tl;dr: I want to handle conflicts automatically on lines like
> KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~mips ~ppc ~ppc64 ~riscv > ~s390 ~sparc ~x86" where conflicts frequently happen by adding/removing ~ before the architecture names or adding/removing whole architectures. I don't know if I should use a custom git merge driver or a custom git merge strategy. So the program in the patch below works, but it's not ideal, because it rejects any hunks that don't touch the KEYWORDS=... assignment. As I understand it, a custom git merge driver is intended to be used to merge whole file formats, like JSON. As a result, you configure it via gitattributes on a per-extension basis. I really just want to make the default recursive git merge handle KEYWORDS=... conflicts automatically, and I don't expect to be able to make a git merge driver that can handle arbitrary conflicts in *.ebuild files. If the merge driver returns non-zero if it was unable to resolve the conflicts, but when it does so git evidently doesn't fallback and insert the typical <<< HEAD ... === ... >>> markers. Maybe I could make my merge driver insert those like git normally does? Seems like git's logic is probably a bit better about handling some conflicts than my tool would be. So... is a git merge strategy the thing I want? I don't know. There doesn't seem to really be any documentation on writing git merge strategies. I've only found [1] and [2]. Cc'ing g...@vger.kernel.org, since I expect that's where the experts are. Hopefully they have suggestions. [1] https://stackoverflow.com/questions/23140240/git-how-do-i-add-a-custom-merge-strategy [2] https://stackoverflow.com/questions/54528824/any-documentation-for-writing-a-custom-git-merge-strategy On Sun, Dec 20, 2020 at 10:44 PM Matt Turner <matts...@gentoo.org> wrote: > > Since the KEYWORDS=... assignment is a single line, git struggles to > handle conflicts. When rebasing a series of commits that modify the > KEYWORDS=... it's usually easier to throw them away and reapply on the > new tree than it is to manually handle conflicts during the rebase. > > git allows a 'merge driver' program to handle conflicts; this program > handles conflicts in the KEYWORDS=... assignment. E.g., given an ebuild > with these keywords: > > KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~mips ~ppc ~ppc64 ~riscv > ~s390 ~sparc ~x86" > > One developer drops the ~alpha keyword and pushes to gentoo.git, and > another developer stabilizes hppa. Without this merge driver, git > requires the second developer to manually resolve the conflict. With > the custom merge driver, it automatically resolves the conflict. > > gentoo.git/.git/config: > > [core] > ... > attributesfile = ~/.gitattributes > [merge "keywords"] > name = KEYWORDS merge driver > driver = merge-driver-ekeyword %O %A %B > > ~/.gitattributes: > > *.ebuild merge=keywords > > Signed-off-by: Matt Turner <matts...@gentoo.org> > --- > One annoying wart in the program is due to the fact that ekeyword > won't work on any file not named *.ebuild. I make a symlink (and set up > an atexit handler to remove it) to work around this. I'm not sure we > could make ekeyword handle arbitrary filenames given its complex multi- > argument parameter support. git merge files are named .merge_file_XXXXX > according to git-unpack-file(1), so we could allow those. Thoughts? > > bin/merge-driver-ekeyword | 125 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 125 insertions(+) > create mode 100755 bin/merge-driver-ekeyword > > diff --git a/bin/merge-driver-ekeyword b/bin/merge-driver-ekeyword > new file mode 100755 > index 0000000..6e645a9 > --- /dev/null > +++ b/bin/merge-driver-ekeyword > @@ -0,0 +1,125 @@ > +#!/usr/bin/python > +# > +# Copyright 2020 Gentoo Authors > +# Distributed under the terms of the GNU General Public License v2 or later > + > +""" > +Custom git merge driver for handling conflicts in KEYWORDS assignments > + > +See https://git-scm.com/docs/gitattributes#_defining_a_custom_merge_driver > +""" > + > +import atexit > +import difflib > +import os > +import shutil > +import sys > + > +from typing import List, Optional, Tuple > + > +from gentoolkit.ekeyword import ekeyword > + > + > +def keyword_array(keyword_line: str) -> List[str]: > + # Find indices of string inside the double-quotes > + i1: int = keyword_line.find('"') + 1 > + i2: int = keyword_line.rfind('"') > + > + # Split into array of KEYWORDS > + return keyword_line[i1:i2].split(' ') > + > + > +def keyword_line_changes(old: str, new: str) -> List[Tuple[Optional[str], > + Optional[str]]]: > + a: List[str] = keyword_array(old) > + b: List[str] = keyword_array(new) > + > + s = difflib.SequenceMatcher(a=a, b=b) > + > + changes = [] > + for tag, i1, i2, j1, j2 in s.opcodes(): > + if tag == 'replace': > + changes.append((a[i1:i2], b[j1:j2]),) > + elif tag == 'delete': > + changes.append((a[i1:i2], None),) > + elif tag == 'insert': > + changes.append((None, b[j1:j2]),) > + else: > + assert tag == 'equal' > + return changes > + > + > +def keyword_changes(ebuild1: str, ebuild2: str) -> List[Tuple[Optional[str], > + > Optional[str]]]: > + with open(ebuild1) as e1, open(ebuild2) as e2: > + lines1 = e1.readlines() > + lines2 = e2.readlines() > + > + diff = difflib.unified_diff(lines1, lines2, n=0) > + assert next(diff) == '--- \n' > + assert next(diff) == '+++ \n' > + > + hunk: int = 0 > + old: str = '' > + new: str = '' > + > + for line in diff: > + if line.startswith('@@ '): > + if hunk > 0: break > + hunk += 1 > + elif line.startswith('-'): > + if old or new: break > + old = line > + elif line.startswith('+'): > + if not old or new: break > + new = line > + else: > + if 'KEYWORDS=' in old and 'KEYWORDS=' in new: > + return keyword_line_changes(old, new) > + return None > + > + > +def apply_keyword_changes(ebuild: str, > + changes: List[Tuple[Optional[str], > + Optional[str]]]) -> int: > + # ekeyword will only modify files named *.ebuild, so make a symlink > + ebuild_symlink = ebuild + '.ebuild' > + os.symlink(ebuild, ebuild_symlink) > + atexit.register(lambda: os.remove(ebuild_symlink)) > + > + for removals, additions in changes: > + args = [] > + for rem in removals: > + # Drop leading '~' and '-' characters and prepend '^' > + i = 1 if rem[0] in ('~', '-') else 0 > + args.append('^' + rem[i:]) > + if additions: > + args.extend(additions) > + args.append(ebuild_symlink) > + > + result = ekeyword.main(args) > + if result != 0: > + return result > + return 0 > + > + > +def main(argv): > + if len(argv) != 4: > + sys.exit(-1) > + > + O = argv[1] # %O - filename of original > + A = argv[2] # %A - filename of our current version > + B = argv[3] # %B - filename of the other branch's version > + > + # Get changes from %O to %B > + changes = keyword_changes(O, B) > + if not changes: > + sys.exit(-1) > + > + # Apply O -> B changes to A > + result: int = apply_keyword_changes(A, changes) > + sys.exit(result) > + > + > +if __name__ == "__main__": > + main(sys.argv) > -- > 2.26.2 >
