How do I re-use gradle definitions across projects - gradle

Question

I am working on a set of projects that each uses Gradle as the build tool. This is not a multi-project setup although I want to be able to re-use some common Gradle scripts across each project for consistency as the projects are related.
For example, for the Java component, I want the manifest file in the generated JAR file to have the same information. In particular, all the projects will have the same major and minor versions numbers, while the patch version will be project specific.
Here's what I've tried so far:
master.gradle - to be shared across projects
group 'com.example'
ext.majorVersion = 2
ext.minorVersion = 3
ext.patchVersion = 0; // Projects to override
def patchVersion() {
return patchVersion;
}
apply plugin: 'java'
jar {
manifest {
attributes 'Bundle-Vendor': 'Example Company',
'Bundle-Description': 'Project ABC',
'Implementation-Title': project.name,
'Implementation-Version': majorVersion + '.' + minorVersion + '.' + patchVersion()
}
}
build.gradle - for one of the projects
apply from: 'master.gradle'
patchVersion = 3
task hello {
println 'Version: ' + majorVersion + '.' + minorVersion + '.' + patchVersion
}
If I run gradle hello jar from the command line, I get Version: 2.3.3 from the hello task. However, the JAR file manifest contains 2.3.0 which is not what I want. How do I get the correct patch version into the manifest? And more generally, how do I let projects supply information to the master scripts?

Answer 1

Based on #Oliver Charlesworth's suggestion I came up with the following. I had to write a simple plugin to hold the version information and use it as an extension object. Please note (as suggested by the comments in the gradle files), the order in which items are applied and set is very important. Different orderings result in compiler errors or values used before they are set.
If anyone wants to suggest improvements, please do so.
master.gradle
group 'com.example'
// N.B. The individual project must have applied the semantic version
// plugin and set the patch version before applying this file.
// Otherwise the following will fail.
// Specify the major and minor version numbers.
project.semver.major = 2
project.semver.minor = 3
project.version = project.semver
apply plugin: 'java'
jar {
manifest {
attributes 'Bundle-Vendor': 'Example Company',
'Bundle-Description': project.description,
'Implementation-Title': project.name,
'Implementation-Version': project.semver
}
}
build.gradle
// Describe the project before importing the master gradle file
project.description = 'Content Upload Assistant'
// Specify the patch version
apply plugin: SemanticVersionPlugin
project.semver.patch = 3
// Load the master gradle file in the context of the project and the semantic version
apply from: 'master.gradle'
The simple plugin can be found below. At the moment it is with the application source code, but it should be moved out into a library, along with the master gradle file.
buildSrc/src/main/groovy/SemanticVersionPlugin.groovy
import org.gradle.api.Plugin
import org.gradle.api.Project
class SemanticVersionPlugin implements Plugin<Project> {
void apply(Project project) {
project.extensions.create('semver', SemanticVersion)
}
}
class SemanticVersion {
int major
int minor
int patch
String toString() {
return major + '.' + minor + '.' + patch
}
}