rank: naive rank property computation and retrieval This stores the rank (size of the ancestor set of a revision, including itself) in a changelog field and allows this property to be retrieved. This new property is used as part of stable-range computations, which will be introduced later on. The value is computed in a naive way from the definition of the rank. This will be replaced by a more efficient version subsequently. Differential Revision: https://phab.mercurial-scm.org/D12139

filemerge: move check for identical sides out of filemerge() `filemerge.filemerge()` returns `None` if no merge was necessary because the two sides were identical. I don't think it should be that function's responsibility to handle that case; we should ideally not even call `filemerge.filemerge()` if the two inputs identical. This patch therefore moves the check out to the caller (`mergestate.py`). The largefiles test changed because we now notice that the two sides made the same change, so we don't consider it a merge. Also note that the new message better matches the line above it in the test output. Differential Revision: https://phab.mercurial-scm.org/D12154

mergestate: use an early return for trivial merges `filemerge.filemerge()` returns `None` if no merge was needed because the two sides were identical. I'd like to move that to the caller. This is a little refactoring to prepare for that. Differential Revision: https://phab.mercurial-scm.org/D12153

simplemerge: remove now-unused arguments The `ui` argument is no longer needed now that we don't handle `--print` in the library code. Differential Revision: https://phab.mercurial-scm.org/D12151

merge: fix documented order of `labels` argument Differential Revision: https://phab.mercurial-scm.org/D12150

filemerge: when not keeping premerge, don't write markers to context When premerge is enabled (as it is for non-binary inputs by default) and the markers are not kept, we currently still write it to the output context and then restore the previous content right after. With the refactoring in the previous patch, we can easily avoid that step and instead write the output in the opposite case (i.e. when it's successful or when the markers are supposed to be kept). Differential Revision: https://phab.mercurial-scm.org/D12149

simplemerge: move printing of merge result to extension The `mercurial.simplemerge` module still has some command-lines processing that doesn't belong in such a low-level module. This patch moves the handling of `hg simplemerge --print` to the extension by having `mercurial.simplemerge.simplemerge()` return the merged text. Differential Revision: https://phab.mercurial-scm.org/D12148

simplemerge: remove code for checking binary input now that callers do it The callers now do the checking for binary inputs and handle warnings and/or errors, so we can remove that code from the low-level `simplemerge` module now. After this patch we just raise an error unless the caller told us to allow binary inputs. Differential Revision: https://phab.mercurial-scm.org/D12169