| // 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) |
| defer func() { |
| check.trace(syntax.EndPos(body), "--- <end>") |
| }() |
| } |
| |
| // set function scope extent |
| sig.scope.pos = body.Pos() |
| sig.scope.end = syntax.EndPos(body) |
| |
| // 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, |
| iota: iota, |
| sig: sig, |
| } |
| check.indent = 0 |
| |
| check.stmtList(0, body.List) |
| |
| if check.hasLabel && !check.conf.IgnoreLabels { |
| 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 |
| ) |
| |
| 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) { |
| 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) |
| 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}) |
| } |
| } |
| } |
| |
| func (check *Checker) caseTypes(x *operand, xtyp *Interface, types []syntax.Expr, seen map[Type]syntax.Expr) (T Type) { |
| L: |
| for _, e := range types { |
| T = check.typOrNil(e) |
| if T == Typ[Invalid] { |
| continue L |
| } |
| if T != nil { |
| check.ordinaryType(e.Pos(), T) |
| } |
| // 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 = T.String() |
| } |
| 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 T != nil { |
| check.typeAssertion(e.Pos(), x, xtyp, T) |
| } |
| } |
| 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)) |
| |
| inner := ctxt &^ (fallthroughOk | finalSwitchCase) |
| 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) |
| 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 |
| } |
| var elem Type |
| if !underIs(ch.typ, func(u Type) bool { |
| uch, _ := u.(*Chan) |
| if uch == nil { |
| check.errorf(s, invalidOp+"cannot send to non-channel %s", &ch) |
| return false |
| } |
| if uch.dir == RecvOnly { |
| check.errorf(s, invalidOp+"cannot send to receive-only channel %s", &ch) |
| return false |
| } |
| if elem != nil && !Identical(uch.elem, elem) { |
| check.errorf(s, invalidOp+"channels of %s must have the same element type", &ch) |
| return false |
| } |
| elem = uch.elem |
| return true |
| }) { |
| return |
| } |
| check.assignment(&val, 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 !isNumeric(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 |
| results := unpackExpr(s.Results) |
| if res.Len() > 0 { |
| // function returns results |
| // (if one, say the first, result parameter is named, all of them are named) |
| if len(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.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 { |
| // return has results or result parameters are unnamed |
| check.initVars(res.vars, results, s.Pos()) |
| } |
| } else if len(results) > 0 { |
| check.error(results[0], "no result values expected") |
| check.use(results...) |
| } |
| |
| case *syntax.BranchStmt: |
| if s.Label != nil { |
| check.hasLabel = true |
| break // checked in 2nd pass (check.labels) |
| } |
| switch s.Tok { |
| case syntax.Break: |
| if ctxt&breakOk == 0 { |
| if check.conf.CompilerErrorMessages { |
| check.error(s, "break is not in a loop, switch, or select statement") |
| } else { |
| check.error(s, "break not in for, switch, or select statement") |
| } |
| } |
| case syntax.Continue: |
| if ctxt&continueOk == 0 { |
| if check.conf.CompilerErrorMessages { |
| check.error(s, "continue is not in a loop") |
| } else { |
| check.error(s, "continue not in for statement") |
| } |
| } |
| case syntax.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, 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 && !isBoolean(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, 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 |
| check.openScope(s, "for") |
| defer check.closeScope() |
| |
| if rclause, _ := s.Init.(*syntax.RangeClause); rclause != nil { |
| check.rangeStmt(inner, s, rclause) |
| break |
| } |
| |
| 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, "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. |
| // Don't call useLHS here because we want to use the lhs in |
| // this erroneous statement so that we don't get errors about |
| // these lhs variables being declared but not used. |
| 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 |
| } |
| // Caution: We're not using asInterface here because we don't want |
| // to switch on a suitably constrained type parameter (for |
| // now). |
| // TODO(gri) Need to revisit this. |
| xtyp, _ := under(x.typ).(*Interface) |
| if xtyp == nil { |
| check.errorf(&x, "%s is not an interface type", &x) |
| return |
| } |
| check.ordinaryType(x.Pos(), xtyp) |
| |
| 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(&x, xtyp, 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) { |
| // scope already opened |
| |
| // check expression to iterate over |
| var x operand |
| check.expr(&x, rclause.X) |
| |
| // determine lhs, if any |
| sKey := rclause.Lhs // possibly nil |
| var sValue syntax.Expr |
| if p, _ := sKey.(*syntax.ListExpr); p != nil { |
| if len(p.ElemList) != 2 { |
| check.error(s, invalidAST+"invalid lhs in range clause") |
| return |
| } |
| sKey = p.ElemList[0] |
| sValue = p.ElemList[1] |
| } |
| |
| // determine key/value types |
| var key, val Type |
| if x.mode != invalid { |
| // Ranging over a type parameter is permitted if it has a structural type. |
| typ := optype(x.typ) |
| if _, ok := typ.(*Chan); ok && sValue != nil { |
| check.softErrorf(sValue, "range over %s permits only one iteration variable", &x) |
| // ok to continue |
| } |
| var msg string |
| key, val, msg = rangeKeyVal(typ, isVarName(sKey), isVarName(sValue)) |
| if key == nil || msg != "" { |
| if msg != "" { |
| msg = ": " + msg |
| } |
| check.softErrorf(&x, "cannot range over %s%s", &x, msg) |
| // 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]syntax.Expr{sKey, sValue} |
| rhs := [2]Type{key, val} // key, val may be nil |
| |
| if rclause.Def { |
| // 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.(*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 := syntax.EndPos(rclause.X) // TODO(gri) should this just be s.Body.Pos (spec clarification)? |
| 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, "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) |
| } |
| |
| // isVarName reports whether x is a non-nil, non-blank (_) expression. |
| func isVarName(x syntax.Expr) bool { |
| if x == nil { |
| return false |
| } |
| ident, _ := unparen(x).(*syntax.Name) |
| return ident == nil || ident.Value != "_" |
| } |
| |
| // rangeKeyVal returns the key and value type produced by a range clause |
| // over an expression of type typ, and possibly an error message. If the |
| // range clause is not permitted the returned key is nil or msg is not |
| // empty (in that case we still may have a non-nil key type which can be |
| // used to reduce the chance for follow-on errors). |
| // The wantKey, wantVal, and hasVal flags indicate which of the iteration |
| // variables are used or present; this matters if we range over a generic |
| // type where not all keys or values are of the same type. |
| func rangeKeyVal(typ Type, wantKey, wantVal bool) (Type, Type, string) { |
| 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: |
| var msg string |
| if typ.dir == SendOnly { |
| msg = "receive from send-only channel" |
| } |
| return typ.elem, Typ[Invalid], msg |
| case *top: |
| // we have a type parameter with no structural type |
| return nil, nil, "no structural type" |
| } |
| return nil, nil, "" |
| } |
