configure()¶

The configure() method should be used for the configuration of settings and options in the recipe for later use in the different methods like generate(), build() or package(). This method executes while building the dependency graph and expanding the packages dependencies, which means that when this method executes the dependencies are still not there, they do not exist, and it is not possible to access self.dependencies.

For example, for a C (not C++) library, the compiler.libcxx and compiler.cppstd settings shouldn’t even exist during the build(). It is not only that they are not part of the package_id, but they shouldn’t be used in the build process at all. They will be defined in the profile, because other packages in the graph can be C++ packages and need them, but it is the responsibility of this recipe to remove them so they are not used in the recipe:

settings = "os", "compiler", "build_type", "arch"

def configure(self):
    # Not all compilers have libcxx subsetting, so we use rm_safe
    # to avoid exceptions
    self.settings.rm_safe("compiler.libcxx")
    self.settings.rm_safe("compiler.cppstd")

def package_id(self):
    # No need to delete those settings here, they were already deleted
    pass

Note

From Conan 2.4, the above configure() is not necessary if defined languages = "C" recipe attribute (experimental).

For packages where you want to remove every subsetting of a setting, you can use the rm_safe method with a wildcard:

settings = "os", "compiler", "build_type", "arch"

def configure(self):
    self.settings.rm_safe("compiler.*")

This will remove all the subsettings of the compiler setting, like compiler.libcxx or compiler.cppstd, but keep the compiler setting itself (Which self.settings.rm_safe("compiler") would remove).

Likewise, for a package containing a library, the fPIC option really only applies when the library is compiled as a static library, but otherwise, the fPIC option doesn’t make sense, so it should be removed:

options = {"shared": [True, False], "fPIC": [True, False]}
default_options = {"shared": False, "fPIC": True}

def configure(self):
    if self.options.shared:
        # fPIC might have been removed in config_options(), so we use rm_safe
        self.options.rm_safe("fPIC")

Available automatic implementations¶

Warning

This feature is experimental and subject to breaking changes. See the Conan stability section for more information.

When the configure() method is not defined, Conan can automatically manage some conventional options if specified in the implements ConanFile attribute:

auto_shared_fpic¶

Options automatically managed:

fPIC (True, False).
shared (True, False).
header_only (True, False).

It can be added to the recipe like this:

from conan import ConanFile

class Pkg(ConanFile):
    implements = ["auto_shared_fpic"]
    ...

Then, if no configure() method is specified in the recipe, Conan will automatically manage the fPIC setting in the configure step like this:

if conanfile.options.get_safe("header_only"):
    conanfile.options.rm_safe("fPIC")
    conanfile.options.rm_safe("shared")
elif conanfile.options.get_safe("shared"):
    conanfile.options.rm_safe("fPIC")

Be aware that adding this implementation to the recipe may also affect the configure step.

If you need to implement custom behaviors in your recipes but also need this logic, it must be explicitly declared:

def configure(self):
    if conanfile.options.get_safe("header_only"):
        conanfile.options.rm_safe("fPIC")
        conanfile.options.rm_safe("shared")
    elif conanfile.options.get_safe("shared"):
        conanfile.options.rm_safe("fPIC")
    self.settings.rm_safe("compiler.libcxx")
    self.settings.rm_safe("compiler.cppstd")

Recipes can suggest values for their dependencies options as default_options = {"*:shared": True}, but it is not possible to do that conditionally. For this purpose, it is also possible to use the configure() method:

def configure(self):
    if something:
        self.options["*"].shared = True

Note

Best practices

Recall that it is not possible to define settings or conf values in recipes, they are read only.
The definition of options values is only a “suggestion”, depending on the graph computation, priorities, etc., the final value of options can be different from the one set by the recipe.