gem-hunter
Language: JavaScript
Apply AST-based macros at build-time
Functions can improve readability. Inlining expanded constants can improve performance.
Build-time AST macros allow you to take advantge of both.
Build-time macro for an IJK-like transform for use with hyperapp, superfine, or preact
MACRO({ H(nodeName, attributes, ...children) { const parts = { nodeName, attributes } if (0 !== children.length) { parts.children = `[${children.join(', ')}]` } const body = Object.entries(parts) .map(e => e.join(': ')) .join(', ') return `({ ${body} })` }, }) export const view = count => H("div", {} , H("h1", {}, count) , H("button", { onclick: () => render(count - 1) }, "-") , H("button", { onclick: () => render(count + 1) }, "+") )
prettier)export const view = count => ({ nodeName: 'div', attributes: {}, children: [ { nodeName: 'h1', attributes: {}, children: [count] }, { nodeName: 'button', attributes: { onclick: () => render(count - 1) }, children: ['-'] }, { nodeName: 'button', attributes: { onclick: () => render(count + 1) }, children: ['+'] } ] })
MACRO({ EXPR: expr => new Function(`return (${expr})`).call(null), LET(expr) { Object.assign(global, this.EXPR(expr)) return '' }, CSS(strings, ...args) { let res = '`' + strings[0] for (let i=0; i<args.length; i++) res += args[i] + (strings[i+1] || '') res += '`' return res }, }) LET({ color: 'blue', height: 100, dayIsOdd: new Date().getDay() & 1, buildDate: new Date().toISOString().replace(/:\d\d\..*Z/, ''), }) const css_styles = CSS` .somewhere { top: ${ EXPR(20 + height) } px; border: ${ EXPR(1 + 2) } px ${ EXPR( dayIsOdd ? 'solid' : 'dashed' ) } ${color}; } .somewhere::before { content: "${ EXPR(buildDate) }"; } `
prettier)const css_styles = ` .somewhere { top: 120 px; border: 3 px solid color; } .somewhere::before { content: "2018-08-31T16:05"; } `;
The heavy lifting for AST transform is provided by the excellent transform-ast and magic-string packages.
Macro functions are evaluated in VM2.NodeVM isolation, providing a measure of protection from abuse.
Allows defining new macros and variables. A single argument of type object is expected.
The expression will be evaluated in a VM2.NodeVM context and the result assigned to
the macro namespace. Any functions defined at the root will define new macros.
The macro's arguments are the getSource() strings of the AST arguments nodes.
(e.g. ast_node.arguments.map(e => e.getSource())
MACRO({ url: require('url'), EXAMPLE_SRC(...args) { return JSON.stringify(args) }, })
require('os')require('util')require('zlib')require('assert')require('path')require('url')require('querystring')require('punycode')This can be customized with {vm2: {builtin: []}}
Additionally, this.ast_node is the macro's CallExpression AST Node,
enabling sophisticated AST-based transformations.
MACRO({ EXAMPLE_ARROW_AST() { // translated from https://github.com/goto-bus-stop/transform-ast#example for (const node of this.ast_node.arguments) { if (node.type !== 'ArrowFunctionExpression') continue; const params = node.params.map(param =>param.getSource()) if (node.body.type !== 'BlockStatement') node.body.edit.update(`{ return ${node.body.getSource()} }`) node.edit.update(`function (${params.join(', ')}) ${node.body.getSource()}`) } }, })
import rpi_ast_macros from 'rollup-plugin-ast-macros' // defaults: const macros = null // or {} const sandbox = null // or {} const builtin = ['os', 'util', 'zlib', 'assert', 'path', 'url', 'querystring', 'punycode'] const plugins = [ rpi_ast_macros({ // include: 'code/**', exclude: ['node_modules/**'], ast_opt: {}, // passed to transform_ast(source, ast_opt) macros, // additional default macros & `this` context for macro invocation vm2_opt: { sandbox, // passed to VM2.NodeVM({sandbox}) builtin, // passed to VM2.NodeVM({require:{builtin}) }, }) ]