Formatting the compiler tree

Dec. 23, 2019 · Mark Rousskov on behalf of the compiler team

What happened

We recently landed two PRs which together reformatted essentially all code in the compiler tree.

The first one, #65939, contained the initial formatting infrastructure. We currently use rustfmt directly, pinned to a version specified in src/stage0.txt. We expect to update it as needed, and otherwise once per cycle (coinciding with the bootstrap bump, most likely).

The second one which reformatted the majority of the codebase is #67540.

This change landed with the following rustfmt config. Note that this configuration is subject to change (in particular, merge_derives may be removed in the future), but should be fairly stable. Your editor should automatically pick this configuration up inside the rust-lang/rust repository (it is located in the rustfmt.toml file in the root).

version = "Two"
use_small_heuristics = "Max"
merge_derives = false

How to use formatting

You can reformat the repository with fmt and fmt --check to verify formatting; these commands are unfortunately somewhat slow today. Tidy will also currently run the latter of these two checks ( fmt --check) internally, but this may change in the future if we can't improve the speed of formatting the entire codebase.

Resolving conflicts

If you have an ongoing branch, you're likely to have merge conflicts. The following should help you resolve them:


set -xeo pipefail

if [ "$1" = "from-rebase" ] ; then
	git rev-parse HEAD > /tmp/commit
	git rev-parse HEAD >> /tmp/old.shas
	./ fmt
	git commit -a --amend --no-edit
	git rev-parse HEAD >> /tmp/new.shas
	git reset --hard $(cat /tmp/commit)
	rm -f /tmp/old.shas /tmp/commit /tmp/new.shas
	git rebase 8eb7c58dbb7 --exec '../ from-rebase'
	branch=$(git rev-parse --abbrev-ref HEAD) # get branch name
	git reset --hard 8eb7c58dbb7
	for sha in $(cat /tmp/new.shas); do
		git cherry-pick $sha -Xtheirs
  # put yourself atop the format the world PR
  git rebase -Xtheirs a916ac22b9f7f1f0f7aba0a41a789b3ecd765018

This script should be saved to in the parent directory of your Rust checkout, and then run git fetch upstream && ../ upstream should be the name of the rust-lang/rust remote.

Once the script runs, you will be based on the a916ac22b9f7f commit. You likely want to then run git rebase -i upstream/master or so to finish, but the script above gets you past the formatting PR at least.

This should mostly resolve conflicts correctly, but occasionally if you've edited something in imports (a common case I've encountered) or otherwise this will not resolve quite right. Usually though this will solve 99% of the problems and the rest can be fixed up manually afterwards.