rank: add context and template keyword This makes the stored rank property accessible, to be expanded and printed. Differential Revision: https://phab.mercurial-scm.org/D12140

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