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Rollup merge of #104206 - compiler-errors:ocx-more-2, r=lcnr

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Remove `save_and_restore_in_snapshot_flag`, use `ObligationCtxt` more

r? ```@lcnr```
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Dylan DPC 2022-11-12 12:02:52 +05:30 • committed by GitHub
commit 662df1ec86
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4 changed files with 119 additions and 179 deletions
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26
compiler/rustc_infer/src/infer/mod.rs
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@ -778,32 +778,6 @@ impl<'tcx> InferCtxt<'tcx> {
}
}
/// Clear the "currently in a snapshot" flag, invoke the closure,
/// then restore the flag to its original value. This flag is a
/// debugging measure designed to detect cases where we start a
/// snapshot, create type variables, and register obligations
/// which may involve those type variables in the fulfillment cx,
/// potentially leaving "dangling type variables" behind.
/// In such cases, an assertion will fail when attempting to
/// register obligations, within a snapshot. Very useful, much
/// better than grovelling through megabytes of `RUSTC_LOG` output.
///
/// HOWEVER, in some cases the flag is unhelpful. In particular, we
/// sometimes create a "mini-fulfilment-cx" in which we enroll
/// obligations. As long as this fulfillment cx is fully drained
/// before we return, this is not a problem, as there won't be any
/// escaping obligations in the main cx. In those cases, you can
/// use this function.
pub fn save_and_restore_in_snapshot_flag<F, R>(&self, func: F) -> R
where
F: FnOnce(&Self) -> R,
{
let flag = self.in_snapshot.replace(false);
let result = func(self);
self.in_snapshot.set(flag);
result
}
fn start_snapshot(&self) -> CombinedSnapshot<'tcx> {
debug!("start_snapshot()");