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RE: Merge Branch to Trunk - Not Deleting Lines in Trunk

From: Jim.Hyslop
Subject: RE: Merge Branch to Trunk - Not Deleting Lines in Trunk
Date: Thu, 24 Jun 2004 11:01:32 -0400

work wrote:
> When I merge from the file on the branch to the file on the 
> trunk, and the file on the branch has deleted lines, the 
> lines are not deleted from the file on the trunk. 
> I'm in the local sandbox for the trunk and using the cvs 
> update -j latest_branch_tag -j latest_trunk_tag and the 
> output says that the file already contains the differences, 
> but it really doesn't because the lines don't exist in the 
> branch, but do in the trunk.
As Todd pointed out, you have your tags reversed. BUT!! Be careful here -
make sure the command is doing what you want. This will not *merge* the
files, this will make the head of the trunk exactly like revision
latest_trunk_tag - which may or may not be what you intended.

'cvs update -jX -jY' means "take the delta from X to Y and apply it to the
working directory." Algebraically, if W is the working directory, and Y-X is
the delta from X to Y:

W = W + Y - X

Since W = X, then  W = X + Y - X

which simplifies to W = Y

For a proper merge, you want to use two tags that are from the same branch
in the 'update' command.

Suppose, for example, the branch tree looks something like:

1.1 --- 1.2 --- 1.3
    \-- ---

and you have the tags:
branch_point: 1.1
latest_trunk_tag: 1.3

If this is the first merge, you want to specify:

cvs update -A
cvs update -jbranch_point -jfirst_branch_tag

Now suppose you commit two more changes to the branch, and apply another tag
second_branch_tag (this will be revision The next merge would be:

cvs update -jfirst_branch_tag -jsecond_branch_tag

This is where a floating tag, such as [branch name]_last_merge would come in
handy. The command sequence would be:

# prepare to branch
cvs tag thebranch_base
cvs tag -b thebranch
cvs tag thebranch_last_merge

# branch!
cvs update -r thebranch
[modify modify modify commit modify some more commit etc.]

#prepare to merge
cvs tag thebranch_merge_head
cvs update -A

cvs up -jthebranch_last_merge -jthebranch_merge_head
cvs tag -F -rthebranch_merge_head thebranch_last_merge
[fix up any conflicts and commit]

("What's with all this prepare s**t? Just do it!" -- Spaceballs)

Jim Hyslop
Senior Software Designer
Leitch Technology International Inc. (
Columnist, C/C++ Users Journal (

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