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// Copyright 2013 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 isTerminating.
package types2
import (
"cmd/compile/internal/syntax"
)
// isTerminating reports if s is a terminating statement.
// If s is labeled, label is the label name; otherwise s
// is "".
func (check *Checker) isTerminating(s syntax.Stmt, label string) bool {
switch s := s.(type) {
default:
unreachable()
case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.SendStmt,
*syntax.AssignStmt, *syntax.CallStmt:
// no chance
case *syntax.LabeledStmt:
return check.isTerminating(s.Stmt, s.Label.Value)
case *syntax.ExprStmt:
// calling the predeclared (possibly parenthesized) panic() function is terminating
if call, ok := unparen(s.X).(*syntax.CallExpr); ok && check.isPanic[call] {
return true
}
case *syntax.ReturnStmt:
return true
case *syntax.BranchStmt:
if s.Tok == syntax.Goto || s.Tok == syntax.Fallthrough {
return true
}
case *syntax.BlockStmt:
return check.isTerminatingList(s.List, "")
case *syntax.IfStmt:
if s.Else != nil &&
check.isTerminating(s.Then, "") &&
check.isTerminating(s.Else, "") {
return true
}
case *syntax.SwitchStmt:
return check.isTerminatingSwitch(s.Body, label)
case *syntax.SelectStmt:
for _, cc := range s.Body {
if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
return false
}
}
return true
case *syntax.ForStmt:
if s.Cond == nil && !hasBreak(s.Body, label, true) {
return true
}
}
return false
}
func (check *Checker) isTerminatingList(list []syntax.Stmt, label string) bool {
// trailing empty statements are permitted - skip them
for i := len(list) - 1; i >= 0; i-- {
if _, ok := list[i].(*syntax.EmptyStmt); !ok {
return check.isTerminating(list[i], label)
}
}
return false // all statements are empty
}
func (check *Checker) isTerminatingSwitch(body []*syntax.CaseClause, label string) bool {
hasDefault := false
for _, cc := range body {
if cc.Cases == nil {
hasDefault = true
}
if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
return false
}
}
return hasDefault
}
// TODO(gri) For nested breakable statements, the current implementation of hasBreak
// will traverse the same subtree repeatedly, once for each label. Replace
// with a single-pass label/break matching phase.
// hasBreak reports if s is or contains a break statement
// referring to the label-ed statement or implicit-ly the
// closest outer breakable statement.
func hasBreak(s syntax.Stmt, label string, implicit bool) bool {
switch s := s.(type) {
default:
unreachable()
case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.ExprStmt,
*syntax.SendStmt, *syntax.AssignStmt, *syntax.CallStmt,
*syntax.ReturnStmt:
// no chance
case *syntax.LabeledStmt:
return hasBreak(s.Stmt, label, implicit)
case *syntax.BranchStmt:
if s.Tok == syntax.Break {
if s.Label == nil {
return implicit
}
if s.Label.Value == label {
return true
}
}
case *syntax.BlockStmt:
return hasBreakList(s.List, label, implicit)
case *syntax.IfStmt:
if hasBreak(s.Then, label, implicit) ||
s.Else != nil && hasBreak(s.Else, label, implicit) {
return true
}
case *syntax.SwitchStmt:
if label != "" && hasBreakCaseList(s.Body, label, false) {
return true
}
case *syntax.SelectStmt:
if label != "" && hasBreakCommList(s.Body, label, false) {
return true
}
case *syntax.ForStmt:
if label != "" && hasBreak(s.Body, label, false) {
return true
}
}
return false
}
func hasBreakList(list []syntax.Stmt, label string, implicit bool) bool {
for _, s := range list {
if hasBreak(s, label, implicit) {
return true
}
}
return false
}
func hasBreakCaseList(list []*syntax.CaseClause, label string, implicit bool) bool {
for _, s := range list {
if hasBreakList(s.Body, label, implicit) {
return true
}
}
return false
}
func hasBreakCommList(list []*syntax.CommClause, label string, implicit bool) bool {
for _, s := range list {
if hasBreakList(s.Body, label, implicit) {
return true
}
}
return false
}
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