go stmt 源码
golang stmt 代码
文件路径：/src/cmd/compile/internal/types2/stmt.go
// Copyright 2012 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 statements.
package types2
import (
"cmd/compile/internal/syntax"
"go/constant"
"sort"
)
func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body *syntax.BlockStmt, iota constant.Value) {
if check.conf.IgnoreFuncBodies {
panic("function body not ignored")
}
if check.conf.Trace {
check.trace(body.Pos(), "-- %s: %s", name, sig)
}
// set function scope extent
sig.scope.pos = body.Pos()
sig.scope.end = syntax.EndPos(body)
// save/restore current environment and set up function environment
// (and use 0 indentation at function start)
defer func(env environment, indent int) {
check.environment = env
check.indent = indent
}(check.environment, check.indent)
check.environment = environment{
decl: decl,
scope: sig.scope,
iota: iota,
sig: sig,
}
check.indent = 0
check.stmtList(0, body.List)
if check.hasLabel && !check.conf.IgnoreBranchErrors {
check.labels(body)
}
if sig.results.Len() > 0 && !check.isTerminating(body, "") {
check.error(body.Rbrace, "missing return")
}
// spec: "Implementation restriction: A compiler may make it illegal to
// declare a variable inside a function body if the variable is never used."
check.usage(sig.scope)
}
func (check *Checker) usage(scope *Scope) {
var unused []*Var
for name, elem := range scope.elems {
elem = resolve(name, elem)
if v, _ := elem.(*Var); v != nil && !v.used {
unused = append(unused, v)
}
}
sort.Slice(unused, func(i, j int) bool {
return unused[i].pos.Cmp(unused[j].pos) < 0
})
for _, v := range unused {
check.softErrorf(v.pos, "%s declared but not used", v.name)
}
for _, scope := range scope.children {
// Don't go inside function literal scopes a second time;
// they are handled explicitly by funcBody.
if !scope.isFunc {
check.usage(scope)
}
}
}
// stmtContext is a bitset describing which
// control-flow statements are permissible,
// and provides additional context information
// for better error messages.
type stmtContext uint
const (
// permissible control-flow statements
breakOk stmtContext = 1 << iota
continueOk
fallthroughOk
// additional context information
finalSwitchCase
inTypeSwitch
)
func (check *Checker) simpleStmt(s syntax.Stmt) {
if s != nil {
check.stmt(0, s)
}
}
func trimTrailingEmptyStmts(list []syntax.Stmt) []syntax.Stmt {
for i := len(list); i > 0; i-- {
if _, ok := list[i-1].(*syntax.EmptyStmt); !ok {
return list[:i]
}
}
return nil
}
func (check *Checker) stmtList(ctxt stmtContext, list []syntax.Stmt) {
ok := ctxt&fallthroughOk != 0
inner := ctxt &^ fallthroughOk
list = trimTrailingEmptyStmts(list) // trailing empty statements are "invisible" to fallthrough analysis
for i, s := range list {
inner := inner
if ok && i+1 == len(list) {
inner |= fallthroughOk
}
check.stmt(inner, s)
}
}
func (check *Checker) multipleSwitchDefaults(list []*syntax.CaseClause) {
var first *syntax.CaseClause
for _, c := range list {
if c.Cases == nil {
if first != nil {
check.errorf(c, "multiple defaults (first at %s)", first.Pos())
// TODO(gri) probably ok to bail out after first error (and simplify this code)
} else {
first = c
}
}
}
}
func (check *Checker) multipleSelectDefaults(list []*syntax.CommClause) {
var first *syntax.CommClause
for _, c := range list {
if c.Comm == nil {
if first != nil {
check.errorf(c, "multiple defaults (first at %s)", first.Pos())
// TODO(gri) probably ok to bail out after first error (and simplify this code)
} else {
first = c
}
}
}
}
func (check *Checker) openScope(node syntax.Node, comment string) {
check.openScopeUntil(node, syntax.EndPos(node), comment)
}
func (check *Checker) openScopeUntil(node syntax.Node, end syntax.Pos, comment string) {
scope := NewScope(check.scope, node.Pos(), end, comment)
check.recordScope(node, scope)
check.scope = scope
}
func (check *Checker) closeScope() {
check.scope = check.scope.Parent()
}
func (check *Checker) suspendedCall(keyword string, call *syntax.CallExpr) {
var x operand
var msg string
switch check.rawExpr(&x, call, nil, false) {
case conversion:
msg = "requires function call, not conversion"
case expression:
msg = "discards result of"
case statement:
return
default:
unreachable()
}
check.errorf(&x, "%s %s %s", keyword, msg, &x)
}
// goVal returns the Go value for val, or nil.
func goVal(val constant.Value) interface{} {
// val should exist, but be conservative and check
if val == nil {
return nil
}
// Match implementation restriction of other compilers.
// gc only checks duplicates for integer, floating-point
// and string values, so only create Go values for these
// types.
switch val.Kind() {
case constant.Int:
if x, ok := constant.Int64Val(val); ok {
return x
}
if x, ok := constant.Uint64Val(val); ok {
return x
}
case constant.Float:
if x, ok := constant.Float64Val(val); ok {
return x
}
case constant.String:
return constant.StringVal(val)
}
return nil
}
// A valueMap maps a case value (of a basic Go type) to a list of positions
// where the same case value appeared, together with the corresponding case
// types.
// Since two case values may have the same "underlying" value but different
// types we need to also check the value's types (e.g., byte(1) vs myByte(1))
// when the switch expression is of interface type.
type (
valueMap map[interface{}][]valueType // underlying Go value -> valueType
valueType struct {
pos syntax.Pos
typ Type
}
)
func (check *Checker) caseValues(x *operand, values []syntax.Expr, seen valueMap) {
L:
for _, e := range values {
var v operand
check.expr(&v, e)
if x.mode == invalid || v.mode == invalid {
continue L
}
check.convertUntyped(&v, x.typ)
if v.mode == invalid {
continue L
}
// Order matters: By comparing v against x, error positions are at the case values.
res := v // keep original v unchanged
check.comparison(&res, x, syntax.Eql, true)
if res.mode == invalid {
continue L
}
if v.mode != constant_ {
continue L // we're done
}
// look for duplicate values
if val := goVal(v.val); val != nil {
// look for duplicate types for a given value
// (quadratic algorithm, but these lists tend to be very short)
for _, vt := range seen[val] {
if Identical(v.typ, vt.typ) {
var err error_
err.errorf(&v, "duplicate case %s in expression switch", &v)
err.errorf(vt.pos, "previous case")
check.report(&err)
continue L
}
}
seen[val] = append(seen[val], valueType{v.Pos(), v.typ})
}
}
}
// isNil reports whether the expression e denotes the predeclared value nil.
func (check *Checker) isNil(e syntax.Expr) bool {
// The only way to express the nil value is by literally writing nil (possibly in parentheses).
if name, _ := unparen(e).(*syntax.Name); name != nil {
_, ok := check.lookup(name.Value).(*Nil)
return ok
}
return false
}
// If the type switch expression is invalid, x is nil.
func (check *Checker) caseTypes(x *operand, types []syntax.Expr, seen map[Type]syntax.Expr) (T Type) {
var dummy operand
L:
for _, e := range types {
// The spec allows the value nil instead of a type.
if check.isNil(e) {
T = nil
check.expr(&dummy, e) // run e through expr so we get the usual Info recordings
} else {
T = check.varType(e)
if T == Typ[Invalid] {
continue L
}
}
// look for duplicate types
// (quadratic algorithm, but type switches tend to be reasonably small)
for t, other := range seen {
if T == nil && t == nil || T != nil && t != nil && Identical(T, t) {
// talk about "case" rather than "type" because of nil case
Ts := "nil"
if T != nil {
Ts = TypeString(T, check.qualifier)
}
var err error_
err.errorf(e, "duplicate case %s in type switch", Ts)
err.errorf(other, "previous case")
check.report(&err)
continue L
}
}
seen[T] = e
if x != nil && T != nil {
check.typeAssertion(e, x, T, true)
}
}
return
}
// TODO(gri) Once we are certain that typeHash is correct in all situations, use this version of caseTypes instead.
// (Currently it may be possible that different types have identical names and import paths due to ImporterFrom.)
//
// func (check *Checker) caseTypes(x *operand, xtyp *Interface, types []syntax.Expr, seen map[string]syntax.Expr) (T Type) {
// var dummy operand
// L:
// for _, e := range types {
// // The spec allows the value nil instead of a type.
// var hash string
// if check.isNil(e) {
// check.expr(&dummy, e) // run e through expr so we get the usual Info recordings
// T = nil
// hash = "<nil>" // avoid collision with a type named nil
// } else {
// T = check.varType(e)
// if T == Typ[Invalid] {
// continue L
// }
// hash = typeHash(T, nil)
// }
// // look for duplicate types
// if other := seen[hash]; other != nil {
// // talk about "case" rather than "type" because of nil case
// Ts := "nil"
// if T != nil {
// Ts = TypeString(T, check.qualifier)
// }
// var err error_
// err.errorf(e, "duplicate case %s in type switch", Ts)
// err.errorf(other, "previous case")
// check.report(&err)
// continue L
// }
// seen[hash] = e
// if T != nil {
// check.typeAssertion(e, x, xtyp, T, true)
// }
// }
// return
// }
// stmt typechecks statement s.
func (check *Checker) stmt(ctxt stmtContext, s syntax.Stmt) {
// statements must end with the same top scope as they started with
if debug {
defer func(scope *Scope) {
// don't check if code is panicking
if p := recover(); p != nil {
panic(p)
}
assert(scope == check.scope)
}(check.scope)
}
// process collected function literals before scope changes
defer check.processDelayed(len(check.delayed))
// reset context for statements of inner blocks
inner := ctxt &^ (fallthroughOk | finalSwitchCase | inTypeSwitch)
switch s := s.(type) {
case *syntax.EmptyStmt:
// ignore
case *syntax.DeclStmt:
check.declStmt(s.DeclList)
case *syntax.LabeledStmt:
check.hasLabel = true
check.stmt(ctxt, s.Stmt)
case *syntax.ExprStmt:
// spec: "With the exception of specific built-in functions,
// function and method calls and receive operations can appear
// in statement context. Such statements may be parenthesized."
var x operand
kind := check.rawExpr(&x, s.X, nil, false)
var msg string
switch x.mode {
default:
if kind == statement {
return
}
msg = "is not used"
case builtin:
msg = "must be called"
case typexpr:
msg = "is not an expression"
}
check.errorf(&x, "%s %s", &x, msg)
case *syntax.SendStmt:
var ch, val operand
check.expr(&ch, s.Chan)
check.expr(&val, s.Value)
if ch.mode == invalid || val.mode == invalid {
return
}
u := coreType(ch.typ)
if u == nil {
check.errorf(s, invalidOp+"cannot send to %s: no core type", &ch)
return
}
uch, _ := u.(*Chan)
if uch == nil {
check.errorf(s, invalidOp+"cannot send to non-channel %s", &ch)
return
}
if uch.dir == RecvOnly {
check.errorf(s, invalidOp+"cannot send to receive-only channel %s", &ch)
return
}
check.assignment(&val, uch.elem, "send")
case *syntax.AssignStmt:
lhs := unpackExpr(s.Lhs)
if s.Rhs == nil {
// x++ or x--
if len(lhs) != 1 {
check.errorf(s, invalidAST+"%s%s requires one operand", s.Op, s.Op)
return
}
var x operand
check.expr(&x, lhs[0])
if x.mode == invalid {
return
}
if !allNumeric(x.typ) {
check.errorf(lhs[0], invalidOp+"%s%s%s (non-numeric type %s)", lhs[0], s.Op, s.Op, x.typ)
return
}
check.assignVar(lhs[0], &x)
return
}
rhs := unpackExpr(s.Rhs)
switch s.Op {
case 0:
check.assignVars(lhs, rhs)
return
case syntax.Def:
check.shortVarDecl(s.Pos(), lhs, rhs)
return
}
// assignment operations
if len(lhs) != 1 || len(rhs) != 1 {
check.errorf(s, "assignment operation %s requires single-valued expressions", s.Op)
return
}
var x operand
check.binary(&x, nil, lhs[0], rhs[0], s.Op)
check.assignVar(lhs[0], &x)
case *syntax.CallStmt:
kind := "go"
if s.Tok == syntax.Defer {
kind = "defer"
}
check.suspendedCall(kind, s.Call)
case *syntax.ReturnStmt:
res := check.sig.results
// Return with implicit results allowed for function with named results.
// (If one is named, all are named.)
results := unpackExpr(s.Results)
if len(results) == 0 && res.Len() > 0 && res.vars[0].name != "" {
// spec: "Implementation restriction: A compiler may disallow an empty expression
// list in a "return" statement if a different entity (constant, type, or variable)
// with the same name as a result parameter is in scope at the place of the return."
for _, obj := range res.vars {
if alt := check.lookup(obj.name); alt != nil && alt != obj {
var err error_
err.errorf(s, "result parameter %s not in scope at return", obj.name)
err.errorf(alt, "inner declaration of %s", obj)
check.report(&err)
// ok to continue
}
}
} else {
var lhs []*Var
if res.Len() > 0 {
lhs = res.vars
}
check.initVars(lhs, results, s)
}
case *syntax.BranchStmt:
if s.Label != nil {
check.hasLabel = true
break // checked in 2nd pass (check.labels)
}
if check.conf.IgnoreBranchErrors {
break
}
switch s.Tok {
case syntax.Break:
if ctxt&breakOk == 0 {
check.error(s, "break not in for, switch, or select statement")
}
case syntax.Continue:
if ctxt&continueOk == 0 {
check.error(s, "continue not in for statement")
}
case syntax.Fallthrough:
if ctxt&fallthroughOk == 0 {
var msg string
switch {
case ctxt&finalSwitchCase != 0:
msg = "cannot fallthrough final case in switch"
case ctxt&inTypeSwitch != 0:
msg = "cannot fallthrough in type switch"
default:
msg = "fallthrough statement out of place"
}
check.error(s, msg)
}
case syntax.Goto:
// goto's must have labels, should have been caught above
fallthrough
default:
check.errorf(s, invalidAST+"branch statement: %s", s.Tok)
}
case *syntax.BlockStmt:
check.openScope(s, "block")
defer check.closeScope()
check.stmtList(inner, s.List)
case *syntax.IfStmt:
check.openScope(s, "if")
defer check.closeScope()
check.simpleStmt(s.Init)
var x operand
check.expr(&x, s.Cond)
if x.mode != invalid && !allBoolean(x.typ) {
check.error(s.Cond, "non-boolean condition in if statement")
}
check.stmt(inner, s.Then)
// The parser produces a correct AST but if it was modified
// elsewhere the else branch may be invalid. Check again.
switch s.Else.(type) {
case nil:
// valid or error already reported
case *syntax.IfStmt, *syntax.BlockStmt:
check.stmt(inner, s.Else)
default:
check.error(s.Else, "invalid else branch in if statement")
}
case *syntax.SwitchStmt:
inner |= breakOk
check.openScope(s, "switch")
defer check.closeScope()
check.simpleStmt(s.Init)
if g, _ := s.Tag.(*syntax.TypeSwitchGuard); g != nil {
check.typeSwitchStmt(inner|inTypeSwitch, s, g)
} else {
check.switchStmt(inner, s)
}
case *syntax.SelectStmt:
inner |= breakOk
check.multipleSelectDefaults(s.Body)
for i, clause := range s.Body {
if clause == nil {
continue // error reported before
}
// clause.Comm must be a SendStmt, RecvStmt, or default case
valid := false
var rhs syntax.Expr // rhs of RecvStmt, or nil
switch s := clause.Comm.(type) {
case nil, *syntax.SendStmt:
valid = true
case *syntax.AssignStmt:
if _, ok := s.Rhs.(*syntax.ListExpr); !ok {
rhs = s.Rhs
}
case *syntax.ExprStmt:
rhs = s.X
}
// if present, rhs must be a receive operation
if rhs != nil {
if x, _ := unparen(rhs).(*syntax.Operation); x != nil && x.Y == nil && x.Op == syntax.Recv {
valid = true
}
}
if !valid {
check.error(clause.Comm, "select case must be send or receive (possibly with assignment)")
continue
}
end := s.Rbrace
if i+1 < len(s.Body) {
end = s.Body[i+1].Pos()
}
check.openScopeUntil(clause, end, "case")
if clause.Comm != nil {
check.stmt(inner, clause.Comm)
}
check.stmtList(inner, clause.Body)
check.closeScope()
}
case *syntax.ForStmt:
inner |= breakOk | continueOk
if rclause, _ := s.Init.(*syntax.RangeClause); rclause != nil {
check.rangeStmt(inner, s, rclause)
break
}
check.openScope(s, "for")
defer check.closeScope()
check.simpleStmt(s.Init)
if s.Cond != nil {
var x operand
check.expr(&x, s.Cond)
if x.mode != invalid && !allBoolean(x.typ) {
check.error(s.Cond, "non-boolean condition in for statement")
}
}
check.simpleStmt(s.Post)
// spec: "The init statement may be a short variable
// declaration, but the post statement must not."
if s, _ := s.Post.(*syntax.AssignStmt); s != nil && s.Op == syntax.Def {
// The parser already reported an error.
check.use(s.Lhs) // avoid follow-up errors
}
check.stmt(inner, s.Body)
default:
check.error(s, "invalid statement")
}
}
func (check *Checker) switchStmt(inner stmtContext, s *syntax.SwitchStmt) {
// init statement already handled
var x operand
if s.Tag != nil {
check.expr(&x, s.Tag)
// By checking assignment of x to an invisible temporary
// (as a compiler would), we get all the relevant checks.
check.assignment(&x, nil, "switch expression")
if x.mode != invalid && !Comparable(x.typ) && !hasNil(x.typ) {
check.errorf(&x, "cannot switch on %s (%s is not comparable)", &x, x.typ)
x.mode = invalid
}
} else {
// spec: "A missing switch expression is
// equivalent to the boolean value true."
x.mode = constant_
x.typ = Typ[Bool]
x.val = constant.MakeBool(true)
// TODO(gri) should have a better position here
pos := s.Rbrace
if len(s.Body) > 0 {
pos = s.Body[0].Pos()
}
x.expr = syntax.NewName(pos, "true")
}
check.multipleSwitchDefaults(s.Body)
seen := make(valueMap) // map of seen case values to positions and types
for i, clause := range s.Body {
if clause == nil {
check.error(clause, invalidAST+"incorrect expression switch case")
continue
}
end := s.Rbrace
inner := inner
if i+1 < len(s.Body) {
end = s.Body[i+1].Pos()
inner |= fallthroughOk
} else {
inner |= finalSwitchCase
}
check.caseValues(&x, unpackExpr(clause.Cases), seen)
check.openScopeUntil(clause, end, "case")
check.stmtList(inner, clause.Body)
check.closeScope()
}
}
func (check *Checker) typeSwitchStmt(inner stmtContext, s *syntax.SwitchStmt, guard *syntax.TypeSwitchGuard) {
// init statement already handled
// A type switch guard must be of the form:
//
// TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" .
// \__lhs__/ \___rhs___/
// check lhs, if any
lhs := guard.Lhs
if lhs != nil {
if lhs.Value == "_" {
// _ := x.(type) is an invalid short variable declaration
check.softErrorf(lhs, "no new variable on left side of :=")
lhs = nil // avoid declared but not used error below
} else {
check.recordDef(lhs, nil) // lhs variable is implicitly declared in each cause clause
}
}
// check rhs
var x operand
check.expr(&x, guard.X)
if x.mode == invalid {
return
}
// TODO(gri) we may want to permit type switches on type parameter values at some point
var sx *operand // switch expression against which cases are compared against; nil if invalid
if isTypeParam(x.typ) {
check.errorf(&x, "cannot use type switch on type parameter value %s", &x)
} else {
if _, ok := under(x.typ).(*Interface); ok {
sx = &x
} else {
check.errorf(&x, "%s is not an interface", &x)
}
}
check.multipleSwitchDefaults(s.Body)
var lhsVars []*Var // list of implicitly declared lhs variables
seen := make(map[Type]syntax.Expr) // map of seen types to positions
for i, clause := range s.Body {
if clause == nil {
check.error(s, invalidAST+"incorrect type switch case")
continue
}
end := s.Rbrace
if i+1 < len(s.Body) {
end = s.Body[i+1].Pos()
}
// Check each type in this type switch case.
cases := unpackExpr(clause.Cases)
T := check.caseTypes(sx, cases, seen)
check.openScopeUntil(clause, end, "case")
// If lhs exists, declare a corresponding variable in the case-local scope.
if lhs != nil {
// spec: "The TypeSwitchGuard may include a short variable declaration.
// When that form is used, the variable is declared at the beginning of
// the implicit block in each clause. In clauses with a case listing
// exactly one type, the variable has that type; otherwise, the variable
// has the type of the expression in the TypeSwitchGuard."
if len(cases) != 1 || T == nil {
T = x.typ
}
obj := NewVar(lhs.Pos(), check.pkg, lhs.Value, T)
// TODO(mdempsky): Just use clause.Colon? Why did I even suggest
// "at the end of the TypeSwitchCase" in #16794 instead?
scopePos := clause.Pos() // for default clause (len(List) == 0)
if n := len(cases); n > 0 {
scopePos = syntax.EndPos(cases[n-1])
}
check.declare(check.scope, nil, obj, scopePos)
check.recordImplicit(clause, obj)
// For the "declared but not used" error, all lhs variables act as
// one; i.e., if any one of them is 'used', all of them are 'used'.
// Collect them for later analysis.
lhsVars = append(lhsVars, obj)
}
check.stmtList(inner, clause.Body)
check.closeScope()
}
// If lhs exists, we must have at least one lhs variable that was used.
// (We can't use check.usage because that only looks at one scope; and
// we don't want to use the same variable for all scopes and change the
// variable type underfoot.)
if lhs != nil {
var used bool
for _, v := range lhsVars {
if v.used {
used = true
}
v.used = true // avoid usage error when checking entire function
}
if !used {
check.softErrorf(lhs, "%s declared but not used", lhs.Value)
}
}
}
func (check *Checker) rangeStmt(inner stmtContext, s *syntax.ForStmt, rclause *syntax.RangeClause) {
// determine lhs, if any
sKey := rclause.Lhs // possibly nil
var sValue, sExtra syntax.Expr
if p, _ := sKey.(*syntax.ListExpr); p != nil {
if len(p.ElemList) < 2 {
check.error(s, invalidAST+"invalid lhs in range clause")
return
}
// len(p.ElemList) >= 2
sKey = p.ElemList[0]
sValue = p.ElemList[1]
if len(p.ElemList) > 2 {
// delay error reporting until we know more
sExtra = p.ElemList[2]
}
}
// check expression to iterate over
var x operand
check.expr(&x, rclause.X)
// determine key/value types
var key, val Type
if x.mode != invalid {
// Ranging over a type parameter is permitted if it has a core type.
var cause string
u := coreType(x.typ)
if t, _ := u.(*Chan); t != nil {
if sValue != nil {
check.softErrorf(sValue, "range over %s permits only one iteration variable", &x)
// ok to continue
}
if t.dir == SendOnly {
cause = "receive from send-only channel"
}
} else {
if sExtra != nil {
check.softErrorf(sExtra, "range clause permits at most two iteration variables")
// ok to continue
}
if u == nil {
cause = check.sprintf("%s has no core type", x.typ)
}
}
key, val = rangeKeyVal(u)
if key == nil || cause != "" {
if cause == "" {
check.softErrorf(&x, "cannot range over %s", &x)
} else {
check.softErrorf(&x, "cannot range over %s (%s)", &x, cause)
}
// ok to continue
}
}
// Open the for-statement block scope now, after the range clause.
// Iteration variables declared with := need to go in this scope (was issue #51437).
check.openScope(s, "range")
defer check.closeScope()
// check assignment to/declaration of iteration variables
// (irregular assignment, cannot easily map to existing assignment checks)
// lhs expressions and initialization value (rhs) types
lhs := [2]syntax.Expr{sKey, sValue}
rhs := [2]Type{key, val} // key, val may be nil
if rclause.Def {
// short variable declaration
var vars []*Var
for i, lhs := range lhs {
if lhs == nil {
continue
}
// determine lhs variable
var obj *Var
if ident, _ := lhs.(*syntax.Name); ident != nil {
// declare new variable
name := ident.Value
obj = NewVar(ident.Pos(), check.pkg, name, nil)
check.recordDef(ident, obj)
// _ variables don't count as new variables
if name != "_" {
vars = append(vars, obj)
}
} else {
check.errorf(lhs, "cannot declare %s", lhs)
obj = NewVar(lhs.Pos(), check.pkg, "_", nil) // dummy variable
}
// initialize lhs variable
if typ := rhs[i]; typ != nil {
x.mode = value
x.expr = lhs // we don't have a better rhs expression to use here
x.typ = typ
check.initVar(obj, &x, "range clause")
} else {
obj.typ = Typ[Invalid]
obj.used = true // don't complain about unused variable
}
}
// declare variables
if len(vars) > 0 {
scopePos := s.Body.Pos()
for _, obj := range vars {
check.declare(check.scope, nil /* recordDef already called */, obj, scopePos)
}
} else {
check.error(s, "no new variables on left side of :=")
}
} else {
// ordinary assignment
for i, lhs := range lhs {
if lhs == nil {
continue
}
if typ := rhs[i]; typ != nil {
x.mode = value
x.expr = lhs // we don't have a better rhs expression to use here
x.typ = typ
check.assignVar(lhs, &x)
}
}
}
check.stmt(inner, s.Body)
}
// rangeKeyVal returns the key and value type produced by a range clause
// over an expression of type typ. If the range clause is not permitted
// the results are nil.
func rangeKeyVal(typ Type) (key, val Type) {
switch typ := arrayPtrDeref(typ).(type) {
case *Basic:
if isString(typ) {
return Typ[Int], universeRune // use 'rune' name
}
case *Array:
return Typ[Int], typ.elem
case *Slice:
return Typ[Int], typ.elem
case *Map:
return typ.key, typ.elem
case *Chan:
return typ.elem, Typ[Invalid]
}
return
}
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