def get_transitive_build_target_deps(self) -> T.Set[T.Union[BuildTarget, 'CustomTarget']]:
        '''
        Recursively fetch the build targets that this custom target depends on,
        whether through `command:`, `depends:`, or `sources:` The recursion is
        only performed on custom targets.
        This is useful for setting PATH on Windows for finding required DLLs.
        F.ex, if you have a python script that loads a C module that links to
        other DLLs in your project.
        '''
        bdeps: T.Set[T.Union[BuildTarget, 'CustomTarget']] = set()
        deps = self.get_target_dependencies()
        for d in deps:
            if isinstance(d, BuildTarget):
                bdeps.add(d)
            elif isinstance(d, CustomTarget):
                bdeps.update(d.get_transitive_build_target_deps())
        return bdeps

        Recursively fetch the build targets that this custom target depends on,
        whether through `command:`, `depends:`, or `sources:` The recursion is
        only performed on custom targets.
        This is useful for setting PATH on Windows for finding required DLLs.
        F.ex, if you have a python script that loads a C module that links to
        other DLLs in your project.
        
mesonbuild/build.py