[tor-bugs] #26497 [Core Tor/Tor]: set CARGO_HOME correctly or stop using it

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#26497: set CARGO_HOME correctly or stop using it
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 Reporter:  catalyst                            |          Owner:  (none)
     Type:  defect                              |         Status:  new
 Priority:  Medium                              |      Milestone:  Tor:
                                                |  unspecified
Component:  Core Tor/Tor                        |        Version:
 Severity:  Normal                              |     Resolution:
 Keywords:  rust, tor-ci, 035-removed-20180711  |  Actual Points:
Parent ID:                                      |         Points:
 Reviewer:                                      |        Sponsor:
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Comment (by catalyst):

 Right now on master `src/rust/tor_rust/include.am` sets `CARGO_HOME` to
 `$(abs_top_builddir)/src/rust` but `src/test/test_rust.sh` sets it to
 `${abs_top_builddir:-../../..}/src/rust/.cargo`.  When building with
 `--enable-cargo-online-mode`, I think this means we get two copies of the
 crate registry and cache: one in `src/rust`, and one in `src/rust/.cargo`.

 We should avoid this redundancy.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26497#comment:3>
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