Fix LTO with doctests. #8657
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Fix LTO with doctests. #8657
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Fix LTO with doctests. This fixes an issue where `cargo test --release` would fail to run doctests if LTO is set in `profile.release` or `profile.bench`. The issue is that dependencies were built with `-Clinker-plugin-lto`, but the final rustdoc invocation did not issue `-C lto`. This causes a link failure (or crash!) because the necessary object code was missing. This is because rustdoc historically did not support codegen flags, so Cargo has never passed them in. Rustdoc now supports codegen flags (via rust-lang/rust#63827), so it should be safe to start passing them in. For now, I am only adding LTO, but more should be added in the future. There are two bugs here. One is that LTO flags aren't passed to rustdoc. The other is that the "doctest" unit was using the wrong profile (it was using dev/release when it should be using test/bench). There are two distinct scenarios here. One where just `release` has `lto` set. And one where both `release` and `bench` have `lto` set. This is relevant because LTO mostly cares about what the final artifact wants, and in the case where `bench` does not have `lto` set, then LTO will not be used for tests. This will hopefully be a little cleaner in the future when rust-lang#6988 is stabilized, which causes the test/bench profiles to *inherit* from the dev/bench profiles, which means you won't need to manually synchronize the test/bench profiles with dev/release. Fixes rust-lang#8654
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[beta] Fix LTO with doctests. Beta packports: * #8653 Fix cache_messages::rustdoc test broken on beta. — so that CI tests pass * #8648 Add spaces after -C and -Z flags for consistency — so that #8657 can be merged * #8657 Fix LTO with doctests. Although the LTO regression is on 1.46, I probably won't do a stable backport even if there is a point release, as I think it would be good to have sufficient time for testing on nightly, and I don't want to rush it. I'm willing to reconsider that, though.
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Update cargo 8 commits in 51b66125ba97d2906f461b3f4e0408f206299bb6..126907a7cfccbe93778530e6a6bbaa3adb6c515c 2020-08-19 20:22:52 +0000 to 2020-08-31 20:42:11 +0000 - Fix flakiness in close_output test (rust-lang/cargo#8668) - Reload unstable table from config file in `reload_rooted_at` (rust-lang/cargo#8656) - Bump to 0.49.0, update changelog (rust-lang/cargo#8659) - Fix LTO with doctests. (rust-lang/cargo#8657) - Add spaces after -C and -Z flags for consistency (rust-lang/cargo#8648) - Fix cache_messages::rustdoc test broken on beta. (rust-lang/cargo#8653) - fix: remove unnecessary allocations (rust-lang/cargo#8641) - Fixed a spelling and some clippy warnings (rust-lang/cargo#8637)
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This fixes an issue where
cargo test --releasewould fail to run doctests if LTO is set inprofile.releaseorprofile.bench.The issue is that dependencies were built with
-Clinker-plugin-lto, but the final rustdoc invocation did not issue-C lto. This causes a link failure (or crash!) because the necessary object code was missing. This is because rustdoc historically did not support codegen flags, so Cargo has never passed them in. Rustdoc now supports codegen flags (via rust-lang/rust#63827), so it should be safe to start passing them in. For now, I am only adding LTO, but more should be added in the future.There are two bugs here. One is that LTO flags aren't passed to rustdoc. The other is that the "doctest" unit was using the wrong profile (it was using dev/release when it should be using test/bench).
There are two distinct scenarios here. One where just
releasehasltoset. And one where bothreleaseandbenchhaveltoset. This is relevant because LTO mostly cares about what the final artifact wants, and in the case wherebenchdoes not haveltoset, then LTO will not be used for tests. This will hopefully be a little cleaner in the future when #6988 is stabilized, which causes the test/bench profiles to inherit from the dev/bench profiles, which means you won't need to manually synchronize the test/bench profiles with dev/release.Fixes #8654