.github, config: use Zig to cross-compile arm64 Linux asset (#460)

Add a script to install Zig, and add a job to the build workflow that
uses `zig cc` to cross compile configlet for arm64 (AKA aarch64) Linux.

This means that the next configlet release will have two new release
assets:

    configlet_4.0.0-beta.14_linux_arm64.tar.gz
    configlet_4.0.0-beta.14_linux_arm64.tar.gz.minisig

and extracting the archive will yield the executable:

    $ file ./configlet
    ./configlet: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, stripped

Also support running `nimble build -d:zig` locally.

For now, the new executable has a large comment section:

    $ readelf -p .comment ./configlet

    String dump of section '.comment':
      [     0]  clang version 16.0.6 (https://github.com/ziglang/zig-bootstrap 1dda86241204c4649f668d46b6a37feed707c7b4)
      [...] (repeat for 39 KiB)
      [  8d82]  clang version 16.0.6 (https://github.com/ziglang/zig-bootstrap 1dda86241204c4649f668d46b6a37feed707c7b4)
      [  8deb]  Linker: LLD 16.0.6

Try to strip it later. Our `strip` doesn't support elf64-aarch64 as a
target, and `zig objcopy` doesn't have a `-R, --remove-section` option
currently. But prepare to use `llvm-strip`.

Cross-compiling for arm64 macos currently produces an error:

    CC: ../nimdir/lib/std/sysrand.nim
    /home/runner/.cache/nim/configlet_r/@m..@snimdir@slib@sstd@ssysrand.nim.c:9:10:
    fatal error: 'Security/SecRandom.h' file not found

which is due to a recent commit [1].

See some posts on cross-compiling with Zig [2][3][4] and the support table [5].

Refs: #24
Refs: #122
Refs: #764

[1] 53a75a2 ("nimble, uuid: generate UUIDs via std/sysrand, not pragmagic/uuids", 2023-08-07)
[2] https://ziglang.org/learn/overview/#cross-compiling-is-a-first-class-use-case
[3] https://andrewkelley.me/post/zig-cc-powerful-drop-in-replacement-gcc-clang.html
[4] https://www.uber.com/blog/bootstrapping-ubers-infrastructure-on-arm64-with-zig/
[5] https://ziglang.org/download/0.11.0/release-notes.html#Support-Table

.github/bin/cross-compile

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+set -eo pipefail
+
+artifacts_dir='artifacts'
+build_tag="${GITHUB_REF_NAME}"
+
+cross_compile() {
+  local target="$1"
+  local arch='arm64'
+  local os
+  os="$(cut -d'-' -f2 <<< "${target}")"
+  local nim_os
+  case "${os}" in
+    macos) nim_os='macosx' ;;
+    *)     nim_os="${os}"  ;;
+  esac
+
+  nimble --verbose build --cpu:"${arch}" --os:"${nim_os}" -d:release -d:zig -d:target:"${target}"
+  local binary_name='configlet'
+  if command -v llvm-strip &> /dev/null; then
+    echo "stripping large comment section from executable..." >&2
+    llvm-strip -R .comment "${binary_name}"
+  fi
+  mkdir -p "${artifacts_dir}"
+  local artifact_file="${artifacts_dir}/${binary_name}_${build_tag}_${os}_${arch}.tar.gz"
+  tar -cvzf "${artifact_file}" "${binary_name}"
+}
+
+main() {
+  nimble --accept install --depsOnly
+
+  local targets=(
+    aarch64-linux-musl
+    # aarch64-macos-none
+    # aarch64-windows-gnu
+  )
+
+  for target in "${targets[@]}"; do
+    cross_compile "${target}"
+  done
+
+  gh release upload "${build_tag}" "${artifacts_dir}"/*
+}
+
+main

.github/bin/linux-install-build-tools → .github/bin/linux-install-musl

@@ -1,4 +1,2 @@
 #!/usr/bin/env sh
-
-# Install musl
 sudo apt-get install musl-dev musl-tools

.github/bin/linux-install-zig

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+set -eo pipefail
+
+version='0.11.0' # 2023-08-04
+release_name="zig-linux-x86_64-${version}"
+archive="${release_name}.tar.xz"
+url="https://ziglang.org/download/${version}/${archive}"
+
+curlopts=(
+  --silent
+  --show-error
+  --fail
+  --location
+  --retry 3
+)
+
+# Download the release archive.
+echo "Downloading Zig release archive..." >&2
+curl "${curlopts[@]}" --output "${archive}" "${url}"
+
+# Check that the archive has the expected hash.
+echo "Verifying archive..." >&2
+archive_sha256='2d00e789fec4f71790a6e7bf83ff91d564943c5ee843c5fd966efc474b423047'
+echo "${archive_sha256} ${archive}" | sha256sum -c -
+
+# Extract the archive, then remove it.
+echo "Extracting archive..." >&2
+tar xJf "${archive}"
+rm "${archive}"
+
+# Add zig directory to `GITHUB_PATH`.
+zig_dir="$(pwd)/${release_name}"
+echo "${zig_dir}" >> "${GITHUB_PATH}"
+
+# Install `zigcc`, which is just a wrapper for `zig cc`. We need this because
+# the value of e.g. `--clang.exe` cannot contain a space (Nim requires the value
+# to be an executable, not a command).
+zigcc_path="${zig_dir}/zigcc"
+printf '#!/usr/bin/env sh\nzig cc $@\n' > "${zigcc_path}"
+chmod +x "${zigcc_path}"
+
+# Print the versions of Zig and Clang.
+"${zig_dir}"/zig version
+"${zig_dir}"/zig cc --version
+echo "Successfully installed Zig ${version}."

.github/workflows/build.yml

@@ -36,7 +36,7 @@ jobs:
 
       - name: On Linux, install musl
         if: matrix.os == 'linux'
-        run: ./.github/bin/linux-install-build-tools
+        run: ./.github/bin/linux-install-musl
 
       - name: Install Nim
         uses: iffy/install-nim@ac410af52523f06e0fa037ee81d06ead7b95692c
@@ -62,9 +62,34 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-  checksums:
+  cross-compile:
     needs: [build]
     runs-on: ubuntu-22.04
+    name: cross-compile
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9
+
+      - name: Install Nim
+        uses: iffy/install-nim@ac410af52523f06e0fa037ee81d06ead7b95692c
+        with:
+          version: "binary:2.0.0"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Install Zig
+        run: ./.github/bin/linux-install-zig
+
+      - name: Cross-compile
+        run: ./.github/bin/cross-compile
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  checksums:
+    needs: [cross-compile]
+    runs-on: ubuntu-22.04
     name: Upload signatures and checksums
     permissions:
       contents: write

.github/workflows/tests.yml

@@ -39,7 +39,7 @@ jobs:
 
       - name: On Linux, install musl
         if: matrix.os == 'linux'
-        run: ./.github/bin/linux-install-build-tools
+        run: ./.github/bin/linux-install-musl
 
       - name: Install Nim
         uses: iffy/install-nim@ac410af52523f06e0fa037ee81d06ead7b95692c

config.nims

@@ -12,16 +12,30 @@ switch("mm", "refc")
 patchFile("stdlib", "json", "src/patched_stdlib/json")
 patchFile("stdlib", "parsejson", "src/patched_stdlib/parsejson")
 
+if defined(zig) and findExe("zigcc").len > 0:
+  switch("cc", "clang")
+  # We can't write `zig cc` below, because the value cannot contain a space.
+  switch("clang.exe", "zigcc")
+  switch("clang.linkerexe", "zigcc")
+  const target {.strdefine.} = ""
+  if target.len > 0:
+    switch("passC", "-target " & target)
+    switch("passL", "-target " & target)
+
 if defined(release):
   switch("opt", "size")
-  switch("passC", "-flto")
-  switch("passL", "-flto")
+
+  if not (defined(zig) and defined(macosx)):
+    # `zig ld` doesn't support LTO.
+    # See https://github.com/ziglang/zig/issues/8680
+    switch("passC", "-flto")
+    switch("passL", "-flto")
 
   if defined(linux) or defined(windows):
     switch("passL", "-s")
     switch("passL", "-static")
 
-  if defined(linux):
+  if defined(linux) and not defined(zig):
     if defined(gcc):
       switch("gcc.exe", "musl-gcc")
       switch("gcc.linkerexe", "musl-gcc")