bazel

#!/bin/bash

#
# ./bazel
#
# Reads the .bazelversion_checksums folder to find which version of Bazel to
# run. If not found, downloads and installs it using the contents of the
# `.bazelversion` file.
#

set -euo pipefail

if [ "${LOCAL_BAZEL_OVERRIDE:-}" != "" ]; then
  exec "$LOCAL_BAZEL_OVERRIDE" "$@"
fi

old_pwd="$PWD"
cd "$(dirname "${BASH_SOURCE[0]}")"
if [[ "$PWD" = */tools ]]; then
  cd ..
fi
repo_root="$PWD"
cd "$old_pwd"

kernel_name="$(uname -s | tr 'A-Z' 'a-z')"
processor_name="$(uname -m)"

bazel_installer_platform="${kernel_name}-${processor_name}"
case "$bazel_installer_platform" in
  linux-x86_64) ;;
  linux-aarch64)
    bazel_installer_platform="linux-arm64"
    ;;
  darwin-x86_64) ;;
  darwin-arm64) ;;
esac

expected_sha_file="$repo_root/.bazelversion_checksums/$bazel_installer_platform"
if ! [ -f "$expected_sha_file" ]; then
    echo >&2 "Building on $bazel_installer_platform is not implemented"
    exit 1
fi

expected_sha="$(< "$expected_sha_file")"
if [ "$expected_sha" != "" ]; then
  bazel_bin_loc="${bazel_bin_loc:-$HOME/.bazel_binaries}"
  bazel_exec_path="$bazel_bin_loc/$expected_sha/bin/bazel-real"

  if [ -f "$bazel_exec_path" ]; then
    exec "$bazel_exec_path" "$@"
  fi
else
  echo >&2 "$expected_sha_file was empty. Falling back to downloading bazel"
fi

# ----- slow path -----

echo >&2 "No cached Bazel found, installing..."

BAZEL_VERSION=$(< "$repo_root/.bazelversion")
export BAZEL_VERSION

BUILD_DIR="$(mktemp -d)"
export BUILD_DIR
mkdir -p "$BUILD_DIR"

(
  set -euo pipefail
  cd "$BUILD_DIR"
  echo "$PWD"

  check_sha () {
    if [ "$actual_sha" != "$expected_sha" ]; then
      echo >&2 "Installer checksum mismatch:"
      echo >&2 "  Expected: $expected_sha"
      echo >&2 "  Actual:   $actual_sha"
      echo >&2 "To accept this mismatch, update $expected_sha_file and re-run."
      exit 1
    fi
  }
  BAZEL_REMOTE_SOURCE="${BAZEL_REMOTE_SOURCE:-https://github.com/bazelbuild/bazel/releases/download}"

  # Bazel for linux-arm64 doesn't have a binary installer
  if [ "$bazel_installer_platform" == "linux-arm64" ]; then
    bazel_name="bazel-${BAZEL_VERSION}-linux-arm64"
    BAZEL_PATH="${BAZEL_PATH:-$BAZEL_REMOTE_SOURCE/${BAZEL_VERSION}/${bazel_name}}"

    curl -O -L "$BAZEL_PATH"

    actual_sha="$(shasum -a 256 "$bazel_name" | awk '{print $1}')"
    check_sha

    mkdir -p "$bazel_bin_loc/${expected_sha}/bin"
    cp "$bazel_name" "$bazel_bin_loc/${expected_sha}/bin/bazel-real"
    chmod +x "$bazel_bin_loc/${expected_sha}/bin/bazel-real"
  else
    installer_name="bazel-${BAZEL_VERSION}-installer-${bazel_installer_platform}.sh"
    BAZEL_INSTALLER_PATH="${BAZEL_INSTALLER_PATH:-$BAZEL_REMOTE_SOURCE/${BAZEL_VERSION}/$installer_name}"

    curl -O -L "$BAZEL_INSTALLER_PATH"

    actual_sha="$(shasum -a 256 "$installer_name" | awk '{print $1}')"
    check_sha

    chmod +x "$installer_name"
    mkdir -p "$bazel_bin_loc"
    "./${installer_name}" --base="${bazel_bin_loc}/${expected_sha}" --bin="${bazel_bin_loc}/${expected_sha}/bin_t"
  fi

)
rm -rf "$BUILD_DIR"

exec "$bazel_exec_path" "$@"