Using VSCode remote containers¶
We recommend using VSCode Remote Containers to reproduce the very same dev environment used by our core team members. The steps to set up the dev environment are:
Do a local clone of the asterius repo
Install VSCode (at least
1.45) and its remote extension
podman, and make sure the
podmancommand works with the current user
Set up a
dockersymlink which points to
podman, according to VSCode announcement of
docker pull terrorjack/asterius:dev
Open the asterius repo with remote containers
Opening the repo with remote containers for the first time will take some time,
since it runs the build script to build
asterius and perform booting. Later
re-opening will be near instant, since it reuses the previous container.
The dev image shall work with
docker too if the
settings are correctly set up. Check the documentation section for
relevant explanation; when using
docker with default settings, there is a file
permission issue when mounting your local filesystem into the prebuilt container
direnv is enabled, the
PATH of the current shell session will be extended
to include the locations of Asterius executables. This means it’s possible to
ahc-link .. instead of
stack exec ahc-link -- ...
A known-to-work workflow of hacking Asterius is using
ghcid. We also include
.ghcid file, so running
ghcid at the project root directory shall
work out of the box.
Some notes regarding the usage of
Multiple lib targets can be loaded at once, but only one main target (exe/test) can be loaded. When hacking a specific exe/test, modify the local
utils/ghcid.shscript first. Before committing changes in the Haskell codebase, it would be nice to run
stack build --test --no-run-teststo make sure all executables are not broken by lib changes.
To boot or not to boot¶
As described in the building guide,
stack build only builds the Asterius
compiler itself; additionally we need to run
stack exec ahc-boot to run the
compiler on the boot libs. This process is typically only needed once, but there
are cases when it needs to be re-run:
The boot libs in
Asterius.Typesmodule is modified, so the IR types have changed.
Asterius.CodeGenmodule is modified and you’re sure different code will be generated when compiling the same Haskell/Cmm files.
Most other modifications in the Asterius lib/exes won’t need a reboot. Specifically:
Asterius.Builtinsmodifications don’t impact the boot cache. The builtin module is generated on the fly with every linker invocation.
When rebooting, run
utils/reboot.sh in the project root directory, so that we
can ensure the booting is used with the up-to-date version of
asterius and the
boot lib sources.
ahc-boot process is configurable via these environment variables:
Doing profiled builds¶
Doing profiled builds within a local git tree¶
stack-profile.yaml to overwrite
stack.yaml, and then run
utils/reboot.sh to kick off the rebooting process. This will be quite slow due
to the nature of profiled builds; all libraries will be rebuilt with the
profiled flavor. Better to perform a profiled build in a standalone git tree.
Once the profiled build is complete, it’s possible to use RTS flags to obtain profile data when compiling Haskell sources. At runtime there are two ways to pass RTS flags to a Haskell executable:
+RTS ... -RTScommand line arguments
GHCRTS when running programs like
ahc-link, since those programs
can spawn other processes (e.g.
ahc-ld), and we’re often interested in the
profile data of all Asterius executables. The
GHCRTS environment variable can
propagate to all processes.
See the relevant
in the GHC user guide for more information on profiling Haskell apps. There are
also some third party applications useful for analyzing the profiling data, e.g.
Fow now, a major problem with the profiled build is: it seems to emit dysfunctional code which doesn’t work. Consequently, this affects the TH runner, so any dependencies relying on TH isn’t supported by the profiled build.
Measuring time/allocation differences¶
When working on a performance-related PR, we often want to measure the time/allocation differences it introduced. The workflow is roughly:
Perform two profiled builds with Docker; one builds from the
masterbranch, one from the PR’s branch.
ahc-linkin the built images on the example program below, setting the necessary
GHCRTSto generate the profile reports. The code should be put in two standalone directories, otherwise the
.ofiles may conflict or be accidentally reused.
The profiled Docker images contain pre-compiled
Cabal. And the example program
we use to stress-test the linker is:
import Distribution.Simple main = defaultMain
We choose this program since it’s classic, and although being short, it pulls in a lot of data segments and functions, so it exposes the linker’s performance bottleneck pretty well.
Adding a test case¶
To add a test case, it is best to replicate what has been done for an existing testcase.
git grep bytearrayminishould show all the places where the test case
bytearrayminihas been used. Replicating the same files for a new test case should “just work”.
In Asterius we use
ormolu for formatting
Though not all parts of the codebase are currently formatted this way, it is
recommended that when you submit a PR you run the respective formatters on the
changed parts of the code, so that gradually the whole codebase is formatted
This section is for Tweagers only.
First, set up your
build01 account according to the
Don’t forget to add the
groups = ["docker"] line in your PR.
Once the PR is merged, you can SSH into a NixOS non-privileged user. You can
check out the
asterius repo, set up your favorite text editor, make edits and
push to the remote.
To build/boot and run tests, a dev container needs to be built first. The
dev.rootless.Dockerfile can be used to build an image which has the same UID
with your user and doesn’t mess up local file permissions:
$ docker build --build-arg UID=$(id -u) --file dev.rootless.Dockerfile --tag my_dev_image .
Building the image can take around 10min.
my_dev_image is built, a dev container can be started:
$ docker run -it -v $(pwd):/asterius -w /asterius --name my_dev_container my_dev_image
The command above will start
my_dev_image, mount the
current project directory to
/asterius and drop into the bash prompt, from
where you can run build commands.
exiting the current bash prompt of
my_dev_container, it can be restarted later:
$ docker start -ai my_dev_container
If you’re using VSCode remote SSH, the first attempt to set up will fail. A known to work workaround is available at https://github.com/microsoft/vscode-remote-release/issues/648#issuecomment-503148523.