Only load ~/.cargo/config for cargo install

[alexcrichton]

This commit tweaks how configuration is loaded for cargo install, ensuring
that we only load configuration from $HOME instead of the current working
directory. This should make installations a little more consistent in that they
probably shouldn't cover project-local configuration but should respect global
configuration!

Closes #6025

[rust-highfive]

r? @matklad

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[alexcrichton]

r? @ehuss

[dwijnand]

LGTM!

Had a look at the issue when it was opened so it's interesting to see how you solved this.

Is this going to be blocked on indiv0/lazycell#90 being reviewed, merged and released, I wonder?

[alexcrichton]

Thanks! Yeah we'll need to wait for that PR to merge, but if it doesn't happen in the next few days I'll figure out another strategy

[ehuss]

Looks good once the lazycell release is resolved.

[Mark-Simulacrum]

I would (loosely) expect that cargo install with a --path argument should use the cargo config from that path since you're probably installing a local package. I could see us warning about that (rare, I believe) case when we detect a local cargo config though.

(Generally it seems like I want an option to override this PR and say "no use this cargo config")

[alexcrichton]

@Mark-Simulacrum that seems plausible to me too! I think I'll leave that for a future PR though :)

[dwijnand]

I agree, best fix the regression in #6025 before stretching for Mark's use case, imo.

[alexcrichton]

@bors: r=ehuss

[bors]

📌 Commit d9534bf has been approved by ehuss

[bors]

⌛ Testing commit d9534bf with merge 77e02e7...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: ehuss
Pushing 77e02e7 to master...