From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Fri, 8 Jun 2018 22:46:41 +0000 (+0100)
Subject: git-debrebase: Some notes on anchor parent ordering
X-Git-Tag: archive/debian/5.0~43
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=dgit.git;a=commitdiff_plain;h=25fa26693587f923061cc4d144297dee29eb4892;hp=236890b58b8255d8d540b5cbd326228489bd0363

git-debrebase: Some notes on anchor parent ordering

This is the result of some playing around with gitk.  Notably,
for example,
  git-branch -f t dgit/stretch-security && ~/things/Dgit/play/swap-pseudomerges -f RELEASE-4.8.0..t
where dgit/stretch-security is c9517ee45383271e90f40b7a9773d1e6fefaeca7
and swap-pseudomerges is something like this

  #!/bin/sh
  #
  # runs
  #   git-filter-branch --some-filters "$@"

  set -e

  git-filter-branch --parent-filter '
	  case "$(git cat-file commit $GIT_COMMIT)" in
	  *"git-debrebase new-upstream breakwater"*|*"git-debrebase anchor"*)
		  perl -ne '\''
			  chomp;
			  print join " ", reverse split / +(?=-p )/;
			  print "\n";
		  '\''
		  ;;
	  *)
		  cat
	  esac
  ' "$@"

or
  ....
	*"git-debrebase new-upstream breakwater"*|*"git-debrebase anchor"*)
  ....

and then runes like

  gitk --first-parent dgit/stretch-security &
  gitk dgit/stretch-security -- ':/' ':!/debian' &

etc.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---

diff --git a/git-debrebase b/git-debrebase
index f6d379ac..d174fe60 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -427,6 +427,23 @@ sub classify ($) {
 	# way also there's also an easy rune to look for the upstream
 	# patches (--topo-order).
 
+	# Also this makes --first-parent be slightly more likely to
+	# be useful - it makes it provide a linearised breakwater history.
+
+	# Of course one can say somthing like
+	#  gitk -- ':/' ':!/debian'
+	# to get _just_ the commits touching upstream files, and by
+	# the TREESAME logic in git-rev-list this will leave the
+	# breakwater into upstream at the first anchor.  But that
+	# doesn't report debian/ changes at all.
+
+	# Other observations about gitk: by default, gitk seems to
+	# produce output in a different order to git-rev-list.  I
+	# can't seem to find this documented anywhere.  gitk
+	# --date-order DTRT.  But, gitk always seems to put the
+	# parents from left to right, in order, so it's easy to see
+	# which way round a pseudomerge is.
+
 	$p[0]{IsOrigin} and $badanchor->("is an origin commit");
 	$p[1]{Differs} & ~DS_DEB and
 	    $badanchor->("upstream files differ from left parent");