build_defs.bzl

# Description:
#   BUILD rules for generating flatbuffer files in various languages.

"""
Rules for building C++ flatbuffers with Bazel.
"""

load("@rules_cc//cc:defs.bzl", "cc_library")

TRUE_FLATC_PATH = "@com_github_google_flatbuffers//:flatc"

DEFAULT_INCLUDE_PATHS = [
    "./",
    "$(GENDIR)",
    "$(BINDIR)",
    "$(execpath @com_github_google_flatbuffers//:flatc).runfiles/com_github_google_flatbuffers",
]

def default_include_paths(flatc_path):
    return [
        "./",
        "$(GENDIR)",
        "$(BINDIR)",
        "$(execpath %s).runfiles/com_github_google_flatbuffers" % (flatc_path),
    ]

DEFAULT_FLATC_ARGS = [
    "--gen-object-api",
    "--gen-compare",
    "--no-includes",
    "--gen-mutable",
    "--reflect-names",
    "--cpp-ptr-type flatbuffers::unique_ptr",
]

def flatbuffer_library_public(
        name,
        srcs,
        outs,
        language_flag,
        out_prefix = "",
        includes = [],
        include_paths = None,
        flatc_args = DEFAULT_FLATC_ARGS,
        reflection_name = "",
        reflection_visibility = None,
        compatible_with = None,
        restricted_to = None,
        target_compatible_with = None,
        flatc_path = "@com_github_google_flatbuffers//:flatc",
        output_to_bindir = False,
        tools = None,
        extra_env = None,
        **kwargs):
    """Generates code files for reading/writing the given flatbuffers in the requested language using the public compiler.

    Args:
      name: Rule name.
      srcs: Source .fbs files. Sent in order to the compiler.
      outs: Output files from flatc.
      language_flag: Target language flag. One of [-c, -j, -js].
      out_prefix: Prepend this path to the front of all generated files except on
          single source targets. Usually is a directory name.
      includes: Optional, list of filegroups of schemas that the srcs depend on.
      include_paths: Optional, list of paths the includes files can be found in.
      flatc_args: Optional, list of additional arguments to pass to flatc.
      reflection_name: Optional, if set this will generate the flatbuffer
        reflection binaries for the schemas.
      reflection_visibility: The visibility of the generated reflection Fileset.
      output_to_bindir: Passed to genrule for output to bin directory.
      compatible_with: Optional, The list of environments this rule can be
        built for, in addition to default-supported environments.
      restricted_to: Optional, The list of environments this rule can be built
        for, instead of default-supported environments.
      target_compatible_with: Optional, The list of target platform constraints
        to use.
      flatc_path: Bazel target corresponding to the flatc compiler to use.
      output_to_bindir: Passed to genrule for output to bin directory.
      tools: Optional, passed to genrule for list of tools to make available
        during the action.
      extra_env: Optional, must be a string of "VAR1=VAL1 VAR2=VAL2". These get
        set as environment variables that "flatc_path" sees.
      **kwargs: Passed to the underlying genrule.


    This rule creates a filegroup(name) with all generated source files, and
    optionally a Fileset([reflection_name]) with all generated reflection
    binaries.
    """
    if include_paths == None:
        include_paths = default_include_paths(flatc_path)
    include_paths_cmd = ["-I %s" % (s) for s in include_paths]

    extra_env = extra_env or ""

    # '$(@D)' when given a single source target will give the appropriate
    # directory. Appending 'out_prefix' is only necessary when given a build
    # target with multiple sources.
    output_directory = (
        ("-o $(@D)/%s" % (out_prefix)) if len(srcs) > 1 else ("-o $(@D)")
    )
    genrule_cmd = " ".join([
        "SRCS=($(SRCS));",
        "for f in $${SRCS[@]:0:%s}; do" % len(srcs),
        "OUTPUT_FILE=\"$(OUTS)\" %s $(location %s)" % (extra_env, flatc_path),
        " ".join(include_paths_cmd),
        " ".join(flatc_args),
        language_flag,
        output_directory,
        "$$f;",
        "done",
    ])
    native.genrule(
        name = name,
        srcs = srcs + includes,
        outs = outs,
        output_to_bindir = output_to_bindir,
        tools = (tools or []) + [flatc_path],
        cmd = genrule_cmd,
        compatible_with = compatible_with,
        target_compatible_with = target_compatible_with,
        restricted_to = restricted_to,
        message = "Generating flatbuffer files for %s:" % (name),
        **kwargs
    )
    if reflection_name:
        reflection_genrule_cmd = " ".join([
            "SRCS=($(SRCS));",
            "for f in $${SRCS[@]:0:%s}; do" % len(srcs),
            "$(location %s)" % (TRUE_FLATC_PATH),
            "-b --schema",
            " ".join(flatc_args),
            " ".join(include_paths_cmd),
            language_flag,
            output_directory,
            "$$f;",
            "done",
        ])
        reflection_outs = [
            (out_prefix + "%s.bfbs") % (s.replace(".fbs", "").split("/")[-1])
            for s in srcs
        ]
        native.genrule(
            name = "%s_srcs" % reflection_name,
            srcs = srcs + includes,
            outs = reflection_outs,
            output_to_bindir = output_to_bindir,
            tools = [TRUE_FLATC_PATH],
            compatible_with = compatible_with,
            restricted_to = restricted_to,
            target_compatible_with = target_compatible_with,
            cmd = reflection_genrule_cmd,
            message = "Generating flatbuffer reflection binary for %s:" % (name),
            visibility = reflection_visibility,
        )
        native.filegroup(
            name = "%s_out" % reflection_name,
            srcs = reflection_outs,
            visibility = reflection_visibility,
            compatible_with = compatible_with,
            restricted_to = restricted_to,
        )

def flatbuffer_cc_library(
        name,
        srcs,
        srcs_filegroup_name = "",
        outs = [],
        out_prefix = "",
        deps = [],
        includes = [],
        include_paths = None,
        cc_include_paths = [],
        flatc_args = DEFAULT_FLATC_ARGS,
        visibility = None,
        compatible_with = None,
        restricted_to = None,
        target_compatible_with = None,
        srcs_filegroup_visibility = None,
        gen_reflections = False):
    """A cc_library with the generated reader/writers for the given flatbuffer definitions.

    Args:
      name: Rule name.
      srcs: Source .fbs files. Sent in order to the compiler.
      srcs_filegroup_name: Name of the output filegroup that holds srcs. Pass this
          filegroup into the `includes` parameter of any other
          flatbuffer_cc_library that depends on this one's schemas.
      outs: Additional outputs expected to be generated by flatc.
      out_prefix: Prepend this path to the front of all generated files. Usually
          is a directory name.
      deps: Optional, list of other flatbuffer_cc_library's to depend on. Cannot be specified
          alongside includes.
      includes: Optional, list of filegroups of schemas that the srcs depend on.
          Use of this is discouraged, and may be deprecated.
      include_paths: Optional, list of paths the includes files can be found in.
      cc_include_paths: Optional, list of paths to add to the cc_library includes attribute.
      flatc_args: Optional list of additional arguments to pass to flatc
          (e.g. --gen-mutable).
      visibility: The visibility of the generated cc_library. By default, use the
          default visibility of the project.
      srcs_filegroup_visibility: The visibility of the generated srcs filegroup.
          By default, use the value of the visibility parameter above.
      gen_reflections: Optional, if true this will generate the flatbuffer
        reflection binaries for the schemas.
      compatible_with: Optional, The list of environments this rule can be built
        for, in addition to default-supported environments.
      restricted_to: Optional, The list of environments this rule can be built
        for, instead of default-supported environments.
      target_compatible_with: Optional, The list of target platform constraints
        to use.

    This produces:
      filegroup([name]_srcs): all generated .h files.
      filegroup(srcs_filegroup_name if specified, or [name]_includes if not):
          Other flatbuffer_cc_library's can pass this in for their `includes`
          parameter, if they depend on the schemas in this library.
      Fileset([name]_reflection): (Optional) all generated reflection binaries.
      cc_library([name]): library with sources and flatbuffers deps.
    """
    output_headers = [
        (out_prefix + "%s_generated.h") % (s.replace(".fbs", "").split("/")[-1].split(":")[-1])
        for s in srcs
    ]
    if deps and includes:
        # There is no inherent reason we couldn't support both, but this discourages
        # use of includes without good reason.
        fail("Cannot specify both deps and include in flatbuffer_cc_library.")
    if deps:
        includes = [d + "_includes" for d in deps]
    reflection_name = "%s_reflection" % name if gen_reflections else ""

    srcs_lib = "%s_srcs" % (name)
    flatbuffer_library_public(
        name = srcs_lib,
        srcs = srcs,
        outs = outs + output_headers,
        language_flag = "-c",
        out_prefix = out_prefix,
        includes = includes,
        include_paths = include_paths,
        flatc_args = flatc_args,
        compatible_with = compatible_with,
        restricted_to = restricted_to,
        target_compatible_with = target_compatible_with,
        reflection_name = reflection_name,
        reflection_visibility = visibility,
    )
    cc_library(
        name = name,
        hdrs = [
            ":" + srcs_lib,
        ],
        srcs = [
            ":" + srcs_lib,
        ],
        features = [
            "-parse_headers",
        ],
        deps = [
            "@com_github_google_flatbuffers//:runtime_cc",
            "@com_github_google_flatbuffers//:flatbuffers",
        ] + deps,
        includes = cc_include_paths,
        compatible_with = compatible_with,
        restricted_to = restricted_to,
        target_compatible_with = target_compatible_with,
        linkstatic = 1,
        visibility = visibility,
    )

    # A filegroup for the `srcs`. That is, all the schema files for this
    # Flatbuffer set.
    native.filegroup(
        name = srcs_filegroup_name if srcs_filegroup_name else "%s_includes" % (name),
        srcs = srcs + includes,
        compatible_with = compatible_with,
        restricted_to = restricted_to,
        visibility = srcs_filegroup_visibility if srcs_filegroup_visibility != None else visibility,
    )