VSTS / TFS Build only run NPM task when Git tag is committed and pushed - node.js

Question

On Microsoft docs it states you can set conditionals for a specific build task. For example to run the build on a specific version of a defined Git branch.
But is it also possible to make an conditional to make the VSTS to build the NPM package only if a commit contains a git-tag?
Update 1: The command $ git describe (source) seems like a possible part of the solution. This command takes the last commit hash and matches it to see if there were annotated tags. However, it doesn't equal it to a boolean value what we need in the custom condition of VSTS.
Update 2: Using npm git-describe you can return wether or not the latest commit has annotated tags. Example of a gulp task:
/** Example of a gulp task using git describe */
var gulp = require('gulp');
var {gitDescribeSync} = require('git-describe');
/**
* #function
* #name checkGitTag
* #description Returns wether or not the latest commit has a tag
* #returns {(String|null)} Git tag or null if no git tag exists on the commit
*/
var checkGitTag = function() {
var gitInfo = gitDescribeSync();
// output the result to debug
console.log(gitInfo.tag);
// gitInfo.tag seems to contain the logic needed
};
gulp.task('checkGitTag', checkGitTag);
module.exports = checkGitTag;
Maybe by installing the NPM package on the build server and using a similar function would work. Going to test it out.

Answer 1

Yes, it’s possible to conditional run a task when the build commit contains tag(s).
But since there is no such predefined variable to record the tag for the build commit $(BUILD.SOURCEVERSION), so you should add the steps (add a variable and a PowerShell task) to check if there has tag(s) on the build commit. Detail step as below:
1. Add a variable (such as result) with the default value 0. And the variable is used for check if the build commit contains tag(s).
2. Then add a PowerShell task before the task which you want to conditional run, and the powershell script as below:
$tag=$(git tag --contains $(BUILD.SOURCEVERSION))
if($tag)
{
Write-Host "##vso[task.setvariable variable=result]1"
echo "The build version $(BUILD.SOURCEVERSION) contains tag(s)"
}
else
{
Write-Host "##vso[task.setvariable variable=result]0"
echo "The build version $(BUILD.SOURCEVERSION) does not contain any tags"
}
3. Finally set custom condition for the task you want to run only when the commit contains tag as below:
and(succeeded(), eq(variables['result'], '1'))