xdiff: add a bdiff hunk mode xdiff generated hunks for the differences (ex. questionmarks in the `@@ -?,? +?,? @@` part from `diff --git` output). However, bdiff generates matched hunks instead. This patch adds a `XDL_EMIT_BDIFFHUNK` flag used by the output function `xdl_call_hunk_func`. Once set, xdiff will generate bdiff-like hunks instead. That makes it easier to use xdiff as a drop-in replacement of bdiff. Note that since `bdiff('', '')` returns `[(0, 0, 0, 0)]`, the shortcut path `if (xscr)` is removed. I have checked functions called with `xscr` argument (`xdl_mark_ignorable`, `xdl_call_hunk_func`, `xdl_emit_diff`, `xdl_free_script`) work just fine with `xscr = NULL`. Test Plan: Will be tested in a later patch. Differential Revision: https://phab.mercurial-scm.org/D2575

xdiff: remove patience and histogram diff algorithms Patience diff is the normal diff algorithm, plus some greediness that unconditionally matches common common unique lines. That means it is easy to construct cases to let it generate suboptimal result, like: ``` open('a', 'w').write('\n'.join(list('a' + 'x' * 300 + 'u' + 'x' * 700 + 'a\n'))) open('b', 'w').write('\n'.join(list('b' + 'x' * 700 + 'u' + 'x' * 300 + 'b\n'))) ``` Patience diff has been advertised as being able to generate better results for some C code changes. However, the more scientific way to do that is the indention heuristic [1]. Since patience diff could generate suboptimal result more easily and its "better" diff feature could be replaced by the new indention heuristic, let's just remove it and its variant histogram diff to simplify the code. [1]: https://github.com/git/git/commit/433860f3d0beb0c6f205290bd16cda413148f098 Test Plan: `gcc -fPIC *.c --shared -o xdiff.so` still builds. Differential Revision: https://phab.mercurial-scm.org/D2573

xdiff: vendor xdiff library from git Vendor git's xdiff library from git commit d7c6c2369d7c6c2369ac21141b7c6cceaebc6414ec3da14ad using GPL2+ license. There is another recent user report that hg diff generates suboptimal result. It seems the fix to issue4074 isn't good enough. I crafted some other interesting cases, and hg diff barely has any advantage compared with gnu diffutils or git diff. | testcase | gnu diffutils | hg diff | git diff | | | lines time | lines time | lines time | | patience | 6 0.00 | 602 0.08 | 6 0.00 | | random | 91772 0.90 | 109462 0.70 | 91772 0.24 | | json | 2 0.03 | 1264814 1.81 | 2 0.29 | "lines" means the size of the output, i.e. the count of "+/-" lines. "time" means seconds needed to do the calculation. Both are the smaller the better. "hg diff" counts Python startup overhead. Git and GNU diffutils generate optimal results. For the "json" case, git can have an optimization that does a scan for common prefix and suffix first, and match them if the length is greater than half of the text. See https://neil.fraser.name/news/2006/03/12/. That would make git the fastest for all above cases. About testcases: patience: Aiming for the weakness of the greedy "patience diff" algorithm. Using git's patience diff option would also get suboptimal result. Generated using the Python script: ``` open('a', 'w').write('\n'.join(list('a' + 'x' * 300 + 'u' + 'x' * 700 + 'a\n'))) open('b', 'w').write('\n'.join(list('b' + 'x' * 700 + 'u' + 'x' * 300 + 'b\n'))) ``` random: Generated using the script in `test-issue4074.t`. It practically makes the algorithm suffer. Impressively, git wins in both performance and diff quality. json: The recent user reported case. It's a single line movement near the end of a very large (800K lines) JSON file. Test Plan: Code taken as-is. Differential Revision: https://phab.mercurial-scm.org/D2572 # no-check-commit for vendored code

templater: provide hint for multi-line templates with parse errors Previously, we punted. Now we "rewrite" the template's newlines to r'\n' and offset the hint appropriately. Differential Revision: https://phab.mercurial-scm.org/D2609

templater: add hint to template parse errors to help locate issues Previously, we would print the error name and location, but this isn't as helpful as we can be. Let's add a hint that shows the location where we encountered the parse error. Differential Revision: https://phab.mercurial-scm.org/D2608

py3: use b"%d" to covert integer to bytes instead of str Differential Revision: https://phab.mercurial-scm.org/D2618