cuelang.org/go@v0.10.1/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 "cuelang.org/go/cue/ast"
    18  
    19  // walkVisitor traverses an AST in depth-first order with a [visitor].
    20  //
    21  // TODO(mvdan): refactor away the need for walkVisitor;
    22  // Resolve and Sanitize should be able to use ast.Walk directly.
    23  func walkVisitor(node ast.Node, v visitor) {
    24  	sv := &stackVisitor{stack: []visitor{v}}
    25  	ast.Walk(node, sv.Before, sv.After)
    26  }
    27  
    28  // stackVisitor helps implement visitor support on top of ast.Walk.
    29  type stackVisitor struct {
    30  	stack []visitor
    31  }
    32  
    33  func (v *stackVisitor) Before(node ast.Node) bool {
    34  	current := v.stack[len(v.stack)-1]
    35  	next := current.Before(node)
    36  	if next == nil {
    37  		return false
    38  	}
    39  	v.stack = append(v.stack, next)
    40  	return true
    41  }
    42  
    43  func (v *stackVisitor) After(node ast.Node) {
    44  	v.stack[len(v.stack)-1] = nil // set visitor to nil so it can be garbage collected
    45  	v.stack = v.stack[:len(v.stack)-1]
    46  }
    47  
    48  // A visitor's before method is invoked for each node encountered by Walk.
    49  // If the result visitor w is true, Walk visits each of the children
    50  // of node with the visitor w, followed by a call of w.After.
    51  type visitor interface {
    52  	Before(node ast.Node) (w visitor)
    53  	After(node ast.Node)
    54  }