tests: use sha256line.py instead of /dev/random in test-censor.t (issue6858) Sometimes the systems that run our test suite don't have enough entropy and they cannot produce target file of the expected size using /dev/random, which results in test failures. Switching to /dev/urandom would give us way more available data at the cost of it being less "random", but we don't really need to use entropy for this task at all, since we only care if the file size after compression is big enough to not be stored inline in the revlog. So let's use something that we already have used to generate this kind of data in other tests.

tests: make sha256line.py available for all tests This was previously only used in test-revlog-delta-find.t, but it will be useful (and used) in other tests that might need to generate poorly-compressible files.

delta-find: pass the full deltainfo to the _DeltaSearch class Having more information is better, so we pass it directly.

delta-find: move sparse-revlog pre-filtering in the associated class Lets move the specialized code in the specialized class.

delta-find: move sparse-revlog delta checks in the associated class Lets move the specialized code in the specialized class.

delta-find: split the _DeltaSearch class in two We now have things sliced small enough to have two class that use different `_iter_groups` implementation to encode their different logic. The filtering code remains to be moved, but I would rather keep this changeset simple and move them in the next.

delta-find: finish reworking the snapshot logic and drop more layer The refining logic only applies to the snapshot logic, and this is now all contained in a dedicated method. Along the way, we drop the refined_groups // raw_groups layer as they no longer make sense. The result is a more explicit `iter_groups` method. This conclude the splitting and simplification of the groups generation. We are now ready to dispatch this in more diverse classes.

delta-find: move the base of the delta search in its own function That logic is complicated enough that is is worth puting in its own function. Another method will be introduced in the next changeset to deal with the actual refining.

delta-find: move the emotion of prev in a dedicated method After splitting the filtering, and with the `_candidate_groups` layer removed, we can start splitting the group generation too. This helps to organize this code and make it easier to modifying the future.

delta-find: move the emotion of parents in a dedicated method After splitting the filtering, and with the `_candidate_groups` layer removed, we can start splitting the group generation too. This helps to organize this code and make it easier to modifying the future.

delta-find: explicitly deal with usage of the cached revision We can remove this from the general logic path and directly deal with this corner case early. This result in a small change in test-generaldelta.t as it turns out that: - at commit time we (sometimes) precompute a delta against p1 and pass it as the cached delta. - since cached delta where going through the same filtering as everything, we could "optimize" the base if it applied to an empty delta, resulting in not using the pre-computed delta. The simpler logic fix the second item, making the cached delta base always actually tested when requested. Note that the computation of a fast delta against p1 only is questionable, but looking into that is out of scope for this series.

delta-find: remove the "candidate groups" layer We have enough pieces to remove this generator and directly bear it load using the underlying object.

delta-find: stop using heuristic to determine if we are creating a snapshot This avoid assuming a changeset is a snapshot when it is actually something simpler.

delta-find: explicitly track stage of the search Being more explicit about what we are doing is going to be useful. We actually start making use of it in later changesets.

delta-find: drop some dead debug code Seems like it was never put to use, so lets simply remove it for now.

delta-find: introduce and use specialized _DeltaSearch class For now, we introduce some very simple variant, but they are still useful to display how having the class can helps keeping the simple case simple and their special case out of more advanced logic.

delta-find: introduce a base class for _DeltaSearch This prepare the introduction of specialized the class in the next changesets.

delta-find: simplify the delta checking function for snapshot Since the function is all about snapshot, we can safely use an early return and make the result simpler.

delta-find: move good delta code earlier in the class Nothing change except the code location. This greatly helps readability of the next future diff,

delta-find: split is_good_delta_info into more thematic function Same logic as for candidate filtering, we group code into related sub method. This will help clarifying later patches as some logic is pre-splitted

delta-find: clarify some comment and code in is_good_delta_info We move the comment closer to the code it describ and we compute an intermediate value without using the `textlen` variable, as it will stop being defined in a future patch. This will clarify future patches.

delta-find: move delta size check earlier in is_good_delta_info This will clarify future patches by regrouping related logic before larger movement.

delta-find: split the delta-chain part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: split the "sparse" part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: split the generic part of `_pre_filter_rev` in a method Since `_pre_filter_rev` contains logic from various sources of constraint, we start splitting is in subfunction to clarify and document the grouping.

delta-find: drop the temporary indent Now that the complicated change is made, we can do the noisy one.

delta-find: move pre-filtering of individual revision in its own function This goes one step further than the previous change by making the pre-filtering of individual candicates revision in its own function. This will allow subclass to easily configure this filtering with their own constrains. The `if True:` part help the readability of this diff a lot and will be drop in to the next changesets.

delta-find: move pre-filtering of candidates in its own function This organise the code further and open the way to specialization via sub-classing. Something important for the coming changes.

delta-find: move away from the generator API for _DeltaSearch We use more explicit function call. This make operations more explicit and will make future refactoring simpler.

delta-find: use "-1" as depth snapshot-dept for non snapshot in debug This will help do distinct full snapshot (level 0) and normal delta (not a snapshot, no snapshot level)