Re: git-rerere observations and feature suggestions

On Mon, 2008-06-23 at 11:49 +0200, Ingo Molnar wrote:

another git-rerere observation: occasionally it happens that i 
accidentally commit a merge marker into the source code.

That's obviously stupid, and it normally gets found by testing quickly, 
but still it would be a really useful avoid-shoot-self-in-foot feature 
if git-commit could warn about such stupidities of mine.

( and if i could configure git-commit to outright reject a commit like 
  that - i never want to commit lines with <<<<<< or >>>>> markers)

Another merge conflict observation is that Git is much worse at figuring 
out the right merge resolution than our previous Quilt based workflow 
was. I eventually found it to be mainly due to the following detail: 
sometimes it's more useful to first apply the merged branch and then 
attempt to merge HEAD, as a patch.

I've got a script for that which also combines it with the "rej" tool, 
and in about 70%-80% of the cases where Git is unable to resolve a merge 
automatically it figures things out. ('rej' is obviously a more relaxed 
merge utility, but it's fairly robust in my experience, with a very low 
false positive rate.)

The ad-hoc "tip-mergetool" script we are using is attached below. It's 
really just for demonstration purposes - it doesnt work when there's a 
rename related conflict, etc.

Peter Zijstra also wrote a git-mergetool extension for the 'rej' tool 
btw., he might want to post that patch. I've attached Chris Mason's rej 
tool too.

This is what I run with.

I added the cp to the 3-way merge tools because I think its stupid to
see the messed up merge markers instead of the original file.

The rej target basically takes the local version and takes the diff
between base and remote and applies that as a patch, upon failure it
invokes rej to fix up the mess.

--- /usr/bin/git-mergetool	2008-04-08 19:01:37.000000000 +0200
+++ git-mergetool	2008-06-02 19:00:55.000000000 +0200

@@ -214,12 +214,14 @@ merge_file () {
 	    ;;
 	meld|vimdiff)
 	    touch "$BACKUP"
+	    cp -- "$BASE" "$path"
 	    "$merge_tool_path" -- "$LOCAL" "$path" "$REMOTE"
 	    check_unchanged
 	    save_backup
 	    ;;
 	gvimdiff)
 		touch "$BACKUP"
+		cp -- "$BASE" "$path"
 		"$merge_tool_path" -f -- "$LOCAL" "$path" "$REMOTE"
 		check_unchanged
 		save_backup

@@ -271,6 +273,13 @@ merge_file () {
 	    status=$?
 	    save_backup
 	    ;;
+        rej)
+	    touch "$BACKUP"
+	    cp -- "$LOCAL" "$path"
+	    diff -up "$BASE" "$REMOTE" | patch "$path" || rej "$path"
+	    check_unchanged
+	    save_backup
+	    ;;
     esac
     if test "$status" -ne 0; then
 	echo "merge of $path failed" 1>&2

@@ -311,7 +320,7 @@ done
 
 valid_tool() {
 	case "$1" in
-		kdiff3 | tkdiff | xxdiff | meld | opendiff | emerge | vimdiff | gvimdiff | ecmerge)
+		kdiff3 | tkdiff | xxdiff | meld | opendiff | emerge | vimdiff | gvimdiff | ecmerge | rej)
 			;; # happy
 		*)
 			return 1