Add tests to rustbuild #48913

This ensures that the working directory of rustbuild has no effect on it's run; since tests will run with a different cwd this is required for consistent behavior.

Ensures that test cases will be somewhat easier to write.

Will permit creating Config in tests without having to parse a toml file.

In order to run tests, previous commits have cfg'd out various parts of rustbuild. Generally speaking, these are filesystem-related operations and process-spawning related parts. Then, rustbuild is run "as normal" and the various steps that where run are retrieved from the cache and checked against the expected results. Note that this means that the current implementation primarily tests "what" we build, but doesn't actually test that what we build *will* build. In other words, it doesn't do any form of dependency verification for any crate. This is possible to implement, but is considered future work. This implementation strives to cfg out as little code as possible; it also does not currently test anywhere near all of rustbuild. The current tests are also not checked for "correctness," rather, they simply represent what we do as of this commit, which may be wrong. Test cases are drawn from the old implementation of rustbuild, though the expected results may vary.

This ensures that each build will support the testing design of "dry running" builds. It's also checked that a dry run build is equivalent step-wise to a "wet" run build; the graphs we generate when running are directly compared node/node and edge/edge, both for order and contents.

This is too likely to cause spurious bounces on CI; what we run may be dependent on what ran successfully before hand (e.g. RLS features with Clippy), which makes this not tenable. There's no good way to ignore specifically these problematic steps so we'll just ignore everything for the time being. We still test that a dry run worked though so largely this is the same from a ensure-that-tests-work perspective. Eventually we'll want to undo this commit, though, to make our tests more accurate.

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Add tests to rustbuild #48913

Add tests to rustbuild #48913

Commits on Apr 3, 2018