Summary:
Previously, `ShadowViewNodePair::List` owned each `ShadowViewNodePair` but whenever we put `ShadowViewNodePair` into a TinyMap, those were unowned pointer references. This worked... 99% of the time. But in some marginal cases, it would cause dangling pointers, leading to difficult-to-track-down issues. So, I'm moving both of these to be unowned pointers and keeping a `std::deque` that owns all `ShadowViewNodePair`s and is itself owned by the main differ function. See comments for more implementation details. I'm moderately concerned about memory usage regressions, but practically speaking this will contain many items when a tree is created for the first time, and then very few items after that (space complexity should be similar to `O(n)` where `n` is the number of changed nodes after the last diff).
See comments as to why I believe `std::deque` is the right choice. Long-term there might be data-structures that are even more optimal, but std::deque has the right tradeoffs compared to other built-in STL structures like std::list and std::vector, and is probably better than std::forward_list too. Long-term we may want a custom data-structure that fits our needs exactly, but std::deque comes close and is possibly optimal.
Changelog: [Internal]
Reviewed By: sammy-SC
Differential Revision: D27730952
fbshipit-source-id: 2194b535439bd309803a221188da5db75242005a
Summary:
Changes in following diffs will be gated by this feature flag.
The differ in the new file is copied from the current stable implementation and will not be modified until it's deleted.
Changelog: [Internal]
Reviewed By: sammy-SC, mdvacca
Differential Revision: D27775698
fbshipit-source-id: 03d9518ffd2b1f25712386c56a38bd2b4d839fc2
Joshua Gross