Emit new events beforeAction and beforeExec

index.js

@@ -289,6 +289,37 @@ class Command extends EventEmitter {
     return this;
   };
 
+  /**
+   * Emit a general event and a sub-event to this command and all of its
+   * parents in the command hierarchy, proceeding bottom-up. The number of
+   * events emitted at each level increases by one so that a given command
+   * can select for events on any of its sub-command trees. Probably overkill,
+   * but given that the depth is usually one it doesn't seem harmful.
+   */
+  _emitToTree(eventName, args) {
+    let val = {
+      command: this,
+      name: this.name(),
+      cmdPath: this.name(), // initially
+      execArg: args.execArg,
+      args: args.args
+    };
+
+    let cmd;
+
+    for (cmd = this; cmd; cmd = cmd.parent) {
+      cmd.emit(eventName, val);
+
+      if (cmd.parent) {
+        const newCmdPath = cmd.parent.name() + '.' + val.cmdPath;
+
+        // Use spread to make a new emitted value, because the event structure
+        // is supposed to be read-only.
+        val = { ...val, cmdPath: newCmdPath };
+      }
+    }
+  }
+
   /**
    * @return {boolean}
    * @api private
@@ -858,14 +889,17 @@ class Command extends EventEmitter {
         // add executable arguments to spawn
         args = incrementNodeInspectorPort(process.execArgv).concat(args);
 
+        this._emitToTree('preSpawn', { execArg: process.argv[0], args: args });
         proc = spawn(process.argv[0], args, { stdio: 'inherit' });
       } else {
+        this._emitToTree('preSpawn', { execArg: bin, args: args });
         proc = spawn(bin, args, { stdio: 'inherit' });
       }
     } else {
       args.unshift(bin);
       // add executable arguments to spawn
       args = incrementNodeInspectorPort(process.execArgv).concat(args);
+      this._emitToTree('preSpawn', { execArg: process.execPath, args: args });
       proc = spawn(process.execPath, args, { stdio: 'inherit' });
     }
 
@@ -972,7 +1006,9 @@ class Command extends EventEmitter {
           }
         });
 
+        this._emitToTree('preAction', { execArg: this.name(), args: args });
         this._actionHandler(args);
+        this._emitToTree('postAction', { execArg: this.name(), args: args });
         this.emit('command:' + this.name(), operands, unknown);
       } else if (operands.length) {
         if (this._findCommand('*')) {