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Add snapshotting to ObligationForest #30965

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Add snapshotting to ObligationForest #30965

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7026faf
Add snapshotting to ObligationForest
soltanmm-google Jan 14, 2016
10de5ec
Change ObligationForest back to using a single vec
soltanmm-google Jan 20, 2016
ca21b0f
Allow no-change snapshots to be done in succession
soltanmm-google Jan 22, 2016
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13 changes: 6 additions & 7 deletions src/librustc_data_structures/obligation_forest/README.md
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Expand Up @@ -60,11 +60,9 @@ which includes three bits of information:

#### Snapshots

The `ObligationForest` supports a limited form of snapshots; see
`start_snapshot`; `commit_snapshot`; and `rollback_snapshot`. In
particular, you can use a snapshot to roll back new root
obligations. However, it is an error to attempt to
`process_obligations` during a snapshot.
The `ObligationForest` supports snapshots; see
`start_snapshot`; `commit_snapshot`; and `rollback_snapshot`. Snapshots roll
back all externally visible state.

### Implementation details

Expand All @@ -74,7 +72,8 @@ the forest is stored in a vector. Each element of the vector is a node
in some tree. Each node in the vector has the index of an (optional)
parent and (for convenience) its root (which may be itself). It also
has a current state, described by `NodeState`. After each
processing step, we compress the vector to remove completed and error
nodes, which aren't needed anymore.
processing step, we compress the vector to remove completed and error nodes (or
mark as 'popped' if we can't remove due to snapshotting), which aren't needed
anymore.


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