Updated: Comment #N
Throughout this cycle we've been working to replace uses of path with route_name to make hot-swapping paths a snap.
The signature of hook_help() is still:
The $path argument is used as follows:
a) The special path "admin/help#modulename" is passed in to retrieve the module overview page accessible from admin/help. This version is invoked from a number of places.
b) Other paths are passed in, when a given page is being rendered/built, to see if a module has any help to add to the top of the page. This version is invoked from SystemHelpBlock::getActiveHelp(). However, it does not work in D8 for pages whose paths contain wildcards, such as:
For case (b), we should definitely be using routes and not paths.
Replace $path and $arg with $request and $route_name in the parameters.
User interface changes
None, except hopefully pages whose help is currently broken will get their help back.
The signature of hook_help() changes
PASSED: [[SimpleTest]]: [PHP 5.4 MySQL] 70,490 pass(es).
PASSED: [[SimpleTest]]: [PHP 5.4 MySQL] 70,389 pass(es).
PASSED: [[SimpleTest]]: [PHP 5.4 MySQL] 70,430 pass(es).