Cargo should tell subcommands the path to itself

[vojtechkral]

Many subcommands listed in the wiki need to run other existing cargo commands one way or another. Most of them seem to just call cargo (that is, the one in PATH) and hope it's the right one.

Cargo should pass the path to itself to subcommands so that they can be sure they're running the right cargo. IMHO the best way would be an environment variable, something like CARGO_BIN.

(In case you feel this is ok, I'm willing to write the patch.)

[matklad]

Related issue: #3744

[alexcrichton]

Yeah sounds like we shoudl just blanket set a CARGO env var or something like that for subprocesses to learn the path to the original Cargo

[matklad]

Fixed by #3789