Use Grgit to generate a "git describe" that considers the tags of all branches.

custom-git-describe.gradle

/**
 * Copyright (c) 2020-present Daniel San
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * This script use the library https://github.com/ajoberstar/grgit.
 */

static final String buildDescribeString(
    final String tag,
    final int commitsCount,
    final /* org.ajoberstar.grgit.Commit */ headCommit
) {
    return "$tag-$commitsCount-g${headCommit.id.substring(0, 7)}"
}

final String unreleasedDescribe() {
    final def headCommit = grgit.head()
    final def commitsCount = grgit.log().size()
    return buildDescribeString("unreleased", commitsCount, headCommit)
}

final String releasedDescribe(final /*Array<org.ajoberstar.grgit.Tag>*/ tags) {
    tags.sort { it.dateTime }

    final def lastTag = tags.last()
    final def headCommit = grgit.head()
    if (headCommit == lastTag.commit)
        return lastTag.getName()

    final def tagName = lastTag.getName()
    final def commitCount = grgit.log { range(tagName, 'HEAD') }.size()
    return buildDescribeString(tagName, commitCount, headCommit)
}

ext.customGitDescribe = {
    if (grgit == null)
        return "0.0.1-0-without_git_repo"

    final def tags = grgit.tag.list()
    if (tags.isEmpty())
        return unreleasedDescribe()

    return releasedDescribe(tags)
}