github.com/joomcode/cue@v0.4.4-0.20221111115225-539fe3512047/cue/ast/astutil/walk.go (about) 1 // Copyright 2018 The CUE Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package astutil 16 17 import ( 18 "fmt" 19 20 "github.com/joomcode/cue/cue/ast" 21 ) 22 23 // TODO: use ast.Walk or adopt that version to allow visitors. 24 25 // A visitor's before method is invoked for each node encountered by Walk. 26 // If the result visitor w is not nil, Walk visits each of the children 27 // of node with the visitor w, followed by a call of w.After. 28 type visitor interface { 29 Before(node ast.Node) (w visitor) 30 After(node ast.Node) 31 } 32 33 // Helper functions for common node lists. They may be empty. 34 35 func walkExprList(v visitor, list []ast.Expr) { 36 for _, x := range list { 37 walk(v, x) 38 } 39 } 40 41 func walkDeclList(v visitor, list []ast.Decl) { 42 for _, x := range list { 43 walk(v, x) 44 } 45 } 46 47 // walk traverses an AST in depth-first order: It starts by calling 48 // v.Visit(node); node must not be nil. If the visitor w returned by 49 // v.Visit(node) is not nil, walk is invoked recursively with visitor 50 // w for each of the non-nil children of node, followed by a call of 51 // w.Visit(nil). 52 // 53 func walk(v visitor, node ast.Node) { 54 if v = v.Before(node); v == nil { 55 return 56 } 57 58 // TODO: record the comment groups and interleave with the values like for 59 // parsing and printing? 60 for _, c := range node.Comments() { 61 walk(v, c) 62 } 63 64 // walk children 65 // (the order of the cases matches the order 66 // of the corresponding node types in go) 67 switch n := node.(type) { 68 // Comments and fields 69 case *ast.Comment: 70 // nothing to do 71 72 case *ast.CommentGroup: 73 for _, c := range n.List { 74 walk(v, c) 75 } 76 77 case *ast.Attribute: 78 // nothing to do 79 80 case *ast.Field: 81 walk(v, n.Label) 82 if n.Value != nil { 83 walk(v, n.Value) 84 } 85 for _, a := range n.Attrs { 86 walk(v, a) 87 } 88 89 case *ast.StructLit: 90 for _, f := range n.Elts { 91 walk(v, f) 92 } 93 94 // Expressions 95 case *ast.BottomLit, *ast.BadExpr, *ast.Ident, *ast.BasicLit: 96 // nothing to do 97 98 case *ast.Interpolation: 99 for _, e := range n.Elts { 100 walk(v, e) 101 } 102 103 case *ast.ListLit: 104 walkExprList(v, n.Elts) 105 106 case *ast.Ellipsis: 107 if n.Type != nil { 108 walk(v, n.Type) 109 } 110 111 case *ast.ParenExpr: 112 walk(v, n.X) 113 114 case *ast.SelectorExpr: 115 walk(v, n.X) 116 walk(v, n.Sel) 117 118 case *ast.IndexExpr: 119 walk(v, n.X) 120 walk(v, n.Index) 121 122 case *ast.SliceExpr: 123 walk(v, n.X) 124 if n.Low != nil { 125 walk(v, n.Low) 126 } 127 if n.High != nil { 128 walk(v, n.High) 129 } 130 131 case *ast.CallExpr: 132 walk(v, n.Fun) 133 walkExprList(v, n.Args) 134 135 case *ast.UnaryExpr: 136 walk(v, n.X) 137 138 case *ast.BinaryExpr: 139 walk(v, n.X) 140 walk(v, n.Y) 141 142 // Declarations 143 case *ast.ImportSpec: 144 if n.Name != nil { 145 walk(v, n.Name) 146 } 147 walk(v, n.Path) 148 149 case *ast.BadDecl: 150 // nothing to do 151 152 case *ast.ImportDecl: 153 for _, s := range n.Specs { 154 walk(v, s) 155 } 156 157 case *ast.EmbedDecl: 158 walk(v, n.Expr) 159 160 case *ast.Alias: 161 walk(v, n.Ident) 162 walk(v, n.Expr) 163 164 case *ast.Comprehension: 165 for _, c := range n.Clauses { 166 walk(v, c) 167 } 168 walk(v, n.Value) 169 170 // Files and packages 171 case *ast.File: 172 walkDeclList(v, n.Decls) 173 174 case *ast.Package: 175 // The package identifier isn't really an identifier. Skip it. 176 177 case *ast.LetClause: 178 walk(v, n.Ident) 179 walk(v, n.Expr) 180 181 case *ast.ForClause: 182 if n.Key != nil { 183 walk(v, n.Key) 184 } 185 walk(v, n.Value) 186 walk(v, n.Source) 187 188 case *ast.IfClause: 189 walk(v, n.Condition) 190 191 default: 192 panic(fmt.Sprintf("Walk: unexpected node type %T", n)) 193 } 194 195 v.After(node) 196 }