What is the usage of Maven pom.xml - <tag> element inside of <scm> when you are using git

Question

We are using maven and git together for a Java project. In <scm> section, <tag> is automatically added by release plugin.

For example,

  <scm>
          <connection>scm:git:http://myserver:7990/scm/project/test.git</connection>
          <tag>releaes-tag</tag>
  </scm>

What does <tag> represent here?

I believe the normal convention is <tag>HEAD</tag>.

When we were using subversion, maven never used <tag></tag>

What is the meaning of <tag></tag>?

I searched google and maven documentation but I cannot find any information on it.

Monty

Answer 1

The <tag> element is used by release:prepare to specify the tag that was created for this release (implemented as MRELEASE-723). Outside of a release it is essentially a placeholder, and HEAD is an appropriate value.

When we were using subversion, maven never used <tag></tag>

As MRELEASE-723 explains:

when I invoke release:prepare with a URL like: https://example.test/svn/REPO/myproject/branches/release it will be replaced by https://example.test/svn/REPO/myproject/tags/myproject-1.0 which is fine because now you know which revision to checkout for building the release.

The <scm> element for a release build should contain enough information to check out the tag that was created for this release.

Subversion allows the tag to be included in the connection URL. Neither Git nor Mercurial allow this, so the <tag> element is used instead.

Crossstitch

But on a branch (snapshot version of the artifact) I can simply remove the <tag>HEAD</tag> right? And have it just set automatically on the maven release for the release tag. Or does it always add it back to HEAD after a release? – Entebbe

Perhaps I'm just thick but I still don't understand the need for automated adding of <tag> in the <scm> section. I tend to remove it when I see it but it keeps popping back. – Krystalkrystalle

So, the value of <tag> is uniquely chosen when running the release:prepare goal (the user is prompted for it). And afterwards the goal is sticking such value into the pom.xml under <scm>/<tag> just to store this information? – Spittoon

The reference for the technical maven project descriptor (i.e. the technical specification of the POM file) states that the default value for the <tag> element is indeed HEAD, so that's what is assumed when you don't specify the tag (just like jar is the default for the <packaging> element). – Tooling