find ros packages from ament index (#746)

When in a path that has ament executed, use the ament index to obtain a list of ros definition files instead of recursively scanning the directory.

This improves the message generation speed, on my pc, i get

old find packages
```
real    0m6.069s
user    0m13.387s
sys     0m3.757s
```

using ament index
```
real    0m2.189s
user    0m13.449s
sys     0m3.722s
```

Fix #747

Author: Teo Koon Peng

rosidl_gen/packages.js

@@ -16,10 +16,13 @@
 
 const debug = require('debug')('rosidl_gen:packages');
 const fs = require('fs');
+const readline = require('readline');
 const path = require('path');
 const walk = require('walk');
 const os = require('os');
 
+const fsp = fs.promises;
+
 const generatedRoot = path.join(__dirname, '../generated/');
 
 function getPackageName(filePath, amentExecuted) {
@@ -70,6 +73,96 @@ function addInterfaceInfo(info, type, pkgMap) {
   pkg[type].push(info);
 }
 
+/**
+ * Gets all ament packages with ros messages in an ament index.
+ * @param {string} rootDir Path to the ament root directory
+ * @returns {string[]} array of package names
+ */
+async function getAmentPackages(rootDir) {
+  try {
+    const files = await fsp.readdir(
+      path.join(
+        rootDir,
+        'share',
+        'ament_index',
+        'resource_index',
+        'rosidl_interfaces'
+      )
+    );
+    return files;
+  } catch (e) {
+    if (!e.code === 'ENOENT') {
+      throw e;
+    }
+    return [];
+  }
+}
+
+/**
+ * Get paths to all rosidl resources in an ament package
+ * @param {string} packageName name of the package
+ * @param {string} amentRoot ament root directory
+ * @returns {string[]} array of rosidl ament resources in a package
+ */
+async function getPackageDefinitionsFiles(packageName, amentRoot) {
+  const rosFiles = [];
+  const rl = readline.createInterface(
+    fs.createReadStream(
+      path.join(
+        amentRoot,
+        'share',
+        'ament_index',
+        'resource_index',
+        'rosidl_interfaces',
+        packageName
+      ),
+      { emitClose: true }
+    )
+  );
+  rl.on('line', (line) => {
+    rosFiles.push(path.join(amentRoot, 'share', packageName, line));
+  });
+  await new Promise((res) => {
+    rl.on('close', res);
+  });
+  return rosFiles;
+}
+
+/**
+ * Collects all packages in a directory by using the ament index.
+ * @param {string} dir - the directory to search in
+ * @return {Promise<Map<string, object>>} A mapping from the package name to some info about it.
+ */
+async function findAmentPackagesInDirectory(dir) {
+  const pkgs = await getAmentPackages(dir);
+  const rosFiles = (
+    await Promise.all(pkgs.map((pkg) => getPackageDefinitionsFiles(pkg, dir)))
+  ).flat();
+  const pkgMap = new Map();
+  return new Promise((resolve, reject) => {
+    rosFiles.forEach((filePath) => {
+      if (path.extname(filePath) === '.msg') {
+        // Some .msg files were generated prior to 0.3.2 for .action files,
+        // which has been disabled. So these files should be ignored here.
+        if (path.dirname(dir).split(path.sep).pop() !== 'action') {
+          addInterfaceInfo(
+            grabInterfaceInfo(filePath, true),
+            'messages',
+            pkgMap
+          );
+        }
+      } else if (path.extname(filePath) === '.srv') {
+        addInterfaceInfo(grabInterfaceInfo(filePath, true), 'services', pkgMap);
+      } else if (path.extname(filePath) === '.action') {
+        addInterfaceInfo(grabInterfaceInfo(filePath, true), 'actions', pkgMap);
+      } else {
+        // we ignore all other files
+      }
+    });
+    resolve(pkgMap);
+  });
+}
+
 /**
  * Collects all packages in a directory.
  * @param {string} dir - the directory to search in
@@ -85,7 +178,10 @@ async function findPackagesInDirectory(dir) {
       if (err) {
         amentExecuted = false;
       }
-      dir = amentExecuted ? path.join(dir, 'share') : dir;
+
+      if (amentExecuted) {
+        return resolve(findAmentPackagesInDirectory(dir));
+      }
 
       let walker = walk.walk(dir, { followLinks: true });
       let pkgMap = new Map();