# Copyright Spack Project Developers. See COPYRIGHT file for details.
#
# SPDX-License-Identifier: (Apache-2.0 OR MIT)

"""This package contains directives that can be used within a package.

Directives are functions that can be called inside a package
definition to modify the package, for example::

    class OpenMpi(Package):
        depends_on("hwloc")
        provides("mpi")
        ...

``provides`` and ``depends_on`` are spack directives.

The available directives are:

* ``build_system``
* ``conflicts``
* ``depends_on``
* ``extends``
* ``license``
* ``patch``
* ``provides``
* ``resource``
* ``variant``
* ``version``
* ``requires``
* ``redistribute``

"""
import collections
import collections.abc
import os
import re
import warnings
from typing import Any, Callable, List, Optional, Tuple, Type, Union

import spack.deptypes as dt
import spack.error
import spack.fetch_strategy
import spack.llnl.util.tty.color
import spack.package_base
import spack.patch
import spack.spec
import spack.util.crypto
import spack.variant
from spack.dependency import Dependency
from spack.directives_meta import DirectiveError, DirectiveMeta
from spack.resource import Resource
from spack.version import (
    GitVersion,
    Version,
    VersionChecksumError,
    VersionError,
    VersionLookupError,
)

__all__ = [
    "DirectiveError",
    "version",
    "conditional",
    "conflicts",
    "depends_on",
    "extends",
    "maintainers",
    "license",
    "provides",
    "patch",
    "variant",
    "resource",
    "build_system",
    "requires",
    "redistribute",
    "can_splice",
]

_patch_order_index = 0


SpecType = str
DepType = Union[Tuple[str, ...], str]
WhenType = Optional[Union[spack.spec.Spec, str, bool]]
Patcher = Callable[[Union[Type[spack.package_base.PackageBase], Dependency]], None]
PatchesType = Union[Patcher, str, List[Union[Patcher, str]]]


def _make_when_spec(value: WhenType) -> Optional[spack.spec.Spec]:
    """Create a ``Spec`` that indicates when a directive should be applied.

    Directives with ``when`` specs, e.g.:

        patch('foo.patch', when='@4.5.1:')
        depends_on('mpi', when='+mpi')
        depends_on('readline', when=sys.platform() != 'darwin')

    are applied conditionally depending on the value of the ``when``
    keyword argument.  Specifically:

      1. If the ``when`` argument is ``True``, the directive is always applied
      2. If it is ``False``, the directive is never applied
      3. If it is a ``Spec`` string, it is applied when the package's
         concrete spec satisfies the ``when`` spec.

    The first two conditions are useful for the third example case above.
    It allows package authors to include directives that are conditional
    at package definition time, in additional to ones that are evaluated
    as part of concretization.

    Arguments:
        value: a conditional Spec, constant ``bool``, or None if not supplied
           value indicating when a directive should be applied.

    """
    if isinstance(value, spack.spec.Spec):
        return value

    # Unsatisfiable conditions are discarded by the caller, and never
    # added to the package class
    if value is False:
        return None

    # If there is no constraint, the directive should always apply;
    # represent this by returning the unconstrained `Spec()`, which is
    # always satisfied.
    if value is None or value is True:
        return spack.spec.Spec()

    # This is conditional on the spec
    return spack.spec.Spec(value)


SubmoduleCallback = Callable[[spack.package_base.PackageBase], Union[str, List[str], bool]]
directive = DirectiveMeta.directive


@directive("versions")
def version(
    ver: Union[str, int],
    # this positional argument is deprecated, use sha256=... instead
    checksum: Optional[str] = None,
    *,
    # generic version options
    preferred: Optional[bool] = None,
    deprecated: Optional[bool] = None,
    no_cache: Optional[bool] = None,
    # url fetch options
    url: Optional[str] = None,
    extension: Optional[str] = None,
    expand: Optional[bool] = None,
    fetch_options: Optional[dict] = None,
    # url archive verification options
    md5: Optional[str] = None,
    sha1: Optional[str] = None,
    sha224: Optional[str] = None,
    sha256: Optional[str] = None,
    sha384: Optional[str] = None,
    sha512: Optional[str] = None,
    # git fetch options
    git: Optional[str] = None,
    commit: Optional[str] = None,
    tag: Optional[str] = None,
    branch: Optional[str] = None,
    get_full_repo: Optional[bool] = None,
    git_sparse_paths: Optional[
        Union[List[str], Callable[[spack.package_base.PackageBase], List[str]]]
    ] = None,
    submodules: Union[SubmoduleCallback, Optional[bool]] = None,
    submodules_delete: Optional[bool] = None,
    # other version control
    svn: Optional[str] = None,
    hg: Optional[str] = None,
    cvs: Optional[str] = None,
    revision: Optional[str] = None,
    date: Optional[str] = None,
):
    """Declare a version for a package with optional metadata for fetching its code.

    Example::

        version("2.1", sha256="...")
        version("2.0", sha256="...", preferred=True)

    .. versionchanged:: v2.3

       The ``git_sparse_paths`` parameter was added.
    """
    kwargs = {
        key: value
        for key, value in (
            ("sha256", sha256),
            ("sha384", sha384),
            ("sha512", sha512),
            ("preferred", preferred),
            ("deprecated", deprecated),
            ("expand", expand),
            ("url", url),
            ("extension", extension),
            ("no_cache", no_cache),
            ("fetch_options", fetch_options),
            ("git", git),
            ("svn", svn),
            ("hg", hg),
            ("cvs", cvs),
            ("get_full_repo", get_full_repo),
            ("git_sparse_paths", git_sparse_paths),
            ("branch", branch),
            ("submodules", submodules),
            ("submodules_delete", submodules_delete),
            ("commit", commit),
            ("tag", tag),
            ("revision", revision),
            ("date", date),
            ("md5", md5),
            ("sha1", sha1),
            ("sha224", sha224),
            ("checksum", checksum),
        )
        if value is not None
    }
    return lambda pkg: _execute_version(pkg, ver, **kwargs)


def _execute_version(pkg: Type[spack.package_base.PackageBase], ver: Union[str, int], **kwargs):
    if (
        (any(s in kwargs for s in spack.util.crypto.hashes) or "checksum" in kwargs)
        and hasattr(pkg, "has_code")
        and not pkg.has_code
    ):
        raise VersionChecksumError(
            "{0}: Checksums not allowed in no-code packages "
            "(see '{1}' version).".format(pkg.name, ver)
        )

    if not isinstance(ver, (int, str)):
        raise VersionError(
            f"{pkg.name}: declared version '{ver!r}' in package should be a string or int."
        )

    # Declared versions are concrete
    version = Version(ver)

    if isinstance(version, GitVersion) and not hasattr(pkg, "git") and "git" not in kwargs:
        args = ", ".join(f"{argname}='{value}'" for argname, value in kwargs.items())
        raise VersionLookupError(
            f"{pkg.name}: spack version directives cannot include git hashes fetched from URLs.\n"
            f"    version('{ver}', {args})"
        )

    # Store kwargs for the package to later with a fetch_strategy.
    pkg.versions[version] = kwargs


def _depends_on(
    pkg: Type[spack.package_base.PackageBase],
    spec: spack.spec.Spec,
    *,
    when: WhenType = None,
    type: DepType = dt.DEFAULT_TYPES,
    patches: Optional[PatchesType] = None,
):
    when_spec = _make_when_spec(when)
    if not when_spec:
        return

    if not spec.name:
        raise DependencyError(
            f"Invalid dependency specification in package '{pkg.name}':", str(spec)
        )
    if pkg.name == spec.name:
        raise CircularReferenceError(f"Package '{pkg.name}' cannot depend on itself.")

    depflag = dt.canonicalize(type)

    # call this patches here for clarity -- we want patch to be a list,
    # but the caller doesn't have to make it one.

    # Note: we cannot check whether a package is virtual in a directive
    # because directives are run as part of class instantiation, and specs
    # instantiate the package class as part of the `virtual` check.
    # To be technical, specs only instantiate the package class as part of the
    # virtual check if the provider index hasn't been created yet.
    # TODO: There could be a cache warming strategy that would allow us to
    # ensure `Spec.virtual` is a valid thing to call in a directive.
    # For now, we comment out the following check to allow for virtual packages
    # with package files.
    # if patches and spec.virtual:
    #     raise DependencyPatchError("Cannot patch a virtual dependency.")

    # ensure patches is a list
    if patches is None:
        patches = []
    elif not isinstance(patches, (list, tuple)):
        patches = [patches]

    # auto-call patch() directive on any strings in patch list
    patches = [patch(p) if isinstance(p, str) else p for p in patches]
    assert all(callable(p) for p in patches)

    # this is where we actually add the dependency to this package
    deps_by_name = pkg.dependencies.setdefault(when_spec, {})
    dependency = deps_by_name.get(spec.name)

    edges = spec.edges_to_dependencies()
    if edges and not all(x.direct for x in edges):
        raise DirectiveError(
            f"the '^' sigil cannot be used in 'depends_on' directives. Please reformulate "
            f"the directive below as multiple directives:\n\n"
            f'\tdepends_on("{spec}", when="{when_spec}")\n'
        )

    if not dependency:
        dependency = Dependency(pkg, spec, depflag=depflag)
        deps_by_name[spec.name] = dependency
    else:
        copy = dependency.spec.copy()
        copy.constrain(spec, deps=False)
        dependency.spec = copy
        dependency.depflag |= depflag

    # apply patches to the dependency
    for execute_patch in patches:
        execute_patch(dependency)


@directive("conflicts")
def conflicts(conflict_spec: SpecType, when: WhenType = None, msg: Optional[str] = None):
    """Declare a conflict for a package.

    A conflict is a spec that is known to be invalid. For example, a package that cannot build
    with GCC 14 and above can declare::

        conflicts("%gcc@14:")

    To express the same constraint only when the ``foo`` variant is activated::

        conflicts("%gcc@14:", when="+foo")

    Args:
        conflict_spec: constraint defining the known conflict
        when: optional condition that triggers the conflict
        msg: optional user defined message
    """

    def _execute_conflicts(pkg: Type[spack.package_base.PackageBase]):
        # If when is not specified the conflict always holds
        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        # Save in a list the conflicts and the associated custom messages
        conflict_spec_list = pkg.conflicts.setdefault(when_spec, [])
        msg_with_name = f"{pkg.name}: {msg}" if msg is not None else msg
        conflict_spec_list.append((spack.spec.Spec(conflict_spec), msg_with_name))

    return _execute_conflicts


@directive(("dependencies"))
def depends_on(
    spec: SpecType,
    when: WhenType = None,
    type: DepType = dt.DEFAULT_TYPES,
    patches: Optional[PatchesType] = None,
):
    """Declare a dependency on another package.

    Example::

        depends_on("hwloc@2:", when="@1:", type="link")

    Args:
        spec: dependency spec
        when: condition when this dependency applies
        type: One or more of ``"build"``, ``"run"``, ``"test"``, or ``"link"`` (either a string or
            tuple). Defaults to ``("build", "link")``.
        patches: single result of :py:func:`patch` directive, a
            ``str`` to be passed to ``patch``, or a list of these
    """
    dep_spec = spack.spec.Spec(spec)

    def _execute_depends_on(pkg: Type[spack.package_base.PackageBase]):
        _depends_on(pkg, dep_spec, when=when, type=type, patches=patches)

    return _execute_depends_on


@directive("disable_redistribute")
def redistribute(
    source: Optional[bool] = None, binary: Optional[bool] = None, when: WhenType = None
):
    """Declare that the package source and/or compiled binaries should not be redistributed.

    By default, packages allow source/binary distribution (in mirrors/build caches resp.).
    This directive allows users to explicitly disable redistribution for specs.
    """

    return lambda pkg: _execute_redistribute(pkg, source, binary, when)


def _execute_redistribute(
    pkg: Type[spack.package_base.PackageBase],
    source: Optional[bool],
    binary: Optional[bool],
    when: WhenType,
):
    if source is None and binary is None:
        return
    elif (source is True) or (binary is True):
        raise DirectiveError(
            "Source/binary distribution are true by default, they can only "
            "be explicitly disabled."
        )

    if source is None:
        source = True
    if binary is None:
        binary = True

    when_spec = _make_when_spec(when)
    if not when_spec:
        return
    if source is False:
        max_constraint = spack.spec.Spec(f"{pkg.name}@{when_spec.versions}")
        if not max_constraint.satisfies(when_spec):
            raise DirectiveError("Source distribution can only be disabled for versions")

    if when_spec in pkg.disable_redistribute:
        disable = pkg.disable_redistribute[when_spec]
        if not source:
            disable.source = True
        if not binary:
            disable.binary = True
    else:
        pkg.disable_redistribute[when_spec] = spack.package_base.DisableRedistribute(
            source=not source, binary=not binary
        )


@directive(("extendees", "dependencies"))
def extends(spec, when=None, type=("build", "run"), patches=None):
    """Same as :func:`depends_on`, but also adds this package to the extendee list.
    In case of Python, also adds a dependency on ``python-venv``.

    .. note::

       Notice that the default ``type`` is ``("build", "run")``, which is different from
       :func:`depends_on` where the default is ``("build", "link")``."""

    def _execute_extends(pkg):
        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        dep_spec = spack.spec.Spec(spec)

        _depends_on(pkg, dep_spec, when=when, type=type, patches=patches)

        # When extending python, also add a dependency on python-venv. This is done so that
        # Spack environment views are Python virtual environments.
        if dep_spec.name == "python" and not pkg.name == "python-venv":
            _depends_on(pkg, spack.spec.Spec("python-venv"), when=when, type=("build", "run"))

        pkg.extendees[dep_spec.name] = (dep_spec, when_spec)

    return _execute_extends


@directive(dicts=("provided", "provided_together"))
def provides(*specs: SpecType, when: WhenType = None):
    """Declare that this package provides a virtual dependency.

    If a package provides ``mpi``, other packages can declare that they depend on ``mpi``,
    and spack can use the providing package to satisfy the dependency.

    Args:
        *specs: virtual specs provided by this package
        when: condition when this provides clause needs to be considered
    """

    def _execute_provides(pkg: Type[spack.package_base.PackageBase]):
        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        # ``when`` specs for ``provides()`` need a name, as they are used
        # to build the ProviderIndex.
        when_spec.name = pkg.name

        spec_objs = [spack.spec.Spec(x) for x in specs]
        spec_names = [x.name for x in spec_objs]
        if len(spec_names) > 1:
            pkg.provided_together.setdefault(when_spec, []).append(set(spec_names))

        for provided_spec in spec_objs:
            if pkg.name == provided_spec.name:
                raise CircularReferenceError("Package '%s' cannot provide itself." % pkg.name)

            provided_set = pkg.provided.setdefault(when_spec, set())
            provided_set.add(provided_spec)

    return _execute_provides


@directive("splice_specs")
def can_splice(
    target: SpecType, *, when: SpecType, match_variants: Union[None, str, List[str]] = None
):
    """Declare whether the package is ABI-compatible with another package and thus can be spliced
    into concrete versions of that package.

    Args:
        target: The spec that the current package is ABI-compatible with.

        when: An anonymous spec constraining current package for when it is ABI-compatible with
            target.

        match_variants: A list of variants that must match between target spec and current package,
            with special value ``*`` which matches all variants. Example: a ``json`` variant is
            defined on two packages, and they are ABI-compatible whenever they agree on
            the json variant (regardless of whether it is turned on or off). Note that this cannot
            be applied to multi-valued variants and multi-valued variants will be skipped by ``*``.
    """

    def _execute_can_splice(pkg: Type[spack.package_base.PackageBase]):
        when_spec = _make_when_spec(when)
        if isinstance(match_variants, str) and match_variants != "*":
            raise ValueError(
                "* is the only valid string for match_variants "
                "if looking to provide a single variant, use "
                f"[{match_variants}] instead"
            )
        if when_spec is None:
            return
        pkg.splice_specs[when_spec] = (spack.spec.Spec(target), match_variants)

    return _execute_can_splice


@directive("patches")
def patch(
    url_or_filename: str,
    level: int = 1,
    when: WhenType = None,
    working_dir: str = ".",
    reverse: bool = False,
    sha256: Optional[str] = None,
    archive_sha256: Optional[str] = None,
) -> Patcher:
    """Declare a patch to apply to package sources. A when spec can be provided to indicate that a
    particular patch should only be applied when the package's spec meets certain conditions.

    Example::

       patch("foo.patch", when="@1.0.0:")
       patch("https://example.com/foo.patch", sha256="...")

    Args:
        url_or_filename: url or relative filename of the patch
        level: patch level (as in the patch shell command)
        when: optional anonymous spec that specifies when to apply the patch
        working_dir: dir to change to before applying
        reverse: reverse the patch
        sha256: sha256 sum of the patch, used to verify the patch (only required for URL patches)
        archive_sha256: sha256 sum of the *archive*, if the patch is compressed (only required for
            compressed URL patches)
    """

    def _execute_patch(
        pkg_or_dep: Union[Type[spack.package_base.PackageBase], Dependency],
    ) -> None:
        pkg = pkg_or_dep.pkg if isinstance(pkg_or_dep, Dependency) else pkg_or_dep

        if hasattr(pkg, "has_code") and not pkg.has_code:
            raise UnsupportedPackageDirective(
                "Patches are not allowed in {0}: package has no code.".format(pkg.name)
            )

        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        # If this spec is identical to some other, then append this
        # patch to the existing list.
        cur_patches = pkg_or_dep.patches.setdefault(when_spec, [])

        global _patch_order_index
        ordering_key = (pkg.name, _patch_order_index)
        _patch_order_index += 1

        patch: spack.patch.Patch
        if "://" in url_or_filename:
            if sha256 is None:
                raise ValueError("patch() with a url requires a sha256")

            patch = spack.patch.UrlPatch(
                pkg,
                url_or_filename,
                level,
                working_dir=working_dir,
                reverse=reverse,
                ordering_key=ordering_key,
                sha256=sha256,
                archive_sha256=archive_sha256,
            )
        else:
            patch = spack.patch.FilePatch(
                pkg, url_or_filename, level, working_dir, reverse, ordering_key=ordering_key
            )

        cur_patches.append(patch)

    return _execute_patch


def conditional(*values: Union[str, bool], when: Optional[WhenType] = None):
    """Conditional values that can be used in variant declarations."""
    # _make_when_spec returns None when the condition is statically false.
    when = _make_when_spec(when)
    return spack.variant.ConditionalVariantValues(
        spack.variant.ConditionalValue(x, when=when) for x in values
    )


@directive("variants")
def variant(
    name: str,
    default: Optional[Union[bool, str, Tuple[str, ...]]] = None,
    description: str = "",
    values: Optional[Union[collections.abc.Sequence, Callable[[Any], bool]]] = None,
    multi: Optional[bool] = None,
    validator: Optional[Callable[[str, str, Tuple[Any, ...]], None]] = None,
    when: Optional[Union[str, bool]] = None,
    sticky: bool = False,
):
    """Declare a variant for a package.

    Packager can specify a default value as well as a text description.

    Args:
        name: Name of the variant
        default: Default value for the variant, if not specified otherwise the default will be
            False for a boolean variant and 'nothing' for a multi-valued variant
        description: Description of the purpose of the variant
        values: Either a tuple of strings containing the allowed values, or a callable accepting
            one value and returning True if it is valid
        multi: If False only one value per spec is allowed for this variant
        validator: Optional group validator to enforce additional logic. It receives the package
            name, the variant name and a tuple of values and should raise an instance of SpackError
            if the group doesn't meet the additional constraints
        when: Optional condition on which the variant applies
        sticky: The variant should not be changed by the concretizer to find a valid concrete spec

    Raises:
        spack.directives_meta.DirectiveError: If arguments passed to the directive are invalid
    """

    # This validation can be removed at runtime and enforced with an audit in Spack v1.0.
    # For now it's a warning to let people migrate faster.
    if not (
        default is None
        or type(default) in (bool, str)
        or (type(default) is tuple and all(type(x) is str for x in default))
    ):
        if isinstance(default, (list, tuple)):
            did_you_mean = f"default={','.join(str(x) for x in default)!r}"
        else:
            did_you_mean = f"default={str(default)!r}"
        warnings.warn(
            f"default value for variant '{name}' is not a boolean or string: default={default!r}. "
            f"Did you mean {did_you_mean}?",
            stacklevel=3,
            category=spack.error.SpackAPIWarning,
        )

    def format_error(msg, pkg):
        msg += " @*r{{[{0}, variant '{1}']}}"
        return spack.llnl.util.tty.color.colorize(msg.format(pkg.name, name))

    if name in spack.variant.RESERVED_NAMES:

        def _raise_reserved_name(pkg):
            msg = "The name '%s' is reserved by Spack" % name
            raise DirectiveError(format_error(msg, pkg))

        return _raise_reserved_name

    # Ensure we have a sequence of allowed variant values, or a
    # predicate for it.
    if values is None:
        if (
            default in (True, False)
            or type(default) is str
            and default.upper() in ("TRUE", "FALSE")
        ):
            values = (True, False)
        else:
            values = lambda x: True

    # The object defining variant values might supply its own defaults for
    # all the other arguments. Ensure we have no conflicting definitions
    # in place.
    for argument in ("default", "multi", "validator"):
        # TODO: we can consider treating 'default' differently from other
        # TODO: attributes and let a packager decide whether to use the fluent
        # TODO: interface or the directive argument
        if hasattr(values, argument) and locals()[argument] is not None:

            def _raise_argument_error(pkg):
                msg = (
                    "Remove specification of {0} argument: it is handled "
                    "by an attribute of the 'values' argument"
                )
                raise DirectiveError(format_error(msg.format(argument), pkg))

            return _raise_argument_error

    # Allow for the object defining the allowed values to supply its own
    # default value and group validator, say if it supports multiple values.
    default = getattr(values, "default", default)
    validator = getattr(values, "validator", validator)
    multi = getattr(values, "multi", bool(multi))

    # Here we sanitize against a default value being either None
    # or the empty string, as the former indicates that a default
    # was not set while the latter will make the variant unparsable
    # from the command line
    if isinstance(default, tuple):
        default = ",".join(default)

    if default is None or default == "":

        def _raise_default_not_set(pkg):
            if default is None:
                msg = "either a default was not explicitly set, or 'None' was used"
            else:
                msg = "the default cannot be an empty string"
            raise DirectiveError(format_error(msg, pkg))

        return _raise_default_not_set

    description = str(description).strip()

    def _execute_variant(pkg):
        when_spec = _make_when_spec(when)

        if not re.match(spack.spec.IDENTIFIER_RE, name):
            directive = "variant"
            msg = "Invalid variant name in {0}: '{1}'"
            raise DirectiveError(directive, msg.format(pkg.name, name))

        # variants are stored by condition then by name (so only the last variant of a
        # given name takes precedence *per condition*).
        # NOTE: variant defaults and values can conflict if when conditions overlap.
        variants_by_name = pkg.variants.setdefault(when_spec, {})
        variants_by_name[name] = spack.variant.Variant(
            name=name,
            default=default,
            description=description,
            values=values,
            multi=multi,
            validator=validator,
            sticky=sticky,
            precedence=pkg.num_variant_definitions(),
        )

    return _execute_variant


@directive("resources")
def resource(
    *,
    name: Optional[str] = None,
    destination: str = "",
    placement: Optional[str] = None,
    when: WhenType = None,
    # additional kwargs are as for `version()`
    **kwargs,
):
    """Declare an external resource to be fetched and staged when building the package.
    Based on the keywords present in the dictionary the appropriate FetchStrategy will
    be used for the resource. Resources are fetched and staged in their own folder
    inside spack stage area, and then moved into the stage area of the package that
    needs them.

    Keyword Arguments:
        name: name for the resource
        when: condition defining when the resource is needed
        destination: path, relative to the package stage area, to which resource should be moved
        placement: optionally rename the expanded resource inside the destination directory

    """

    def _execute_resource(pkg):
        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        # Check if the path is relative
        if os.path.isabs(destination):
            msg = "The destination keyword of a resource directive can't be an absolute path.\n"
            msg += f"\tdestination : '{destination}\n'"
            raise RuntimeError(msg)

        # Check if the path falls within the main package stage area
        test_path = "stage_folder_root"

        # Normalized absolute path
        normalized_destination = os.path.normpath(os.path.join(test_path, destination))

        if test_path not in normalized_destination:
            msg = "Destination of a resource must be within the package stage directory.\n"
            msg += f"\tdestination : '{destination}'\n"
            raise RuntimeError(msg)

        resources = pkg.resources.setdefault(when_spec, [])
        resources.append(
            Resource(name, spack.fetch_strategy.from_kwargs(**kwargs), destination, placement)
        )

    return _execute_resource


def build_system(*values, **kwargs):
    """Define the build system used by the package. This defines the ``build_system`` variant.

    Example::

        build_system("cmake", "autotools", "meson", default="cmake")
    """
    default = kwargs.get("default", None) or values[0]
    return variant(
        "build_system",
        values=tuple(values),
        description="Build systems supported by the package",
        default=default,
        multi=False,
    )


@directive(dicts=())
def maintainers(*names: str):
    """Declare the maintainers of a package.

    Args:
        names: GitHub username for the maintainer
    """

    def _execute_maintainer(pkg):
        maintainers = set(getattr(pkg, "maintainers", []))
        maintainers.update(names)
        pkg.maintainers = sorted(maintainers)

    return _execute_maintainer


def _execute_license(
    pkg: Type[spack.package_base.PackageBase], license_identifier: str, when: WhenType
):
    # If when is not specified the license always holds
    when_spec = _make_when_spec(when)
    if not when_spec:
        return

    for other_when_spec in pkg.licenses:
        if when_spec.intersects(other_when_spec):
            when_message = ""
            if when_spec != _make_when_spec(None):
                when_message = f"when {when_spec}"
            other_when_message = ""
            if other_when_spec != _make_when_spec(None):
                other_when_message = f"when {other_when_spec}"
            err_msg = (
                f"{pkg.name} is specified as being licensed as {license_identifier} "
                f"{when_message}, but it is also specified as being licensed under "
                f"{pkg.licenses[other_when_spec]} {other_when_message}, which conflict."
            )
            raise OverlappingLicenseError(err_msg)

    pkg.licenses[when_spec] = license_identifier


@directive("licenses")
def license(
    license_identifier: str,
    checked_by: Optional[Union[str, List[str]]] = None,
    when: Optional[Union[str, bool]] = None,
):
    """Declare the license(s) the software is distributed under.

    Args:
        license_identifiers: SPDX identifier specifying the license(s) the software
            is distributed under.
        checked_by: string or list of strings indicating which github user checked the
            license (if any).
        when: A spec specifying when the license applies.
    """

    return lambda pkg: _execute_license(pkg, license_identifier, when)


@directive("requirements")
def requires(
    *requirement_specs: str, policy="one_of", when: Optional[str] = None, msg: Optional[str] = None
):
    """Declare that a spec must be satisfied for a package.

    For instance, a package whose Fortran code can only be compiled with GCC can declare::

        requires("%fortran=gcc")

    A package that requires Apple-Clang on Darwin can declare instead::

        requires("%apple-clang", when="platform=darwin", msg="Apple Clang is required on Darwin")

    Args:
        requirement_specs: spec expressing the requirement
        policy: either ``"one_of"`` or ``"any_of"``. If ``"one_of"``, exactly one of the
            requirements must be satisfied. If ``"any_of"``, at least one of the requirements must
            be satisfied. Defaults to ``"one_of"``.
        when: optional constraint that triggers the requirement. If None the requirement
            is applied unconditionally.
        msg: optional user defined message
    """

    def _execute_requires(pkg: Type[spack.package_base.PackageBase]):
        if policy not in ("one_of", "any_of"):
            err_msg = (
                f"the 'policy' argument of the 'requires' directive in {pkg.name} is set "
                f"to a wrong value (only 'one_of' or 'any_of' are allowed)"
            )
            raise DirectiveError(err_msg)

        when_spec = _make_when_spec(when)
        if not when_spec:
            return

        # Save in a list the requirements and the associated custom messages
        requirement_list = pkg.requirements.setdefault(when_spec, [])
        msg_with_name = f"{pkg.name}: {msg}" if msg is not None else msg
        requirements = tuple(spack.spec.Spec(s) for s in requirement_specs)
        requirement_list.append((requirements, policy, msg_with_name))

    return _execute_requires


class DependencyError(DirectiveError):
    """This is raised when a dependency specification is invalid."""


class CircularReferenceError(DependencyError):
    """This is raised when something depends on itself."""


class DependencyPatchError(DirectiveError):
    """Raised for errors with patching dependencies."""


class UnsupportedPackageDirective(DirectiveError):
    """Raised when an invalid or unsupported package directive is specified."""


class OverlappingLicenseError(DirectiveError):
    """Raised when two licenses are declared that apply on overlapping specs."""
