linting-asts.md

Notes from Code Transformation and Linting with Abstract Syntax Trees

Abstract Syntax Trees

• AST is a concept to transform source code into data structures that are easy to work with for various static analysis tools, e.g. ESLint's espree

• AST visualizer

• AST Explorer

• Esprima

• Parsers transform code into Syntax Trees, they might diffefrom one another due to different implementation goals

• Visitor pattern allows you to traverse the tree and perform some action on each node, e.g.

  // ESLint example
  function create(context) {
    return {
      // This executes for every node with if statement
      IfStatement(node) {
        if (node.consequent.type !== "BlockStatement") {
          context.report({
            node,
            message: "Use blocks with if statements",
          });
        }
      },
    };
  }

• Creating custom ESLint rules

ESLint plugins

Babel plugins

Codemods