fix(builtin): always hide bazel files in yarn_install & npm install---

---if @bazel/hide-bazel-files is detected.

Fixes a @bazel/hide-bazel-files bug when adding an npm package with a bazel BUILD files after the initial node_modules install. In this case @bazel/hide-bazel-files postinstall does not run so it does not hide the newly added BUILD files. The repo rules, however, will run before the next build as the package.json & lock files will have changed so we can hide the bazel BUILD files at that point and avoid any build failures.

internal/npm_install/generate_build_file.js

@@ -127,11 +127,21 @@ function flattenDependencies(pkgs) {
  * Handles Bazel files in npm distributions.
  */
 function hideBazelFiles(pkg) {
+  const hasHideBazelFiles = isDirectory('node_modules/@bazel/hide-bazel-files');
   pkg._files = pkg._files.map(file => {
     const basename = path.basename(file);
     const basenameUc = basename.toUpperCase();
     if (basenameUc === 'BUILD' || basenameUc === 'BUILD.BAZEL') {
-      if (ERROR_ON_BAZEL_FILES) {
+      // If bazel files are detected and there is no @bazel/hide-bazel-files npm
+      // package then error out and suggest adding the package. It is possible to
+      // have bazel BUILD files with the package installed as it's postinstall
+      // step, which hides bazel BUILD files, only runs when the @bazel/hide-bazel-files
+      // is installed and not when new packages are added (via `yarn add`
+      // for example) after the initial install. In this case, however, the repo rule
+      // will re-run as the package.json && lock file has changed so we just
+      // hide the added BUILD files during the repo rule run here since @bazel/hide-bazel-files
+      // was not run.
+      if (!hasHideBazelFiles && ERROR_ON_BAZEL_FILES) {
         console.error(`npm package '${pkg._dir}' from @${WORKSPACE} ${RULE_TYPE} rule
 has a Bazel BUILD file '${file}'. Use the @bazel/hide-bazel-files utility to hide these files.
 See https://github.com/bazelbuild/rules_nodejs/blob/master/packages/hide-bazel-files/README.md
@@ -446,6 +456,7 @@ function findPackages(p = 'node_modules') {
                        .filter(f => !f.startsWith('.'))
                        .map(f => path.posix.join(p, f))
                        .filter(f => isDirectory(f));
+
   packages.forEach(
       f => pkgs.push(parsePackage(f), ...findPackages(path.posix.join(f, 'node_modules'))));