tools/build_rules/fortran.bzl

load("@//tools/build_rules:select.bzl", "compiler_select")

def _single_fortran_object_impl(ctx):
    toolchain_cflags = (ctx.fragments.cpp.compiler_options([]) +
                        ctx.fragments.cpp.c_options +
                        ctx.fragments.cpp.unfiltered_compiler_options([]) +
                        [
                            "-fPIC",
                            "-Wno-maybe-uninitialized",
                            "-Wno-unused-dummy-argument",
                            "-Wno-conversion",
                            "-Wno-unused-variable",
                            "-Wno-character-truncation",
                        ])

    cmd = toolchain_cflags + ["-c", ctx.file.src.path, "-o", ctx.outputs.pic_o.path]
    filtered_cmd = []

    # Strip out the C/C++/Clang specific flags.
    exclude_flags = [
        "-fcolor-diagnostics",
        "-Wswitch-enum",
        "-Wpointer-arith",
        "-Wcast-qual",
        "-Wwrite-strings",
        "-Wsign-compare",
        "-Wformat=2",
        "-Werror",
        "-Wextra",
        "-Wno-builtin-macro-redefined",
        "-Wunused-local-typedefs",
        "-D__has_feature(x)=0",
        "-fmacro-backtrace-limit=0",
    ]

    for flag in cmd:
        if flag not in exclude_flags and not (flag.startswith("-fsanitize") or
                                              flag.startswith("-fno-sanitize")):
            filtered_cmd.append(flag)

    ctx.action(
        inputs = [ctx.file.src] + ctx.files._cc_toolchain,
        outputs = [ctx.outputs.pic_o],
        mnemonic = "Fortran",
        executable = ctx.fragments.cpp.compiler_executable,
        arguments = filtered_cmd,
        progress_message = "Building %s" % ctx.outputs.pic_o.short_path,
    )

def _define_fortran_output(src):
    if not src.name.endswith(".f"):
        fail("Fortran files must end in '.f'", "src")

    fortran_file_base = src.name[:-2]
    return {
        "pic_o": fortran_file_base + ".pic.o",
    }

_single_fortran_object = rule(
    attrs = {
        "src": attr.label(
            single_file = True,
            allow_files = FileType([".f"]),
        ),
        "cc_libs": attr.label_list(providers = ["cc"]),
        # TODO(Brian): Replace this with something more fine-grained from the
        # configuration fragment or something.
        "_cc_toolchain": attr.label(
            default = Label("@//tools/cpp:toolchain"),
        ),
    },
    fragments = [
        "cpp",
    ],
    outputs = _define_fortran_output,
    implementation = _single_fortran_object_impl,
)

def fortran_library(name, srcs, deps = [], visibility = None):
    """Builds a shared library from a set of fortran files.

    Args:
      srcs: list of fortran files ending in .f
      deps: cc_library or fortran_library dependencies.
    """
    pic_o_files = []
    for src in srcs:
        pic_o_file = src[:-2] + ".pic.o"
        _single_fortran_object(
            name = name + "_" + pic_o_file,
            src = src,
            visibility = ["//visibility:private"],
            restricted_to = ["@//tools:k8"],
        )
        pic_o_files.append(pic_o_file)

    native.cc_library(
        name = name,
        deps = deps,
        srcs = pic_o_files,
        linkopts = [
            "-lgfortran",
        ],
        visibility = visibility,
        restricted_to = ["@//tools:k8"],
    )

f2c_copts = compiler_select({
    "clang": [
        "-Wno-incompatible-pointer-types-discards-qualifiers",
        # Clang appears to be a bit over-eager about this and the comma operator.
        "-Wno-sometimes-uninitialized",
    ],
    "gcc": [
        # TODO(Brian): Remove this once we can actually disable all the warnings.
        # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43245 isn't fixed in our
        # roborio toolchain yet, so we can't for now.
        "-Wno-error",
    ],
}) + [
    # f2c appears to know what it's doing without adding extra ().
    "-Wno-parentheses",
    "-Wno-unused-parameter",
    "-Wno-missing-field-initializers",
    "-Wno-unused-variable",
]

"""Copts to use when compiling f2c-generated files.

This is useful when building externally-f2ced files."""

def f2c_library(name, srcs, copts = [], **kwargs):
    """Converts Fortran code to C and then compiles it.

    Attrs:
      srcs: .f source files
      **kwargs: passed to native.cc_library
    """
    c_srcs = [f[:-2] + ".c" for f in srcs]

    out_dir = c_srcs[0].split("/")[:-1]
    for c_src in c_srcs:
        if c_src.split("/")[:-1] != out_dir:
            # Need to figure out how to make multiple f2c calls or something to
            # support this, and we haven't had a use case yet.
            fail("Multiple output directories not supported", "srcs")

    native.genrule(
        name = "_%s_f2c" % name,
        visibility = ["//visibility:private"],
        srcs = srcs,
        outs = c_srcs,
        tools = [
            "@f2c",
            "@//tools/build_rules:quiet_success",
        ],
        cmd = " ".join([
            "$(location @//tools/build_rules:quiet_success)",
            "$(location @f2c)",
            "-d$(@D)/%s" % ("/".join(out_dir),),
            "$(SRCS)",
        ]),
    )
    native.cc_library(
        name = name,
        srcs = c_srcs,
        copts = f2c_copts + copts,
        **kwargs
    )