tools/build_defs/apple/swift.bzl

# Copyright 2016 The Bazel Authors. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Skylark rules for Swift."""

load("shared",
     "xcrun_action",
     "XCRUNWRAPPER_LABEL",
     "module_cache_path",
     "label_scoped_path")

def _parent_dirs(dirs):
  """Returns a set of parent directories for each directory in dirs."""
  return set([f.rpartition("/")[0] for f in dirs])


def _intersperse(separator, iterable):
  """Inserts separator before each item in iterable."""
  result = []
  for x in iterable:
    result.append(separator)
    result.append(x)

  return result


def _swift_target(cpu, platform, sdk_version):
  """Returns a target triplet for Swift compiler."""
  platform_string = str(platform.platform_type)
  if platform_string not in ["ios", "watchos", "tvos"]:
    fail("Platform '%s' is not supported" % platform_string)

  return "%s-apple-%s%s" % (cpu, platform_string, sdk_version)


def _swift_compilation_mode_flags(ctx):
  """Returns additional swiftc flags for the current compilation mode."""
  mode = ctx.var["COMPILATION_MODE"]

  flags = []
  if mode == "dbg" or mode == "fastbuild":
    # TODO(dmishe): Find a way to test -serialize-debugging-options
    flags += [
        "-Onone", "-DDEBUG", "-enable-testing", "-Xfrontend",
        "-serialize-debugging-options"
    ]
  elif mode == "opt":
    flags += ["-O", "-DNDEBUG"]

  if mode == "dbg" or ctx.fragments.objc.generate_dsym:
    flags.append("-g")

  return flags


def _clang_compilation_mode_flags(ctx):
  """Returns additional clang flags for the current compilation mode."""

  # In general, every compilation mode flag from native objc_ rules should be
  # passed, but -g seems to break Clang module compilation. Since this flag does
  # not make much sense for module compilation and only touches headers,
  # it's ok to omit.
  native_clang_flags = ctx.fragments.objc.copts_for_current_compilation_mode

  return [x for x in native_clang_flags if x != "-g"]


def _swift_bitcode_flags(ctx):
  """Returns bitcode flags based on selected mode."""
  mode = str(ctx.fragments.apple.bitcode_mode)
  if mode == "embedded":
    return ["-embed-bitcode"]
  elif mode == "embedded_markers":
    return ["-embed-bitcode-marker"]

  return []


def swift_module_name(label):
  """Returns a module name for the given label."""
  return label.package.lstrip("//").replace("/", "_") + "_" + label.name


def _swift_lib_dir(ctx):
  """Returns the location of swift runtime directory to link against."""
  platform_str = ctx.fragments.apple.single_arch_platform.name_in_plist.lower()

  toolchain_name = "XcodeDefault"
  if hasattr(ctx.fragments.apple, "xcode_toolchain"):
    toolchain = ctx.fragments.apple.xcode_toolchain

    # We cannot use non Xcode-packaged toolchains, and the only one non-default
    # toolchain known to exist (as of Xcode 8.1) is this one.
    # TODO(b/29338444): Write an integration test when Xcode 8 is available.
    if toolchain == "com.apple.dt.toolchain.Swift_2_3":
      toolchain_name = "Swift_2.3"

  return "{0}/Toolchains/{1}.xctoolchain/usr/lib/swift/{2}".format(
      apple_common.apple_toolchain().developer_dir(), toolchain_name, platform_str)


def _swift_linkopts(ctx):
  """Returns additional linker arguments for the given rule context."""
  return set(["-L" + _swift_lib_dir(ctx)])


def _swift_xcrun_args(ctx):
  """Returns additional arguments that should be passed to xcrun."""
  if ctx.fragments.apple.xcode_toolchain:
    return ["--toolchain", ctx.fragments.apple.xcode_toolchain]

  return []


def _swift_parsing_flags(ctx):
  """Returns additional parsing flags for swiftc."""
  srcs = ctx.files.srcs

  # swiftc has two different parsing modes: script and library.
  # The difference is that in script mode top-level expressions are allowed.
  # This mode is triggered when the file compiled is called main.swift.
  # Additionally, script mode is used when there's just one file in the
  # compilation. we would like to avoid that and therefore force library mode
  # when there's only one source and it's not called main.
  if len(srcs) == 1 and srcs[0].basename != "main.swift":
    return ["-parse-as-library"]
  return []


def _is_valid_swift_module_name(string):
  """Returns True if the string is a valid Swift module name."""
  if not string:
    return False

  for char in string:
    # Check that the character is in [a-zA-Z0-9_]
    if not (char.isalnum() or char == "_"):
      return False

  return True


def _validate_rule_and_deps(ctx):
  """Validates the target and its dependencies."""

  name_error_str = ("Error in target '%s', Swift target and its dependencies' "+
                    "names can only contain characters in [a-zA-Z0-9_].")

  # Validate the name of the target
  if not _is_valid_swift_module_name(ctx.label.name):
    fail(name_error_str % ctx.label)

  # Validate names of the dependencies
  for dep in ctx.attr.deps:
    if not _is_valid_swift_module_name(dep.label.name):
      fail(name_error_str % dep.label)


def swiftc_inputs(ctx):
  """Determine the list of inputs required for the compile action.

  Args:
    ctx: rule context.

  Returns:
    A list of files needed by swiftc.
  """
  swift_providers = [x.swift for x in ctx.attr.deps if hasattr(x, "swift")]
  objc_providers = [x.objc for x in ctx.attr.deps if hasattr(x, "objc")]

  dep_modules = []
  for swift in swift_providers:
    dep_modules += swift.transitive_modules

  objc_files = set()
  for objc in objc_providers:
    objc_files += objc.header
    objc_files += objc.module_map
    objc_files += set(objc.static_framework_file)
    objc_files += set(objc.dynamic_framework_file)

  return ctx.files.srcs + dep_modules + list(objc_files)


def swiftc_args(ctx):
  """Returns an almost compelete array of arguments to be passed to swiftc.

  This macro is intended to be used by the swift_library rule implementation
  below but it also may be used by other rules outside this file. It has no
  side effects and does not modify ctx. It expects ctx to contain the same
  fragments and attributes as swift_library (you're encouraged to depend on
  SWIFT_LIBRARY_ATTRS in your rule definition).

  Args:
    ctx: rule context

  Returns:
    A list of command line arguments for swiftc. The returned arguments
    include everything except the arguments generation of which would require
    adding new files or actions.
  """

  apple_fragment = ctx.fragments.apple

  cpu = apple_fragment.single_arch_cpu
  platform = apple_fragment.single_arch_platform

  target_os = apple_fragment.minimum_os_for_platform_type(
      platform.platform_type)
  target = _swift_target(cpu, platform, target_os)
  apple_toolchain = apple_common.apple_toolchain()

  module_name = ctx.attr.module_name or swift_module_name(ctx.label)

  # A list of paths to pass with -F flag.
  framework_dirs = set([
      apple_toolchain.platform_developer_framework_dir(apple_fragment)])

  # Collect transitive dependecies.
  dep_modules = []
  swiftc_defines = ctx.attr.defines

  swift_providers = [x.swift for x in ctx.attr.deps if hasattr(x, "swift")]
  objc_providers = [x.objc for x in ctx.attr.deps if hasattr(x, "objc")]

  for swift in swift_providers:
    dep_modules += swift.transitive_modules
    swiftc_defines += swift.transitive_defines

  objc_includes = set()     # Everything that needs to be included with -I
  objc_module_maps = set()  # Module maps for dependent targets
  objc_defines = set()
  for objc in objc_providers:
    objc_includes += objc.include
    objc_module_maps += objc.module_map

    framework_dirs += _parent_dirs(objc.framework_dir)
    framework_dirs += _parent_dirs(objc.dynamic_framework_dir)

    # objc_library#copts is not propagated to its dependencies and so it is not
    # collected here. In theory this may lead to un-importable targets (since
    # their module cannot be compiled by clang), but did not occur in practice.
    objc_defines += objc.define

  srcs_args = [f.path for f in ctx.files.srcs]

  # Include each swift module's parent directory for imports to work.
  include_dirs = set([x.dirname for x in dep_modules])

  # Include the genfiles root so full-path imports can work for generated protos.
  include_dirs += set([ctx.genfiles_dir.path])

  include_args = ["-I%s" % d for d in include_dirs + objc_includes]
  framework_args = ["-F%s" % x for x in framework_dirs]
  define_args = ["-D%s" % x for x in swiftc_defines]

  clang_args = _intersperse(
      "-Xcc",

      # Add the current directory to clang's search path.
      # This instance of clang is spawned by swiftc to compile module maps and
      # is not passed the current directory as a search path by default.
      ["-iquote", "."]

      # Pass DEFINE or copt values from objc configuration and rules to clang
      + ["-D" + x for x in objc_defines] + ctx.fragments.objc.copts
      + _clang_compilation_mode_flags(ctx)

      # Load module maps explicitly instead of letting Clang discover them on
      # search paths. This is needed to avoid a case where Clang may load the
      # same header both in modular and non-modular contexts, leading to
      # duplicate definitions in the same file.
      # https://llvm.org/bugs/show_bug.cgi?id=19501
      + ["-fmodule-map-file=%s" % x.path for x in objc_module_maps])

  args = [
      "-emit-object",
      "-module-name",
      module_name,
      "-target",
      target,
      "-sdk",
      apple_toolchain.sdk_dir(),
      "-module-cache-path",
      module_cache_path(ctx),
  ]

  if ctx.configuration.coverage_enabled:
    args.extend(["-profile-generate", "-profile-coverage-mapping"])

  args.extend(_swift_compilation_mode_flags(ctx))
  args.extend(_swift_bitcode_flags(ctx))
  args.extend(_swift_parsing_flags(ctx))
  args.extend(srcs_args)
  args.extend(include_args)
  args.extend(framework_args)
  args.extend(clang_args)
  args.extend(define_args)
  args.extend(ctx.fragments.swift.copts())
  args.extend(ctx.attr.copts)

  return args


def _swift_library_impl(ctx):
  """Implementation for swift_library Skylark rule."""

  _validate_rule_and_deps(ctx)

  # Collect transitive dependecies.
  dep_modules = []
  dep_libs = []
  swiftc_defines = ctx.attr.defines

  swift_providers = [x.swift for x in ctx.attr.deps if hasattr(x, "swift")]
  objc_providers = [x.objc for x in ctx.attr.deps if hasattr(x, "objc")]

  for swift in swift_providers:
    dep_libs += swift.transitive_libs
    dep_modules += swift.transitive_modules
    swiftc_defines += swift.transitive_defines

  # A unique path for rule's outputs.
  objs_outputs_path = label_scoped_path(ctx, "_objs/")

  module_name = ctx.attr.module_name or swift_module_name(ctx.label)
  output_lib = ctx.new_file(objs_outputs_path + module_name + ".a")
  output_module = ctx.new_file(objs_outputs_path + module_name + ".swiftmodule")

  # These filenames are guaranteed to be unique, no need to scope.
  output_header = ctx.new_file(ctx.label.name + "-Swift.h")
  swiftc_output_map_file = ctx.new_file(ctx.label.name + ".output_file_map.json")

  swiftc_output_map = struct()  # Maps output types to paths.
  output_objs = []  # Object file outputs, used in archive action.
  swiftc_outputs = []  # Other swiftc outputs that aren't processed further.

  # Check if the user enabled Whole Module Optimization (WMO)
  # This is highly experimental and tracked in b/29465250
  has_wmo = ("-wmo" in ctx.attr.copts) or ("-whole-module-optimization" in ctx.attr.copts)

  for source in ctx.files.srcs:
    basename = source.basename
    output_map_entry = {}

    # Output an object file
    obj = ctx.new_file(objs_outputs_path + basename + ".o")
    output_objs.append(obj)
    output_map_entry["object"] = obj.path

    # Output a partial module file, unless WMO is enabled in which case only
    # the final, complete module will be generated.
    if not has_wmo:
      partial_module = ctx.new_file(objs_outputs_path + basename +
                                    ".partial_swiftmodule")
      swiftc_outputs.append(partial_module)
      output_map_entry["swiftmodule"] = partial_module.path

    swiftc_output_map += struct(**{source.path: struct(**output_map_entry)})

  # Write down the intermediate outputs map for this compilation, to be used
  # with -output-file-map flag.
  # It's a JSON file that maps each source input (.swift) to its outputs
  # (.o, .bc, .d, ...)
  # Example:
  #   {'foo.swift':
  #       {'object': 'foo.o', 'bitcode': 'foo.bc', 'dependencies': 'foo.d'}}
  # There's currently no documentation on this option, however all of the keys
  # are listed here https://github.com/apple/swift/blob/swift-2.2.1-RELEASE/include/swift/Driver/Types.def
  ctx.file_action(output=swiftc_output_map_file, content=swiftc_output_map.to_json())

  args = _swift_xcrun_args(ctx) + ["swiftc"] + swiftc_args(ctx)
  args += [
      "-I" + output_module.dirname,
      "-emit-module-path",
      output_module.path,
      "-emit-objc-header-path",
      output_header.path,
      "-output-file-map",
      swiftc_output_map_file.path,
  ]

  if has_wmo:
    # WMO has two modes: threaded and not. We want the threaded mode because it
    # will use the output map we generate. This leads to a better debug
    # experience in lldb and Xcode.
    # TODO(b/32571265): 12 has been chosen as the best option for a Mac Pro,
    # we should get an interface in Bazel to get core count.
    args.extend(["-num-threads", "12"])

  xcrun_action(
      ctx,
      inputs=swiftc_inputs(ctx) + [swiftc_output_map_file],
      outputs=[output_module, output_header] + output_objs + swiftc_outputs,
      mnemonic="SwiftCompile",
      arguments=args,
      use_default_shell_env=False,
      progress_message=("Compiling Swift module %s (%d files)" %
                        (ctx.label.name, len(ctx.files.srcs))))

  xcrun_action(ctx,
               inputs=output_objs,
               outputs=(output_lib,),
               mnemonic="SwiftArchive",
               arguments=[
                   "libtool", "-static", "-o", output_lib.path
               ] + [x.path for x in output_objs],
               progress_message=("Archiving Swift objects %s" % ctx.label.name))

  # This tells the linker to write a reference to .swiftmodule as an AST symbol
  # in the final binary.
  # With dSYM enabled, this results in a __DWARF,__swift_ast section added to
  # the dSYM binary, from where LLDB is able deserialize module information.
  # Without dSYM, LLDB will follow the AST references, however there is a bug
  # where it follows only the first one https://bugs.swift.org/browse/SR-2637
  # This means that dSYM is required for debugging until that is resolved.
  extra_linker_args = ["-Xlinker -add_ast_path -Xlinker " + output_module.path]

  objc_provider = apple_common.new_objc_provider(
      library=set([output_lib] + dep_libs),
      header=set([output_header]),
      providers=objc_providers,
      linkopt=_swift_linkopts(ctx) + extra_linker_args,
      link_inputs=set([output_module]),
      uses_swift=True,)

  return struct(
      swift=struct(
          transitive_libs=[output_lib] + dep_libs,
          transitive_modules=[output_module] + dep_modules,
          transitive_defines=swiftc_defines),
      objc=objc_provider,
      files=set([output_lib, output_module, output_header]))

SWIFT_LIBRARY_ATTRS = {
    "srcs": attr.label_list(allow_files = [".swift"], allow_empty=False),
    "deps": attr.label_list(providers=[["swift"], ["objc"]]),
    "module_name": attr.string(mandatory=False),
    "defines": attr.string_list(mandatory=False, allow_empty=True),
    "copts": attr.string_list(mandatory=False, allow_empty=True),
    "_xcrunwrapper": attr.label(
        executable=True,
        cfg="host",
        default=Label(XCRUNWRAPPER_LABEL))
}

swift_library = rule(
    _swift_library_impl,
    attrs = SWIFT_LIBRARY_ATTRS,
    fragments = ["apple", "objc", "swift"],
    output_to_genfiles=True,
)
"""
Builds a Swift module.

A module is a pair of static library (.a) + module header (.swiftmodule).
Dependant targets can import this module as "import RuleName".

Args:
  srcs: Swift sources that comprise this module.
  deps: Other Swift modules.
  module_name: Optional. Sets the Swift module name for this target. By default
      the module name is the target path with all special symbols replaced
      by "_", e.g. //foo:bar can be imported as "foo_bar".
  copts: A list of flags passed to swiftc command line.
  defines: Each VALUE in this attribute is passed as -DVALUE to the compiler for
      this and dependent targets.
"""