core/pkgs/build-support/build-bazel-package/default.nix

{
  stdenv,
  cacert,
  lib,
  writeCBin,
}:

args@{
  name ? "${args.pname}-${args.version}",
  bazel,
  bazelFlags ? [ ],
  bazelBuildFlags ? [ ],
  bazelTestFlags ? [ ],
  bazelRunFlags ? [ ],
  runTargetFlags ? [ ],
  bazelFetchFlags ? [ ],
  bazelTargets ? [ ],
  bazelTestTargets ? [ ],
  bazelRunTarget ? null,
  buildAttrs,
  fetchAttrs,

  # Newer versions of Bazel are moving away from built-in rules_cc and instead
  # allow fetching it as an external dependency in a WORKSPACE file[1]. If
  # removed in the fixed-output fetch phase, building will fail to download it.
  # This can be seen e.g. in #73097
  #
  # This option allows configuring the removal of rules_cc in cases where a
  # project depends on it via an external dependency.
  #
  # [1]: https://github.com/bazelbuild/rules_cc
  removeRulesCC ? true,
  removeLocalConfigCc ? true,
  removeLocal ? true,

  # Use build --nobuild instead of fetch. This allows fetching the dependencies
  # required for the build as configured, rather than fetching all the dependencies
  # which may not work in some situations (e.g. Java code which ends up relying on
  # Debian-specific /usr/share/java paths, but doesn't in the configured build).
  fetchConfigured ? true,

  # Don’t add Bazel --copt and --linkopt from NIX_CFLAGS_COMPILE /
  # NIX_LDFLAGS. This is necessary when using a custom toolchain which
  # Bazel wants all headers / libraries to come from, like when using
  # CROSSTOOL. Weirdly, we can still get the flags through the wrapped
  # compiler.
  dontAddBazelOpts ? false,
  ...
}:

let
  fArgs =
    removeAttrs args [
      "buildAttrs"
      "fetchAttrs"
      "removeRulesCC"
    ]
    // {
      inherit
        name
        bazelFlags
        bazelBuildFlags
        bazelTestFlags
        bazelRunFlags
        runTargetFlags
        bazelFetchFlags
        bazelTargets
        bazelTestTargets
        bazelRunTarget
        dontAddBazelOpts
        ;
    };
  fBuildAttrs = fArgs // buildAttrs;
  fFetchAttrs = fArgs // removeAttrs fetchAttrs [ "sha256" ];
  bazelCmd =
    {
      cmd,
      additionalFlags,
      targets,
      targetRunFlags ? [ ],
    }:
    lib.optionalString (targets != [ ]) ''
      # See footnote called [USER and BAZEL_USE_CPP_ONLY_TOOLCHAIN variables]
      BAZEL_USE_CPP_ONLY_TOOLCHAIN=1 \
      USER=homeless-shelter \
      bazel \
        --batch \
        --output_base="$bazelOut" \
        --output_user_root="$bazelUserRoot" \
        ${cmd} \
        --curses=no \
        "''${copts[@]}" \
        "''${host_copts[@]}" \
        "''${linkopts[@]}" \
        "''${host_linkopts[@]}" \
        $bazelFlags \
        ${lib.strings.concatStringsSep " " additionalFlags} \
        ${lib.strings.concatStringsSep " " targets} \
        ${
          lib.optionalString (targetRunFlags != [ ]) " -- " + lib.strings.concatStringsSep " " targetRunFlags
        }
    '';
  # we need this to chmod dangling symlinks on darwin, gnu coreutils refuses to do so:
  # chmod: cannot operate on dangling symlink '$symlink'
  chmodder = writeCBin "chmodder" ''
    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <errno.h>
    #include <string.h>

    int main(int argc, char** argv) {
      mode_t mode = S_IRWXU | S_IRWXG | S_IRWXO;
      if (argc != 2) {
        fprintf(stderr, "usage: chmodder file");
        exit(EXIT_FAILURE);
      }
      if (lchmod(argv[1], mode) != 0) {
        fprintf(stderr, "failed to lchmod '%s': %s", argv[0], strerror(errno));
        exit(EXIT_FAILURE);
      }
    }
  '';
in
stdenv.mkDerivation (
  fBuildAttrs
  // {

    deps = stdenv.mkDerivation (
      fFetchAttrs
      // {
        name = "${name}-deps.tar.gz";

        impureEnvVars = lib.fetchers.proxyImpureEnvVars ++ fFetchAttrs.impureEnvVars or [ ];

        nativeBuildInputs = fFetchAttrs.nativeBuildInputs or [ ] ++ [ bazel ];

        preHook =
          fFetchAttrs.preHook or ""
          + ''
            export bazelOut="$(echo ''${NIX_BUILD_TOP}/output | sed -e 's,//,/,g')"
            export bazelUserRoot="$(echo ''${NIX_BUILD_TOP}/tmp | sed -e 's,//,/,g')"
            export HOME="$NIX_BUILD_TOP"
            export USER="nix"
            # This is needed for git_repository with https remotes
            export GIT_SSL_CAINFO="${cacert}/etc/ssl/certs/ca-bundle.crt"
            # This is needed for Bazel fetchers that are themselves programs (e.g.
            # rules_go using the go toolchain)
            export SSL_CERT_FILE="${cacert}/etc/ssl/certs/ca-bundle.crt"
          '';

        buildPhase =
          fFetchAttrs.buildPhase or ''
            runHook preBuild

            ${bazelCmd {
              cmd = if fetchConfigured then "build --nobuild" else "fetch";
              additionalFlags =
                [
                  # We disable multithreading for the fetching phase since it can lead to timeouts with many dependencies/threads:
                  # https://github.com/bazelbuild/bazel/issues/6502
                  "--loading_phase_threads=1"
                  "$bazelFetchFlags"
                ]
                ++ (
                  if fetchConfigured then
                    [
                      "--jobs"
                      "$NIX_BUILD_CORES"
                    ]
                  else
                    [ ]
                );
              targets = fFetchAttrs.bazelTargets ++ fFetchAttrs.bazelTestTargets;
            }}

            runHook postBuild
          '';

        installPhase =
          fFetchAttrs.installPhase or (
            ''
              runHook preInstall

              # Remove all built in external workspaces, Bazel will recreate them when building
              rm -rf $bazelOut/external/{bazel_tools,\@bazel_tools.marker}
              ${lib.optionalString removeRulesCC "rm -rf $bazelOut/external/{rules_cc,\\@rules_cc.marker}"}
              rm -rf $bazelOut/external/{embedded_jdk,\@embedded_jdk.marker}
              ${lib.optionalString removeLocalConfigCc "rm -rf $bazelOut/external/{local_config_cc,\\@local_config_cc.marker}"}
              ${lib.optionalString removeLocal "rm -rf $bazelOut/external/{local_*,\\@local_*.marker}"}

              # Clear markers
              find $bazelOut/external -name '@*\.marker' -exec sh -c 'echo > {}' \;

              # Remove all vcs files
              rm -rf $(find $bazelOut/external -type d -name .git)
              rm -rf $(find $bazelOut/external -type d -name .svn)
              rm -rf $(find $bazelOut/external -type d -name .hg)

              # Removing top-level symlinks along with their markers.
              # This is needed because they sometimes point to temporary paths (?).
              # For example, in Tensorflow-gpu build:
              # platforms -> NIX_BUILD_TOP/tmp/install/35282f5123611afa742331368e9ae529/_embedded_binaries/platforms
              find $bazelOut/external -maxdepth 1 -type l | while read symlink; do
                name="$(basename "$symlink")"
                rm "$symlink"
                test -f "$bazelOut/external/@$name.marker" && rm "$bazelOut/external/@$name.marker" || true
              done

              # Patching symlinks to remove build directory reference
              find $bazelOut/external -type l | while read symlink; do
                new_target="$(readlink "$symlink" | sed "s,$NIX_BUILD_TOP,NIX_BUILD_TOP,")"
                rm "$symlink"
                ln -sf "$new_target" "$symlink"
            ''
            + lib.optionalString stdenv.isDarwin ''
              # on linux symlink permissions cannot be modified, so we modify those on darwin to match the linux ones
              ${chmodder}/bin/chmodder "$symlink"
            ''
            + ''
              done

              echo '${bazel.name}' > $bazelOut/external/.nix-bazel-version

              (cd $bazelOut/ && tar czf $out --sort=name --mtime='@1' --owner=0 --group=0 --numeric-owner external/)

              runHook postInstall
            ''
          );

        dontFixup = true;
        allowedRequisites = [ ];

        outputHashAlgo = "sha256";
        outputHash = fetchAttrs.sha256;
      }
    );

    nativeBuildInputs = fBuildAttrs.nativeBuildInputs or [ ] ++ [
      (bazel.override { enableNixHacks = true; })
    ];

    preHook =
      fBuildAttrs.preHook or ""
      + ''
        export bazelOut="$NIX_BUILD_TOP/output"
        export bazelUserRoot="$NIX_BUILD_TOP/tmp"
        export HOME="$NIX_BUILD_TOP"
      '';

    preConfigure =
      ''
        mkdir -p "$bazelOut"

        (cd $bazelOut && tar xfz $deps)

        test "${bazel.name}" = "$(<$bazelOut/external/.nix-bazel-version)" || {
          echo "fixed output derivation was built for a different bazel version" >&2
          echo "     got: $(<$bazelOut/external/.nix-bazel-version)" >&2
          echo "expected: ${bazel.name}" >&2
          exit 1
        }

        chmod -R +w $bazelOut
        find $bazelOut -type l | while read symlink; do
          if [[ $(readlink "$symlink") == *NIX_BUILD_TOP* ]]; then
            ln -sf $(readlink "$symlink" | sed "s,NIX_BUILD_TOP,$NIX_BUILD_TOP,") "$symlink"
          fi
        done
      ''
      + fBuildAttrs.preConfigure or "";

    buildPhase =
      fBuildAttrs.buildPhase or ''
        runHook preBuild

        # Bazel sandboxes the execution of the tools it invokes, so even though we are
        # calling the correct nix wrappers, the values of the environment variables
        # the wrappers are expecting will not be set. So instead of relying on the
        # wrappers picking them up, pass them in explicitly via `--copt`, `--linkopt`
        # and related flags.

        copts=()
        host_copts=()
        linkopts=()
        host_linkopts=()
        if [ -z "''${dontAddBazelOpts:-}" ]; then
          for flag in $NIX_CFLAGS_COMPILE; do
            copts+=( "--copt=$flag" )
            host_copts+=( "--host_copt=$flag" )
          done
          for flag in $NIX_CXXSTDLIB_COMPILE; do
            copts+=( "--copt=$flag" )
            host_copts+=( "--host_copt=$flag" )
          done
          for flag in $NIX_LDFLAGS; do
            linkopts+=( "--linkopt=-Wl,$flag" )
            host_linkopts+=( "--host_linkopt=-Wl,$flag" )
          done
        fi

        ${bazelCmd {
          cmd = "test";
          additionalFlags =
            [ "--test_output=errors" ]
            ++ fBuildAttrs.bazelTestFlags
            ++ [
              "--jobs"
              "$NIX_BUILD_CORES"
            ];
          targets = fBuildAttrs.bazelTestTargets;
        }}
        ${bazelCmd {
          cmd = "build";
          additionalFlags = fBuildAttrs.bazelBuildFlags ++ [
            "--jobs"
            "$NIX_BUILD_CORES"
          ];
          targets = fBuildAttrs.bazelTargets;
        }}
        ${bazelCmd {
          cmd = "run";
          additionalFlags = fBuildAttrs.bazelRunFlags ++ [
            "--jobs"
            "$NIX_BUILD_CORES"
          ];
          # Bazel run only accepts a single target, but `bazelCmd` expects `targets` to be a list.
          targets = lib.optionals (fBuildAttrs.bazelRunTarget != null) [ fBuildAttrs.bazelRunTarget ];
          targetRunFlags = fBuildAttrs.runTargetFlags;
        }}
        runHook postBuild
      '';
  }
)

# [USER and BAZEL_USE_CPP_ONLY_TOOLCHAIN variables]:
#   Bazel computes the default value of output_user_root before parsing the
#   flag. The computation of the default value involves getting the $USER
#   from the environment. Code here :
#   https://github.com/bazelbuild/bazel/blob/9323c57607d37f9c949b60e293b573584906da46/src/main/cpp/startup_options.cc#L123-L124
#
#   On macOS Bazel will use the system installed Xcode or CLT toolchain instead of the one in the PATH unless we pass BAZEL_USE_CPP_ONLY_TOOLCHAIN.