
check.recordInferred(inst, targs, res)
}
x.typ = res
x.mode = value
x.expr = inst
}
func (check *Checker) callExpr(x *operand, call *ast.CallExpr) exprKind {
var inst *ast.IndexExpr
if iexpr, _ := call.Fun.(*ast.IndexExpr); iexpr != nil {
if check.indexExpr(x, iexpr) {
// Delay function instantiation to argument checking,
// where we combine type and value arguments for type
// inference.
assert(x.mode == value)
inst = iexpr
}
x.expr = iexpr
check.record(x)
} else {
check.exprOrType(x, call.Fun)
}
switch x.mode {
case invalid:
check.use(call.Args...)
x.expr = call
return statement
case typexpr:
// conversion
T := x.typ
x.mode = invalid
switch n := len(call.Args); n {
case 0:
check.errorf(inNode(call, call.Rparen), _WrongArgCount, "missing argument in conversion to %s", T)
case 1:
check.expr(x, call.Args[0])
if x.mode != invalid {
if call.Ellipsis.IsValid() {
check.errorf(call.Args[0], _BadDotDotDotSyntax, "invalid use of ... in conversion to %s", T)
break
}
if t := asInterface(T); t != nil {
check.completeInterface(token.NoPos, t)
if t._IsConstraint() {
check.errorf(call, _Todo, "cannot use interface %s in conversion (contains type list or is comparable)", T)
break
}
}
check.conversion(x, T)
}
default:
check.use(call.Args...)
check.errorf(call.Args[n-1], _WrongArgCount, "too many arguments in conversion to %s", T)
}
x.expr = call
return conversion
case builtin:
id := x.id
if !check.builtin(x, call, id) {
x.mode = invalid
}
x.expr = call
// a non-constant result implies a function call
if x.mode != invalid && x.mode != constant_ {
check.hasCallOrRecv = true
}
return predeclaredFuncs[id].kind
}
// ordinary function/method call
cgocall := x.mode == cgofunc
sig := asSignature(x.typ)
if sig == nil {
check.invalidOp(x, _InvalidCall, "cannot call non-function %s", x)
x.mode = invalid
x.expr = call
return statement
}
// evaluate type arguments, if any
var targs []Type
if inst != nil {
xlist := typeparams.UnpackExpr(inst.Index)
targs = check.typeList(xlist)
if targs == nil {
check.use(call.Args...)
x.mode = invalid
x.expr = call
return statement
}
assert(len(targs) == len(xlist))
// check number of type arguments (got) vs number of type parameters (want)
got, want := len(targs), len(sig.tparams)
if got > want {
check.errorf(xlist[want], _Todo, "got %d type arguments but want %d", got, want)
check.use(call.Args...)
x.mode = invalid
x.expr = call
return statement
}
}
// evaluate arguments
args, _ := check.exprList(call.Args, false)
sig = check.arguments(call, sig, targs, args)
// determine result
switch sig.results.Len() {
case 0:
x.mode = novalue
case 1:
if cgocall {
x.mode = commaerr
} else {
x.mode = value
}
x.typ = sig.results.vars[0].typ // unpack tuple
default:
x.mode = value
x.typ = sig.results
}
x.expr = call
check.hasCallOrRecv = true
// if type inference failed, a parametrized result must be invalidated
// (operands cannot have a parametrized type)
if x.mode == value && len(sig.tparams) > 0 && isParameterized(sig.tparams, x.typ) {
x.mode = invalid
}
return statement
}
func (check *Checker) exprList(elist []ast.Expr, allowCommaOk bool) (xlist []*operand, commaOk bool) {
switch len(elist) {
case 0:
// nothing to do
case 1:
// single (possibly comma-ok) value, or function returning multiple values
e := elist[0]
var x operand
check.multiExpr(&x, e)
if t, ok := x.typ.(*Tuple); ok && x.mode != invalid {
// multiple values
xlist = make([]*operand, t.Len())
for i, v := range t.vars {
xlist[i] = &operand{mode: value, expr: e, typ: v.typ}
}
break
}
// exactly one (possibly invalid or comma-ok) value
xlist = []*operand{&x}
if allowCommaOk && (x.mode == mapindex || x.mode == commaok || x.mode == commaerr) {
x2 := &operand{mode: value, expr: e, typ: Typ[UntypedBool]}
if x.mode == commaerr {
x2.typ = universeError
}
xlist = append(xlist, x2)
commaOk = true
}
default:
// multiple (possibly invalid) values
xlist = make([]*operand, len(elist))
for i, e := range elist {
var x operand
check.expr(&x, e)
xlist[i] = &x
}
}
return
}
func (check *Checker) arguments(call *ast.CallExpr, sig *Signature, targs []Type, args []*operand) (rsig *Signature) {
rsig = sig
// TODO(gri) try to eliminate this extra verification loop
for _, a := range args {
switch a.mode {
case typexpr:
check.errorf(a, 0, "%s used as value", a)
return
case invalid:
return
}
}
// Function call argument/parameter count requirements
//
// | standard call | dotdotdot call |
// --------------+------------------+----------------+
// standard func | nargs == npars | invalid |
// --------------+------------------+----------------+
// variadic func | nargs >= npars-1 | nargs == npars |
// --------------+------------------+----------------+
nargs := len(args)
npars := sig.params.Len()
ddd := call.Ellipsis.IsValid()
// set up parameters
sigParams := sig.params // adjusted for variadic functions (may be nil for empty parameter lists!)
adjusted := false // indicates if sigParams is different from t.params
if sig.variadic {
if ddd {
// variadic_func(a, b, c...)
if len(call.Args) == 1 && nargs > 1 {
// f()... is not permitted if f() is multi-valued
check.errorf(inNode(call, call.Ellipsis), _InvalidDotDotDot, "cannot use ... with %d-valued %s", nargs, call.Args[0])
return
}
} else {
// variadic_func(a, b, c)
if nargs >= npars-1 {
// Create custom parameters for arguments: keep
// the first npars-1 parameters and add one for
// each argument mapping to the ... parameter.
vars := make([]*Var, npars-1) // npars > 0 for variadic functions
copy(vars, sig.params.vars)
last := sig.params.vars[npars-1]
typ := last.typ.(*Slice).elem
for len(vars) < nargs {
vars = append(vars, NewParam(last.pos, last.pkg, last.name, typ))
}
sigParams = NewTuple(vars...) // possibly nil!
adjusted = true
npars = nargs
} else {
// nargs < npars-1
npars-- // for correct error message below
}
}
} else {
if ddd {
// standard_func(a, b, c...)
check.errorf(inNode(call, call.Ellipsis), _NonVariadicDotDotDot, "cannot use ... in call to non-variadic %s", call.Fun)
return
}
// standard_func(a, b, c)
}
// check argument count
switch {
case nargs < npars:
check.errorf(inNode(call, call.Rparen), _WrongArgCount, "not enough arguments in call to %s", call.Fun)
return
case nargs > npars:
check.errorf(args[npars], _WrongArgCount, "too many arguments in call to %s", call.Fun) // report at first extra argument
return
}
// infer type arguments and instantiate signature if necessary
if len(sig.tparams) > 0 {
// TODO(gri) provide position information for targs so we can feed
// it to the instantiate call for better error reporting
targs := check.infer(call, sig.tparams, targs, sigParams, args, true)
if targs == nil {
return // error already reported
}
// compute result signature
rsig = check.instantiate(call.Pos(), sig, targs, nil).(*Signature)
assert(rsig.tparams == nil) // signature is not generic anymore
check.recordInferred(call, targs, rsig)
// Optimization: Only if the parameter list was adjusted do we
// need to compute it from the adjusted list; otherwise we can
// simply use the result signature's parameter list.
if adjusted {
sigParams = check.subst(call.Pos(), sigParams, makeSubstMap(sig.tparams, targs)).(*Tuple)
} else {
sigParams = rsig.params
}
}
// check arguments
for i, a := range args {
check.assignment(a, sigParams.vars[i].typ, check.sprintf("argument to %s", call.Fun))
}
return
}
var cgoPrefixes = [...]string{
"_Ciconst_",
"_Cfconst_",
"_Csconst_",
"_Ctype_",
"_Cvar_", // actually a pointer to the var
"_Cfpvar_fp_",
"_Cfunc_",
"_Cmacro_", // function to evaluate the expanded expression
}
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 {
obj := check.lookup(ident.Name)
if pname, _ := obj.(*PkgName); pname != nil {
assert(pname.pkg == check.pkg)
check.recordUse(ident, pname)
pname.used = true
pkg := pname.imported
var exp Object
funcMode := value
if pkg.cgo {
// cgo special cases C.malloc: it's
// rewritten to _CMalloc and does not
// support two-result calls.
if sel == "malloc" {
sel = "_CMalloc"
} else {
funcMode = cgofunc
}
for _, prefix := range cgoPrefixes {
// cgo objects are part of the current package (in file
// _cgo_gotypes.go). Use regular lookup.
_, exp = check.scope.LookupParent(prefix+sel, check.pos)
if exp != nil {
break
}
}
if exp == nil {
check.errorf(e.Sel, _UndeclaredImportedName, "%s not declared by package C", sel)
goto Error
}
check.objDecl(exp, nil)
} else {
exp = pkg.scope.Lookup(sel)
if exp == nil {
if !pkg.fake {
check.errorf(e.Sel, _UndeclaredImportedName, "%s not declared by package %s", sel, pkg.name)
}
goto Error
}
if !exp.Exported() {
check.errorf(e.Sel, _UnexportedName, "%s not exported by package %s", sel, pkg.name)
// ok to continue
}
}
check.recordUse(e.Sel, exp)
// Simplified version of the code for *ast.Idents:
// - 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
if pkg.cgo && strings.HasPrefix(exp.name, "_Cvar_") {
x.typ = x.typ.(*Pointer).base
}
case *Func:
x.mode = funcMode
x.typ = exp.typ
if pkg.cgo && strings.HasPrefix(exp.name, "_Cmacro_") {
x.mode = value
x.typ = x.typ.(*Signature).results.vars[0].typ
}
case *Builtin:
x.mode = builtin
x.typ = exp.typ
x.id = exp.id
default:
check.dump("%v: unexpected object %v", e.Sel.Pos(), exp)
unreachable()
}
x.expr = e
return
}
}
check.exprOrType(x, e.X)
if x.mode == invalid {
goto Error
}
check.instantiatedOperand(x)
obj, index, indirect = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
if obj == nil {
switch {
case index != nil:
// TODO(gri) should provide actual type where the conflict happens
check.errorf(e.Sel, _AmbiguousSelector, "ambiguous selector %s.%s", x.expr, sel)
case indirect:
check.errorf(e.Sel, _InvalidMethodExpr, "cannot call pointer method %s on %s", sel, x.typ)
default:
var why string
if tpar := asTypeParam(x.typ); tpar != nil {
// Type parameter bounds don't specify fields, so don't mention "field".
switch obj := tpar.Bound().obj.(type) {
case nil:
why = check.sprintf("type bound for %s has no method %s", x.typ, sel)
case *TypeName:
why = check.sprintf("interface %s has no method %s", obj.name, sel)
}
} else {
why = check.sprintf("type %s has no field or method %s", x.typ, sel)
}
// Check if capitalization of sel matters and provide better error message in that case.
if len(sel) > 0 {
var changeCase string
if r := rune(sel[0]); unicode.IsUpper(r) {
changeCase = string(unicode.ToLower(r)) + sel[1:]
} else {
changeCase = string(unicode.ToUpper(r)) + sel[1:]
}
if obj, _, _ = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
why += ", but does have " + changeCase
}
}
check.errorf(e.Sel, _MissingFieldOrMethod, "%s.%s undefined (%s)", x.expr, sel, why)
}
goto Error
}
// methods may not have a fully set up signature yet
if m, _ := obj.(*Func); m != nil {
check.objDecl(m, nil)
// If m has a parameterized receiver type, infer the type arguments from
// the actual receiver provided and then substitute the type parameters in
// the signature accordingly.
// TODO(gri) factor this code out
sig := m.typ.(*Signature)
if len(sig.rparams) > 0 {
// For inference to work, we must use the receiver type
// matching the receiver in the actual method declaration.
// If the method is embedded, the matching receiver is the
// embedded struct or interface that declared the method.
// Traverse the embedding to find that type (issue #44688).
recv := x.typ
for i := 0; i < len(index)-1; i++ {
// The embedded type is either a struct or a pointer to
// a struct except for the last one (which we don't need).
recv = asStruct(derefStructPtr(recv)).Field(index[i]).typ
}
// The method may have a pointer receiver, but the actually provided receiver
// may be a (hopefully addressable) non-pointer value, or vice versa. Here we
// only care about inferring receiver type parameters; to make the inference
// work, match up pointer-ness of receiver and argument.
if ptrRecv := isPointer(sig.recv.typ); ptrRecv != isPointer(recv) {
if ptrRecv {
recv = NewPointer(recv)
} else {
recv = recv.(*Pointer).base
}
}
// Disable reporting of errors during inference below. If we're unable to infer
// the receiver type arguments here, the receiver must be be otherwise invalid
// and an error has been reported elsewhere.
arg := operand{mode: variable, expr: x.expr, typ: recv}
targs := check.infer(m, sig.rparams, nil, NewTuple(sig.recv), []*operand{&arg}, false /* no error reporting */)
if targs == nil {
// We may reach here if there were other errors (see issue #40056).
goto Error
}
// Don't modify m. Instead - for now - make a copy of m and use that instead.
// (If we modify m, some tests will fail; possibly because the m is in use.)
// TODO(gri) investigate and provide a correct explanation here
copy := *m
copy.typ = check.subst(e.Pos(), m.typ, makeSubstMap(sig.rparams, targs))
obj = &copy
}
// TODO(gri) we also need to do substitution for parameterized interface methods
// (this breaks code in testdata/linalg.go2 at the moment)
// 12/20/2019: Is this TODO still correct?
}
if x.mode == typexpr {
// method expression
m, _ := obj.(*Func)
if m == nil {
// TODO(gri) should check if capitalization of sel matters and provide better error message in that case
check.errorf(e.Sel, _MissingFieldOrMethod, "%s.%s undefined (type %s has no method %s)", x.expr, sel, x.typ, sel)
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{
tparams: sig.tparams,
params: NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "_", x.typ)}, params...)...),
results: sig.results,
variadic: sig.variadic,
}
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) If we needed to take into account the receiver's
// addressability, should we report the type &(x.typ) instead?
check.recordSelection(e, MethodVal, x.typ, obj, index, indirect)
// TODO(gri) The verification pass below is disabled for now because
// method sets don't match method lookup in some cases.
// For instance, if we made a copy above when creating a
// custom method for a parameterized received type, the
// method set method doesn't match (no copy there). There
/// may be other situations.
disabled := true
if !disabled && debug {
// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
// TODO(gri) This only works because we call LookupFieldOrMethod
// _before_ calling NewMethodSet: LookupFieldOrMethod completes
// any incomplete interfaces so they are available to NewMethodSet
// (which assumes that interfaces have been completed already).
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 := NewMethodSet(typ)
if m := mset.Lookup(check.pkg, sel); m == nil || m.obj != obj {
check.dump("%v: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
check.dump("%s\n", mset)
// Caution: MethodSets are supposed to be used externally
// only (after all interface types were completed). It's
// now possible that we get here incorrectly. Not urgent
// to fix since we only run this code in debug mode.
// TODO(gri) fix this eventually.
panic("method sets and lookup don't agree")
}
}
x.mode = value
// remove receiver
sig := *obj.typ.(*Signature)
sig.recv = nil
x.typ = &sig
check.addDeclDep(obj)
default:
unreachable()
}
}
// everything went well
x.expr = e
return
Error:
x.mode = invalid
x.expr = e
}
// use type-checks each argument.
// Useful to make sure expressions are evaluated
// (and variables are "used") in the presence of other errors.
// The arguments may be nil.
func (check *Checker) use(arg ...ast.Expr) {
var x operand
for _, e := range arg {
// The nil check below is necessary since certain AST fields
// may legally be nil (e.g., the ast.SliceExpr.High field).
if e != nil {
check.rawExpr(&x, e, nil)
}
}
}
// useLHS is like use, but doesn't "use" top-level identifiers.
// It should be called instead of use if the arguments are
// expressions on the lhs of an assignment.
// The arguments must not be nil.
func (check *Checker) useLHS(arg ...ast.Expr) {
var x operand
for _, e := range arg {
// If the lhs is an identifier denoting a variable v, this assignment
// is not a 'use' of v. Remember current value of v.used and restore
// after evaluating the lhs via check.rawExpr.
var v *Var
var v_used bool
if ident, _ := unparen(e).(*ast.Ident); ident != nil {
// never type-check the blank name on the lhs
if ident.Name == "_" {
continue
}
if _, obj := check.scope.LookupParent(ident.Name, token.NoPos); obj != nil {
// It's ok to mark non-local variables, but ignore variables
// from other packages to avoid potential race conditions with
// dot-imported variables.
if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
v = w
v_used = v.used
}
}
}
check.rawExpr(&x, e, nil)
if v != nil {
v.used = v_used // restore v.used
}
}
}
// instantiatedOperand reports an error of x is an uninstantiated (generic) type and sets x.typ to Typ[Invalid].
func (check *Checker) instantiatedOperand(x *operand) {
if x.mode == typexpr && isGeneric(x.typ) {
check.errorf(x, _Todo, "cannot use generic type %s without instantiation", x.typ)
x.typ = Typ[Invalid]
}
}