Tagging — polylith/clj-poly 0.2.21

Tagging

We touched on the concept of a stable point in time in our Git docs. Now, we’ll show how we use git tagging to mark and move a workspace’s stable point in time.

We consider a workspace stable when the whole workspace is in a valid state. For example, when all code compiles, all tests pass, and the check command executes without error.

The test command leverages the concept of stability to support running tests incrementally. It can reduce a test run to only those tests affected by changes since the last known stable point in time. As you can imagine, skipping unnecessary tests can significantly reduce test run times!

To mark a stable point in time, we use a git tag.

Let’s continue with our tutorial. We last left off by adding and committing your workspace files to git.

Mark your example workspace as stable by tagging it with git:

git tag -f stable-lisa (1)

1	`-f` tells git to move the tag if it already exists

Run git log --pretty=format'%h %d%n %s', you’ll see something like:

e7ebe68  (HEAD -> main, tag: stable-lisa)  (1)
 Created the user and cli bricks.
c91fdad
 Workspace created.

1	Notice the `stable-lisa` tag you added is on the second commit.

We used git log --pretty=format'%h %d%n %s for compact documentation-friendly output. Feel free to use git log --pretty=oneline or even git log.

Rerun the poly info command, and you’ll see something like this:

Remember that git hashes (SHAs and short-SHAs) are globally unique. Yours will differ from our e7ebe68 and c91fdad.

Notice that:

The stable since line shows:
- A short-SHA e7ebe68 that matches the second commit.
- The stable-lisa tag.
All the * (asterisk) markers you saw in the previous info output are gone because no brick (component or base) or project has changed since our new stable point in time.

Run poly diff; you’ll see no output because nothing has changed.

Our example uses the git tag stable-lisa, but poly recognizes any tag that starts with stable- as a stable point in time. We chose stable-lisa because Lisa is our name (let’s pretend, at least!). This convention allows every developer to have their own unique stable point in time.

Your continuous integration (CI) build should use its own unique git tag pattern to mark successful builds (and, therefore, stable workspaces). A convention like stable- plus branch name or stable- plus build number can work nicely.

We recommend that you start with stable- tags created by your CI server and add developer-specific stable- tags when needed.

We think that git tags that start with stable- is a magnificent naming convention, but if you really prefer something different, you can override this default in your workspace.edn file:

 :tag-patterns {:stable "stable-*" (1)
                :release "v[0-9]*"}

1	Override the default `stable-*` regular expression to your own convention, if you wish

Internally, poly finds the stable point in time commit via:

git log --pretty=format:'%H %d'

For our current example, this outputs:

e7ebe683a775ec28b7c2b5d77e01e79d48149d13 (HEAD -> master, tag: stable-lisa)
c91fdad4a34927d9aacfe4b04ea2f304f3303282

The poly tool parses the output for the first line that matches the :stable tag pattern (by default stable-*). If it finds no matches, the first commit in the git repository is the stable point in time commit.

You’ve seen the info command output when all bricks and projects have changed since the stable point in time; all bricks and projects showed a trailing * (asterisk).

What happens if only some bricks have changed? Let’s find out. Add a comment to the user.core namespace by editing ./components/user/src/se/example/user/core.clj:

(ns se.example.user.core)

; hi! (1)
(defn hello [name]
  (str "Hello " name "!"))

1	Add a comment line

Run poly info again:

As expected, the user component now shows a trailing *. Notice that both command-line and development projects show a trailing +. The + indicates the projects have no changes, but at least one of their bricks has changed.

Release

When you release, we recommend your CI server git tag the release. But here, we’ll have you experiment from your command line shell.

Run git log --pretty=format'%h %d%n %s to look at your current commit history and tags:

e7ebe68  (HEAD -> master, tag: stable-lisa)
 Created the user and cli bricks.
c91fdad
 Workspace created.

Tag the first commit as v1.1.0 and the second as v1.2.0:

git tag v1.1.0 c91fdad (1)
git tag v1.2.0

1	replace `c91fdad` with your corresponding SHA for your first commit

Rerun git log --pretty=format'%h %d%n %s to verify your new tags:

e7ebe68  (HEAD -> master, tag: v1.2.0, tag: stable-lisa)
 Created the user and cli bricks.
c91fdad  (tag: v1.1.0)
 Workspace created.

Now run poly info against your latest release:

poly info since:release

If you execute poly info against the previous release:

poly info since:previous-release

The poly tool has picked up the second latest release tag.

The poly tool matches release tags as defined by your workspace.edn:

 :tag-patterns {:stable "stable-*"
                :release "v[0-9]*"} (1)

1	Default regular expression for git `:release` tags is `v[0-9]*`.

You can use the since argument on your CI server to run only the necessary tests since the previous release. Unaffected code does not need to be retested.

poly test since:previous-release

You’ll use:

since:previous-release if your release process adds a release tag before your build.
since:release if it adds a release tag after your build

If the since argument is not specified, since:stable is used by default.
Other variants, like since:e7ebe68v, since:head, and since:head~1 are also valid.

See Continuous Integration for tagging and release strategies.