error: Argument to option 'emit' missing
       Usage:
           --emit <TYPE>[=<FILE>]
                               Comma separated list of types of output for the
                               compiler to emit.
                               Each TYPE has the default FILE name:
                               * asm - CRATE_NAME.s
                               * llvm-bc - CRATE_NAME.bc
                               * dep-info - CRATE_NAME.d
                               * link - (platform and crate-type dependent)
                               * llvm-ir - CRATE_NAME.ll
                               * metadata - libCRATE_NAME.rmeta
                               * mir - CRATE_NAME.mir
                               * obj - CRATE_NAME.o
                               * thin-link-bitcode - CRATE_NAME.indexing.o