EXPERIMENT: build jujutsu with buck2

.buckconfig

@@ -0,0 +1,115 @@
+[cells]
+# 'cells' that are defined in the project. all 'jj' code should remain under
+# 'root', while 'prelude' is the prelude, and third-party is where any vendored
+# code should go.
+root = .
+mode = buck/mode
+prelude = buck/prelude
+toolchains = buck/toolchains
+third-party = buck/third-party
+none = none
+
+[external_cells]
+# use the built-in prelude that is packaged inside of the buck2 executable. at
+# any time we could vendor it, or use a 'git' cell, if we needed to apply custom
+# patches
+prelude = bundled
+
+[cell_aliases]
+# these aliases are all required by the upstream buck2 prelude, with stubs for
+# meta-specific cells. 'config//' is occasionally useful for select() calls
+config = prelude
+buck = none
+fbcode = none
+fbsource = none
+
+[buildfile]
+name = BUILD
+# for the sake of future compatibility and migrations, we don't want any BUILD
+# files in the project to use raw, un-imported symbols from the prelude like
+# 'cxx_library()'; we instead want to make sure every rule is explicitly
+# wrapped, load()ed and called, i.e. they should use 'jj.cxx_library()' instead.
+# do this by loading noprelude.bzl into every BUILD file, which will stub out
+# these bad symbols with an error message.
+includes = root//buck/shims/noprelude.bzl
+
+[buck2]
+# use sha256 since everything supports it. XXX FIXME (aseipp): blake3?
+digest_algorithms = SHA256
+
+# enable deferred materialization. this means that intermediate outputs will
+# never get written to disk, and instead will be stored in the remote cache for
+# all intermediate execution steps.
+#
+# we don' use RE yet, but keep these enabled so we don' have to change things or
+# find problems later. this also enables (local disk) sqlite materialization
+# state, and defers writes to the end of actions to help improve performance.
+materializations = deferred
+sqlite_materializer_state = true
+defer_write_actions = true
+
+# hash all commands in the action graph; this helps avoid some spurious
+# recompilations when the action graph changes, but the actual commands don't.
+# NOTE: this requires `materializations = deferred`
+hash_all_commands = true
+
+# deferred materialization requires that cache outputs never expire. if they do,
+# a command might fail if it expects a hit on an object that was supposed to be
+# an input. in that case, the buck2d daemon needs to restart to 'purge' its
+# knowledge of that object. this enables that.
+restarter = true
+
+# enable checking the peak memory in the interpreter, and also set a byte limit
+# for the interpreter. this is useful for catching runaway memory usage in BUILD
+# files just in case people start going crazy with them.
+check_starlark_peak_memory = true
+# default limit is 5MiB = 5 * 1024 * 1024 = 5242880 bytes
+default_starlark_peak_memory = 5242880
+# also, enforce a max callstack size to prevent ridiculous stack sizes and
+# put a limit on how deep/abstract things can get.
+starlark_max_callstack_size = 50
+
+[build]
+# set the default execution platform for builds on this machine. NOTE: this
+# platform definition is where remote execution (optionally) is enabled via
+# ExecutionPlatformRegistrationInfo
+execution_platforms = root//buck/platforms:default
+
+[parser]
+# set the default execution platform for several target patterns. this is
+# required; the main documentation for the format is the source code, I think...
+target_platform_detector_spec = \
+  target:root//...->root//buck/platforms:default \
+  target:third-party//...->root//buck/platforms:default \
+  target:toolchains//...->root//buck/platforms:default
+
+[project]
+# things that should not be scanned by buck2 for file changes. if you notice
+# something strange is being scanned, it might be worth adding here.
+ignore = \
+  .jj, \
+  .git, \
+  .direnv, \
+  .watchman-cookie** \
+  target
+
+[buck2_re_client]
+# default address for the cas/actioncache. this should be public for users so
+# they can always get build results. this does NOT include the 'engine_address'
+# service, which enables actual remote execution. that must be enabled
+# explicitly in .buckconfig.local
+cas_address          = https://builds.example.com
+action_cache_address = https://builds.example.com
+
+# 'instance name', which in RBE is the basic unit of isolation for projects; we
+# always default this for simplicity
+instance_name = jujutsu
+
+# always use TLS for all build products
+tls = true
+
+# in .buckconfig.local:
+#
+# [buck2_re_client]
+# engine_address = https://builds.jujutsu.dev
+# http_headers   = x-build-api-key:$BUILD_API_KEY

.github/actions/install-dotslash/action.yml

@@ -0,0 +1,30 @@
+name: Install DotSlash
+description: Install DotSlash on the current system
+inputs:
+  version:
+    description: "version of dotslash"
+    required: false
+    default: "0.4.1"
+runs:
+  using: "composite"
+  steps:
+    - name: Install DotSlash
+      shell: bash
+      run: |
+        mkdir -p $RUNNER_TEMP/dotslash
+        echo "$RUNNER_TEMP/dotslash" >> $GITHUB_PATH
+
+        if [[ "$RUNNER_OS" == "Windows" ]]; then
+          C:\\msys64\\usr\\bin\\wget.exe https://github.com/facebook/dotslash/releases/download/v0.4.1/dotslash-windows.v0.4.1.tar.gz
+          tar xf dotslash-windows.v0.4.1.tar.gz
+          mv dotslash.exe $RUNNER_TEMP/dotslash
+        else
+          if [[ "$RUNNER_OS" == "macOS" ]]; then
+            wget https://github.com/facebook/dotslash/releases/download/v0.4.1/dotslash-macos.v0.4.1.tar.gz
+            tar xf dotslash-macos.v0.4.1.tar.gz
+          elif [[ "$RUNNER_OS" == "Linux" ]]; then
+            wget https://github.com/facebook/dotslash/releases/download/v0.4.1/dotslash-ubuntu-22.04.x86_64.v0.4.1.tar.gz
+            tar xf dotslash-ubuntu-22.04.x86_64.v0.4.1.tar.gz
+          fi
+          mv dotslash $RUNNER_TEMP/dotslash
+        fi

.github/workflows/build-buck2.yml

@@ -0,0 +1,55 @@
+name: buck2
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+permissions: read-all
+
+jobs:
+  buck2:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-latest
+            abi: x86_64-unknown-linux-gnu
+          - os: windows-latest
+            abi: x86_64-pc-windows-msvc
+          - os: macos-latest
+            abi: aarch64-apple-darwin
+          # NOTE: macos-13 is the most recent x86_64 macos runner
+          #- os: macos-13
+          #  abi: x86_64-apple-darwin
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 15 # NOTE (aseipp): keep in-sync with the build.yml timeout limit
+
+    name: build with buck2
+    steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332
+      - name: (Linux) Install Mold
+        if: runner.os == 'Linux'
+        run: |
+          sudo apt-get update && sudo apt-get install -y mold
+      - name: Install DotSlash
+        uses: ./.github/actions/install-dotslash
+      - name: Add build tools to $PATH
+        run: echo "$PWD/tools/bin" >> $GITHUB_PATH
+      # FIXME (aseipp): use 'buck2' out of `$PATH` after we have dotslash .exe
+      # shim files for windows. until then just invoke manually
+      - name: buck2 build //...
+        run: |
+          mkdir -p out
+          dotslash ./tools/bin/buck2 build @mode//debug //...
+          cp buck-out/v2/log/*.pb.zst out
+          dotslash ./tools/bin/buck2 build @mode//debug cli --out out/jj.exe
+          ./out/jj.exe version
+
+      - name: "Upload artifact"
+        uses: actions/upload-artifact@65462800fd760344b1a7b4382951275a0abb4808
+        with:
+          name: jj-${{ matrix.abi }}
+          path: out
+          retention-days: 14

.github/workflows/codespell.yml

@@ -18,5 +18,5 @@ jobs:
         with:
           check_filenames: true
           check_hidden: true
-          skip: ./target,./.jj,*.lock
+          skip: ./target,./.jj,*.lock,./buck/third-party/rust/BUILD
           ignore_words_list: crate,NotIn,Wirth

.vscode/settings.json

@@ -0,0 +1,30 @@
+{
+    "files.insertFinalNewline": true,
+    "files.trimTrailingWhitespace": true,
+
+    "files.associations": {
+        ".buckconfig": "ini",
+        ".buckconfig.local": "ini",
+        "*.bzl": "starlark",
+        "*.bxl": "starlark",
+        "BUILD": "starlark",
+        "PACKAGE": "starlark",
+    },
+
+    "rust-analyzer.workspace.discoverConfig": {
+        "command": [
+            "rust-project",
+            "develop-json",
+            "--sysroot-mode=rustc",
+            "{arg}"
+        ],
+        "progressLabel": "rust-analyzer[buck2]",
+        "filesToWatch": ["BUILD", "PACKAGE"]
+    },
+
+    "rust-analyzer.check.overrideCommand": [
+        "rust-project",
+        "check",
+        "$saved_file",
+    ]
+}

Cargo.toml

@@ -16,6 +16,9 @@ documentation = "https://martinvonz.github.io/jj/"
 categories = ["version-control", "development-tools"]
 keywords = ["VCS", "DVCS", "SCM", "Git", "Mercurial"]
 
+[workspace.lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(buck_build)'] }
+
 [workspace.dependencies]
 anyhow = "1.0.89"
 assert_cmd = "2.0.8"

buck/.gitattributes

@@ -0,0 +1,2 @@
+prelude/*    linguist-generated=true merge=binary
+prelude/**/* linguist-generated=true merge=binary

buck/mode/.buckconfig

@@ -0,0 +1,5 @@
+[cells]
+mode = .
+
+[buildfile]
+name = BUILD

buck/mode/BUILD

@@ -0,0 +1,18 @@
+
+MODES = [ 'debug', 'release' ]
+
+constraint_setting(name = 'build-mode')
+
+[
+    constraint_value(
+        name = f'build-mode-{name}',
+        constraint_setting = ':build-mode'
+    ) for name in MODES
+]
+
+[
+    config_setting(
+        name = name,
+        constraint_values = [ f'mode//:build-mode-{name}' ]
+    ) for name in MODES
+]

buck/mode/PACKAGE

@@ -0,0 +1,4 @@
+
+package(
+    visibility = [ 'PUBLIC' ],
+)

buck/mode/debug

@@ -0,0 +1 @@
+--config=jj.buildmode=debug

buck/mode/local

@@ -0,0 +1 @@
+--config=buck2_re_client.default_enabled=false

buck/mode/release

@@ -0,0 +1 @@
+--config=jj.buildmode=release

buck/mode/remote

@@ -0,0 +1 @@
+--config=buck2_re_client.default_enabled=true

buck/platforms/BUILD

@@ -0,0 +1,14 @@
+load("@prelude//utils/buckconfig.bzl", "read_choice")
+load(":defs.bzl", "generate_platforms", "default_platforms")
+
+build_config = read_choice("jj", "buildmode", [
+    "debug",
+    "release",
+], "debug")
+
+default_constraints = [
+    # build mode: debug or release
+    ('mode//:{}'.format(build_config))
+]
+
+generate_platforms(default_platforms, default_constraints)