Always produce sub-obligations when using cached projection result

[Aaron1011]

See #85360

When we skip adding the sub-obligations to the obligation list, we can affect whether or not the final result is EvaluatedToOk or EvaluatedToOkModuloObligations. This creates problems for incremental compilation, since the projection cache is untracked shared state.

To solve this issue, we unconditionally process the sub-obligations. Surprisingly, this is a slight performance win in many cases.

[rust-highfive]

r? @varkor

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[Aaron1011]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 8657bb2 with merge c3a39b612f192447636019e943fd635f36375fb6...

[bors]

☀️ Try build successful - checks-actions
Build commit: c3a39b612f192447636019e943fd635f36375fb6 (c3a39b612f192447636019e943fd635f36375fb6)

[rust-timer]

Queued c3a39b612f192447636019e943fd635f36375fb6 with parent 7dc9ff5, future comparison URL.

[rust-timer]

Finished benchmarking try commit (c3a39b612f192447636019e943fd635f36375fb6): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf

[Aaron1011]

r? @nikomatsakis

[nikomatsakis]

@bors r+

[bors]

📌 Commit 8657bb2 has been approved by nikomatsakis

[nikomatsakis]

Well, can't argue with the benchmark results!

[bors]

⌛ Testing commit 8657bb2 with merge 6f5a198...

[bors]

☀️ Test successful - checks-actions
Approved by: nikomatsakis
Pushing 6f5a198 to master...