cargo test suite fails if default branch is not master

[bk2204]

Problem
Running cargo test in the cargo repository fails many tests if the user has set the default branch to something other than master.

Steps

1. git config --global init.defaultBranch dev
2. cargo test
3. Notice failures

Possible Solution(s)
When using Git in a test suite, it's necessary to set HOME to a controlled location and to also set GIT_CONFIG_NOSYSTEM to avoid reading the system configuration file; otherwise, the global or system configuration files can break tests. Cargo probably needs to set these values during setup in the test suite; this is probably not the only configuration option that will have the effect of breaking tests.

Notes

Output of cargo version:

cargo 1.47.0 (f3c7e066a 2020-08-28)

(Note that this is not the version being tested, about which this report is being made.)

Debian GNU Linux amd64/sid, rustc 1.47.0, cargo repository revision 2af662e.

[ehuss]

Thanks for the report! The tests run in a sandbox with a custom HOME, but I believe the issue is that the index created for each test is built outside of the sandbox. The git repo is created around here. It definitely would be good to have the tests ignore outside settings, though I'm not sure the easiest way to do that. #7944 recently added a special-cased fix for the cargo new tests, but a more general solution would be nice! It looks like libgit2's testsuite manually calls cl_sandbox_set_search_path_defaults to control the search paths.