url: don't ignore timeout for https connections For http, we use the stdlib's HTTPConnection.connect which passes the timeout down to socket.create_connection; for https, we override the connect method but weren't handling the timeout, so connections could hang for hours even with http.timeout set to low values.

debugdeltachain: stop summing the same chain over and over Before this patch, delta chain size was computed from scratch for each chain, disregarding the fact very likely already computed the same of length-1 prefix for another revisions. We not cache delta chain size and shortcut the computation when we see them. Just for my mercurial-devel clone, this move the computation from about 17.5 second to about 4.8 seconds.

revlog: improve the robustness of the splitting process The previous "in-place" splitting, preserving the splitting on transaction failure had a couple of issue in case of transaction rollback: - a race windows that could still lead to a crash and data loss - it corrupted the `fncache`. So instead, we use a new approach that we summarized as "we do a backup of the inline revlog pre-split, and we restore this in case of failure". To make readers live easier, we don't overwrite the inline index file until transaction finalization. (once the transaction get into its finalization phase, it is not expected to rollback, unless some crash happens). To do so, we write the index of the split index in a temporary file that we use until transaction finalization. We also keep a backup of the initial inline file to be able to rollback the split if needed. As a result, transaction rollback cancel the split and no longer corrupt fncache. We also no longer have a small inconsistency windows where the transaction could be unrecoverable.

fncache: make it possible to ignore some file In the next changeset, we need to able to ignore some temporary file. This changeset teach the fncache about that.

revlog: test that pending hooks properly see the repository on split This seems important to explicitly cover this case before changing the code.

revlog: test possible read race condition with splitting This is currently working fine, but could break with another approach (for example, with the one we are about to use in the next changesets…) So we make sure the case is covered.