Get SVN URL of removed git-svn file

I would like to track a removed file as far back in history as possible, while using git-svn on a subdirectory of the SVN repository.

Using git log --full-history -- path/to/removed_file.py, I can get see the history starting with the time the file was moved into the subdirectory I checked out using git-svn.
I can see which SVN revision that was in the git-svn commit message postfix, so I would now like to use svn log <full_url>@revision to see the rest of the history.
I know that I could use git svn info --url path/to/existing_file.py to see the required full SVN url, but what is a quick (ideally scriptable) way of getting the SVN URL of a file that is no longer in the repository?

Solution

To git, it doesn't matter much that a file foo/bar.py is removed in HEAD — as long as you have it in history, you can view every past version of it.

For clarity of concreteness, I'll take this git-svn repo from the LLVM project as an example. There, the file docs/todo.rst has been deleted in svn revision 308987, git commit fb572868… and is absent in master.

Let's first init a local clone.

$ git clone https://github.com/llvm-mirror/lnt && cd lnt
Cloning into 'lnt'...
...
$ git svn init https://llvm.org/svn/llvm-project/lnt/trunk
$ git update-ref refs/remotes/git-svn refs/remotes/origin/master
$ 
$ #-- ask svn info of anything to check setup and/or force laziness
$ git svn info --url README.md
Rebuilding .git/svn/refs/remotes/git-svn/.rev_map.91177308-0d34-0410-b5e6-96231b3b80d8 ...
r154126 = 3c3062527ac17b5fac440c55a3e1510d0ab8c9d9
r154135 = 82a95d29ac7d25c355fbd0898a44dc3e71a75fd8
...
r374687 = 446f9a3b651086e87684d643705273ef78045279
r374824 = 8c57bba3687ada10de5653ae46c537e957525bdb
Done rebuilding .git/svn/refs/remotes/git-svn/.rev_map.91177308-0d34-0410-b5e6-96231b3b80d8
https://llvm.org/svn/llvm-project/lnt/trunk/README.md

So it gives back the README.md URL as expected. Now let's try the case of a deleted file:

$ git svn info --url docs/todo.rst
svn: 'docs/todo.rst' is not under version control

Fails, just like you say. man git-svn says that info Does not currently support a -r/--revision argument.

OK then, let's try emulating what it does, first by hand.

https://llvm.org/svn/llvm-project/lnt/trunk/README.md?r=374824 — this is the URL for given file at given revision.

Our vanished docs/todo.rst is available at https://llvm.org/svn/llvm-project/lnt/trunk/docs/todo.rst?p=308986 Notice the decrement: per git show fb572868 | grep git-svn-id, docs/todo.rst is already deleted in r308987 — so we request r308986.

On to scripting it... rather simple job.

git-svn-oldinfo () {
  relfname="$1"
  git log -n1 -- "$relfname" \
    | awk '/git-svn-id:/ {sub(/@/, " ", $2); print $2}' \
    | { read baseurl rev; echo "${baseurl}/${relfname}?p=$((rev-1))"; }
}

#-- test:
$ git-svn-oldinfo docs/todo.rst
https://llvm.org/svn/llvm-project/lnt/trunk/docs/todo.rst?p=308986

Quick-n-dirty but tested — you're welcome to adjust & extend as needed.

Edit

Despite git log being a "porcelain" command (i.e. not really designed for scripting), it's quite possible to parse out the filenames from it too, if you're to query by globs like **/removed_file.py:

git-svn-oldinfo-glob () {
  fileglob="$1"
  git log -n1 --stat --format=oneline -- "$fileglob" \
    | { read commit msg; \
        read fullname _remainder_dummy; \
        git cat-file -p $commit \
          | tail -n1 \
          | awk '/git-svn-id:/ {sub(/@/, " ", $2); print $2}' \
          | { read baseurl rev; echo "${baseurl}/${fullname}?p=$((rev-1))"; } \
      }
}

#-- test:
$ git-svn-oldinfo-glob '**/todo.rst'
https://llvm.org/svn/llvm-project/lnt/trunk/docs/todo.rst?p=308986

Take it with a grain of salt: it'll probably break in hilarious ways or output garbage if the glob matches multiple files, non-removed files, files with whitespace in the name, etc.

As always, check out man git-log and customize as needed.