test-editor-filename: fix portability of fake editor command - /bin/bash doesn't exist on FreeBSD - edit is executed by cmd.exe on Windows

amend: moving first assignment of newid closer to its use newid was needlessly further away from where its intended to be used leading to bad readability. This commit moves it to address the same. The end goal is to remove the redundant commit in the amend code path and this commit takes care of cleaning up some unrelated code before that change. Test Plan: ran the test suite Differential Revision: https://phab.mercurial-scm.org/D597

amend: rectify comment Comment was ambiguous as there can be two parents of a changeset in mercurial. This commit fixes the comment to clarify that the first parent is being considered. Test Plan: ran the test suite Differential Revision: https://phab.mercurial-scm.org/D595

amend: removing redundant if condition There is needless checking for the new commit hash not being equal to the old commit hash. This condition will always be true at this point in the code path and thus, can be removed safely. This commit removes the redundant condition. Test Plan: ran the test suite. Differential Revision: https://phab.mercurial-scm.org/D594

editor: file created for diff action should have .diff suffix This is a follow-up to https://phab.mercurial-scm.org/D464 (6e6452bc441d) that introduced the new file extension behavior. It erroneously changed `.diff` to `.diff.hg.txt`. Test Plan: Verified `make tests` passes, particularly `test-editor-filename.t`. Differential Revision: https://phab.mercurial-scm.org/D607

test-amend: match output using conditional test case name D466 (6cc8f848b4c3) allows output to be conditionally matched by test name. This patch changes test-amend.t to use that feature, instead of duplicating `hg amend` command or use `-q` to silence its output. Differential Revision: https://phab.mercurial-scm.org/D601

util: use set for reserved Windows filenames Previously, we were performing membership testing against a list. Change it to a set for a minor perf win. While we're at it, explode the assignment in place so less work is needed at module import time. Differential Revision: https://phab.mercurial-scm.org/D600

context: add arbitraryfilectx, which can represent files outside the workdir Move it from contrib/simplemerge so it can be re-used in the future. Differential Revision: https://phab.mercurial-scm.org/D604

simplemerge: remove unused `filtereddata` parameter Differential Revision: https://phab.mercurial-scm.org/D603

simplemerge: remove unused `repo` parameter This is now no longer used or needed thanks to the `decodeddata()` context function. Differential Revision: https://phab.mercurial-scm.org/D602

extensions: prohibit unicode defaults If the default value of an option is a unicode string (something than happen easily when using a 'from __future__ import unicode_literals'), any value passed on the command line will be ignored because the fancyopts module only checks for byte strings and not unicode strings. Changing fancyopts behavior is easy but would make assumptions on how the python3 port should be done, which is outside the scope of this patch. The chosen approach is to stop an extension from being loaded when a unicode default value is detected, with a hint for the developer.

revsetlang: remove unused functions Superseded by the _match() function.

revsetlang: match tree by helper function on optimize This should make optimize() more readable and less error-prone, but it doubles the parsing cost. (original) $ python -m timeit -n10000 -s 'from mercurial import revsetlang as L' \ 'L.optimize(L.analyze(L.parse("ancestors(x) and not ancestors(y)")))' 10000 loops, best of 3: 79.3 usec per loop (this patch) $ python -m timeit -n10000 -s 'from mercurial import revsetlang as L' \ 'L._treecache.clear(); \ L.optimize(L.analyze(L.parse("ancestors(x) and not ancestors(y)")))' 10000 loops, best of 3: 201 usec per loop

parser: add helper function to test if pattern matches parsed tree This function will be used as follows: match('ancestors(_) and not ancestors(_)', x) See the next patch for details.