Quick Start

Hello World

hello.f90

program hello
    print *, "Hello, Fortran!"
end program hello

BUILD.bazel

load("@rules_fortran//fortran:defs.bzl", "fortran_binary")

fortran_binary(
    name = "hello",
    srcs = ["hello.f90"],
)

bazel run //:hello

Modules and Libraries

Fortran organizes code into modules. Unlike C/C++ headers, Fortran modules are compiled artifacts (.mod files) that must be built before any code that uses them.

math.f90

module math
    implicit none
contains
    function square(x) result(y)
        real, intent(in) :: x
        real :: y
        y = x * x
    end function square
end module math

main.f90

program main
    use math
    implicit none
    print *, "4^2 =", square(4.0)
end program main

BUILD.bazel

load("@rules_fortran//fortran:defs.bzl", "fortran_binary", "fortran_library")

fortran_library(
    name = "math",
    srcs = ["math.f90"],
)

fortran_binary(
    name = "main",
    srcs = ["main.f90"],
    deps = [":math"],
)

rules_fortran handles module dependency ordering automatically. When you declare deps = [":math"], the build system ensures math.mod is generated before compiling main.f90.

Tests

load("@rules_fortran//fortran:defs.bzl", "fortran_test")

fortran_test(
    name = "math_test",
    srcs = ["math_test.f90"],
    deps = [":math"],
)

bazel test //...