$ git checkout -b revert-c99 master-
One of the changes I pulled into the master branch turns out to -break building GIT with GCC 2.95. While they were well intentioned -portability fixes, keeping things working with gcc-2.95 was also -important. Here is what I did to revert the change in the master -branch and to adjust the pu branch, using core GIT tools and -barebone Porcelain.
-First, prepare a throw-away branch in case I screw things up.
-$ git checkout -b revert-c99 master-
Now I am on the revert-c99 branch. Let's figure out which commit to -revert. I happen to know that the top of the master branch is a -merge, and its second parent (i.e. foreign commit I merged from) has -the change I would want to undo. Further I happen to know that that -merge introduced 5 commits or so:
-$ git show-branch --more=4 master master^2 | head -* [master] Merge refs/heads/portable from http://www.cs.berkeley.... - ! [master^2] Replace C99 array initializers with code. --- -- [master] Merge refs/heads/portable from http://www.cs.berkeley.... -*+ [master^2] Replace C99 array initializers with code. -*+ [master^2~1] Replace unsetenv() and setenv() with older putenv(). -*+ [master^2~2] Include sys/time.h in daemon.c. -*+ [master^2~3] Fix ?: statements. -*+ [master^2~4] Replace zero-length array decls with []. -* [master~1] tutorial note about git branch-
The —more=4 above means "after we reach the merge base of refs, -show until we display four more common commits". That last commit -would have been where the "portable" branch was forked from the main -git.git repository, so this would show everything on both branches -since then. I just limited the output to the first handful using -head.
-Now I know master^2~4 (pronounce it as "find the second parent of -the master, and then go four generations back following the first -parent") is the one I would want to revert. Since I also want to say -why I am reverting it, the -n flag is given to git revert. This -prevents it from actually making a commit, and instead git revert -leaves the commit log message it wanted to use in .msg file:
-$ git revert -n master^2~4 -$ cat .msg -Revert "Replace zero-length array decls with []." - -This reverts 6c5f9baa3bc0d63e141e0afc23110205379905a4 commit. -$ git diff HEAD ;# to make sure what we are reverting makes sense. -$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage. -$ make clean test ;# make sure it did not cause other breakage.-
The reverted change makes sense (from reading the diff output), does -fix the problem (from make CC=gcc-2.95 test), and does not cause new -breakage (from the last make test). I'm ready to commit:
-$ git commit -a -s ;# read .msg into the log, - # and explain why I am reverting.-
I could have screwed up in any of the above steps, but in the worst -case I could just have done git checkout master to start over. -Fortunately I did not have to; what I have in the current branch -revert-c99 is what I want. So merge that back into master:
-$ git checkout master -$ git resolve master revert-c99 fast ;# this should be a fast forward -Updating from 10d781b9caa4f71495c7b34963bef137216f86a8 to e3a693c... - cache.h | 8 ++++---- - commit.c | 2 +- - ls-files.c | 2 +- - receive-pack.c | 2 +- - server-info.c | 2 +- - 5 files changed, 8 insertions(+), 8 deletions(-)-
The fast in the above git resolve is not a magic. I knew this -resolve would result in a fast forward merge, and if not, there is -something very wrong (so I would do git reset on the master branch -and examine the situation). When a fast forward merge is done, the -message parameter to git resolve is discarded, because no new commit -is created. You could have said junk or nothing there as well.
-There is no need to redo the test at this point. We fast forwarded -and we know master matches revert-c99 exactly. In fact:
-$ git diff master..revert-c99-
says nothing.
-Then we rebase the pu branch as usual.
-$ git checkout pu -$ git tag pu-anchor pu -$ git rebase master -* Applying: Redo "revert" using three-way merge machinery. -First trying simple merge strategy to cherry-pick. -Finished one cherry-pick. -* Applying: Remove git-apply-patch-script. -First trying simple merge strategy to cherry-pick. -Simple cherry-pick fails; trying Automatic cherry-pick. -Removing Documentation/git-apply-patch-script.txt -Removing git-apply-patch-script -Finished one cherry-pick. -* Applying: Document "git cherry-pick" and "git revert" -First trying simple merge strategy to cherry-pick. -Finished one cherry-pick. -* Applying: mailinfo and applymbox updates -First trying simple merge strategy to cherry-pick. -Finished one cherry-pick. -* Applying: Show commits in topo order and name all commits. -First trying simple merge strategy to cherry-pick. -Finished one cherry-pick. -* Applying: More documentation updates. -First trying simple merge strategy to cherry-pick. -Finished one cherry-pick.-
The temporary tag pu-anchor is me just being careful, in case git -rebase screws up. After this, I can do these for sanity check:
-$ git diff pu-anchor..pu ;# make sure we got the master fix. -$ make CC=gcc-2.95 clean test ;# make sure it fixed the breakage. -$ make clean test ;# make sure it did not cause other breakage.-
Everything is in the good order. I do not need the temporary branch -nor tag anymore, so remove them:
-$ rm -f .git/refs/tags/pu-anchor -$ git branch -d revert-c99-
It was an emergency fix, so we might as well merge it into the -release candidate branch, although I expect the next release would -be some days off:
-$ git checkout rc -$ git pull . master -Packing 0 objects -Unpacking 0 objects - -* committish: e3a693c... refs/heads/master from . -Trying to merge e3a693c... into 8c1f5f0... using 10d781b... -Committed merge 7fb9b7262a1d1e0a47bbfdcbbcf50ce0635d3f8f - cache.h | 8 ++++---- - commit.c | 2 +- - ls-files.c | 2 +- - receive-pack.c | 2 +- - server-info.c | 2 +- - 5 files changed, 8 insertions(+), 8 deletions(-)-
And the final repository status looks like this:
-$ git show-branch --more=1 master pu rc -! [master] Revert "Replace zero-length array decls with []." - ! [pu] git-repack: Add option to repack all objects. - * [rc] Merge refs/heads/master from . ---- - + [pu] git-repack: Add option to repack all objects. - + [pu~1] More documentation updates. - + [pu~2] Show commits in topo order and name all commits. - + [pu~3] mailinfo and applymbox updates - + [pu~4] Document "git cherry-pick" and "git revert" - + [pu~5] Remove git-apply-patch-script. - + [pu~6] Redo "revert" using three-way merge machinery. - - [rc] Merge refs/heads/master from . -++* [master] Revert "Replace zero-length array decls with []." - - [rc~1] Merge refs/heads/master from . -... [master~1] Merge refs/heads/portable from http://www.cs.berkeley....-
caret=^ +startsb=[ +endsb=]
+This file, by convention among Porcelains, stores the - exclude pattern list. git status looks at it, but - otherwise it is not looked at by any of the core git - commands. + exclude pattern list. .gitignore is the per-directory + ignore file. git status, git add, git rm and git + clean look at it but the core git commands do not look + at it. See also: git-ls-files(1) —exclude-from + and —exclude-per-directory.