Higher level emacs functions as optimized tramp operations

Normally a tramp handler only contains implementations of the emacs primitive file operations. Implementing this set of operations allows emacs to do anything on a remote host, but many of the common functions in the emacs standard library will trigger multiple file operations for a single call. This can cause performance issues, because each file operation involves a roundtrip to the remote host.

This module implements some of those operations as single round trip tramp operations. The bulk of the operation is implemented as a server side bash script, rather than an elisp function. In practice this makes a lot of day to day editing on remote hosts much more responsive.

Install from GNU ELPA:

M-x package-install <RET> tramp-hlo
M-x tramp-hlo-setup

(use-package tramp-hlo
    :ensure t
    :config
    (tramp-hlo-setup)
)

• Enable: M-x tramp-hlo-setup or add (tramp-hlo-setup) to init.el.
• Disable: M-x tramp-hlo-remove or add (tramp-hlo-remove) to init.el

A first set of operations were targetted that perform poorly over tramp due to roundtrips, andhave a large impact on day to day use,

The emacs builtin function locate-dominating-file doesn't have a tramp specific implementation, relying on regular directory traversal and test functions. This can result in 10s of round-trips per-call, depending on the depth of the path searched and the dominating file name searched for. Rewriting this as a server-side script reduces this to a single round-trip. This greatly speeds up packages like vc which repeatedly look for repository root files.

The function dir-locals-find-file not only makes use of locate-dominating-file, but uses it with a predicate that performs tramp operations of its own. Encapsulating the logic to use one large server side script also reduces 10s of round-trips to just two.

A suite of tests is included using ERT, in addition to using it in my day to day workflow. If you are using it in an environment I haven't tested and find an issue, feel free to report issues on github.