| // 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 types |
| |
| import ( |
| "fmt" |
| "go/ast" |
| "go/constant" |
| "go/token" |
| ) |
| |
| func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body *ast.BlockStmt) { |
| if trace { |
| if name == "" { |
| name = "<function literal>" |
| } |
| fmt.Printf("--- %s: %s {\n", name, sig) |
| defer fmt.Println("--- <end>") |
| } |
| |
| // set function scope extent |
| sig.scope.pos = body.Pos() |
| sig.scope.end = body.End() |
| |
| // save/restore current context and setup function context |
| // (and use 0 indentation at function start) |
| defer func(ctxt context, indent int) { |
| check.context = ctxt |
| check.indent = indent |
| }(check.context, check.indent) |
| check.context = context{ |
| decl: decl, |
| scope: sig.scope, |
| sig: sig, |
| } |
| check.indent = 0 |
| |
| check.stmtList(0, body.List) |
| |
| if check.hasLabel { |
| 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." |
| // (One could check each scope after use, but that distributes this check |
| // over several places because CloseScope is not always called explicitly.) |
| check.usage(sig.scope) |
| } |
| |
| func (check *Checker) usage(scope *Scope) { |
| for _, obj := range scope.elems { |
| if v, _ := obj.(*Var); v != nil && !v.used { |
| check.softErrorf(v.pos, "%s declared but not used", v.name) |
| } |
| } |
| for _, scope := range scope.children { |
| 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 |
| ) |
| |
| func (check *Checker) simpleStmt(s ast.Stmt) { |
| if s != nil { |
| check.stmt(0, s) |
| } |
| } |
| |
| func trimTrailingEmptyStmts(list []ast.Stmt) []ast.Stmt { |
| for i := len(list); i > 0; i-- { |
| if _, ok := list[i-1].(*ast.EmptyStmt); !ok { |
| return list[:i] |
| } |
| } |
| return nil |
| } |
| |
| func (check *Checker) stmtList(ctxt stmtContext, list []ast.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) multipleDefaults(list []ast.Stmt) { |
| var first ast.Stmt |
| for _, s := range list { |
| var d ast.Stmt |
| switch c := s.(type) { |
| case *ast.CaseClause: |
| if len(c.List) == 0 { |
| d = s |
| } |
| case *ast.CommClause: |
| if c.Comm == nil { |
| d = s |
| } |
| default: |
| check.invalidAST(s.Pos(), "case/communication clause expected") |
| } |
| if d != nil { |
| if first != nil { |
| check.errorf(d.Pos(), "multiple defaults (first at %s)", check.fset.Position(first.Pos())) |
| } else { |
| first = d |
| } |
| } |
| } |
| } |
| |
| func (check *Checker) openScope(s ast.Stmt, comment string) { |
| scope := NewScope(check.scope, s.Pos(), s.End(), comment) |
| check.recordScope(s, scope) |
| check.scope = scope |
| } |
| |
| func (check *Checker) closeScope() { |
| check.scope = check.scope.Parent() |
| } |
| |
| func assignOp(op token.Token) token.Token { |
| // token_test.go verifies the token ordering this function relies on |
| if token.ADD_ASSIGN <= op && op <= token.AND_NOT_ASSIGN { |
| return op + (token.ADD - token.ADD_ASSIGN) |
| } |
| return token.ILLEGAL |
| } |
| |
| func (check *Checker) suspendedCall(keyword string, call *ast.CallExpr) { |
| var x operand |
| var msg string |
| switch check.rawExpr(&x, call, nil) { |
| case conversion: |
| msg = "requires function call, not conversion" |
| case expression: |
| msg = "discards result of" |
| case statement: |
| return |
| default: |
| unreachable() |
| } |
| check.errorf(x.pos(), "%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 token.Pos |
| typ Type |
| } |
| ) |
| |
| func (check *Checker) caseValues(x *operand, values []ast.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, token.EQL) |
| 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 { |
| if list := seen[val]; list != nil { |
| // look for duplicate types for a given value |
| // (quadratic algorithm, but these lists tend to be very short) |
| for _, vt := range list { |
| if Identical(v.typ, vt.typ) { |
| check.errorf(v.pos(), "duplicate case %s in expression switch", &v) |
| check.error(vt.pos, "\tprevious case") // secondary error, \t indented |
| continue L |
| } |
| } |
| } |
| seen[val] = append(seen[val], valueType{v.pos(), v.typ}) |
| } |
| } |
| } |
| |
| func (check *Checker) caseTypes(x *operand, xtyp *Interface, types []ast.Expr, seen map[Type]token.Pos) (T Type) { |
| L: |
| for _, e := range types { |
| T = check.typOrNil(e) |
| if T == Typ[Invalid] { |
| continue L |
| } |
| // look for duplicate types |
| // (quadratic algorithm, but type switches tend to be reasonably small) |
| for t, pos := 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 = T.String() |
| } |
| check.errorf(e.Pos(), "duplicate case %s in type switch", Ts) |
| check.error(pos, "\tprevious case") // secondary error, \t indented |
| continue L |
| } |
| } |
| seen[T] = e.Pos() |
| if T != nil { |
| check.typeAssertion(e.Pos(), x, xtyp, T) |
| } |
| } |
| return |
| } |
| |
| // stmt typechecks statement s. |
| func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) { |
| // statements cannot use iota in general |
| // (constant declarations set it explicitly) |
| assert(check.iota == nil) |
| |
| // 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) |
| } |
| |
| inner := ctxt &^ (fallthroughOk | finalSwitchCase) |
| switch s := s.(type) { |
| case *ast.BadStmt, *ast.EmptyStmt: |
| // ignore |
| |
| case *ast.DeclStmt: |
| check.declStmt(s.Decl) |
| |
| case *ast.LabeledStmt: |
| check.hasLabel = true |
| check.stmt(ctxt, s.Stmt) |
| |
| case *ast.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) |
| 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.pos(), "%s %s", &x, msg) |
| |
| case *ast.SendStmt: |
| var ch, x operand |
| check.expr(&ch, s.Chan) |
| check.expr(&x, s.Value) |
| if ch.mode == invalid || x.mode == invalid { |
| return |
| } |
| |
| tch, ok := ch.typ.Underlying().(*Chan) |
| if !ok { |
| check.invalidOp(s.Arrow, "cannot send to non-chan type %s", ch.typ) |
| return |
| } |
| |
| if tch.dir == RecvOnly { |
| check.invalidOp(s.Arrow, "cannot send to receive-only type %s", tch) |
| return |
| } |
| |
| check.assignment(&x, tch.elem, "send") |
| |
| case *ast.IncDecStmt: |
| var op token.Token |
| switch s.Tok { |
| case token.INC: |
| op = token.ADD |
| case token.DEC: |
| op = token.SUB |
| default: |
| check.invalidAST(s.TokPos, "unknown inc/dec operation %s", s.Tok) |
| return |
| } |
| |
| var x operand |
| check.expr(&x, s.X) |
| if x.mode == invalid { |
| return |
| } |
| if !isNumeric(x.typ) { |
| check.invalidOp(s.X.Pos(), "%s%s (non-numeric type %s)", s.X, s.Tok, x.typ) |
| return |
| } |
| |
| Y := &ast.BasicLit{ValuePos: s.X.Pos(), Kind: token.INT, Value: "1"} // use x's position |
| check.binary(&x, nil, s.X, Y, op) |
| if x.mode == invalid { |
| return |
| } |
| check.assignVar(s.X, &x) |
| |
| case *ast.AssignStmt: |
| switch s.Tok { |
| case token.ASSIGN, token.DEFINE: |
| if len(s.Lhs) == 0 { |
| check.invalidAST(s.Pos(), "missing lhs in assignment") |
| return |
| } |
| if s.Tok == token.DEFINE { |
| check.shortVarDecl(s.TokPos, s.Lhs, s.Rhs) |
| } else { |
| // regular assignment |
| check.assignVars(s.Lhs, s.Rhs) |
| } |
| |
| default: |
| // assignment operations |
| if len(s.Lhs) != 1 || len(s.Rhs) != 1 { |
| check.errorf(s.TokPos, "assignment operation %s requires single-valued expressions", s.Tok) |
| return |
| } |
| op := assignOp(s.Tok) |
| if op == token.ILLEGAL { |
| check.invalidAST(s.TokPos, "unknown assignment operation %s", s.Tok) |
| return |
| } |
| var x operand |
| check.binary(&x, nil, s.Lhs[0], s.Rhs[0], op) |
| if x.mode == invalid { |
| return |
| } |
| check.assignVar(s.Lhs[0], &x) |
| } |
| |
| case *ast.GoStmt: |
| check.suspendedCall("go", s.Call) |
| |
| case *ast.DeferStmt: |
| check.suspendedCall("defer", s.Call) |
| |
| case *ast.ReturnStmt: |
| res := check.sig.results |
| if res.Len() > 0 { |
| // function returns results |
| // (if one, say the first, result parameter is named, all of them are named) |
| if len(s.Results) == 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.scope.LookupParent(obj.name, check.pos); alt != nil && alt != obj { |
| check.errorf(s.Pos(), "result parameter %s not in scope at return", obj.name) |
| check.errorf(alt.Pos(), "\tinner declaration of %s", obj) |
| // ok to continue |
| } |
| } |
| } else { |
| // return has results or result parameters are unnamed |
| check.initVars(res.vars, s.Results, s.Return) |
| } |
| } else if len(s.Results) > 0 { |
| check.error(s.Results[0].Pos(), "no result values expected") |
| check.use(s.Results...) |
| } |
| |
| case *ast.BranchStmt: |
| if s.Label != nil { |
| check.hasLabel = true |
| return // checked in 2nd pass (check.labels) |
| } |
| switch s.Tok { |
| case token.BREAK: |
| if ctxt&breakOk == 0 { |
| check.error(s.Pos(), "break not in for, switch, or select statement") |
| } |
| case token.CONTINUE: |
| if ctxt&continueOk == 0 { |
| check.error(s.Pos(), "continue not in for statement") |
| } |
| case token.FALLTHROUGH: |
| if ctxt&fallthroughOk == 0 { |
| msg := "fallthrough statement out of place" |
| if ctxt&finalSwitchCase != 0 { |
| msg = "cannot fallthrough final case in switch" |
| } |
| check.error(s.Pos(), msg) |
| } |
| default: |
| check.invalidAST(s.Pos(), "branch statement: %s", s.Tok) |
| } |
| |
| case *ast.BlockStmt: |
| check.openScope(s, "block") |
| defer check.closeScope() |
| |
| check.stmtList(inner, s.List) |
| |
| case *ast.IfStmt: |
| check.openScope(s, "if") |
| defer check.closeScope() |
| |
| check.simpleStmt(s.Init) |
| var x operand |
| check.expr(&x, s.Cond) |
| if x.mode != invalid && !isBoolean(x.typ) { |
| check.error(s.Cond.Pos(), "non-boolean condition in if statement") |
| } |
| check.stmt(inner, s.Body) |
| // 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, *ast.BadStmt: |
| // valid or error already reported |
| case *ast.IfStmt, *ast.BlockStmt: |
| check.stmt(inner, s.Else) |
| default: |
| check.error(s.Else.Pos(), "invalid else branch in if statement") |
| } |
| |
| case *ast.SwitchStmt: |
| inner |= breakOk |
| check.openScope(s, "switch") |
| defer check.closeScope() |
| |
| check.simpleStmt(s.Init) |
| 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") |
| } 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) |
| x.expr = &ast.Ident{NamePos: s.Body.Lbrace, Name: "true"} |
| } |
| |
| check.multipleDefaults(s.Body.List) |
| |
| seen := make(valueMap) // map of seen case values to positions and types |
| for i, c := range s.Body.List { |
| clause, _ := c.(*ast.CaseClause) |
| if clause == nil { |
| check.invalidAST(c.Pos(), "incorrect expression switch case") |
| continue |
| } |
| check.caseValues(&x, clause.List, seen) |
| check.openScope(clause, "case") |
| inner := inner |
| if i+1 < len(s.Body.List) { |
| inner |= fallthroughOk |
| } else { |
| inner |= finalSwitchCase |
| } |
| check.stmtList(inner, clause.Body) |
| check.closeScope() |
| } |
| |
| case *ast.TypeSwitchStmt: |
| inner |= breakOk |
| check.openScope(s, "type switch") |
| defer check.closeScope() |
| |
| check.simpleStmt(s.Init) |
| |
| // A type switch guard must be of the form: |
| // |
| // TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" . |
| // |
| // The parser is checking syntactic correctness; |
| // remaining syntactic errors are considered AST errors here. |
| // TODO(gri) better factoring of error handling (invalid ASTs) |
| // |
| var lhs *ast.Ident // lhs identifier or nil |
| var rhs ast.Expr |
| switch guard := s.Assign.(type) { |
| case *ast.ExprStmt: |
| rhs = guard.X |
| case *ast.AssignStmt: |
| if len(guard.Lhs) != 1 || guard.Tok != token.DEFINE || len(guard.Rhs) != 1 { |
| check.invalidAST(s.Pos(), "incorrect form of type switch guard") |
| return |
| } |
| |
| lhs, _ = guard.Lhs[0].(*ast.Ident) |
| if lhs == nil { |
| check.invalidAST(s.Pos(), "incorrect form of type switch guard") |
| return |
| } |
| |
| if lhs.Name == "_" { |
| // _ := x.(type) is an invalid short variable declaration |
| check.softErrorf(lhs.Pos(), "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 |
| } |
| |
| rhs = guard.Rhs[0] |
| |
| default: |
| check.invalidAST(s.Pos(), "incorrect form of type switch guard") |
| return |
| } |
| |
| // rhs must be of the form: expr.(type) and expr must be an interface |
| expr, _ := rhs.(*ast.TypeAssertExpr) |
| if expr == nil || expr.Type != nil { |
| check.invalidAST(s.Pos(), "incorrect form of type switch guard") |
| return |
| } |
| var x operand |
| check.expr(&x, expr.X) |
| if x.mode == invalid { |
| return |
| } |
| xtyp, _ := x.typ.Underlying().(*Interface) |
| if xtyp == nil { |
| check.errorf(x.pos(), "%s is not an interface", &x) |
| return |
| } |
| |
| check.multipleDefaults(s.Body.List) |
| |
| var lhsVars []*Var // list of implicitly declared lhs variables |
| seen := make(map[Type]token.Pos) // map of seen types to positions |
| for _, s := range s.Body.List { |
| clause, _ := s.(*ast.CaseClause) |
| if clause == nil { |
| check.invalidAST(s.Pos(), "incorrect type switch case") |
| continue |
| } |
| // Check each type in this type switch case. |
| T := check.caseTypes(&x, xtyp, clause.List, seen) |
| check.openScope(clause, "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(clause.List) != 1 || T == nil { |
| T = x.typ |
| } |
| obj := NewVar(lhs.Pos(), check.pkg, lhs.Name, T) |
| scopePos := clause.Pos() + token.Pos(len("default")) // for default clause (len(List) == 0) |
| if n := len(clause.List); n > 0 { |
| scopePos = clause.List[n-1].End() |
| } |
| 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. |
| 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.Pos(), "%s declared but not used", lhs.Name) |
| } |
| } |
| |
| case *ast.SelectStmt: |
| inner |= breakOk |
| |
| check.multipleDefaults(s.Body.List) |
| |
| for _, s := range s.Body.List { |
| clause, _ := s.(*ast.CommClause) |
| if clause == nil { |
| continue // error reported before |
| } |
| |
| // clause.Comm must be a SendStmt, RecvStmt, or default case |
| valid := false |
| var rhs ast.Expr // rhs of RecvStmt, or nil |
| switch s := clause.Comm.(type) { |
| case nil, *ast.SendStmt: |
| valid = true |
| case *ast.AssignStmt: |
| if len(s.Rhs) == 1 { |
| rhs = s.Rhs[0] |
| } |
| case *ast.ExprStmt: |
| rhs = s.X |
| } |
| |
| // if present, rhs must be a receive operation |
| if rhs != nil { |
| if x, _ := unparen(rhs).(*ast.UnaryExpr); x != nil && x.Op == token.ARROW { |
| valid = true |
| } |
| } |
| |
| if !valid { |
| check.error(clause.Comm.Pos(), "select case must be send or receive (possibly with assignment)") |
| continue |
| } |
| |
| check.openScope(s, "case") |
| if clause.Comm != nil { |
| check.stmt(inner, clause.Comm) |
| } |
| check.stmtList(inner, clause.Body) |
| check.closeScope() |
| } |
| |
| case *ast.ForStmt: |
| inner |= breakOk | continueOk |
| 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 && !isBoolean(x.typ) { |
| check.error(s.Cond.Pos(), "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.(*ast.AssignStmt); s != nil && s.Tok == token.DEFINE { |
| check.softErrorf(s.Pos(), "cannot declare in post statement") |
| check.use(s.Lhs...) // avoid follow-up errors |
| } |
| check.stmt(inner, s.Body) |
| |
| case *ast.RangeStmt: |
| inner |= breakOk | continueOk |
| check.openScope(s, "for") |
| defer check.closeScope() |
| |
| // check expression to iterate over |
| var x operand |
| check.expr(&x, s.X) |
| |
| // determine key/value types |
| var key, val Type |
| if x.mode != invalid { |
| switch typ := x.typ.Underlying().(type) { |
| case *Basic: |
| if isString(typ) { |
| key = Typ[Int] |
| val = universeRune // use 'rune' name |
| } |
| case *Array: |
| key = Typ[Int] |
| val = typ.elem |
| case *Slice: |
| key = Typ[Int] |
| val = typ.elem |
| case *Pointer: |
| if typ, _ := typ.base.Underlying().(*Array); typ != nil { |
| key = Typ[Int] |
| val = typ.elem |
| } |
| case *Map: |
| key = typ.key |
| val = typ.elem |
| case *Chan: |
| key = typ.elem |
| val = Typ[Invalid] |
| if typ.dir == SendOnly { |
| check.errorf(x.pos(), "cannot range over send-only channel %s", &x) |
| // ok to continue |
| } |
| if s.Value != nil { |
| check.errorf(s.Value.Pos(), "iteration over %s permits only one iteration variable", &x) |
| // ok to continue |
| } |
| } |
| } |
| |
| if key == nil { |
| check.errorf(x.pos(), "cannot range over %s", &x) |
| // ok to continue |
| } |
| |
| // 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]ast.Expr{s.Key, s.Value} |
| rhs := [2]Type{key, val} // key, val may be nil |
| |
| if s.Tok == token.DEFINE { |
| // short variable declaration; variable scope starts after the range clause |
| // (the for loop opens a new scope, so variables on the lhs never redeclare |
| // previously declared variables) |
| var vars []*Var |
| for i, lhs := range lhs { |
| if lhs == nil { |
| continue |
| } |
| |
| // determine lhs variable |
| var obj *Var |
| if ident, _ := lhs.(*ast.Ident); ident != nil { |
| // declare new variable |
| name := ident.Name |
| 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.Pos(), "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.X.End() |
| for _, obj := range vars { |
| // spec: "The scope of a constant or variable identifier declared inside |
| // a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl |
| // for short variable declarations) and ends at the end of the innermost |
| // containing block." |
| check.declare(check.scope, nil /* recordDef already called */, obj, scopePos) |
| } |
| } else { |
| check.error(s.TokPos, "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) |
| |
| default: |
| check.error(s.Pos(), "invalid statement") |
| } |
| } |