structured attrs: improve support / usage of NIX_ATTRS_{SH,JSON}_FILE
(cherry picked from commit 3c042f3b0b0a7ef9c47bf049f5410dbd4aac9e90)
Change-Id: I7e41838338ee1edf31fff6f9e354c3db2bba6c0e
structured attrs: improve support / usage of NIX_ATTRS_{SH,JSON}_FILE
(cherry picked from commit 3c042f3b0b0a7ef9c47bf049f5410dbd4aac9e90)
Change-Id: I7e41838338ee1edf31fff6f9e354c3db2bba6c0e