Having "tag =" in subversion block may cause confusion

[mnlevy1981]

Summary of Issue:

Having tag = in a component block using protocol = svn is a little misleading; first of all, svn "tags" are really just branches combined with a web-hook to make them read-only. Also, it's not really clear where repo_url ends and tag begins. As far as I can tell, all of the following are the same

[pop]
tag = trunk_tags/cesm_pop_2_1_20171008
protocol = svn
repo_url = https://svn-ccsm-models.cgd.ucar.edu/pop2
local_path = components/pop
required = True

[pop]
tag = pop2/trunk_tags/cesm_pop_2_1_20171008
protocol = svn
repo_url = https://svn-ccsm-models.cgd.ucar.edu
local_path = components/pop
required = True

[pop]
tag = cesm_pop_2_1_20171008
protocol = svn
repo_url = https://svn-ccsm-models.cgd.ucar.edu/pop2/trunk_tags
local_path = components/pop
required = True

Expected behavior and actual behavior:

What I'd rather see is the full URL in repo_url and no tag field:

[pop]
protocol = svn
repo_url = https://svn-ccsm-models.cgd.ucar.edu/pop2/trunk_tags/cesm_pop_2_1_20171008
local_path = components/pop
required = True

[mnlevy1981]

On a more nitpicky note, I think the following field ordering is more readable:

[pop]
local_path = components/pop
repo_url = https://svn-ccsm-models.cgd.ucar.edu/pop2/trunk_tags/cesm_pop_2_1_20171008
protocol = svn
required = True

From top to bottom, that's

1. where is this external going?
2. where is it coming from?
3. How should I get it?
4. Is it required?

For git-based externals, tag = (which could also be a branch, right? so maybe branch_or_tag =) is part of "where is it coming from" and should be listed between repo_url and protocol. For components with additional externals to manage, I think the best place for the optional external = is following protocol.

[billsacks]

@mnlevy1981 I see your point about the equivalence of different paths for svn repo_url / tag. However, I feel that it should be kept the way it is for consistency between svn and git listings.

To reply to some of your specific points:

For git-based externals, tag = (which could also be a branch, right? so maybe branch_or_tag =)

For git, the semantics of branches and tags differ. e.g., see #34 (and also possibly #26 for some other subtleties).

Regarding field ordering: I like your idea of listing local_path at the top. To me it makes sense to have protocol listed before repo_url, though. I believe that manage_externals doesn't enforce any ordering, so this would just involve changes in the cesm repository.

[mnlevy1981]

I see your point about the equivalence of different paths for svn repo_url / tag. However, I feel that it should be kept the way it is for consistency between svn and git listings.

If I'm reading #34 correctly, work is being done to support either

[$COMPNAME]
tag = $TAGNAME
protocol = git
repo_url = $REPO_URL
local_path = $LOCAL_PATH
required = True

or

[$COMPNAME]
branch = $BRANCHNAME
protocol = git
repo_url = $REPO_URL
local_path = $LOCAL_PATH
required = True

If that's an accurate statement, then it seems like you're introducing more functionality that is vital for git but not necessary for svn... and I see that as a stronger reason to omit fields from svn repositories. What if you named the fields git_tag and git_branch so it's clear that it's git-only?

[billsacks]

@mnlevy1981 okay I see your point. I'd be okay with having this labeled git_tag or git_branch, but will defer to @bandre-ucar to weigh in on how hard this would be to implement.