* guix/scripts/build.scm (transform-package-inputs): New procedure. (%transformations): Add it. (%transformation-options, show-transformation-options-help): Add --with-input. * tests/scripts-build.scm ("options->transformation, with-input"): ("options->transformation, with-input, no matches"): New tests. * tests/guix-build.sh: Add tests. * doc/guix.texi (Package Transformation Options): Document it.