dogfooding fixes: astryx theme build --watch

.changeset/theme-build-watch.md

@@ -0,0 +1,5 @@
+---
+'@astryxdesign/cli': patch
+---
+
+[feat] `astryx theme build --watch`: rebuild a theme automatically whenever the source file changes, until interrupted with Ctrl-C. Removes the manual re-run step (and the stale-CSS confusion that comes with forgetting it) from the theme-authoring loop. Each rebuild runs in a child process so a build error is contained and the watcher keeps running. Not supported with `--json`. (#3375)

packages/cli/src/commands/build-theme.mjs

@@ -15,6 +15,7 @@
 import * as fs from 'node:fs';
 import * as path from 'node:path';
 import {pathToFileURL, fileURLToPath} from 'node:url';
+import {spawn} from 'node:child_process';
 import {createJiti} from 'jiti';
 import {getRunPrefix} from '../utils/package-manager.mjs';
 import {
@@ -597,6 +598,104 @@ function validatePrivateVars(themeDef) {
   return errors;
 }
 
+/**
+ * Path to this CLI's real entry (bin/astryx.mjs), resolved from this module's
+ * location (src/commands/build-theme.mjs → ../../bin/astryx.mjs). Used to
+ * re-invoke `theme build` as a child process in watch mode.
+ */
+function resolveCliBin() {
+  const commandsDir = path.dirname(fileURLToPath(import.meta.url));
+  return path.resolve(commandsDir, '../../bin/astryx.mjs');
+}
+
+/**
+ * Run a single `theme build` as a child process, reusing the exact
+ * single-build code path (and its error handling) rather than duplicating it.
+ * Resolves with the child's exit code; never rejects.
+ *
+ * @param {string} file - The theme file argument, as the user passed it.
+ * @param {object} options - Parsed command options (only `out` is forwarded).
+ * @returns {Promise<number>}
+ */
+function runThemeBuildOnceChild(file, options) {
+  const cliBin = resolveCliBin();
+  const args = [cliBin, 'theme', 'build', file];
+  if (options.out) args.push('--out', options.out);
+  return new Promise(resolve => {
+    const child = spawn(process.execPath, args, {
+      stdio: 'inherit',
+      env: process.env,
+    });
+    child.on('close', code => resolve(code ?? 0));
+    child.on('error', () => resolve(1));
+  });
+}
+
+/**
+ * Watch a theme file and rebuild on change. Runs an initial build, then
+ * rebuilds (debounced) whenever the file changes, until interrupted with
+ * Ctrl-C. Each rebuild runs in a child process so a build error (which the
+ * single-build path reports via a hard exit) is contained and the watcher
+ * keeps running.
+ *
+ * @param {string} file - The theme file argument, as the user passed it.
+ * @param {string} filePath - Absolute path to the theme file.
+ * @param {object} options - Parsed command options.
+ * @returns {Promise<void>} Resolves when the watcher is stopped (Ctrl-C).
+ */
+async function runThemeBuildWatch(file, filePath, options) {
+  const rel = path.relative(process.cwd(), filePath);
+
+  // Initial build.
+  await runThemeBuildOnceChild(file, options);
+
+  humanLog(`\n👀 Watching ${rel} for changes — press Ctrl-C to stop.`);
+
+  let building = false;
+  let queued = false;
+  let debounce = null;
+
+  const rebuild = async () => {
+    if (building) {
+      // Coalesce changes that land mid-build into a single follow-up run.
+      queued = true;
+      return;
+    }
+    building = true;
+    humanLog(`\n♻️  Change detected — rebuilding ${rel}...`);
+    await runThemeBuildOnceChild(file, options);
+    building = false;
+    humanLog(`\n👀 Watching ${rel} for changes — press Ctrl-C to stop.`);
+    if (queued) {
+      queued = false;
+      rebuild();
+    }
+  };
+
+  // Some editors replace the file (rename) rather than writing in place, which
+  // can drop the watch. Watch the containing directory and filter to our file
+  // so edits survive atomic-save/rename.
+  const watchDir = path.dirname(filePath);
+  const baseName = path.basename(filePath);
+  const watcher = fs.watch(watchDir, (_eventType, changed) => {
+    if (changed && changed !== baseName) return;
+    clearTimeout(debounce);
+    // Debounce: editors often emit several events per save.
+    debounce = setTimeout(rebuild, 100);
+  });
+
+  await new Promise(resolve => {
+    const stop = () => {
+      clearTimeout(debounce);
+      watcher.close();
+      humanLog('\nStopped watching.');
+      resolve();
+    };
+    process.once('SIGINT', stop);
+    process.once('SIGTERM', stop);
+  });
+}
+
 export function registerTheme(program) {
   const theme = program
     .command('theme')
@@ -621,6 +720,10 @@ export function registerTheme(program) {
     .command('build <file>')
     .description('Compile a defineTheme file to CSS + JS')
     .option('-o, --out <path>', 'Output CSS file path')
+    .option(
+      '-w, --watch',
+      'Rebuild automatically when the theme file changes (Ctrl-C to stop)',
+    )
     .action(async (file, options) => {
       const filePath = path.resolve(process.cwd(), file);
       const json = program.opts().json || false;
@@ -630,6 +733,20 @@ export function registerTheme(program) {
         return;
       }
 
+      // Watch mode: run an initial build, then rebuild on every change to the
+      // theme file. Watch is a human-interactive, long-running mode — it is not
+      // supported in --json (machine) mode, which expects a single envelope.
+      if (options.watch) {
+        if (json) {
+          cliError('--watch is not supported with --json', {
+            code: ERROR_CODES.ERR_THEME_INVALID,
+          });
+          return;
+        }
+        await runThemeBuildWatch(file, filePath, options);
+        return;
+      }
+
       if (!json) humanLog(`\nBuilding theme from ${path.relative(process.cwd(), filePath)}...`);
 
       // Extract theme definition

packages/cli/src/commands/build-theme.watch.test.mjs

@@ -0,0 +1,157 @@
+// Copyright (c) Meta Platforms, Inc. and affiliates.
+
+/**
+ * @file Tests for `astryx theme build --watch` (#3375).
+ *
+ * Watch mode runs an initial build, then rebuilds whenever the theme file
+ * changes, until interrupted. Each rebuild runs in a child process so a build
+ * error (reported by the single-build path via a hard exit) is contained and
+ * the watcher keeps running.
+ *
+ * Building `astryx theme build` requires a compiled @astryxdesign/core, so this
+ * suite builds core once in beforeAll (mirrors build-theme.prose.test.mjs).
+ */
+
+import {describe, it, expect, beforeAll, beforeEach, afterEach} from 'vitest';
+import {execFileSync, spawn} from 'node:child_process';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import * as os from 'node:os';
+import {fileURLToPath} from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const CLI_BIN = path.resolve(__dirname, '../../bin/astryx.mjs');
+const REPO_ROOT = path.resolve(__dirname, '../../../..');
+const CORE_THEME_ENTRY = path.join(
+  REPO_ROOT,
+  'packages/core/dist/theme/index.js',
+);
+
+function runCli(args, cwd) {
+  try {
+    const out = execFileSync('node', [CLI_BIN, ...args], {
+      cwd,
+      encoding: 'utf-8',
+      stdio: ['ignore', 'pipe', 'pipe'],
+      env: {...process.env, FORCE_COLOR: '0'},
+    });
+    return {code: 0, stdout: out, stderr: ''};
+  } catch (e) {
+    return {
+      code: e.status ?? 1,
+      stdout: e.stdout?.toString() ?? '',
+      stderr: e.stderr?.toString() ?? '',
+    };
+  }
+}
+
+/** Poll until `predicate()` is true or the timeout elapses. */
+async function waitFor(predicate, {timeout = 8000, interval = 50} = {}) {
+  const start = Date.now();
+  for (;;) {
+    if (predicate()) return true;
+    if (Date.now() - start > timeout) return false;
+    await new Promise(r => setTimeout(r, interval));
+  }
+}
+
+beforeAll(() => {
+  if (!fs.existsSync(CORE_THEME_ENTRY)) {
+    execFileSync('pnpm', ['-F', '@astryxdesign/core', 'build'], {
+      cwd: REPO_ROOT,
+      stdio: 'pipe',
+      timeout: 180_000,
+    });
+  }
+}, 200_000);
+
+let tmpDir;
+beforeEach(() => {
+  tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'astryx-build-theme-watch-'));
+});
+afterEach(() => {
+  fs.rmSync(tmpDir, {recursive: true, force: true});
+});
+
+describe('theme build --watch', () => {
+  it('advertises the flag in --help', () => {
+    const result = runCli(['theme', 'build', '--help'], process.cwd());
+    const out = result.stdout + result.stderr;
+    expect(out).toMatch(/--watch/);
+  });
+
+  it('rejects --watch together with --json (single-envelope contract)', () => {
+    const themeFile = path.join(tmpDir, 'wt.mjs');
+    fs.writeFileSync(
+      themeFile,
+      `export default { name: 'wt', tokens: { '--color-bg': '#fff' } };\n`,
+    );
+    const result = runCli(
+      ['--json', 'theme', 'build', path.relative(tmpDir, themeFile), '--watch'],
+      tmpDir,
+    );
+    expect(result.code).not.toBe(0);
+    expect(result.stdout + result.stderr).toMatch(/watch/i);
+  });
+
+  it('builds initially, rebuilds on change, and stops cleanly on SIGINT', async () => {
+    const themeFile = path.join(tmpDir, 'wt.mjs');
+    const cssFile = path.join(tmpDir, 'wt.css');
+    fs.writeFileSync(
+      themeFile,
+      `export default { name: 'wt', tokens: { '--color-bg': '#ffffff' } };\n`,
+    );
+
+    const child = spawn(
+      process.execPath,
+      [CLI_BIN, 'theme', 'build', 'wt.mjs', '--watch'],
+      {cwd: tmpDir, env: {...process.env, FORCE_COLOR: '0'}},
+    );
+    let stdout = '';
+    child.stdout.on('data', d => (stdout += d.toString()));
+    child.stderr.on('data', d => (stdout += d.toString()));
+
+    try {
+      // Initial build produces the CSS.
+      const built = await waitFor(() => fs.existsSync(cssFile));
+      expect(built).toBe(true);
+      const firstCss = fs.readFileSync(cssFile, 'utf-8');
+      expect(firstCss).toMatch(/#ffffff/);
+
+      // Wait until the watcher is actually watching before editing, so the
+      // change isn't missed.
+      await waitFor(() => /Watching/i.test(stdout));
+
+      // Change the theme — the token value changes so the CSS must change.
+      fs.writeFileSync(
+        themeFile,
+        `export default { name: 'wt', tokens: { '--color-bg': '#010203' } };\n`,
+      );
+
+      // The rebuilt CSS should reflect the new value.
+      const rebuilt = await waitFor(() => {
+        try {
+          return fs.readFileSync(cssFile, 'utf-8').includes('#010203');
+        } catch {
+          return false;
+        }
+      });
+      expect(rebuilt).toBe(true);
+      expect(stdout).toMatch(/rebuild/i);
+    } finally {
+      // SIGINT must stop the watcher and exit cleanly.
+      child.kill('SIGINT');
+    }
+
+    const exited = await new Promise(resolve => {
+      let done = false;
+      child.on('exit', () => {
+        done = true;
+        resolve(true);
+      });
+      setTimeout(() => resolve(done), 4000);
+    });
+    expect(exited).toBe(true);
+    expect(stdout).toMatch(/Stopped watching/);
+  }, 30_000);
+});