In Git, what does "deletion" of a branch mean?
Will it be gone from the repository? Or will it still be navigable to via git branch?
What I really want to do is mark a branch as "dead end", i.e., the branch is so far from master, that nobody should use it as a starting point, though there were some good ideas down that branch, so we'd like to keep it, for reference.
Answer
You can delete the branch, but tag it first, so that it's history doesn't disappear. This way, the branch doesn't show up in the branch list, which should hopefully deter people from working on it, but the work won't be permanently erased (even after garbage collection is run). For instance, whenever I have a branch that has become irrelevant, but I'm not prepared to permanently delete it, I tag it as "archive/<branch-name>".
While on master or some other branch:
git tag archive/foo foo
git branch -D foo
This creates a tag named archive/foo from the foo branch before deleting foo. You can also add a message to the tag, that explains what is in the branch, why it existed, why it's now a dead end, etc.
git tag -m 'Foo is deprecated in favor of bar' archive/foo foo
The ability to record why a branch is being deprecated is perhaps an advantage of tagging versus moving branches to an alternate namespace.
If you ever need to resurrect a branch that has been archived this way, it's as simple as:
git branch foo archive/foo
git tag -d archive/foo # Optional
Now the branch is back as though it was never deleted.