python_configure.bzl

"""Repository rule for Python autoconfiguration.

`python_configure` depends on the following environment variables:

  * `PYTHON_BIN_PATH`: Location of python binary.
  * `PYTHON_LIB_PATH`: Location of python libraries.

These can be directly set with the `python_interpreter_target` and
`python_library_target` respectively.
"""

_BAZEL_SH = "BAZEL_SH"
_PYTHON_BIN_PATH = "PYTHON_BIN_PATH"
_PYTHON_CONFIG_BIN_PATH = "PYTHON_CONFIG_BIN_PATH"
_PYTHON_LIB_PATH = "PYTHON_LIB_PATH"

# TODO: Move scripts to respective files and expose to rule.
_INCLUDE_SCRIPT = """
from __future__ import print_function
from sysconfig import get_path
print(get_path("include"))"""

_LIBRARY_SCRIPT = """
from __future__ import print_function
import site
import os

try:
    input = raw_input
except NameError:
    pass

python_paths = []
if os.getenv('PYTHONPATH') is not None:
    python_paths = os.getenv('PYTHONPATH').split(':')
try:
    library_paths = site.getsitepackages()
except AttributeError:
    from sysconfig import get_path
    library_paths = [get_path("purelib")]

all_paths = set(python_paths + library_paths)
paths = []
for path in all_paths:
   if os.path.isdir(path):
       paths.append(path)
if len(paths) >=1:
   print(paths[0])
"""

def _tpl(repository_ctx, tpl, substitutions = {}, out = None):
    if not out:
        out = tpl
    repository_ctx.template(
        out,
        Label("//py:%s.tpl" % tpl),
        substitutions,
    )

def _fail(msg):
    """Output failure message when auto configuration fails."""
    red = "\033[0;31m"
    no_color = "\033[0m"
    fail("%sPython Configuration Error:%s %s\n" % (red, no_color, msg))

def _is_windows(repository_ctx):
    """Returns true if the host operating system is windows."""
    os_name = repository_ctx.os.name.lower()
    if os_name.find("windows") != -1:
        return True
    return False

def _execute(
        repository_ctx,
        cmdline,
        error_msg = None,
        error_details = None,
        empty_stdout_fine = False):
    """Executes an arbitrary shell command.

    Args:
      repository_ctx: the repository_ctx object
      cmdline: list of strings, the command to execute
      error_msg: string, a summary of the error if the command fails
      error_details: string, details about the error or steps to fix it
      empty_stdout_fine: bool, if True, an empty stdout result is fine, otherwise
        it's an error
    Return:
      the result of repository_ctx.execute(cmdline)
    """
    result = repository_ctx.execute(cmdline)
    if result.stderr or not (empty_stdout_fine or result.stdout):
        _fail("\n".join([
            error_msg.strip() if error_msg else "Repository command failed",
            result.stderr.strip(),
            error_details if error_details else "",
        ]))
    return result

def _read_dir(repository_ctx, src_dir):
    """Returns a string with all files in a directory.

    Finds all files inside a directory, traversing subfolders and following
    symlinks. The returned string contains the full path of all files
    separated by line breaks.
    """
    if _is_windows(repository_ctx):
        src_dir = src_dir.replace("/", "\\")
        find_result = _execute(
            repository_ctx,
            ["cmd.exe", "/c", "dir", src_dir, "/b", "/s", "/a-d"],
            empty_stdout_fine = True,
        )

        # src_files will be used in genrule.outs where the paths must
        # use forward slashes.
        result = find_result.stdout.replace("\\", "/")
    else:
        find_result = _execute(
            repository_ctx,
            ["find", src_dir, "-follow", "-type", "f"],
            empty_stdout_fine = True,
        )
        result = find_result.stdout
    return result

def _genrule(src_dir, genrule_name, command, outs, local):
    """Returns a string with a genrule.

    Genrule executes the given command and produces the given outputs.
    """
    return (
        "genrule(\n" +
        '    name = "' +
        genrule_name + '",\n' + (
            "    local = 1,\n" if local else ""
        ) +
        "    outs = [\n" +
        outs +
        "\n    ],\n" +
        '    cmd = """\n' +
        command +
        '\n   """,\n' +
        ")\n"
    )

def _norm_path(path):
    """Returns a path with '/' and remove the trailing slash."""
    path = path.replace("\\", "/")
    if path[-1] == "/":
        path = path[:-1]
    return path

def _symlink_genrule_for_dir(
        repository_ctx,
        src_dir,
        dest_dir,
        genrule_name,
        src_files = [],
        dest_files = []):
    """Returns a genrule to symlink(or copy if on Windows) a set of files.

    If src_dir is passed, files will be read from the given directory; otherwise
    we assume files are in src_files and dest_files
    """
    if src_dir != None:
        src_dir = _norm_path(src_dir)
        dest_dir = _norm_path(dest_dir)
        files = "\n".join(sorted(_read_dir(repository_ctx, src_dir).splitlines()))

        # Create a list with the src_dir stripped to use for outputs.
        dest_files = files.replace(src_dir, "").splitlines()
        src_files = files.splitlines()
    command = []
    outs = []
    for i in range(len(dest_files)):
        if dest_files[i] != "":
            # If we have only one file to link we do not want to use the dest_dir, as
            # $(@D) will include the full path to the file.
            dest = "$(@D)/" + dest_dir + dest_files[i] if len(dest_files) != 1 else "$(@D)/" + dest_files[i]

            # Copy the headers to create a sandboxable setup.
            cmd = "cp -f"
            command.append(cmd + ' "%s" "%s"' % (src_files[i], dest))
            outs.append('        "' + dest_dir + dest_files[i] + '",')
    genrule = _genrule(
        src_dir,
        genrule_name,
        " && ".join(command),
        "\n".join(outs),
        local = True,
    )
    return genrule

def _get_python_bin(repository_ctx):
    """Gets the python bin path."""
    if repository_ctx.attr.python_interpreter_target != None:
        return str(repository_ctx.path(repository_ctx.attr.python_interpreter_target))

    python_bin = repository_ctx.os.environ.get(_PYTHON_BIN_PATH)
    if python_bin != None:
        return python_bin

    python_short_name = "python" + repository_ctx.attr.python_version
    python_bin_path = repository_ctx.which(python_short_name)

    if python_bin_path != None:
        return str(python_bin_path)
    _fail("Cannot find python in PATH, please make sure " +
          "python is installed and add its directory in PATH, or --define " +
          "%s='/something/else'.\nPATH=%s" % (
              _PYTHON_BIN_PATH,
              repository_ctx.os.environ.get("PATH", ""),
          ))

def _get_bash_bin(repository_ctx):
    """Gets the bash bin path."""
    bash_bin = repository_ctx.os.environ.get(_BAZEL_SH)
    if bash_bin != None:
        return bash_bin
    else:
        bash_bin_path = repository_ctx.which("bash")
        if bash_bin_path != None:
            return str(bash_bin_path)
        else:
            _fail("Cannot find bash in PATH, please make sure " +
                  "bash is installed and add its directory in PATH, or --define " +
                  "%s='/path/to/bash'.\nPATH=%s" % (
                      _BAZEL_SH,
                      repository_ctx.os.environ.get("PATH", ""),
                  ))

def _get_python_lib(repository_ctx, python_bin):
    """Gets the python lib path."""
    if repository_ctx.attr.python_library_target:
        return str(repository_ctx.path(repository_ctx.attr.python_library_target))

    # If an interpreter is explicitly passed down, we should should not regard
    # the environmental variable.
    if repository_ctx.attr.python_interpreter_target == None:
        python_lib = repository_ctx.os.environ.get(_PYTHON_LIB_PATH)
        if python_lib:
            return python_lib

    result = _execute(
        repository_ctx,
        [
            python_bin,
            "-c",
            _LIBRARY_SCRIPT,
        ],
        error_msg = "Unable to detect library path.",
        error_details = ("Is Python installed correctly?"),
    )
    return result.stdout.strip("\n")

def _check_python_lib(repository_ctx, python_lib):
    """Checks the python lib path."""
    cmd = 'test -d "%s" -a -x "%s"' % (python_lib, python_lib)
    result = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", cmd])
    if result.return_code == 1:
        _fail("Invalid python library path: %s" % python_lib)

def _check_python_bin(repository_ctx, python_bin):
    """Checks the python bin path."""
    cmd = '[[ -x "%s" ]] && [[ ! -d "%s" ]]' % (python_bin, python_bin)
    result = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", cmd])
    if result.return_code == 1:
        _fail("--define %s='%s' is not executable. Is it the python binary?" % (
            _PYTHON_BIN_PATH,
            python_bin,
        ))

def _get_python_include(repository_ctx, python_bin):
    """Gets the python include path."""
    result = _execute(
        repository_ctx,
        [
            python_bin,
            "-c",
            _INCLUDE_SCRIPT,
        ],
        error_msg = "Problem getting python include path.",
        error_details = ("Is the Python binary path set up right? " +
                         "(See ./configure or " + _PYTHON_BIN_PATH + ".)"),
    )
    return result.stdout.splitlines()[0]

def _get_python_import_lib_name(repository_ctx, python_bin):
    """Get Python import library name (pythonXY.lib) on Windows."""
    result = _execute(
        repository_ctx,
        [
            python_bin,
            "-c",
            "import sys;" +
            'print("python" + str(sys.version_info[0]) + ' +
            '      str(sys.version_info[1]) + ".lib")',
        ],
        error_msg = "Problem getting python import library.",
        error_details = ("Is the Python binary path set up right? " +
                         "(See ./configure or " + _PYTHON_BIN_PATH + ".) "),
    )
    return result.stdout.splitlines()[0]

def _find_python_config(repository_ctx, python_bin):
    """Searches for python-config in the Python bin directory through the Python environment symlinks

    Returns a string path to python-config, or None if not found
    """
    python_config = repository_ctx.os.environ.get(_PYTHON_CONFIG_BIN_PATH)
    if python_config != None:
        return python_config

    bin_dir = repository_ctx.path(python_bin).dirname
    bin_name = "python%s-config" % repository_ctx.attr.python_version

    for i in bin_dir.readdir():
        if bin_name == i.basename:
            return str(bin_dir.get_child(bin_name))

    symlink_base_dir = repository_ctx.path(python_bin).realpath.dirname
    for i in symlink_base_dir.readdir():
        if bin_name == i.basename:
            return str(symlink_base_dir.get_child(bin_name))

    return None

def _get_embed_flags(repository_ctx, python_config):
    """Identifies compiler and linker flags output by python-config required to embed Python

    Returns a tuple containing the copts and linkopts, or empty strings if unsuccessful.
    """
    err_cmd = python_config + " --help"
    comp_cmd = python_config + " --cflags"

    # --embed is an undocumented python >=3.8 flag.
    # See https://github.com/python/cpython/pull/13500
    link_cmd = python_config + " --ldflags --embed"

    # TODO: Resolve ctx.execute vs _execute.
    err = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", err_cmd]).stdout.strip("\n")
    compiler_flags = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", comp_cmd]).stdout.strip("\n")
    linker_flags = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", link_cmd]).stdout.strip("\n")

    if linker_flags == err:
        # Try again without --embed
        link_cmd = python_config + " --ldflags"
        linker_flags = repository_ctx.execute([_get_bash_bin(repository_ctx), "-c", link_cmd]).stdout.strip("\n")

    if linker_flags == err or compiler_flags == err:
        return "", ""

    return compiler_flags, linker_flags

def _create_local_python_repository(repository_ctx):
    """Creates the repository containing files set up to build with Python."""
    python_bin = _get_python_bin(repository_ctx)
    _check_python_bin(repository_ctx, python_bin)
    python_lib = _get_python_lib(repository_ctx, python_bin)
    _check_python_lib(repository_ctx, python_lib)
    python_include = _get_python_include(repository_ctx, python_bin)
    python_include_rule = _symlink_genrule_for_dir(
        repository_ctx,
        python_include,
        "python_include",
        "python_include",
    )

    # To embed python in C++, we need the linker and compiler flags required to embed the Python interpreter
    # See https://docs.python.org/3/extending/embedding.html#embedding-python-in-c
    python_config = _find_python_config(repository_ctx, python_bin)
    python_embed_copts = ""
    python_embed_linkopts = ""
    if python_config:
        python_embed_copts, python_embed_linkopts = _get_embed_flags(repository_ctx, python_config)

    python_import_lib_genrule = ""

    # To build Python C/C++ extension on Windows, we need to link to python import library pythonXY.lib
    # See https://docs.python.org/3/extending/windows.html
    if _is_windows(repository_ctx):
        python_include = _norm_path(python_include)
        python_import_lib_name = _get_python_import_lib_name(repository_ctx, python_bin)
        python_import_lib_src = python_include.rsplit("/", 1)[0] + "/libs/" + python_import_lib_name
        python_import_lib_genrule = _symlink_genrule_for_dir(
            repository_ctx,
            None,
            "",
            "python_import_lib",
            [python_import_lib_src],
            [python_import_lib_name],
        )
    _tpl(repository_ctx, "BUILD", {
        "%{PYTHON_BIN_PATH}": python_bin,
        "%{PYTHON_INCLUDE_GENRULE}": python_include_rule,
        "%{PYTHON_IMPORT_LIB_GENRULE}": python_import_lib_genrule,
        "%{PYTHON_EMBED_COPTS}": python_embed_copts,
        "%{PYTHON_EMBED_LINKOPTS}": python_embed_linkopts,
    })

def _create_remote_python_repository(repository_ctx, remote_config_repo):
    """Creates pointers to a remotely configured repo set up to build with Python.
    """
    repository_ctx.template("BUILD", Label(remote_config_repo + ":BUILD"), {})

def _python_autoconf_impl(repository_ctx):
    """Implementation of the python_autoconf repository rule."""
    if repository_ctx.attr.python_version not in ("2", "3", ""):
        _fail("Invalid python_version value, must be '2', '3' or '' (default).")

    _create_local_python_repository(repository_ctx)

# Configure Activated Python Environment
python_configure = repository_rule(
    implementation = _python_autoconf_impl,
    environ = [
        _BAZEL_SH,
        _PYTHON_BIN_PATH,
        _PYTHON_LIB_PATH,
    ],
    attrs = {
        "python_version": attr.string(default = ""),
        "python_interpreter_target": attr.label(),
        "python_library_target": attr.string(),
    },
)
"""Detects and configures the local Python.

Add the following to your WORKSPACE FILE:

```python
python_configure(name = "local_config_python")
```

Args:
  name: A unique name for this workspace rule.
  python_version: If set to "3", will build for Python 3, i.e. will build
      against the installation corresponding to the binary returned by
      `which python3`.
      If set to "2", will build for Python 2 (`which python2`).
      By default, will build for whatever Python version is returned by
      `which python`.
  python_interpreter_target: If set to a target providing a Python binary,
      this will configure for that Python version instead of the installed
      binary. This configuration takes precedence over python_version. In
      addition, setting this label will ignore `PYTHON_LIB_PATH`- if needed
      use `python_library_target` to explicitly set the desired library.
  python_library_target: If this string is set, this will override the
      environmental variable `PYTHON_LIB_PATH`. Otherwise implicit discovery,
      is used from the availible binary.
"""