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// 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 ast
import "fmt"
// A Visitor's Visit method is invoked for each node encountered by [Walk].
// If the result visitor w is not nil, [Walk] visits each of the children
// of node with the visitor w, followed by a call of w.Visit(nil).
type Visitor interface {
Visit(node Node) (w Visitor)
}
// Helper functions for common node lists. They may be empty.
func walkIdentList(v Visitor, list []*Ident) {
for _, x := range list {
Walk(v, x)
}
}
func walkExprList(v Visitor, list []Expr) {
for _, x := range list {
Walk(v, x)
}
}
func walkStmtList(v Visitor, list []Stmt) {
for _, x := range list {
Walk(v, x)
}
}
func walkDeclList(v Visitor, list []Decl) {
for _, x := range list {
Walk(v, x)
}
}
// TODO(gri): Investigate if providing a closure to Walk leads to
// simpler use (and may help eliminate Inspect in turn).
// Walk traverses an AST in depth-first order: It starts by calling
// v.Visit(node); node must not be nil. If the visitor w returned by
// v.Visit(node) is not nil, Walk is invoked recursively with visitor
// w for each of the non-nil children of node, followed by a call of
// w.Visit(nil).
func Walk(v Visitor, node Node) {
if v = v.Visit(node); v == nil {
return
}
// walk children
// (the order of the cases matches the order
// of the corresponding node types in ast.go)
switch n := node.(type) {
// Comments and fields
case *Comment:
// nothing to do
case *CommentGroup:
for _, c := range n.List {
Walk(v, c)
}
case *Field:
if n.Doc != nil {
Walk(v, n.Doc)
}
walkIdentList(v, n.Names)
if n.Type != nil {
Walk(v, n.Type)
}
if n.Tag != nil {
Walk(v, n.Tag)
}
if n.Comment != nil {
Walk(v, n.Comment)
}
case *FieldList:
for _, f := range n.List {
Walk(v, f)
}
// Expressions
case *BadExpr, *Ident, *BasicLit:
// nothing to do
case *Ellipsis:
if n.Elt != nil {
Walk(v, n.Elt)
}
case *FuncLit:
Walk(v, n.Type)
Walk(v, n.Body)
case *CompositeLit:
if n.Type != nil {
Walk(v, n.Type)
}
walkExprList(v, n.Elts)
case *ParenExpr:
Walk(v, n.X)
case *SelectorExpr:
Walk(v, n.X)
Walk(v, n.Sel)
case *IndexExpr:
Walk(v, n.X)
Walk(v, n.Index)
case *IndexListExpr:
Walk(v, n.X)
for _, index := range n.Indices {
Walk(v, index)
}
case *SliceExpr:
Walk(v, n.X)
if n.Low != nil {
Walk(v, n.Low)
}
if n.High != nil {
Walk(v, n.High)
}
if n.Max != nil {
Walk(v, n.Max)
}
case *TypeAssertExpr:
Walk(v, n.X)
if n.Type != nil {
Walk(v, n.Type)
}
case *CallExpr:
Walk(v, n.Fun)
walkExprList(v, n.Args)
case *StarExpr:
Walk(v, n.X)
case *UnaryExpr:
Walk(v, n.X)
case *BinaryExpr:
Walk(v, n.X)
Walk(v, n.Y)
case *KeyValueExpr:
Walk(v, n.Key)
Walk(v, n.Value)
// Types
case *ArrayType:
if n.Len != nil {
Walk(v, n.Len)
}
Walk(v, n.Elt)
case *StructType:
Walk(v, n.Fields)
case *FuncType:
if n.TypeParams != nil {
Walk(v, n.TypeParams)
}
if n.Params != nil {
Walk(v, n.Params)
}
if n.Results != nil {
Walk(v, n.Results)
}
case *InterfaceType:
Walk(v, n.Methods)
case *MapType:
Walk(v, n.Key)
Walk(v, n.Value)
case *ChanType:
Walk(v, n.Value)
// Statements
case *BadStmt:
// nothing to do
case *DeclStmt:
Walk(v, n.Decl)
case *EmptyStmt:
// 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:
walkExprList(v, n.Lhs)
walkExprList(v, n.Rhs)
case *GoStmt:
Walk(v, n.Call)
case *DeferStmt:
Walk(v, n.Call)
case *ReturnStmt:
walkExprList(v, n.Results)
case *BranchStmt:
if n.Label != nil {
Walk(v, n.Label)
}
case *BlockStmt:
walkStmtList(v, n.List)
case *IfStmt:
if n.Init != nil {
Walk(v, n.Init)
}
Walk(v, n.Cond)
Walk(v, n.Body)
if n.Else != nil {
Walk(v, n.Else)
}
case *CaseClause:
walkExprList(v, n.List)
walkStmtList(v, n.Body)
case *SwitchStmt:
if n.Init != nil {
Walk(v, n.Init)
}
if n.Tag != nil {
Walk(v, n.Tag)
}
Walk(v, n.Body)
case *TypeSwitchStmt:
if n.Init != nil {
Walk(v, n.Init)
}
Walk(v, n.Assign)
Walk(v, n.Body)
case *CommClause:
if n.Comm != nil {
Walk(v, n.Comm)
}
walkStmtList(v, n.Body)
case *SelectStmt:
Walk(v, n.Body)
case *ForStmt:
if n.Init != nil {
Walk(v, n.Init)
}
if n.Cond != nil {
Walk(v, n.Cond)
}
if n.Post != nil {
Walk(v, n.Post)
}
Walk(v, n.Body)
case *RangeStmt:
if n.Key != nil {
Walk(v, n.Key)
}
if n.Value != nil {
Walk(v, n.Value)
}
Walk(v, n.X)
Walk(v, n.Body)
// Declarations
case *ImportSpec:
if n.Doc != nil {
Walk(v, n.Doc)
}
if n.Name != nil {
Walk(v, n.Name)
}
Walk(v, n.Path)
if n.Comment != nil {
Walk(v, n.Comment)
}
case *ValueSpec:
if n.Doc != nil {
Walk(v, n.Doc)
}
walkIdentList(v, n.Names)
if n.Type != nil {
Walk(v, n.Type)
}
walkExprList(v, n.Values)
if n.Comment != nil {
Walk(v, n.Comment)
}
case *TypeSpec:
if n.Doc != nil {
Walk(v, n.Doc)
}
Walk(v, n.Name)
if n.TypeParams != nil {
Walk(v, n.TypeParams)
}
Walk(v, n.Type)
if n.Comment != nil {
Walk(v, n.Comment)
}
case *BadDecl:
// nothing to do
case *GenDecl:
if n.Doc != nil {
Walk(v, n.Doc)
}
for _, s := range n.Specs {
Walk(v, s)
}
case *FuncDecl:
if n.Doc != nil {
Walk(v, n.Doc)
}
if n.Recv != nil {
Walk(v, n.Recv)
}
Walk(v, n.Name)
Walk(v, n.Type)
if n.Body != nil {
Walk(v, n.Body)
}
// Files and packages
case *File:
if n.Doc != nil {
Walk(v, n.Doc)
}
Walk(v, n.Name)
walkDeclList(v, n.Decls)
// don't walk n.Comments - they have been
// visited already through the individual
// nodes
case *Package:
for _, f := range n.Files {
Walk(v, f)
}
default:
panic(fmt.Sprintf("ast.Walk: unexpected node type %T", n))
}
v.Visit(nil)
}
type inspector func(Node) bool
func (f inspector) Visit(node Node) Visitor {
if f(node) {
return f
}
return nil
}
// Inspect traverses an AST in depth-first order: It starts by calling
// f(node); node must not be nil. If f returns true, Inspect invokes f
// recursively for each of the non-nil children of node, followed by a
// call of f(nil).
func Inspect(node Node, f func(Node) bool) {
Walk(inspector(f), node)
}