src/cmd/compile/internal/typecheck/stmt.go - go - Git at Google

 // Copyright 2009 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.

 package typecheck

 import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/types"
 	"cmd/internal/src"
 	"internal/types/errors"
 )

 func RangeExprType(t *types.Type) *types.Type {
 	if t.IsPtr() && t.Elem().IsArray() {
 		return t.Elem()
 	}
 	return t
 }

 func typecheckrangeExpr(n *ir.RangeStmt) {
 }

 // type check assignment.
 // if this assignment is the definition of a var on the left side,
 // fill in the var's type.
 func tcAssign(n *ir.AssignStmt) {
 	if base.EnableTrace && base.Flag.LowerT {
 		defer tracePrint("tcAssign", n)(nil)
 	}

 	if n.Y == nil {
 		n.X = AssignExpr(n.X)
 		return
 	}

 	lhs, rhs := []ir.Node{n.X}, []ir.Node{n.Y}
 	assign(n, lhs, rhs)
 	n.X, n.Y = lhs[0], rhs[0]

 	// TODO(mdempsky): This seems out of place.
 	if !ir.IsBlank(n.X) {
 		types.CheckSize(n.X.Type()) // ensure width is calculated for backend
 	}
 }

 func tcAssignList(n *ir.AssignListStmt) {
 	if base.EnableTrace && base.Flag.LowerT {
 		defer tracePrint("tcAssignList", n)(nil)
 	}

 	assign(n, n.Lhs, n.Rhs)
 }

 func assign(stmt ir.Node, lhs, rhs []ir.Node) {
 	// delicate little dance.
 	// the definition of lhs may refer to this assignment
 	// as its definition, in which case it will call tcAssign.
 	// in that case, do not call typecheck back, or it will cycle.
 	// if the variable has a type (ntype) then typechecking
 	// will not look at defn, so it is okay (and desirable,
 	// so that the conversion below happens).

 	checkLHS := func(i int, typ *types.Type) {
 		if n := lhs[i]; typ != nil && ir.DeclaredBy(n, stmt) && n.Type() == nil {
 			base.Assertf(typ.Kind() == types.TNIL, "unexpected untyped nil")
 			n.SetType(defaultType(typ))
 		}
 		if lhs[i].Typecheck() == 0 {
 			lhs[i] = AssignExpr(lhs[i])
 		}
 		checkassign(lhs[i])
 	}

 	assignType := func(i int, typ *types.Type) {
 		checkLHS(i, typ)
 		if typ != nil {
 			checkassignto(typ, lhs[i])
 		}
 	}

 	cr := len(rhs)
 	if len(rhs) == 1 {
 		rhs[0] = typecheck(rhs[0], ctxExpr|ctxMultiOK)
 		if rtyp := rhs[0].Type(); rtyp != nil && rtyp.IsFuncArgStruct() {
 			cr = rtyp.NumFields()
 		}
 	} else {
 		Exprs(rhs)
 	}

 	// x, ok = y
 assignOK:
 	for len(lhs) == 2 && cr == 1 {
 		stmt := stmt.(*ir.AssignListStmt)
 		r := rhs[0]

 		switch r.Op() {
 		case ir.OINDEXMAP:
 			stmt.SetOp(ir.OAS2MAPR)
 		case ir.ORECV:
 			stmt.SetOp(ir.OAS2RECV)
 		case ir.ODOTTYPE:
 			r := r.(*ir.TypeAssertExpr)
 			stmt.SetOp(ir.OAS2DOTTYPE)
 			r.SetOp(ir.ODOTTYPE2)
 		case ir.ODYNAMICDOTTYPE:
 			r := r.(*ir.DynamicTypeAssertExpr)
 			stmt.SetOp(ir.OAS2DOTTYPE)
 			r.SetOp(ir.ODYNAMICDOTTYPE2)
 		default:
 			break assignOK
 		}

 		assignType(0, r.Type())
 		assignType(1, types.UntypedBool)
 		return
 	}

 	if len(lhs) != cr {
 		if r, ok := rhs[0].(*ir.CallExpr); ok && len(rhs) == 1 {
 			if r.Type() != nil {
 				base.ErrorfAt(stmt.Pos(), errors.WrongAssignCount, "assignment mismatch: %d variable%s but %v returns %d value%s", len(lhs), plural(len(lhs)), r.Fun, cr, plural(cr))
 			}
 		} else {
 			base.ErrorfAt(stmt.Pos(), errors.WrongAssignCount, "assignment mismatch: %d variable%s but %v value%s", len(lhs), plural(len(lhs)), len(rhs), plural(len(rhs)))
 		}

 		for i := range lhs {
 			checkLHS(i, nil)
 		}
 		return
 	}

 	// x,y,z = f()
 	if cr > len(rhs) {
 		stmt := stmt.(*ir.AssignListStmt)
 		stmt.SetOp(ir.OAS2FUNC)
 		r := rhs[0].(*ir.CallExpr)
 		rtyp := r.Type()

 		mismatched := false
 		failed := false
 		for i := range lhs {
 			result := rtyp.Field(i).Type
 			assignType(i, result)

 			if lhs[i].Type() == nil || result == nil {
 				failed = true
 			} else if lhs[i] != ir.BlankNode && !types.Identical(lhs[i].Type(), result) {
 				mismatched = true
 			}
 		}
 		if mismatched && !failed {
 			RewriteMultiValueCall(stmt, r)
 		}
 		return
 	}

 	for i, r := range rhs {
 		checkLHS(i, r.Type())
 		if lhs[i].Type() != nil {
 			rhs[i] = AssignConv(r, lhs[i].Type(), "assignment")
 		}
 	}
 }

 func plural(n int) string {
 	if n == 1 {
 		return ""
 	}
 	return "s"
 }

 // tcCheckNil typechecks an OCHECKNIL node.
 func tcCheckNil(n *ir.UnaryExpr) ir.Node {
 	n.X = Expr(n.X)
 	if !n.X.Type().IsPtrShaped() {
 		base.FatalfAt(n.Pos(), "%L is not pointer shaped", n.X)
 	}
 	return n
 }

 // tcFor typechecks an OFOR node.
 func tcFor(n *ir.ForStmt) ir.Node {
 	Stmts(n.Init())
 	n.Cond = Expr(n.Cond)
 	n.Cond = DefaultLit(n.Cond, nil)
 	if n.Cond != nil {
 		t := n.Cond.Type()
 		if t != nil && !t.IsBoolean() {
 			base.Errorf("non-bool %L used as for condition", n.Cond)
 		}
 	}
 	n.Post = Stmt(n.Post)
 	Stmts(n.Body)
 	return n
 }

 // tcGoDefer typechecks (normalizes) an OGO/ODEFER statement.
 func tcGoDefer(n *ir.GoDeferStmt) {
 	call := normalizeGoDeferCall(n.Pos(), n.Op(), n.Call, n.PtrInit())
 	call.GoDefer = true
 	n.Call = call
 }

 // normalizeGoDeferCall normalizes call into a normal function call
 // with no arguments and no results, suitable for use in an OGO/ODEFER
 // statement.
 //
 // For example, it normalizes:
 //
 //	f(x, y)
 //
 // into:
 //
 //	x1, y1 := x, y          // added to init
 //	func() { f(x1, y1) }()  // result
 func normalizeGoDeferCall(pos src.XPos, op ir.Op, call ir.Node, init *ir.Nodes) *ir.CallExpr {
 	init.Append(ir.TakeInit(call)...)

 	if call, ok := call.(*ir.CallExpr); ok && call.Op() == ir.OCALLFUNC {
 		if sig := call.Fun.Type(); sig.NumParams()+sig.NumResults() == 0 {
 			return call // already in normal form
 		}
 	}

 	// Create a new wrapper function without parameters or results.
 	wrapperFn := ir.NewClosureFunc(pos, pos, op, types.NewSignature(nil, nil, nil), ir.CurFunc, Target)
 	wrapperFn.DeclareParams(true)
 	wrapperFn.SetWrapper(true)

 	// argps collects the list of operands within the call expression
 	// that must be evaluated at the go/defer statement.
 	var argps []*ir.Node

 	var visit func(argp *ir.Node)
 	visit = func(argp *ir.Node) {
 		arg := *argp
 		if arg == nil {
 			return
 		}

 		// Recognize a few common expressions that can be evaluated within
 		// the wrapper, so we don't need to allocate space for them within
 		// the closure.
 		switch arg.Op() {
 		case ir.OLITERAL, ir.ONIL, ir.OMETHEXPR, ir.ONEW:
 			return
 		case ir.ONAME:
 			arg := arg.(*ir.Name)
 			if arg.Class == ir.PFUNC {
 				return // reference to global function
 			}
 		case ir.OADDR:
 			arg := arg.(*ir.AddrExpr)
 			if arg.X.Op() == ir.OLINKSYMOFFSET {
 				return // address of global symbol
 			}

 		case ir.OCONVNOP:
 			arg := arg.(*ir.ConvExpr)

 			// For unsafe.Pointer->uintptr conversion arguments, save the
 			// unsafe.Pointer argument. This is necessary to handle cases
 			// like fixedbugs/issue24491a.go correctly.
 			//
 			// TODO(mdempsky): Limit to static callees with
 			// //go:uintptr{escapes,keepalive}?
 			if arg.Type().IsUintptr() && arg.X.Type().IsUnsafePtr() {
 				visit(&arg.X)
 				return
 			}

 		case ir.OARRAYLIT, ir.OSLICELIT, ir.OSTRUCTLIT:
 			// TODO(mdempsky): For very large slices, it may be preferable
 			// to construct them at the go/defer statement instead.
 			list := arg.(*ir.CompLitExpr).List
 			for i, el := range list {
 				switch el := el.(type) {
 				case *ir.KeyExpr:
 					visit(&el.Value)
 				case *ir.StructKeyExpr:
 					visit(&el.Value)
 				default:
 					visit(&list[i])
 				}
 			}
 			return
 		}

 		argps = append(argps, argp)
 	}

 	visitList := func(list []ir.Node) {
 		for i := range list {
 			visit(&list[i])
 		}
 	}

 	switch call.Op() {
 	default:
 		base.Fatalf("unexpected call op: %v", call.Op())

 	case ir.OCALLFUNC:
 		call := call.(*ir.CallExpr)

 		// If the callee is a named function, link to the original callee.
 		if wrapped := ir.StaticCalleeName(call.Fun); wrapped != nil {
 			wrapperFn.WrappedFunc = wrapped.Func
 		}

 		visit(&call.Fun)
 		visitList(call.Args)

 	case ir.OCALLINTER:
 		call := call.(*ir.CallExpr)
 		argps = append(argps, &call.Fun.(*ir.SelectorExpr).X) // must be first for OCHECKNIL; see below
 		visitList(call.Args)

 	case ir.OAPPEND, ir.ODELETE, ir.OPRINT, ir.OPRINTLN, ir.ORECOVERFP:
 		call := call.(*ir.CallExpr)
 		visitList(call.Args)
 		visit(&call.RType)

 	case ir.OCOPY:
 		call := call.(*ir.BinaryExpr)
 		visit(&call.X)
 		visit(&call.Y)
 		visit(&call.RType)

 	case ir.OCLEAR, ir.OCLOSE, ir.OPANIC:
 		call := call.(*ir.UnaryExpr)
 		visit(&call.X)
 	}

 	if len(argps) != 0 {
 		// Found one or more operands that need to be evaluated upfront
 		// and spilled to temporary variables, which can be captured by
 		// the wrapper function.

 		stmtPos := base.Pos
 		callPos := base.Pos

 		as := ir.NewAssignListStmt(callPos, ir.OAS2, make([]ir.Node, len(argps)), make([]ir.Node, len(argps)))
 		for i, argp := range argps {
 			arg := *argp

 			pos := callPos
 			if ir.HasUniquePos(arg) {
 				pos = arg.Pos()
 			}

 			// tmp := arg
 			tmp := TempAt(pos, ir.CurFunc, arg.Type())
 			init.Append(Stmt(ir.NewDecl(pos, ir.ODCL, tmp)))
 			tmp.Defn = as
 			as.Lhs[i] = tmp
 			as.Rhs[i] = arg

 			// Rewrite original expression to use/capture tmp.
 			*argp = ir.NewClosureVar(pos, wrapperFn, tmp)
 		}
 		init.Append(Stmt(as))

 		// For "go/defer iface.M()", if iface is nil, we need to panic at
 		// the point of the go/defer statement.
 		if call.Op() == ir.OCALLINTER {
 			iface := as.Lhs[0]
 			init.Append(Stmt(ir.NewUnaryExpr(stmtPos, ir.OCHECKNIL, ir.NewUnaryExpr(iface.Pos(), ir.OITAB, iface))))
 		}
 	}

 	// Move call into the wrapper function, now that it's safe to
 	// evaluate there.
 	wrapperFn.Body = []ir.Node{call}

 	// Finally, construct a call to the wrapper.
 	return Call(call.Pos(), wrapperFn.OClosure, nil, false).(*ir.CallExpr)
 }

 // tcIf typechecks an OIF node.
 func tcIf(n *ir.IfStmt) ir.Node {
 	Stmts(n.Init())
 	n.Cond = Expr(n.Cond)
 	n.Cond = DefaultLit(n.Cond, nil)
 	if n.Cond != nil {
 		t := n.Cond.Type()
 		if t != nil && !t.IsBoolean() {
 			base.Errorf("non-bool %L used as if condition", n.Cond)
 		}
 	}
 	Stmts(n.Body)
 	Stmts(n.Else)
 	return n
 }

 // range
 func tcRange(n *ir.RangeStmt) {
 	n.X = Expr(n.X)

 	// delicate little dance.  see tcAssignList
 	if n.Key != nil {
 		if !ir.DeclaredBy(n.Key, n) {
 			n.Key = AssignExpr(n.Key)
 		}
 		checkassign(n.Key)
 	}
 	if n.Value != nil {
 		if !ir.DeclaredBy(n.Value, n) {
 			n.Value = AssignExpr(n.Value)
 		}
 		checkassign(n.Value)
 	}

 	// second half of dance
 	n.SetTypecheck(1)
 	if n.Key != nil && n.Key.Typecheck() == 0 {
 		n.Key = AssignExpr(n.Key)
 	}
 	if n.Value != nil && n.Value.Typecheck() == 0 {
 		n.Value = AssignExpr(n.Value)
 	}

 	Stmts(n.Body)
 }

 // tcReturn typechecks an ORETURN node.
 func tcReturn(n *ir.ReturnStmt) ir.Node {
 	if ir.CurFunc == nil {
 		base.FatalfAt(n.Pos(), "return outside function")
 	}

 	typecheckargs(n)
 	if len(n.Results) != 0 {
 		typecheckaste(ir.ORETURN, nil, false, ir.CurFunc.Type().Results(), n.Results, func() string { return "return argument" })
 	}
 	return n
 }

 // select
 func tcSelect(sel *ir.SelectStmt) {
 	var def *ir.CommClause
 	lno := ir.SetPos(sel)
 	Stmts(sel.Init())
 	for _, ncase := range sel.Cases {
 		if ncase.Comm == nil {
 			// default
 			if def != nil {
 				base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in select (first at %v)", ir.Line(def))
 			} else {
 				def = ncase
 			}
 		} else {
 			n := Stmt(ncase.Comm)
 			ncase.Comm = n
 			oselrecv2 := func(dst, recv ir.Node, def bool) {
 				selrecv := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
 				selrecv.Def = def
 				selrecv.SetTypecheck(1)
 				selrecv.SetInit(n.Init())
 				ncase.Comm = selrecv
 			}
 			switch n.Op() {
 			default:
 				pos := n.Pos()
 				if n.Op() == ir.ONAME {
 					// We don't have the right position for ONAME nodes (see #15459 and
 					// others). Using ncase.Pos for now as it will provide the correct
 					// line number (assuming the expression follows the "case" keyword
 					// on the same line). This matches the approach before 1.10.
 					pos = ncase.Pos()
 				}
 				base.ErrorfAt(pos, errors.InvalidSelectCase, "select case must be receive, send or assign recv")

 			case ir.OAS:
 				// convert x = <-c into x, _ = <-c
 				// remove implicit conversions; the eventual assignment
 				// will reintroduce them.
 				n := n.(*ir.AssignStmt)
 				if r := n.Y; r.Op() == ir.OCONVNOP || r.Op() == ir.OCONVIFACE {
 					r := r.(*ir.ConvExpr)
 					if r.Implicit() {
 						n.Y = r.X
 					}
 				}
 				if n.Y.Op() != ir.ORECV {
 					base.ErrorfAt(n.Pos(), errors.InvalidSelectCase, "select assignment must have receive on right hand side")
 					break
 				}
 				oselrecv2(n.X, n.Y, n.Def)

 			case ir.OAS2RECV:
 				n := n.(*ir.AssignListStmt)
 				if n.Rhs[0].Op() != ir.ORECV {
 					base.ErrorfAt(n.Pos(), errors.InvalidSelectCase, "select assignment must have receive on right hand side")
 					break
 				}
 				n.SetOp(ir.OSELRECV2)

 			case ir.ORECV:
 				// convert <-c into _, _ = <-c
 				n := n.(*ir.UnaryExpr)
 				oselrecv2(ir.BlankNode, n, false)

 			case ir.OSEND:
 				break
 			}
 		}

 		Stmts(ncase.Body)
 	}

 	base.Pos = lno
 }

 // tcSend typechecks an OSEND node.
 func tcSend(n *ir.SendStmt) ir.Node {
 	n.Chan = Expr(n.Chan)
 	n.Value = Expr(n.Value)
 	n.Chan = DefaultLit(n.Chan, nil)
 	t := n.Chan.Type()
 	if t == nil {
 		return n
 	}
 	if !t.IsChan() {
 		base.Errorf("invalid operation: %v (send to non-chan type %v)", n, t)
 		return n
 	}

 	if !t.ChanDir().CanSend() {
 		base.Errorf("invalid operation: %v (send to receive-only type %v)", n, t)
 		return n
 	}

 	n.Value = AssignConv(n.Value, t.Elem(), "send")
 	if n.Value.Type() == nil {
 		return n
 	}
 	return n
 }

 // tcSwitch typechecks a switch statement.
 func tcSwitch(n *ir.SwitchStmt) {
 	Stmts(n.Init())
 	if n.Tag != nil && n.Tag.Op() == ir.OTYPESW {
 		tcSwitchType(n)
 	} else {
 		tcSwitchExpr(n)
 	}
 }

 func tcSwitchExpr(n *ir.SwitchStmt) {
 	t := types.Types[types.TBOOL]
 	if n.Tag != nil {
 		n.Tag = Expr(n.Tag)
 		n.Tag = DefaultLit(n.Tag, nil)
 		t = n.Tag.Type()
 	}

 	var nilonly string
 	if t != nil {
 		switch {
 		case t.IsMap():
 			nilonly = "map"
 		case t.Kind() == types.TFUNC:
 			nilonly = "func"
 		case t.IsSlice():
 			nilonly = "slice"

 		case !types.IsComparable(t):
 			if t.IsStruct() {
 				base.ErrorfAt(n.Pos(), errors.InvalidExprSwitch, "cannot switch on %L (struct containing %v cannot be compared)", n.Tag, types.IncomparableField(t).Type)
 			} else {
 				base.ErrorfAt(n.Pos(), errors.InvalidExprSwitch, "cannot switch on %L", n.Tag)
 			}
 			t = nil
 		}
 	}

 	var defCase ir.Node
 	for _, ncase := range n.Cases {
 		ls := ncase.List
 		if len(ls) == 0 { // default:
 			if defCase != nil {
 				base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in switch (first at %v)", ir.Line(defCase))
 			} else {
 				defCase = ncase
 			}
 		}

 		for i := range ls {
 			ir.SetPos(ncase)
 			ls[i] = Expr(ls[i])
 			ls[i] = DefaultLit(ls[i], t)
 			n1 := ls[i]
 			if t == nil || n1.Type() == nil {
 				continue
 			}

 			if nilonly != "" && !ir.IsNil(n1) {
 				base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch (can only compare %s %v to nil)", n1, nilonly, n.Tag)
 			} else if t.IsInterface() && !n1.Type().IsInterface() && !types.IsComparable(n1.Type()) {
 				base.ErrorfAt(ncase.Pos(), errors.UndefinedOp, "invalid case %L in switch (incomparable type)", n1)
 			} else {
 				op1, _ := assignOp(n1.Type(), t)
 				op2, _ := assignOp(t, n1.Type())
 				if op1 == ir.OXXX && op2 == ir.OXXX {
 					if n.Tag != nil {
 						base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch on %v (mismatched types %v and %v)", n1, n.Tag, n1.Type(), t)
 					} else {
 						base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch (mismatched types %v and bool)", n1, n1.Type())
 					}
 				}
 			}
 		}

 		Stmts(ncase.Body)
 	}
 }

 func tcSwitchType(n *ir.SwitchStmt) {
 	guard := n.Tag.(*ir.TypeSwitchGuard)
 	guard.X = Expr(guard.X)
 	t := guard.X.Type()
 	if t != nil && !t.IsInterface() {
 		base.ErrorfAt(n.Pos(), errors.InvalidTypeSwitch, "cannot type switch on non-interface value %L", guard.X)
 		t = nil
 	}

 	// We don't actually declare the type switch's guarded
 	// declaration itself. So if there are no cases, we won't
 	// notice that it went unused.
 	if v := guard.Tag; v != nil && !ir.IsBlank(v) && len(n.Cases) == 0 {
 		base.ErrorfAt(v.Pos(), errors.UnusedVar, "%v declared but not used", v.Sym())
 	}

 	var defCase, nilCase ir.Node
 	var ts typeSet
 	for _, ncase := range n.Cases {
 		ls := ncase.List
 		if len(ls) == 0 { // default:
 			if defCase != nil {
 				base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in switch (first at %v)", ir.Line(defCase))
 			} else {
 				defCase = ncase
 			}
 		}

 		for i := range ls {
 			ls[i] = typecheck(ls[i], ctxExpr|ctxType)
 			n1 := ls[i]
 			if t == nil || n1.Type() == nil {
 				continue
 			}

 			if ir.IsNil(n1) { // case nil:
 				if nilCase != nil {
 					base.ErrorfAt(ncase.Pos(), errors.DuplicateCase, "multiple nil cases in type switch (first at %v)", ir.Line(nilCase))
 				} else {
 					nilCase = ncase
 				}
 				continue
 			}
 			if n1.Op() == ir.ODYNAMICTYPE {
 				continue
 			}
 			if n1.Op() != ir.OTYPE {
 				base.ErrorfAt(ncase.Pos(), errors.NotAType, "%L is not a type", n1)
 				continue
 			}
 			if !n1.Type().IsInterface() {
 				why := ImplementsExplain(n1.Type(), t)
 				if why != "" {
 					base.ErrorfAt(ncase.Pos(), errors.ImpossibleAssert, "impossible type switch case: %L cannot have dynamic type %v (%s)", guard.X, n1.Type(), why)
 				}
 				continue
 			}

 			ts.add(ncase.Pos(), n1.Type())
 		}

 		if ncase.Var != nil {
 			// Assign the clause variable's type.
 			vt := t
 			if len(ls) == 1 {
 				if ls[0].Op() == ir.OTYPE || ls[0].Op() == ir.ODYNAMICTYPE {
 					vt = ls[0].Type()
 				} else if !ir.IsNil(ls[0]) {
 					// Invalid single-type case;
 					// mark variable as broken.
 					vt = nil
 				}
 			}

 			nvar := ncase.Var
 			nvar.SetType(vt)
 			if vt != nil {
 				nvar = AssignExpr(nvar).(*ir.Name)
 			} else {
 				// Clause variable is broken; prevent typechecking.
 				nvar.SetTypecheck(1)
 			}
 			ncase.Var = nvar
 		}

 		Stmts(ncase.Body)
 	}
 }

 type typeSet struct {
 	m map[string]src.XPos
 }

 func (s *typeSet) add(pos src.XPos, typ *types.Type) {
 	if s.m == nil {
 		s.m = make(map[string]src.XPos)
 	}

 	ls := typ.LinkString()
 	if prev, ok := s.m[ls]; ok {
 		base.ErrorfAt(pos, errors.DuplicateCase, "duplicate case %v in type switch\n\tprevious case at %s", typ, base.FmtPos(prev))
 		return
 	}
 	s.m[ls] = pos
 }
	// Copyright 2009 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.

	package typecheck

	import (
	"cmd/compile/internal/base"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/types"
	"cmd/internal/src"
	"internal/types/errors"
	)

	func RangeExprType(t types.Type) types.Type {
	if t.IsPtr() && t.Elem().IsArray() {
	return t.Elem()
	}
	return t
	}

	func typecheckrangeExpr(n *ir.RangeStmt) {
	}

	// type check assignment.
	// if this assignment is the definition of a var on the left side,
	// fill in the var's type.
	func tcAssign(n *ir.AssignStmt) {
	if base.EnableTrace && base.Flag.LowerT {
	defer tracePrint("tcAssign", n)(nil)
	}

	if n.Y == nil {
	n.X = AssignExpr(n.X)
	return
	}

	lhs, rhs := []ir.Node{n.X}, []ir.Node{n.Y}
	assign(n, lhs, rhs)
	n.X, n.Y = lhs[0], rhs[0]

	// TODO(mdempsky): This seems out of place.
	if !ir.IsBlank(n.X) {
	types.CheckSize(n.X.Type()) // ensure width is calculated for backend
	}
	}

	func tcAssignList(n *ir.AssignListStmt) {
	if base.EnableTrace && base.Flag.LowerT {
	defer tracePrint("tcAssignList", n)(nil)
	}

	assign(n, n.Lhs, n.Rhs)
	}

	func assign(stmt ir.Node, lhs, rhs []ir.Node) {
	// delicate little dance.
	// the definition of lhs may refer to this assignment
	// as its definition, in which case it will call tcAssign.
	// in that case, do not call typecheck back, or it will cycle.
	// if the variable has a type (ntype) then typechecking
	// will not look at defn, so it is okay (and desirable,
	// so that the conversion below happens).

	checkLHS := func(i int, typ *types.Type) {
	if n := lhs[i]; typ != nil && ir.DeclaredBy(n, stmt) && n.Type() == nil {
	base.Assertf(typ.Kind() == types.TNIL, "unexpected untyped nil")
	n.SetType(defaultType(typ))
	}
	if lhs[i].Typecheck() == 0 {
	lhs[i] = AssignExpr(lhs[i])
	}
	checkassign(lhs[i])
	}

	assignType := func(i int, typ *types.Type) {
	checkLHS(i, typ)
	if typ != nil {
	checkassignto(typ, lhs[i])
	}
	}

	cr := len(rhs)
	if len(rhs) == 1 {
	rhs[0] = typecheck(rhs[0], ctxExpr\|ctxMultiOK)
	if rtyp := rhs[0].Type(); rtyp != nil && rtyp.IsFuncArgStruct() {
	cr = rtyp.NumFields()
	}
	} else {
	Exprs(rhs)
	}

	// x, ok = y
	assignOK:
	for len(lhs) == 2 && cr == 1 {
	stmt := stmt.(*ir.AssignListStmt)
	r := rhs[0]

	switch r.Op() {
	case ir.OINDEXMAP:
	stmt.SetOp(ir.OAS2MAPR)
	case ir.ORECV:
	stmt.SetOp(ir.OAS2RECV)
	case ir.ODOTTYPE:
	r := r.(*ir.TypeAssertExpr)
	stmt.SetOp(ir.OAS2DOTTYPE)
	r.SetOp(ir.ODOTTYPE2)
	case ir.ODYNAMICDOTTYPE:
	r := r.(*ir.DynamicTypeAssertExpr)
	stmt.SetOp(ir.OAS2DOTTYPE)
	r.SetOp(ir.ODYNAMICDOTTYPE2)
	default:
	break assignOK
	}

	assignType(0, r.Type())
	assignType(1, types.UntypedBool)
	return
	}

	if len(lhs) != cr {
	if r, ok := rhs[0].(*ir.CallExpr); ok && len(rhs) == 1 {
	if r.Type() != nil {
	base.ErrorfAt(stmt.Pos(), errors.WrongAssignCount, "assignment mismatch: %d variable%s but %v returns %d value%s", len(lhs), plural(len(lhs)), r.Fun, cr, plural(cr))
	}
	} else {
	base.ErrorfAt(stmt.Pos(), errors.WrongAssignCount, "assignment mismatch: %d variable%s but %v value%s", len(lhs), plural(len(lhs)), len(rhs), plural(len(rhs)))
	}

	for i := range lhs {
	checkLHS(i, nil)
	}
	return
	}

	// x,y,z = f()
	if cr > len(rhs) {
	stmt := stmt.(*ir.AssignListStmt)
	stmt.SetOp(ir.OAS2FUNC)
	r := rhs[0].(*ir.CallExpr)
	rtyp := r.Type()

	mismatched := false
	failed := false
	for i := range lhs {
	result := rtyp.Field(i).Type
	assignType(i, result)

	if lhs[i].Type() == nil \|\| result == nil {
	failed = true
	} else if lhs[i] != ir.BlankNode && !types.Identical(lhs[i].Type(), result) {
	mismatched = true
	}
	}
	if mismatched && !failed {
	RewriteMultiValueCall(stmt, r)
	}
	return
	}

	for i, r := range rhs {
	checkLHS(i, r.Type())
	if lhs[i].Type() != nil {
	rhs[i] = AssignConv(r, lhs[i].Type(), "assignment")
	}
	}
	}

	func plural(n int) string {
	if n == 1 {
	return ""
	}
	return "s"
	}

	// tcCheckNil typechecks an OCHECKNIL node.
	func tcCheckNil(n *ir.UnaryExpr) ir.Node {
	n.X = Expr(n.X)
	if !n.X.Type().IsPtrShaped() {
	base.FatalfAt(n.Pos(), "%L is not pointer shaped", n.X)
	}
	return n
	}

	// tcFor typechecks an OFOR node.
	func tcFor(n *ir.ForStmt) ir.Node {
	Stmts(n.Init())
	n.Cond = Expr(n.Cond)
	n.Cond = DefaultLit(n.Cond, nil)
	if n.Cond != nil {
	t := n.Cond.Type()
	if t != nil && !t.IsBoolean() {
	base.Errorf("non-bool %L used as for condition", n.Cond)
	}
	}
	n.Post = Stmt(n.Post)
	Stmts(n.Body)
	return n
	}

	// tcGoDefer typechecks (normalizes) an OGO/ODEFER statement.
	func tcGoDefer(n *ir.GoDeferStmt) {
	call := normalizeGoDeferCall(n.Pos(), n.Op(), n.Call, n.PtrInit())
	call.GoDefer = true
	n.Call = call
	}

	// normalizeGoDeferCall normalizes call into a normal function call
	// with no arguments and no results, suitable for use in an OGO/ODEFER
	// statement.
	//
	// For example, it normalizes:
	//
	// f(x, y)
	//
	// into:
	//
	// x1, y1 := x, y // added to init
	// func() { f(x1, y1) }() // result
	func normalizeGoDeferCall(pos src.XPos, op ir.Op, call ir.Node, init ir.Nodes) ir.CallExpr {
	init.Append(ir.TakeInit(call)...)

	if call, ok := call.(*ir.CallExpr); ok && call.Op() == ir.OCALLFUNC {
	if sig := call.Fun.Type(); sig.NumParams()+sig.NumResults() == 0 {
	return call // already in normal form
	}
	}

	// Create a new wrapper function without parameters or results.
	wrapperFn := ir.NewClosureFunc(pos, pos, op, types.NewSignature(nil, nil, nil), ir.CurFunc, Target)
	wrapperFn.DeclareParams(true)
	wrapperFn.SetWrapper(true)

	// argps collects the list of operands within the call expression
	// that must be evaluated at the go/defer statement.
	var argps []*ir.Node

	var visit func(argp *ir.Node)
	visit = func(argp *ir.Node) {
	arg := *argp
	if arg == nil {
	return
	}

	// Recognize a few common expressions that can be evaluated within
	// the wrapper, so we don't need to allocate space for them within
	// the closure.
	switch arg.Op() {
	case ir.OLITERAL, ir.ONIL, ir.OMETHEXPR, ir.ONEW:
	return
	case ir.ONAME:
	arg := arg.(*ir.Name)
	if arg.Class == ir.PFUNC {
	return // reference to global function
	}
	case ir.OADDR:
	arg := arg.(*ir.AddrExpr)
	if arg.X.Op() == ir.OLINKSYMOFFSET {
	return // address of global symbol
	}

	case ir.OCONVNOP:
	arg := arg.(*ir.ConvExpr)

	// For unsafe.Pointer->uintptr conversion arguments, save the
	// unsafe.Pointer argument. This is necessary to handle cases
	// like fixedbugs/issue24491a.go correctly.
	//
	// TODO(mdempsky): Limit to static callees with
	// //go:uintptr{escapes,keepalive}?
	if arg.Type().IsUintptr() && arg.X.Type().IsUnsafePtr() {
	visit(&arg.X)
	return
	}

	case ir.OARRAYLIT, ir.OSLICELIT, ir.OSTRUCTLIT:
	// TODO(mdempsky): For very large slices, it may be preferable
	// to construct them at the go/defer statement instead.
	list := arg.(*ir.CompLitExpr).List
	for i, el := range list {
	switch el := el.(type) {
	case *ir.KeyExpr:
	visit(&el.Value)
	case *ir.StructKeyExpr:
	visit(&el.Value)
	default:
	visit(&list[i])
	}
	}
	return
	}

	argps = append(argps, argp)
	}

	visitList := func(list []ir.Node) {
	for i := range list {
	visit(&list[i])
	}
	}

	switch call.Op() {
	default:
	base.Fatalf("unexpected call op: %v", call.Op())

	case ir.OCALLFUNC:
	call := call.(*ir.CallExpr)

	// If the callee is a named function, link to the original callee.
	if wrapped := ir.StaticCalleeName(call.Fun); wrapped != nil {
	wrapperFn.WrappedFunc = wrapped.Func
	}

	visit(&call.Fun)
	visitList(call.Args)

	case ir.OCALLINTER:
	call := call.(*ir.CallExpr)
	argps = append(argps, &call.Fun.(*ir.SelectorExpr).X) // must be first for OCHECKNIL; see below
	visitList(call.Args)

	case ir.OAPPEND, ir.ODELETE, ir.OPRINT, ir.OPRINTLN, ir.ORECOVERFP:
	call := call.(*ir.CallExpr)
	visitList(call.Args)
	visit(&call.RType)

	case ir.OCOPY:
	call := call.(*ir.BinaryExpr)
	visit(&call.X)
	visit(&call.Y)
	visit(&call.RType)

	case ir.OCLEAR, ir.OCLOSE, ir.OPANIC:
	call := call.(*ir.UnaryExpr)
	visit(&call.X)
	}

	if len(argps) != 0 {
	// Found one or more operands that need to be evaluated upfront
	// and spilled to temporary variables, which can be captured by
	// the wrapper function.

	stmtPos := base.Pos
	callPos := base.Pos

	as := ir.NewAssignListStmt(callPos, ir.OAS2, make([]ir.Node, len(argps)), make([]ir.Node, len(argps)))
	for i, argp := range argps {
	arg := *argp

	pos := callPos
	if ir.HasUniquePos(arg) {
	pos = arg.Pos()
	}

	// tmp := arg
	tmp := TempAt(pos, ir.CurFunc, arg.Type())
	init.Append(Stmt(ir.NewDecl(pos, ir.ODCL, tmp)))
	tmp.Defn = as
	as.Lhs[i] = tmp
	as.Rhs[i] = arg

	// Rewrite original expression to use/capture tmp.
	*argp = ir.NewClosureVar(pos, wrapperFn, tmp)
	}
	init.Append(Stmt(as))

	// For "go/defer iface.M()", if iface is nil, we need to panic at
	// the point of the go/defer statement.
	if call.Op() == ir.OCALLINTER {
	iface := as.Lhs[0]
	init.Append(Stmt(ir.NewUnaryExpr(stmtPos, ir.OCHECKNIL, ir.NewUnaryExpr(iface.Pos(), ir.OITAB, iface))))
	}
	}

	// Move call into the wrapper function, now that it's safe to
	// evaluate there.
	wrapperFn.Body = []ir.Node{call}

	// Finally, construct a call to the wrapper.
	return Call(call.Pos(), wrapperFn.OClosure, nil, false).(*ir.CallExpr)
	}

	// tcIf typechecks an OIF node.
	func tcIf(n *ir.IfStmt) ir.Node {
	Stmts(n.Init())
	n.Cond = Expr(n.Cond)
	n.Cond = DefaultLit(n.Cond, nil)
	if n.Cond != nil {
	t := n.Cond.Type()
	if t != nil && !t.IsBoolean() {
	base.Errorf("non-bool %L used as if condition", n.Cond)
	}
	}
	Stmts(n.Body)
	Stmts(n.Else)
	return n
	}

	// range
	func tcRange(n *ir.RangeStmt) {
	n.X = Expr(n.X)

	// delicate little dance. see tcAssignList
	if n.Key != nil {
	if !ir.DeclaredBy(n.Key, n) {
	n.Key = AssignExpr(n.Key)
	}
	checkassign(n.Key)
	}
	if n.Value != nil {
	if !ir.DeclaredBy(n.Value, n) {
	n.Value = AssignExpr(n.Value)
	}
	checkassign(n.Value)
	}

	// second half of dance
	n.SetTypecheck(1)
	if n.Key != nil && n.Key.Typecheck() == 0 {
	n.Key = AssignExpr(n.Key)
	}
	if n.Value != nil && n.Value.Typecheck() == 0 {
	n.Value = AssignExpr(n.Value)
	}

	Stmts(n.Body)
	}

	// tcReturn typechecks an ORETURN node.
	func tcReturn(n *ir.ReturnStmt) ir.Node {
	if ir.CurFunc == nil {
	base.FatalfAt(n.Pos(), "return outside function")
	}

	typecheckargs(n)
	if len(n.Results) != 0 {
	typecheckaste(ir.ORETURN, nil, false, ir.CurFunc.Type().Results(), n.Results, func() string { return "return argument" })
	}
	return n
	}

	// select
	func tcSelect(sel *ir.SelectStmt) {
	var def *ir.CommClause
	lno := ir.SetPos(sel)
	Stmts(sel.Init())
	for _, ncase := range sel.Cases {
	if ncase.Comm == nil {
	// default
	if def != nil {
	base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in select (first at %v)", ir.Line(def))
	} else {
	def = ncase
	}
	} else {
	n := Stmt(ncase.Comm)
	ncase.Comm = n
	oselrecv2 := func(dst, recv ir.Node, def bool) {
	selrecv := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
	selrecv.Def = def
	selrecv.SetTypecheck(1)
	selrecv.SetInit(n.Init())
	ncase.Comm = selrecv
	}
	switch n.Op() {
	default:
	pos := n.Pos()
	if n.Op() == ir.ONAME {
	// We don't have the right position for ONAME nodes (see #15459 and
	// others). Using ncase.Pos for now as it will provide the correct
	// line number (assuming the expression follows the "case" keyword
	// on the same line). This matches the approach before 1.10.
	pos = ncase.Pos()
	}
	base.ErrorfAt(pos, errors.InvalidSelectCase, "select case must be receive, send or assign recv")

	case ir.OAS:
	// convert x = <-c into x, _ = <-c
	// remove implicit conversions; the eventual assignment
	// will reintroduce them.
	n := n.(*ir.AssignStmt)
	if r := n.Y; r.Op() == ir.OCONVNOP \|\| r.Op() == ir.OCONVIFACE {
	r := r.(*ir.ConvExpr)
	if r.Implicit() {
	n.Y = r.X
	}
	}
	if n.Y.Op() != ir.ORECV {
	base.ErrorfAt(n.Pos(), errors.InvalidSelectCase, "select assignment must have receive on right hand side")
	break
	}
	oselrecv2(n.X, n.Y, n.Def)

	case ir.OAS2RECV:
	n := n.(*ir.AssignListStmt)
	if n.Rhs[0].Op() != ir.ORECV {
	base.ErrorfAt(n.Pos(), errors.InvalidSelectCase, "select assignment must have receive on right hand side")
	break
	}
	n.SetOp(ir.OSELRECV2)

	case ir.ORECV:
	// convert <-c into _, _ = <-c
	n := n.(*ir.UnaryExpr)
	oselrecv2(ir.BlankNode, n, false)

	case ir.OSEND:
	break
	}
	}

	Stmts(ncase.Body)
	}

	base.Pos = lno
	}

	// tcSend typechecks an OSEND node.
	func tcSend(n *ir.SendStmt) ir.Node {
	n.Chan = Expr(n.Chan)
	n.Value = Expr(n.Value)
	n.Chan = DefaultLit(n.Chan, nil)
	t := n.Chan.Type()
	if t == nil {
	return n
	}
	if !t.IsChan() {
	base.Errorf("invalid operation: %v (send to non-chan type %v)", n, t)
	return n
	}

	if !t.ChanDir().CanSend() {
	base.Errorf("invalid operation: %v (send to receive-only type %v)", n, t)
	return n
	}

	n.Value = AssignConv(n.Value, t.Elem(), "send")
	if n.Value.Type() == nil {
	return n
	}
	return n
	}

	// tcSwitch typechecks a switch statement.
	func tcSwitch(n *ir.SwitchStmt) {
	Stmts(n.Init())
	if n.Tag != nil && n.Tag.Op() == ir.OTYPESW {
	tcSwitchType(n)
	} else {
	tcSwitchExpr(n)
	}
	}

	func tcSwitchExpr(n *ir.SwitchStmt) {
	t := types.Types[types.TBOOL]
	if n.Tag != nil {
	n.Tag = Expr(n.Tag)
	n.Tag = DefaultLit(n.Tag, nil)
	t = n.Tag.Type()
	}

	var nilonly string
	if t != nil {
	switch {
	case t.IsMap():
	nilonly = "map"
	case t.Kind() == types.TFUNC:
	nilonly = "func"
	case t.IsSlice():
	nilonly = "slice"

	case !types.IsComparable(t):
	if t.IsStruct() {
	base.ErrorfAt(n.Pos(), errors.InvalidExprSwitch, "cannot switch on %L (struct containing %v cannot be compared)", n.Tag, types.IncomparableField(t).Type)
	} else {
	base.ErrorfAt(n.Pos(), errors.InvalidExprSwitch, "cannot switch on %L", n.Tag)
	}
	t = nil
	}
	}

	var defCase ir.Node
	for _, ncase := range n.Cases {
	ls := ncase.List
	if len(ls) == 0 { // default:
	if defCase != nil {
	base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in switch (first at %v)", ir.Line(defCase))
	} else {
	defCase = ncase
	}
	}

	for i := range ls {
	ir.SetPos(ncase)
	ls[i] = Expr(ls[i])
	ls[i] = DefaultLit(ls[i], t)
	n1 := ls[i]
	if t == nil \|\| n1.Type() == nil {
	continue
	}

	if nilonly != "" && !ir.IsNil(n1) {
	base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch (can only compare %s %v to nil)", n1, nilonly, n.Tag)
	} else if t.IsInterface() && !n1.Type().IsInterface() && !types.IsComparable(n1.Type()) {
	base.ErrorfAt(ncase.Pos(), errors.UndefinedOp, "invalid case %L in switch (incomparable type)", n1)
	} else {
	op1, _ := assignOp(n1.Type(), t)
	op2, _ := assignOp(t, n1.Type())
	if op1 == ir.OXXX && op2 == ir.OXXX {
	if n.Tag != nil {
	base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch on %v (mismatched types %v and %v)", n1, n.Tag, n1.Type(), t)
	} else {
	base.ErrorfAt(ncase.Pos(), errors.MismatchedTypes, "invalid case %v in switch (mismatched types %v and bool)", n1, n1.Type())
	}
	}
	}
	}

	Stmts(ncase.Body)
	}
	}

	func tcSwitchType(n *ir.SwitchStmt) {
	guard := n.Tag.(*ir.TypeSwitchGuard)
	guard.X = Expr(guard.X)
	t := guard.X.Type()
	if t != nil && !t.IsInterface() {
	base.ErrorfAt(n.Pos(), errors.InvalidTypeSwitch, "cannot type switch on non-interface value %L", guard.X)
	t = nil
	}

	// We don't actually declare the type switch's guarded
	// declaration itself. So if there are no cases, we won't
	// notice that it went unused.
	if v := guard.Tag; v != nil && !ir.IsBlank(v) && len(n.Cases) == 0 {
	base.ErrorfAt(v.Pos(), errors.UnusedVar, "%v declared but not used", v.Sym())
	}

	var defCase, nilCase ir.Node
	var ts typeSet
	for _, ncase := range n.Cases {
	ls := ncase.List
	if len(ls) == 0 { // default:
	if defCase != nil {
	base.ErrorfAt(ncase.Pos(), errors.DuplicateDefault, "multiple defaults in switch (first at %v)", ir.Line(defCase))
	} else {
	defCase = ncase
	}
	}

	for i := range ls {
	ls[i] = typecheck(ls[i], ctxExpr\|ctxType)
	n1 := ls[i]
	if t == nil \|\| n1.Type() == nil {
	continue
	}

	if ir.IsNil(n1) { // case nil:
	if nilCase != nil {
	base.ErrorfAt(ncase.Pos(), errors.DuplicateCase, "multiple nil cases in type switch (first at %v)", ir.Line(nilCase))
	} else {
	nilCase = ncase
	}
	continue
	}
	if n1.Op() == ir.ODYNAMICTYPE {
	continue
	}
	if n1.Op() != ir.OTYPE {
	base.ErrorfAt(ncase.Pos(), errors.NotAType, "%L is not a type", n1)
	continue
	}
	if !n1.Type().IsInterface() {
	why := ImplementsExplain(n1.Type(), t)
	if why != "" {
	base.ErrorfAt(ncase.Pos(), errors.ImpossibleAssert, "impossible type switch case: %L cannot have dynamic type %v (%s)", guard.X, n1.Type(), why)
	}
	continue
	}

	ts.add(ncase.Pos(), n1.Type())
	}

	if ncase.Var != nil {
	// Assign the clause variable's type.
	vt := t
	if len(ls) == 1 {
	if ls[0].Op() == ir.OTYPE \|\| ls[0].Op() == ir.ODYNAMICTYPE {
	vt = ls[0].Type()
	} else if !ir.IsNil(ls[0]) {
	// Invalid single-type case;
	// mark variable as broken.
	vt = nil
	}
	}

	nvar := ncase.Var
	nvar.SetType(vt)
	if vt != nil {
	nvar = AssignExpr(nvar).(*ir.Name)
	} else {
	// Clause variable is broken; prevent typechecking.
	nvar.SetTypecheck(1)
	}
	ncase.Var = nvar
	}

	Stmts(ncase.Body)
	}
	}

	type typeSet struct {
	m map[string]src.XPos
	}

	func (s typeSet) add(pos src.XPos, typ types.Type) {
	if s.m == nil {
	s.m = make(map[string]src.XPos)
	}

	ls := typ.LinkString()
	if prev, ok := s.m[ls]; ok {
	base.ErrorfAt(pos, errors.DuplicateCase, "duplicate case %v in type switch\n\tprevious case at %s", typ, base.FmtPos(prev))
	return
	}
	s.m[ls] = pos
	}