Description
There is noticeable lag when trying to autocomplete string types on thy fly with company-mode. Taking the example from the guessing game in the rust book
extern crate rand;
use std::io;
use std::cmp::Ordering;
use rand::Rng;
fn main() {
println!("Guess the number!");
let secret_number = rand::thread_rng().gen_range(1, 101);
println!("The secret number is: {}", secret_number);
println!("Please input your guess.");
let mut guess = String::new();
io::stdin().read_line(&mut guess)
.expect("Failed to read line");
println!("You guessed: {}", guess);
match guess.cmp(&secret_number) {
Ordering::Less => println!("Too small!"),
Ordering::Greater => println!("Too big!"),
Ordering::Equal => println!("You win!"),
}
}
When typing out the match guess.cmp ... line, Emacs noticeably stalls as soon as it tries to do completion at point, i.e. when I pause at match guess. and then subsequently after every letter I type.
At first I thought that something isn't playing well with company-mode, which did turn out to be the case, but that also turned out not to be the bottleneck. Having played around with it a bit further, I think the slow down is due to Emacs making a synchronous call to racer with every keystroke and in this case the racer command doesn't return fast enough to allow for smooth typing.
i) Is there some known configuration I can use to avoid this problem?
My current configuration for company, and racer is as follows:
(use-package company
:init
(add-hook 'after-init-hook 'global-company-mode)
:config
;; For this to correctly complete headers, need to add all include paths to
;; `company-c-headers-path-system'.
(add-to-list 'company-backends 'company-c-headers)
(setq company-backends (delete 'company-clang company-backends)))
(use-package rust-mode
:defer t)
;; This requires some additional setup as the racer binary must be installed
;; and the Rust libstd sources must be installed.
;; $ rustup component add rust-src
;; $ cargo install racer
(use-package racer
:init
(add-hook 'rust-mode-hook #'racer-mode)
(add-hook 'racer-mode-hook #'eldoc-mode)
:config
(setq-default
racer-rust-src-path
"~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/")
(require 'rust-mode)
(define-key rust-mode-map (kbd "TAB") #'company-indent-or-complete-common)
(setq company-tooltip-align-annotations t))
ii) If not, is this a known limitation? If so, are there any ideas how it can be fixed? Recently, I finally learned Elisp properly and have been hacking away at my config so I'm happy to help out myself, I just want to make sure I'm not going to be foolishly trying something that simply won't work. I don't think Emacs-racer currently does any caching and the calls are synchronous so those are two areas of improvement I can think of the top of my head with the latter perhaps being more attractive seeing as it could follow the example set by emacs-clang-complete-async.