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arborist.js
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arborist.js
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const {generateCode, generateFlatAST,} = require('./flast');
const Arborist = class {
/**
* @param {string|ASTNode[]} scriptOrFlatAstArr - the target script or a flat AST array
* @param {Function} logFunc - (optional) Logging function
*/
constructor(scriptOrFlatAstArr, logFunc = null) {
this.script = '';
this.ast = [];
this.log = logFunc || (() => true);
this.markedForDeletion = []; // Array of node ids.
this.appliedCounter = 0; // Track the number of times changes were applied.
this.replacements = [];
if (typeof scriptOrFlatAstArr === 'string') {
this.script = scriptOrFlatAstArr;
this.ast = generateFlatAST(scriptOrFlatAstArr);
} else if (Array.isArray(scriptOrFlatAstArr)) {
this.ast = scriptOrFlatAstArr;
} else throw Error(`Undetermined argument`);
}
/**
* When applicable, replace the provided node with its nearest parent node that can be removed without breaking the code.
* @param {ASTNode} startNode
* @return {ASTNode}
*/
_getCorrectTargetForDeletion(startNode) {
let currentNode = startNode;
while (
['ExpressionStatement', 'UnaryExpression', 'UpdateExpression'].includes(currentNode?.parentNode?.type) ||
(currentNode.parentNode.type === 'VariableDeclaration' &&
(currentNode.parentNode.declarations.length === 1 ||
!currentNode.parentNode.declarations.filter(d => d.nodeId !== currentNode.nodeId && !d.isMarked).length)
)) currentNode = currentNode.parentNode;
if (['consequent', 'alternate'].includes(currentNode.parentKey)) currentNode.isEmpty = true;
return currentNode;
}
/**
*
* @returns {number} The number of changes to be applied.
*/
getNumberOfChanges() {
return this.replacements.length + this.markedForDeletion.length;
}
/**
* Replace the target node with another node or delete the target node completely, depending on whether a replacement
* node is provided.
* @param targetNode The node to replace or remove.
* @param replacementNode If exists, replace the target node with this node.
*/
markNode(targetNode, replacementNode) {
if (!targetNode.isMarked) {
if (replacementNode) { // Mark for replacement
this.replacements.push([targetNode, replacementNode]);
targetNode.isMarked = true;
} else { // Mark for deletion
targetNode = this._getCorrectTargetForDeletion(targetNode);
if (targetNode.isEmpty) this.markNode(targetNode, {type: 'EmptyStatement'});
else if (!targetNode.isMarked) {
this.markedForDeletion.push(targetNode.nodeId);
targetNode.isMarked = true;
}
}
}
}
/**
* Iterate over the complete AST and replace / remove marked nodes,
* then rebuild code and AST to validate changes.
* @return {number} The number of modifications made.
*/
applyChanges() {
let changesCounter = 0;
try {
const that = this;
if (this.getNumberOfChanges() > 0) {
let rootNode = this.ast[0];
const rootNodeReplacement = this.replacements.find(n => n[0].nodeId === 0);
if (rootNodeReplacement) {
++changesCounter;
this.log(`[+] Applying changes to the root node...`);
const leadingComments = rootNode.leadingComments || [];
const trailingComments = rootNode.trailingComments || [];
rootNode = rootNodeReplacement[1];
if (leadingComments.length) rootNode.leadingComments = (rootNode.leadingComments || []).concat(leadingComments);
if (trailingComments.length) rootNode.trailingComments = (rootNode.trailingComments || []).concat(trailingComments);
} else {
for (const targetNodeId of this.markedForDeletion) {
try {
const targetNode = this.ast.find(n => n.nodeId === targetNodeId);
if (targetNode) {
const parent = targetNode.parentNode;
if (parent[targetNode.parentKey] === targetNode) {
parent[targetNode.parentKey] = undefined;
const comments = (targetNode.leadingComments || []).concat(targetNode.trailingComments || []);
if (comments.length) parent.trailingComments = (parent.trailingComments || []).concat(comments);
++changesCounter;
} else if (Array.isArray(parent[targetNode.parentKey])) {
const idx = parent[targetNode.parentKey].indexOf(targetNode);
parent[targetNode.parentKey][idx] = undefined;
parent[targetNode.parentKey] = parent[targetNode.parentKey].filter(n => n);
const comments = (targetNode.leadingComments || []).concat(targetNode.trailingComments || []);
if (comments.length) {
const targetParent = idx > 0 ? parent[targetNode.parentKey][idx - 1] : parent[targetNode.parentKey].length > 1 ? parent[targetNode.parentKey][idx + 1] : parent;
targetParent.trailingComments = (targetParent.trailingComments || []).concat(comments);
}
++changesCounter;
}
}
} catch (e) {
that.log(`[-] Unable to delete node: ${e}`);
}
}
for (const [targetNode, replacementNode] of this.replacements) {
try {
if (targetNode) {
const parent = targetNode.parentNode;
if (parent[targetNode.parentKey] === targetNode) {
parent[targetNode.parentKey] = replacementNode;
const leadingComments = targetNode.leadingComments || [];
const trailingComments = targetNode.trailingComments || [];
if (leadingComments.length) replacementNode.leadingComments = (replacementNode.leadingComments || []).concat(leadingComments);
if (trailingComments.length) replacementNode.trailingComments = (replacementNode.trailingComments || []).concat(trailingComments);
++changesCounter;
} else if (Array.isArray(parent[targetNode.parentKey])) {
const idx = parent[targetNode.parentKey].indexOf(targetNode);
parent[targetNode.parentKey][idx] = replacementNode;
const comments = (targetNode.leadingComments || []).concat(targetNode.trailingComments || []);
if (idx > 0) {
const commentsTarget = parent[targetNode.parentKey][idx - 1];
commentsTarget.trailingComments = (commentsTarget.trailingComments || []).concat(comments);
} else if (parent[targetNode.parentKey].length > 1) {
const commentsTarget = parent[targetNode.parentKey][idx + 1];
commentsTarget.leadingComments = (commentsTarget.leadingComments || []).concat(comments);
} else parent.trailingComments = (parent.trailingComments || []).concat(comments);
++changesCounter;
}
}
} catch (e) {
that.log(`[-] Unable to replace node: ${e}`);
}
}
}
if (changesCounter) {
this.replacements.length = 0;
this.markedForDeletion.length = 0;
// If any of the changes made will break the script the next line will fail and the
// script will remain the same. If it doesn't break, the changes are valid and the script can be marked as modified.
const script = generateCode(rootNode);
const ast = generateFlatAST(script);
if (ast && ast.length) {
this.ast = ast;
this.script = script;
}
else {
this.log(`[-] Modified script is invalid. Reverting ${changesCounter} changes...`);
changesCounter = 0;
}
}
}
} catch (e) {
this.log(`[-] Unable to apply changes to AST: ${e}`);
}
++this.appliedCounter;
return changesCounter;
}
};
module.exports = {
Arborist,
};