feat(wpcarro/blog): git revision numbers as refs r/5206

See blog post

Change-Id: I4b7dcdc85e5125876441b2f157e3d6ddc3cd3140
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7103
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>

2 files changed, 92 insertions, 0 deletions

diff --git a/users/wpcarro/website/blog/posts.nix b/users/wpcarro/website/blog/posts.nix
index 27a184a22ca7..514e3130b50e 100644
--- a/users/wpcarro/website/blog/posts.nix
+++ b/users/wpcarro/website/blog/posts.nix
@@ -78,4 +78,11 @@
     content = ./posts/nixos-disk-full-note.md;
     draft = false;
   }
+  {
+    key = "git-rev-refs";
+    title = "git revision numbers as refs (note to self)";
+    date = 1666823030;
+    content = ./posts/git-rev-refs.md;
+    draft = false;
+  }
 ]
diff --git a/users/wpcarro/website/blog/posts/git-rev-refs.md b/users/wpcarro/website/blog/posts/git-rev-refs.md
new file mode 100644
index 000000000000..fdc0aaf5cc9f
--- /dev/null
+++ b/users/wpcarro/website/blog/posts/git-rev-refs.md
@@ -0,0 +1,85 @@
+## Credit
+
+Credit goes to `tazjin@` for this idea :)
+
+## Background
+
+Using `git` revisions to pin versions is nice, but git SHAs aren't very
+human-friendly:
+
+- They're difficult to type.
+- They're difficult to say in conversation.
+- They're difficult to compare. e.g. Which is newer? `2911fcd` or `db6ac90`?
+
+## Solution
+
+Let's assign monotonically increasing natural numbers to each of
+our repo's mainline commits and create `git` refs so we can use references like
+`r/123` instead of `2911fcd`.
+
+- They're easy to type: `r/123`
+- They're easy to say in conversion: "Check-out rev one-twenty-three."
+- They're easy to compare: `r/123` is an earlier version than `r/147`.
+
+## Backfilling
+
+Let's start-off by assigning "revision numbers" as refs for each of the mainline
+commits:
+
+```shell
+for commit in $(git rev-list --first-parent HEAD); do
+  git update-ref "refs/r/$(git rev-list --count --first-parent $commit)" $commit
+done
+```
+
+We can verify with:
+
+```shell
+λ git log --first-parent --oneline
+```
+
+If everything looks good, we can publish the refs to the remote:
+
+```shell
+λ git push origin 'refs/r/*:refs/r/*'
+```
+
+## Staying Current
+
+In order to make sure that any newly merged commits have an associated revision
+number as a ref, add something like the following to your CI system to run on
+the builds of your repo's mainline branch:
+
+```shell
+λ git push origin "HEAD:refs/r/$(git rev-list --count --first-parent HEAD)"
+```
+
+## Summary
+
+To verify that the remote now has the expected refs, we can use:
+
+```shell
+λ git ls-remote origin | less # grep for refs/r
+```
+
+If that looks good, you should now be able to *manually* fetch the refs with:
+
+```shell
+λ git fetch origin 'refs/r/*:refs/r/*'
+```
+
+Or you can use `git config` to automate this:
+
+```shell
+λ git config --add remote.origin.fetch '+refs/r/*:refs/r/*'
+λ git fetch origin
+```
+
+Now you can run fun commands like:
+
+```shell
+λ git show r/1234
+λ git diff r/123{4,8} # see changes from 1234 -> 1238
+```
+
+Thanks for reading!