chore: speedup `npm install` from a github checkout (#1545)

Many of us are running a watchdog in the background that
keeps `//lib` folder up-to-date, so there's no need to re-build
Playwright from source on every `npm install` command.

This patch does a crude timestatmp comparison between typescript
files and their javascript counterparts. If some files are missing in
`//lib`, or if some `//src` files are newer than `//lib`, then
it re-builds the Playwright.

This cuts off 10 seconds for me on in case I have a watchdog in the
background.

install-from-github.js

@@ -15,27 +15,57 @@
  * limitations under the License.
  */
 
- // This file is only run when someone installs via the github repo
+// This file is only run when someone installs via the github repo
 
 const {execSync} = require('child_process');
-
-try {
-  console.log('Building playwright...');
-  execSync('npm run build', {
-    stdio: 'ignore'
-  });
-} catch (e) {
-}
-
 const path = require('path');
 const fs = require('fs');
 const util = require('util');
 const rmAsync = util.promisify(require('rimraf'));
 const existsAsync = path => fs.promises.access(path).then(() => true, e => false);
-const {downloadBrowserWithProgressBar, localDownloadOptions} = require('./download-browser');
-const protocolGenerator = require('./utils/protocol-types-generator');
 
-(async function() {
+(async () => {
+  const SRC_FOLDER = path.join(__dirname, 'src');
+  const LIB_FOLDER = path.join(__dirname, 'lib');
+  const srcTypeScriptFiles = (await listFiles(path.join(__dirname, 'src'))).filter(filepath => filepath.toLowerCase().endsWith('.ts'));
+  const outdatedFiles = await Promise.all(srcTypeScriptFiles.map(async srcFile => {
+    const libFileTS = path.join(LIB_FOLDER, path.relative(SRC_FOLDER, srcFile));
+    const libFile = libFileTS.substring(0, libFileTS.lastIndexOf('.')) + '.js';
+    try {
+      const [srcStat, libStat] = await Promise.all([fs.promises.stat(srcFile), fs.promises.stat(libFile)]);
+      return srcStat.ctimeMs > libStat.ctimeMs;
+    } catch (e) {
+      // Either `.ts` of `.js` file is missing - rebuild is required.
+      return true;
+    }
+  }));
+  if (outdatedFiles.some(Boolean)) {
+    console.log(`Rebuilding playwright...`);
+    try {
+      execSync('npm run build', {
+        stdio: 'ignore'
+      });
+    } catch (e) {
+    }
+  }
+  await downloadAllBrowsersAndGenerateProtocolTypes();
+})();
+
+async function listFiles(dirpath) {
+  const files = [];
+  await dfs(dirpath);
+  return files;
+
+  async function dfs(dirpath) {
+    const entries = await fs.promises.readdir(dirpath, {withFileTypes: true});
+    files.push(...entries.filter(entry => entry.isFile()).map(entry => path.join(dirpath, entry.name)));
+    await Promise.all(entries.filter(entry => entry.isDirectory()).map(entry => dfs(path.join(dirpath, entry.name))));
+  }
+}
+
+async function downloadAllBrowsersAndGenerateProtocolTypes() {
+  const {downloadBrowserWithProgressBar, localDownloadOptions} = require('./download-browser');
+  const protocolGenerator = require('./utils/protocol-types-generator');
   const chromiumOptions = localDownloadOptions('chromium');
   const firefoxOptions = localDownloadOptions('firefox');
   const webkitOptions = localDownloadOptions('webkit');
@@ -72,4 +102,4 @@ const protocolGenerator = require('./utils/protocol-types-generator');
   async function readdirAsync(dirpath) {
     return fs.promises.readdir(dirpath).then(dirs => dirs.map(dir => path.join(dirpath, dir)));
   }
-})();
+}