def _cli(env: Environment, for_machine: MachineChoice, silent: bool = False) -> T.Optional[PkgConfigCLI]:
        '''Return the CLI pkg-config implementation singleton
        Even when we use another implementation internally, external tools might
        still need the CLI implementation.
        '''
        for_machine = for_machine if env.is_cross_build() else MachineChoice.HOST
        impl: T.Union[Literal[False], T.Optional[PkgConfigInterface]] # Help confused mypy
        impl = PkgConfigInterface.instance(env, for_machine, silent)
        if impl and not isinstance(impl, PkgConfigCLI):
            impl = PkgConfigInterface.class_cli_impl[for_machine]
            if impl is False:
                impl = PkgConfigCLI(env, for_machine, silent, PkgConfigInterface.pkg_bin_per_machine[for_machine])
                if not impl.found():
                    impl = None
                PkgConfigInterface.class_cli_impl[for_machine] = impl
        return T.cast('T.Optional[PkgConfigCLI]', impl) # Trust me, mypy
Return the CLI pkg-config implementation singleton
        Even when we use another implementation internally, external tools might
        still need the CLI implementation.
        
mesonbuild/dependencies/pkgconfig.py