bazel

#!/bin/bash

#
# ./bazel
#
# Reads the BAZEL_VERSION variable in the WORKSPACE file and executes the
# corresponding Bazel version. Downloads and installs it if needed.
#

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"

if ! [ -f WORKSPACE ]; then
  echo >&2 "Didn't find the workspace"
  exit 1
fi

cd "$old_pwd"

workspace_contents=$(< "$repo_root/WORKSPACE")

bazel_version_regex='BAZEL_VERSION = "([^"]+)"'
if [[ $workspace_contents =~ $bazel_version_regex ]]; then
  export BAZEL_VERSION="${BASH_REMATCH[1]}"
else
  echo >&2 "$0: Failed to extract BAZEL_VERSION from WORKSPACE"
  exit 1
fi

bazel_bin_loc="${bazel_bin_loc:-$HOME/.bazel_binaries}"
bazel_exec_path="$bazel_bin_loc/$BAZEL_VERSION/bin/bazel-real"

if [ -f "$bazel_exec_path" ]; then
  exec "$bazel_exec_path" "$@"
fi

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

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

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) ;;
  darwin-x86_64) ;;
  darwin-arm64)
    # Pseudo Apple Silicon support by forcing x86_64 (Rosetta) for now
    bazel_installer_platform="darwin-x86_64"
    ;;
  *)
    echo >&2 "Building on $bazel_installer_platform is not implemented"
    exit 1
    ;;
esac

bazel_installer_platform_var="$(echo "$bazel_installer_platform" | tr 'a-z-' 'A-Z_')"
bazel_installer_sha_variable="BAZEL_INSTALLER_VERSION_${bazel_installer_platform_var}_SHA"
bazel_installer_sha_regex="$bazel_installer_sha_variable = \"([^\"]+)\""
if [[ $workspace_contents =~ $bazel_installer_sha_regex ]]; then
  export expected_sha="${BASH_REMATCH[1]}"
else
  echo >&2 "$0: Failed to extract Bazel version from WORKSPACE"
  exit 1
fi

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

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

  installer_name="bazel-${BAZEL_VERSION}-installer-${bazel_installer_platform}.sh"
  BAZEL_REMOTE_SOURCE="${BAZEL_REMOTE_SOURCE:-https://github.com/bazelbuild/bazel/releases/download}"
  BAZEL_INSTALLER_PATH="${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 $1}')"
  if [ "$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 $bazel_installer_sha_variable in the WORKSPACE file and re-run."
    exit 1
  fi

  chmod +x "$installer_name"
  mkdir -p "$bazel_bin_loc"
  "./${installer_name}" --base="${bazel_bin_loc}/${BAZEL_VERSION}" --bin="${bazel_bin_loc}/${BAZEL_VERSION}/bin_t"
)
rm -rf "$BUILD_DIR"

exec "$bazel_exec_path" "$@"