// is "".
func (check *Checker) isTerminating(s ast.Stmt, label string) bool {
	switch s := s.(type) {
	default:
		panic("unreachable")

	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.SendStmt,
		*ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt, *ast.DeferStmt,
		*ast.RangeStmt:
		// no chance

	case *ast.LabeledStmt:
		return check.isTerminating(s.Stmt, s.Label.Name)

	case *ast.ExprStmt:

	case *ast.AssignStmt,
		*ast.BadStmt,
		*ast.DeclStmt,
		*ast.DeferStmt,
		*ast.EmptyStmt,
		*ast.ExprStmt,
		*ast.GoStmt,
		*ast.IncDecStmt,
		*ast.ReturnStmt,
		*ast.SendStmt:
		// no statements inside

	case *ast.BlockStmt:
		for _, stmt := range x.List {
			d.findLabels(stmt)
		}

	case *ast.BranchStmt:
		switch x.Tok {

	case *ast.GoStmt:
		return 1 << nGoStmt
	case *ast.Ident:
		return 1 << nIdent
	case *ast.IfStmt:
		return 1 << nIfStmt
	case *ast.ImportSpec:
		return 1 << nImportSpec
	case *ast.IncDecStmt:
		return 1 << nIncDecStmt
	case *ast.IndexExpr:
		return 1 << nIndexExpr
	case *ast.IndexListExpr:
		return 1 << nIndexListExpr
	case *ast.InterfaceType:
		return 1 << nInterfaceType

	}

	// A SendStmt node represents a send statement.
	SendStmt struct {
		Chan  Expr
		Arrow token.Pos // position of "<-"
		Value Expr
	}

	// An IncDecStmt node represents an increment or decrement statement.
	IncDecStmt struct {
		X      Expr
		TokPos token.Pos   // position of Tok
		Tok    token.Token // INC or DEC
	}

	// An AssignStmt node represents an assignment or

			tok(n.NamePos, len(n.Name)))

	case *ast.IfStmt:
		children = append(children,
			tok(n.If, len("if")))

	case *ast.ImportSpec:
		// TODO(adonovan): ImportSpec.{Doc,EndPos}?

	case *ast.IncDecStmt:
		children = append(children,
			tok(n.TokPos, len(n.Tok.String())))

	case *ast.IndexExpr:
		children = append(children,
			tok(n.Lbrack, len("[")),
			tok(n.Rbrack, len("]")))

		// nothing to do

	case *LabeledStmt:
		Walk(v, n.Label)
		Walk(v, n.Stmt)

	case *ExprStmt:
		Walk(v, n.X)

	case *SendStmt:
		Walk(v, n.Chan)
		Walk(v, n.Value)

	case *IncDecStmt:
		Walk(v, n.X)

	case *AssignStmt:
		walkList(v, n.Lhs)
		walkList(v, n.Rhs)

	case *GoStmt:
		Walk(v, n.Call)

	case *DeferStmt:
		Walk(v, n.Call)

	case *ReturnStmt:

	// It is effectively an additional default-nil parameter of stmt().
	var label *lblock
start:
	switch s := _s.(type) {
	case *ast.BadStmt,
		*ast.SendStmt,
		*ast.IncDecStmt,
		*ast.GoStmt,
		*ast.DeferStmt,
		*ast.EmptyStmt,
		*ast.AssignStmt:
		// No effect on control flow.
		b.add(s)

	case *ast.ExprStmt:
		b.add(s)

			body = n.Body
			switch post := n.Post.(type) {
			case *ast.AssignStmt:
				// e.g. for p = head; p != nil; p = p.next
				for _, lhs := range post.Lhs {
					addVar(lhs)
				}
			case *ast.IncDecStmt:
				// e.g. for i := 0; i < n; i++
				addVar(post.X)
			}
		}
		if vars == nil {
			return true
		}

		// Inspect statements to find function literals that may be run outside of

	case *ast.LabeledStmt:
		f.walk(n.Stmt, ctxStmt, visit)
	case *ast.ExprStmt:
		f.walk(&n.X, ctxExpr, visit)
	case *ast.SendStmt:
		f.walk(&n.Chan, ctxExpr, visit)
		f.walk(&n.Value, ctxExpr, visit)
	case *ast.IncDecStmt:
		f.walk(&n.X, ctxExpr, visit)
	case *ast.AssignStmt:
		f.walk(n.Lhs, ctxExpr, visit)
		if len(n.Lhs) == 2 && len(n.Rhs) == 1 {
			f.walk(n.Rhs, ctxAssign2, visit)
		} else {
			f.walk(n.Rhs, ctxExpr, visit)

		a.apply(n, "Stmt", nil, n.Stmt)

	case *ast.ExprStmt:
		a.apply(n, "X", nil, n.X)

	case *ast.SendStmt:
		a.apply(n, "Chan", nil, n.Chan)
		a.apply(n, "Value", nil, n.Value)

	case *ast.IncDecStmt:
		a.apply(n, "X", nil, n.X)

	case *ast.AssignStmt:
		a.applyList(n, "Lhs")
		a.applyList(n, "Rhs")

	case *ast.GoStmt:
		a.apply(n, "Call", nil, n.Call)

	case *ast.DeferStmt: