simplex-chat/scripts/nix/README.md

# Haskell builds with Nix

The compiler and all cross-compilers come from the haskell.nix input pinned in
`flake.lock`. The `ghc914-sh` compiler is the stable-haskell fork, not the stock
GHC 9.14 release from GHCup. Use the same source checkout and lock file for every
platform; Android ARMv7 does not require a separate branch or tag.

`compiler-selection.nix` and `compiler-cache-overlay.nix` match Hydra's compiler
build context, including auxiliary iserv projects, so the pinned compiler can use
its existing cache. Application dependencies keep the project's current packages.

Run these commands from the repository root:

```sh
make help
make nix-list                  # list this host's existing Hydra outputs
make nix-native                # native library and CLI
make nix-android               # ARM64 + ARMv7 libraries, on x86_64-linux
make nix-windows               # Windows library and CLI, on x86_64-linux
make nix-linux-static          # x86_64, i686, and ARM64 static Linux CLIs
make nix-build                 # all existing outputs for this build host
```

Each command builds this checkout, without cloning another branch. Output links
are placed under `result-nix/<build-system>/<package>`. ZIP filenames inside the
outputs retain the existing Hydra names. For example, the ARMv7 client library is
`result-nix/x86_64-linux/armv7a-android:lib:simplex-chat/pkg-armv7a-android-libsimplex.zip`.
Nix includes tracked working-tree changes; add new source files to Git before
building so they are included.

For a remote builder, select its build system explicitly. Nix must already have
that builder configured:

```sh
make nix-ios NIX_SYSTEM=aarch64-darwin
make nix-darwin-libs NIX_SYSTEM=x86_64-darwin
make nix-build NIX_SYSTEM=aarch64-linux
```

`nix-ios` produces the Haskell static-library ZIP. It does not run Xcode, sign an
iOS application, or upload to TestFlight. ARM64 device libraries and Intel
simulator libraries retain their separate outputs. The existing iOS preparation
scripts retag ARM64 archives with `mac2ios -s` when an Apple Silicon simulator is
needed.

The Cabal v2 builder stores ordinary package archives in its staged store.
`link-mobile-library.sh` relinks the selected package and its dependencies before
that store is pruned. iOS ZIPs contain both the plain `libHSsimplex-chat-*.a` and
the rolled `libHSsimplex-chat-*-ghc*.a` used by `update-pbxproj.sh`. Android and
Windows clients link the threaded RTS into `libsimplex.so` or `libsimplex.dll`;
Android's separate `libsupport.so` resolves RTS symbols from the client library.
ARM64 Android libraries retain the 16 KiB linker alignment. These steps run in
the derivation's build/install phases because v2 component overrides do not run
the older `postBuild` and `postInstall` hooks.

Mobile builds keep the RTS's small-address-space setting. On Darwin, the final
link uses ABI-checked replacement RTS registrations, plus a replacement `text`
on ARM64. These boot libraries and all ARM64 mobile app C/C++ code target the
Apple A7 instruction baseline before `mac2ios` retags the archives. The cached
native compiler itself stays unchanged. Android applies the RTS source patch
when building its boot libraries.

`NIX_ARGS` passes additional options to `nix build`, and `NIX_OUT_DIR` changes the
output-link directory. Each derivation has a two-hour timeout by default; set
`NIX_BUILD_TIMEOUT` in seconds to change it. For a wall-clock limit on a local
batch, use `timeout` from GNU coreutils to include environment setup in the limit:

```sh
timeout 6h nix develop -c make nix-build
make nix-native NIX_ARGS=--dry-run
```

`.github/workflows/nix.yml` runs these same outputs on Linux ARM64/x86_64 and
Darwin ARM64/x86_64, with a six-hour job limit. It uploads the existing library ZIPs
and CLIs under an artifact named for the source SHA. Each native CLI also runs
the encrypted-store and profile-password smoke test, which can be repeated with
`python3 scripts/nix/smoke-cli.py result-nix/BUILD_SYSTEM/exe:simplex-chat/bin/simplex-chat`.
Hydra continues to consume
the same `hydraJobs` attributes. The older application release workflow still
uses its existing GHCup/Docker compiler settings; migrating that packaging and
release path is separate from this Nix build lane.

Hydra needs builders advertising `aarch64-darwin` and `x86_64-darwin` to run the
corresponding Mac/iOS jobs. Check its [builder pool](https://ci.zw3rk.com/machines)
when jobs remain queued. For cross builds, the pinned haskell.nix also uses
`recursive-nix` as a scheduling marker for slices that require a real x86_64
Linux host. Advertise that feature on a native x86_64 Linux builder; keep it off
x86_64 Linux slots running through Rosetta on Apple Silicon. The GitHub workflow
sets it only for its native x86_64 Linux runner.

To build both Android APK ABIs from the current checkout, preserving the same
compiler and source, use the existing builder's source/skip-checkout flags:

```sh
scripts/android/build-android.sh -sg VERSION_CODE
```

This command also needs the Android SDK, Gradle, and its other existing tools.
The APK reproduction script now checks out the supplied tag for both ABIs.
Historical releases that used a separate `-armv7a` tag must be reproduced with
their historical build scripts.

## Migration validation

On 2026-10-15, all 21 existing Hydra derivations evaluated successfully at
`c72da15836d9b154532db29eb5013c3b8fb37a14`: 11 on x86_64 Linux, two on ARM64 Linux,
and four on each Darwin architecture. This includes both Android ABIs, Windows,
and all three static Linux targets.

The native ARM64 Darwin library and CLI compiled with the pinned compiler using
Cabal. Encrypted-store/profile-password, BBS, and native mobile C API smoke checks
passed. The replacement RTS and `text` also built with Nix and passed ABI,
instruction-baseline, UTF-8, and GC checks. These checks do not establish that all
21 final Nix artifacts build: that artifact matrix is still unverified. Android
device tests and an Xcode application build remain unverified too.

## Updating package hashes

1. Install `nix`, `gawk` and `jq`.

2. Start nix-shell from repo root:

```sh
nix-shell -p nix-prefetch-git
```

3. Run in nix shell:

```sh
gawk -f ./scripts/nix/update-sha256.awk cabal.project > ./scripts/nix/sha256map.nix
```