rust-index: add append method This is the first time the Rust index has any notion of mutability. This will be used in a future patch from Python, to start synchronizing the Rust index and the C index.

rust-index: add an abstraction to support bytes added at runtimes In order to support appending data to the Rust index, we need to abstract data access away from the immutable (on-disk) bytes, to seemlessly fetch either from the preexisting data or from the newly added data.

rust-mixed-index: move the mmap keepalive into a function The same code will be used for keeping the new index mmap around.

rust-mixed-index: rename variable to make the next change clearer We're going to add another mmap reference holder, so let's rename this one first.

rust: fix cargo doc for hg-cpython

branching: merge with default We merge with the current children of the bad merge (37b52b938579)

branching: merge with stable This recreates `37b52b938579` right as a `hg branch --rev 5b186ba40001` screwed up the content.

changelog: disallow delayed write on inline changesets Since this will never happens, we can make the situation invalid and to stop to handling the associated the case. This simplify the random access file reading too.

changelog: never inline changelog The test suite mostly use small repositories, that implies that most changelog in the tests are inlined. As a result, non-inlined changelog are quite poorly tested. Since non-inline changelog are most common case for serious repositories, this lack of testing is a significant problem that results in high profile issue like the one recently fixed by 66417f55ea33 and 849745d7da89. Inlining the changelog does not bring much to the table, the number of total file saved is negligible, and the changelog will be read by most operation anyway. So this changeset is make it so we never inline the changelog, and de-inline the one that are still inlined whenever we touch them. By doing that, we remove the "dual code path" situation for writing new entry to the changelog and move to a "single code path" situation. Having a single code path simplify the code and make sure it is covered by test (if test cover that situation obviously) This impact all tests that care about the number of file and the exchange size, but there is nothing too complicated in them just a lot of churn. The churn is made "worse" by the fact rust will use the persistent nodemap on any changelog now. Which is overall a win as it means testing the persistent nodemap more and having less special cases. In short, having inline changelog is mostly useless and an endless source of pain. We get rid of it.

test-transaction-safety: glog out irrelevant flag The test is focussing on the inline flag, so we glob out the other to highlight that fact and prevent noise in the future.