"cargo install --target-dir" does not work

[RalfJung]

cargo install clearly needs a target dir, and honors the CARGO_TARGET_DIR env var. But for some reason it does not accept the --target-dir flag, unlike the other commands.

Would be nice to make this consistent. :)

[ehuss]

@alexcrichton mentioned in #4725 (comment) that you would prefer not to add the flag at that time. I wonder if your mind has changed on that? I don't see any particular downsides to adding it, and it would provide consistency with all the other build commands.

[alexcrichton]

I believe that comment was more in reference to "let's not add a single flag for just cargo install", but now that --target-dir is everywhere except cargo install then makes sense to me to add support there.

[bl2e]

Would like to work on this!

[ehuss]

Great! Let us know if you have any questions.

[AlvinKuruvilla]

Hello Im considering working on this issue, where exactly would this new flag be added I'm thinking it would be in the same file as 3fbd5ae or would there be a more suitable place ?

[ehuss]

@AlvinKuruvilla I think @bl2e mentioned they were working on this. @bl2e are you still working on it?

Some brief instructions:

• There is an arg_target_dir function that needs to be called in the install command.
• Install has special consideration for the target dir, so this code will need to be updated.
• At least one test should be added (perhaps more to test different source behavior). Tests would go in install.rs. There are some existing tests for target-dir behavior there already. More details about running and writing tests can be found in CONTRIBUTING.md and cargo-test-support.
• The documentation needs to be updated. There is some discussion of how to update the man pages in the docs README. The help item also needs to be updated.

[bl2e]

Yes still working on it.

[thiagoarrais]

Should be closed as of #8391?

[ehuss]

Yes, thanks!