rules_foreign_cc

Rules for building C/C++ projects using foreign build systems inside Bazel projects.

• Experimental - API will most definitely change.
• This is not an officially supported Google product (meaning, support and/or new releases may be limited.)

NOTE: this requires Bazel version starting from 0.17.1.

It also requires passing Bazel the following flag:

--experimental_cc_skylark_api_enabled_packages=@rules_foreign_cc//tools/build_defs,tools/build_defs

Where rules_foreign_cc is the name of this repository in your WORKSPACE file.

Building CMake projects:

• Build libraries/binaries with CMake from sources using cmake_external rule
• Use cmake_external targets in cc_library, cc_binary targets as dependency
• Bazel cc_toolchain parameters are used inside cmake_external build
• See full list of cmake_external arguments below 'example'
• cmake_external is defined in ./tools/build_defs
• Works on Ubuntu, Mac OS and Windows(* see special notes below in Windows section) operating systems

Example: (Please see full examples in ./examples)
The example for Windows is below, in the section 'Usage on Windows'.

• In WORKSPACE, we use a http_archive to download tarballs with the libraries we use.
• In BUILD, we instantiate a cmake_external rule which behaves similarly to a cc_library, which can then be used in a C++ rule (cc_binary in this case).

In WORKSPACE, put

workspace(name = "rules_foreign_cc_usage_example")

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

# Group the sources of the library so that CMake rule have access to it
all_content = """filegroup(name = "all", srcs = glob(["**"]), visibility = ["//visibility:public"])"""

# Rule repository
http_archive(
   name = "rules_foreign_cc",
   strip_prefix = "rules_foreign_cc-master",
   url = "https://github.com/bazelbuild/rules_foreign_cc/archive/master.zip",
)

load("@rules_foreign_cc//:workspace_definitions.bzl", "rules_foreign_cc_dependencies")

# Workspace initialization function; includes repositories needed by rules_foreign_cc,
# and creates some utilities for the host operating system
rules_foreign_cc_dependencies()

# OpenBLAS source code repository
http_archive(
   name = "openblas",
   build_file_content = all_content,
   strip_prefix = "OpenBLAS-0.3.2",
   urls = ["https://github.com/xianyi/OpenBLAS/archive/v0.3.2.tar.gz"],
)

# Eigen source code repository
http_archive(
   name = "eigen",
   build_file_content = all_content,
   strip_prefix = "eigen-git-mirror-3.3.5",
   urls = ["https://github.com/eigenteam/eigen-git-mirror/archive/3.3.5.tar.gz"],
)

and in BUILD, put

load("@rules_foreign_cc//tools/build_defs:cmake.bzl", "cmake_external")

cmake_external(
   name = "openblas",
   # Values to be passed as -Dkey=value on the CMake command line;
   # here are serving to provide some CMake script configuration options
   cache_entries = {
       "NOFORTRAN": "on",
       "BUILD_WITHOUT_LAPACK": "no",
   },
   lib_source = "@openblas//:all",

   # We are selecting the resulting static library to be passed in C/C++ provider
   # as the result of the build;
   # However, the cmake_external dependants could use other artefacts provided by the build,
   # according to their CMake script
   static_libraries = ["libopenblas.a"],
)

cmake_external(
   name = "eigen",
   # These options help CMake to find prebuilt OpenBLAS, which will be copied into
   # $EXT_BUILD_DEPS/openblas by the cmake_external script
   cache_entries = {
       "BLA_VENDOR": "OpenBLAS",
       "BLAS_LIBRARIES": "$EXT_BUILD_DEPS/openblas/lib/libopenblas.a",
   },
   headers_only = True,
   lib_source = "@eigen//:all",
   # Dependency on other cmake_external rule; can also depend on cc_import, cc_library rules
   deps = [":openblas"],
)

then build as usual:

$ devbazel build //examples/cmake_pcl:eigen

Usage on Windows

When using on Windows, you should start Bazel in MSYS2 shell, as the shell script inside cmake_external assumes this. Also, you should explicitly specify make commands and option to generate CMake crosstool file.
The default generator for CMake will be detected automatically, or you can specify it explicitly.
The tested generators: Visual Studio 15, Ninja and NMake. The extension '.lib' is assumed for the static libraries by default.

Example usage (see full example in ./examples/cmake_hello_world_lib): Example assumes that MS Visual Studio and Ninja are installed on the host machine, and Ninja bin directory is added to PATH.

cmake_external(
    # expect to find ./lib/hello.lib as the result of the build
    name = "hello",
    # This option can be omitted
    cmake_options = ["-G \"Visual Studio 15 2017 Win64\""],
    generate_crosstool_file = True,
    lib_source = ":srcs",
    # .vcxproj or .sln file must be specified argument, as multiple files are generated by CMake
    make_commands = ["MSBuild.exe INSTALL.vcxproj"],
)

cmake_external(
    name = "hello_ninja",
    # expect to find ./lib/hello.lib as the result of the build
    lib_name = "hello",
    # explicitly specify the generator
    cmake_options = ["-GNinja"],
    generate_crosstool_file = True,
    lib_source = ":srcs",
    # specify to call ninja after configuring
    make_commands = [
        "ninja",
        "ninja install",
    ],
)

cmake_external(
    name = "hello_nmake",
    # explicitly specify the generator
    cmake_options = ["-G \"NMake Makefiles\""],
    generate_crosstool_file = True,
    lib_source = ":srcs",
    # specify to call nmake after configuring
    make_commands = [
        "nmake",
        "nmake install",
    ],
    # expect to find ./lib/hello.lib as the result of the build
    static_libraries = ["hello.lib"]
)

cmake_external arguments:

Mandatory arguments: name, lib_source

attrs: {
    # CMake only:
    #
    # Relative install prefix to be passed to CMake in -DCMAKE_INSTALL_PREFIX
    "install_prefix": attr.string(mandatory = False),
    # CMake cache entries to initialize (they will be passed with -Dkey=value)
    # Values, defined by the toolchain, will be joined with the values, passed here.
    # (Toolchain values come first)
    "cache_entries": attr.string_dict(mandatory = False, default = {}),
    # CMake environment variable values to join with toolchain-defined.
    # For example, additional CXXFLAGS.
    "env_vars": attr.string_dict(mandatory = False, default = {}),
    # Other CMake options
    "cmake_options": attr.string_list(mandatory = False, default = []),
    # When True, CMake crosstool file will be generated from the toolchain values,
    # provided cache-entries and env_vars (some values will still be passed as -Dkey=value
    # and environment variables).
    # If CMAKE_TOOLCHAIN_FILE cache entry is passed, specified crosstool file will be used
    # When using this option, it makes sense to specify CMAKE_SYSTEM_NAME in the
    # cache_entries - the rule makes only a poor guess about the target system,
    # it is better to specify it manually.
    "generate_crosstool_file": attr.bool(mandatory = False, default = False),
    #
    # From framework.bzl:
    # 
    # Library name. Defines the name of the install directory and the name of the static library,
    # if no output files parameters are defined (any of static_libraries, shared_libraries,
    # interface_libraries, binaries_names)
    # Optional. If not defined, defaults to the target's name.
    "lib_name": attr.string(mandatory = False),
    # Label with source code to build. Typically a filegroup for the source of remote repository.
    # Mandatory.
    "lib_source": attr.label(mandatory = True, allow_files = True),
    # Optional compilation definitions to be passed to the dependencies of this library.
    # They are NOT passed to the compiler, you should duplicate them in the configuration options.
    "defines": attr.string_list(mandatory = False, default = []),
    #
    # Optional additional inputs to be declared as needed for the shell script action.
    # Not used by the shell script part in cc_external_rule_impl.
    "additional_inputs": attr.label_list(mandatory = False, allow_files = True, default = []),
    # Optional additional tools needed for the building.
    # Not used by the shell script part in cc_external_rule_impl.
    "additional_tools": attr.label_list(mandatory = False, allow_files = True, default = []),
    #
    # Optional part of the shell script to be added after the make commands
    "postfix_script": attr.string(mandatory = False),
    # Optinal make commands, defaults to ["make", "make install"]
    "make_commands": attr.string_list(mandatory = False, default = ["make", "make install"]),
    #
    # Optional dependencies to be copied into the directory structure.
    # Typically those directly required for the external building of the library/binaries.
    # (i.e. those that the external buidl system will be looking for and paths to which are
    # provided by the calling rule)
    "deps": attr.label_list(mandatory = False, allow_files = True, default = []),
    # Optional tools to be copied into the directory structure.
    # Similar to deps, those directly required for the external building of the library/binaries.
    "tools_deps": attr.label_list(mandatory = False, allow_files = True, default = []),
    #
    # Optional name of the output subdirectory with the header files, defaults to 'include'.
    "out_include_dir": attr.string(mandatory = False, default = "include"),
    # Optional name of the output subdirectory with the library files, defaults to 'lib'.
    "out_lib_dir": attr.string(mandatory = False, default = "lib"),
    # Optional name of the output subdirectory with the binary files, defaults to 'bin'.
    "out_bin_dir": attr.string(mandatory = False, default = "bin"),
    #
    # Optional. if true, link all the object files from the static library,
    # even if they are not used.
    "alwayslink": attr.bool(mandatory = False, default = False),
    # Optional link options to be passed up to the dependencies of this library
    "linkopts": attr.string_list(mandatory = False, default = []),
    #
    # Output files names parameters. If any of them is defined, only these files are passed to
    # Bazel providers.
    # if no of them is defined, default lib_name.a/lib_name.lib static library is assumed.
    #
    # Optional names of the resulting static libraries.
    "static_libraries": attr.string_list(mandatory = False),
    # Optional names of the resulting shared libraries.
    "shared_libraries": attr.string_list(mandatory = False),
    # Optional names of the resulting interface libraries.
    "interface_libraries": attr.string_list(mandatory = False),
    # Optional names of the resulting binaries.
    "binaries": attr.string_list(mandatory = False),
    # Flag variable to indicate that the library produces only headers
    "headers_only": attr.bool(mandatory = False, default = False),
  }

Design document:

External C/C++ libraries rules