In a subversion repository, the organization of the paths is of fundamental importance for the everyday work and usability. We want to follow the standard (but not enforced) basic hierarchy of a project hosted on SVN, which consists of the 3 directories:
trunk: the main trunk of development
tags: fixed versions of the project identified by symbolic names
branches: branches of evolution of the project parallel to the trunk
Out development model requires the necessity to have package level tags and branches. At the same time, we need something that can be used as a tag on the whole project. Moreover, LHCb unique CVS repository is hosting many CMT projects and a global tag is pointless, but we can profit from the possibility of check out a complete tagged project in one command.
Version 2.0
After having gained more experience with the usage model of the Gaudi SVN repository, I think we need to restructure it.
Motivation
Even though the previous structure is valid, it makes working with whole projects more problematic that what it could be. Mainly because of the usage of svn:externals, which is more powerful than the CVS aliases, but it is not flexible enough for our use case (URL pointing to the repository may change).
For Gaudi the package tags and the project tags have more or less the same importance (LHCb uses local tags while Atlas and other experiments use only the project tags), and for Dirac (which is being migrated to SVN too) the local tags were never used. This, essentially, means that the projects tags are more important than what was thought when devising the first structure of the repository.
The current structure makes also problematic to work with RADs like eclipse.
Structure
A structure that allows good integration between project-level and package-level tags can be achieved with something like:
One directory per project (all capital letters, by convention) is visible at the top level of the repository. Inside that directory the three standard directories: trunk, tags and branches. The trunk directory contains the structure of the project as it should be checked out: a cmt directory and one directory per package (with or without a "hat" level).
The tags and branches directories sport the same structure. A directory with the same name of the project will contain the project-level tags/branches, while a directory per package will contain the package-level tags/branches.
User tags (or branches) could be stored in further subdirectories in the normal package tags (or branches) directory, for example PROJECT/tags/Package/username/tag.
Not all the foreseen directories are needed for a working repository. A repository can be fully functional without project-level tags or without package-level tags.
In case the grouping of the packages on a per project basis (like in the LHCb repository) is not wanted, a fake project can be used to host all (or part) of the packages (for example called packages). Of course, in this case it is possible to check out a project only using some dedicated tool, like the "getpack" utility used in LHCb.
The special project packages can also be used to host the packages the do not belong (yet/anymore) to a project.
Note that to simplify the maintenance of the repository, when a package needs to be moved from a project to another (or to the special project packages), also the tags and branches directories must be moved.
Meta-data (and getpack)
To make it possible for tools to work with both version 1.0 or version 2.0 of the repository and to take into account the fact that the packages are distributed between various projects (and not grouped in a single directory) some properties of the top-level directory have to be set:
version
must be set to "2.0" to declare the version of the structure of the repository
projects
newline-separated list of projects in the repository, the correct case can should be used
packages
newline-separated list of known packages in the repository
Empty lines or lines starting with # should be ignored.
A line of the packages property must be a space-separated list containing the name of the package (with hat), the name of the project owning it. Optionally it can contain tag specifications (a string representing a path in the repository where %v stands for the version id), to be used to locate special tags (useful if the package has been moved from one project to another). For example:
in this case, the tags for Hat/PackageA should be found with the patterns
Project/tags/PROJECT/%v/Hat/PackageA
Project/tags/Hat/PackageA/%v
Project/branches/PROJECT/%v/Hat/PackageA
Project/branches/Hat/PackageA/%v
OldProject/tags/OLDPROJECT/%v/Hat/PackageA
Version 1.0
Proposal
The repository contains the 3 main directories packages, projects and distribution.
packages will contain one directory per package, each of them with the 3 standard directories trunk, tags and branches. In case of CMT "hats", we can have packages/Hat/Package/trunk etc. The list of known packages can be obtained scanning the content of the directory packages, going down one level to take into account the possibility of hats. The scanning is very inefficient, so we can add a property called modules to the packages directory containing a newline-separated list of the known modules. This property can be updated automatically with a cron job or on demand.
The projects directory will contain one directory per hosted project (as container of packages), with the usual 3 standard directories. The content of the trunk for one this projects is only the content of the cmt directory that lives at the project level:
projects/GAUDI/trunk/project.cmt
The distribution directory contains the 3 standard directories. The tags and branches directory will have one subdirectory per hosted project, each of them containing one directory per "global tag". Those global tag directories will be empty and the internal structure will be described with svn externals definitions. External definitions are metadata of a directory that instruct svn to populate the directory checking out the subdirectories from other svn locations (more or less as cvs module aliases). The trunk directory will contain one empty directory per project, that, with the externals definitions, will allow to check out the trunks of all the related packages in one go.
Note: due to the non-locality of the external definitions (svn allows to check out from different repositories), we cannot use the same distribution sub directory for the public anonymous access and the read/write access, so distribution/trunk/GAUDI should be used by developers, while anonymous users will have to use distribution/tags/GAUDI/GAUDI_HEAD which will checkout the same files as trunk, but using the read-only http protocol.
svn Quick Reference for cvs Users (version 2.0 of the repository)
mkdir GAUDI
cd GAUDI
cvs -d $GAUDICVS checkout all
svn
svn checkout $GAUDISVN/Gaudi/trunk GAUDI
Checkout tagged version of a complete project
cvs (Gaudi only)
mkdir -p GAUDI/GAUDI_v20r0
cd GAUDI/GAUDI_v20r0
cvs -d $GAUDICVS checkout -r GAUDI_v20r0 all
svn
mkdir GAUDI
cd GAUDI
svn checkout $GAUDISVN/Gaudi/tags/GAUDI/GAUDI_v20r0
Commit
The commit is identical in CVS and Subversion
Commit the changes in the current directory (and subdirectories)
cvs
cvs commit
svn
svn commit
Commit the changes of a single file
cvs
cvs commit "myfile"
svn
svn commit "myfile"
Update
I want to distinguish between two use cases:
simple update: synchronize the local copy with the latest (or a specific) revision of the repository
update with tags: move from a tagged local version to the head one or to a branch
Simple Update
Nothing really special:
cvs
cvs update
svn
svn update
The way to select a revision or a moment in time a slightly different, but easy to sort out using the help.
Update with Tags
This is the complex part, since tags do not exists (as such) in Subversion. With SVN, tags are represented by copies of the trunk directory, so moving the working copy from a tag to another (or trunk or branch) means changing the path of the origin of the working copy.
Move the working copy from the current tag to the trunk/HEAD (assuming you are in the top directory of the package)
cvs
cvs update -APd
svn
svn switch $GAUDISVN/Project/trunk/MyPackage
Move the working copy from the current tag to the another tag (assuming you are in the top directory of the package)
To just check if there are changes in the repository that you didn't get yet, you can do a "dry-run" update with cvs. That does not exist in svn, you have to ask the status of the repository.
cvs
cvs -n update
svn
svn status -u
or
svn status --show-updates
Comparison (diff)
Comparison between the base of the working copy and the working copy