handlebars.js/tests/bench/perf.js

import { execSync } from 'node:child_process';
import { Bench } from 'tinybench';
import Handlebars from '../../lib/index.js';
import { templates as allTemplates } from './templates.js';
import {
  printResults,
  printSectionHeader,
  saveMarkdownReport,
} from './report.js';

// ─── Configuration ───────────────────────────────────────────────────────────
// Compilation happens once at app startup — low warmup reflects real-world conditions.
// Execution happens thousands of times — higher warmup lets V8 optimize hot paths.

const COMPILE_BENCH_CONFIG = {
  warmupIterations: 10,
  iterations: 1000,
  time: 3000,
};

const EXEC_BENCH_CONFIG = {
  warmupIterations: 500,
  iterations: 5000,
  time: 3000,
};

// ─── CLI Args ────────────────────────────────────────────────────────────────

function getGitBranch() {
  try {
    return execSync('git rev-parse --abbrev-ref HEAD', {
      encoding: 'utf8',
    }).trim();
  } catch {
    return null;
  }
}

const args = process.argv.slice(2);
const labelIdx = args.indexOf('--label');
const label = labelIdx !== -1 ? args[labelIdx + 1] : getGitBranch();

const grepIdx = args.indexOf('--grep');
let grepPattern = null;
if (grepIdx !== -1 && args[grepIdx + 1]) {
  try {
    grepPattern = new RegExp(args[grepIdx + 1], 'i');
  } catch (e) {
    console.error(`Invalid --grep pattern: ${e.message}`);
    process.exit(1);
  }
}

const sectionIdx = args.indexOf('--section');
let sectionPattern = null;
if (sectionIdx !== -1 && args[sectionIdx + 1]) {
  try {
    sectionPattern = new RegExp(args[sectionIdx + 1], 'i');
  } catch (e) {
    console.error(`Invalid --section pattern: ${e.message}`);
    process.exit(1);
  }
}

// ─── Filter templates ───────────────────────────────────────────────────────

const templates = Object.fromEntries(
  Object.entries(allTemplates).filter(
    ([name]) => !grepPattern || grepPattern.test(name)
  )
);

if (Object.keys(templates).length === 0) {
  console.error(
    `No templates match --grep ${grepPattern}. Available: ${Object.keys(allTemplates).join(', ')}`
  );
  process.exit(1);
}

if (grepPattern) {
  console.log(
    `Filtering templates: ${Object.keys(templates).length}/${Object.keys(allTemplates).length} match /${grepPattern.source}/i`
  );
  console.log();
}

// ─── Bench helpers ───────────────────────────────────────────────────────────

function newBench(config) {
  return new Bench(config);
}

function createEnv(def) {
  const hb = Handlebars.create();
  if (def.helpers) {
    hb.registerHelper(def.helpers);
  }
  if (def.partials) {
    for (const [name, tpl] of Object.entries(def.partials)) {
      hb.registerPartial(name, tpl);
    }
  }
  return hb;
}

function shouldRunSection(title) {
  if (!sectionPattern) return true;
  return sectionPattern.test(title);
}

async function runSection(title, config, setup) {
  if (!shouldRunSection(title)) return null;

  printSectionHeader(title);

  const bench = newBench(config);
  setup(bench);
  await bench.run();
  printResults(bench);
  console.log();

  return { title, bench };
}

// ─── Main ────────────────────────────────────────────────────────────────────

async function run() {
  const now = new Date();
  const headerLabel = label ? ` [${label}]` : '';

  console.log(`Handlebars Performance Benchmark${headerLabel}`);
  console.log('================================');
  console.log(
    `tinybench | compile: warmup ${COMPILE_BENCH_CONFIG.warmupIterations}, min ${COMPILE_BENCH_CONFIG.iterations} | exec: warmup ${EXEC_BENCH_CONFIG.warmupIterations}, min ${EXEC_BENCH_CONFIG.iterations} | time: ${EXEC_BENCH_CONFIG.time}ms per bench`
  );
  console.log(`Node ${process.version} | ${process.platform} ${process.arch}`);
  console.log();

  const allSections = [];

  if (sectionPattern) {
    console.log(`Filtering sections: /${sectionPattern.source}/i`);
    console.log();
  }

  // ─── COMPILATION ────────────────────────────────────────────────────────────

  allSections.push(
    await runSection(
      'COMPILATION (Handlebars.compile + first render)',
      COMPILE_BENCH_CONFIG,
      (bench) => {
        for (const [name, def] of Object.entries(templates)) {
          const hb = createEnv(def);
          // Handlebars.compile() uses lazy evaluation — actual compilation
          // (parsing, codegen, new Function()) only happens on first invocation.
          bench.add(`compile: ${name}`, () => {
            hb.compile(def.template)({});
          });
        }
      }
    )
  );

  // ─── EXECUTION + output verification ────────────────────────────────────────

  const expectedOutputs = {};

  const execResult = await runSection(
    'EXECUTION (template rendering)',
    EXEC_BENCH_CONFIG,
    (bench) => {
      for (const [name, def] of Object.entries(templates)) {
        const compiled = createEnv(def).compile(def.template);
        expectedOutputs[name] = compiled(def.context);
        bench.add(`exec: ${name}`, () => {
          compiled(def.context);
        });
      }
    }
  );
  allSections.push(execResult);

  // Verify outputs haven't changed during benchmarking
  if (execResult) {
    let verifyFails = 0;
    for (const [name, def] of Object.entries(templates)) {
      const compiled = createEnv(def).compile(def.template);
      const actual = compiled(def.context);
      if (actual !== expectedOutputs[name]) {
        console.warn(
          `  WARNING: output mismatch for "${name}"\n    expected: ${JSON.stringify(expectedOutputs[name])}\n    actual:   ${JSON.stringify(actual)}`
        );
        verifyFails++;
      }
    }
    if (verifyFails === 0) {
      console.log('Output verification: all templates OK');
    } else {
      console.warn(`Output verification: ${verifyFails} mismatch(es)`);
    }
    console.log();
  }

  // ─── PRECOMPILATION ─────────────────────────────────────────────────────────

  allSections.push(
    await runSection(
      'PRECOMPILATION (Handlebars.precompile)',
      COMPILE_BENCH_CONFIG,
      (bench) => {
        for (const [name, def] of Object.entries(templates)) {
          bench.add(`precompile: ${name}`, () => {
            Handlebars.precompile(def.template);
          });
        }
      }
    )
  );

  // ─── END-TO-END ─────────────────────────────────────────────────────────────

  allSections.push(
    await runSection(
      'END-TO-END (compile + render)',
      COMPILE_BENCH_CONFIG,
      (bench) => {
        for (const [name, def] of Object.entries(templates)) {
          const hb = createEnv(def);
          bench.add(`e2e: ${name}`, () => {
            const fn = hb.compile(def.template);
            fn(def.context);
          });
        }
      }
    )
  );

  // ─── COMPILE OPTIONS ───────────────────────────────────────────────────────

  allSections.push(
    await runSection(
      'COMPILE OPTIONS COMPARISON',
      EXEC_BENCH_CONFIG,
      (bench) => {
        const src = allTemplates['complex (if/each/helpers)'].template;
        const ctx = allTemplates['complex (if/each/helpers)'].context;

        const defaultFn = Handlebars.compile(src);
        bench.add('exec: default options', () => defaultFn(ctx));

        const noEscapeFn = Handlebars.compile(src, { noEscape: true });
        bench.add('exec: noEscape=true', () => noEscapeFn(ctx));

        const strictFn = Handlebars.compile(src, {
          strict: true,
          assumeObjects: true,
        });
        bench.add('exec: strict + assumeObjects', () => strictFn(ctx));

        const knownFn = Handlebars.compile(src, {
          knownHelpers: { if: true, each: true },
          knownHelpersOnly: false,
        });
        bench.add('exec: knownHelpers', () => knownFn(ctx));

        const compatFn = Handlebars.compile(src, { compat: true });
        bench.add('exec: compat=true', () => compatFn(ctx));

        const noDataFn = Handlebars.compile(src, { data: false });
        bench.add('exec: data=false', () => noDataFn(ctx));
      }
    )
  );

  const filepath = saveMarkdownReport(allSections.filter(Boolean), {
    label,
    compileConfig: COMPILE_BENCH_CONFIG,
    execConfig: EXEC_BENCH_CONFIG,
    date: now,
  });
  console.log(`Results saved to: ${filepath}`);
}

run().catch((err) => {
  console.error(err);
  process.exit(1);
});