How to write custom substitution rules for ResolutionStrategy

Help/Discuss
1

I started playing around with 2.5 rc-1 yesterday and combed through the documentation, and for the life of me, I couldn’t figure out how given the options of ResolutionStrategy, using “substitute project with project” or “substitute project with module” to make this work for our case, which is one of using a pre-built binary from a local directory hierarchy in place of a project dependency. First of all, “module” is not well-documented anywhere that I looked. Second, it appears only to handle group,name, version. I’m guessing that what we want is closer to substitute project with library which isn’t in the API.

I had originally thought that using an artifacts closure with an associated configuration in each project on which we would have a dependency and then using something like this:

      substitute project(':core:utilities:utils') with project(path:':core:utilties:utils', configuration: 'archive'),

would be what we might have to do, but given the docs and examples, I’m completely stumped. I understand that I may have to put some custom ResolutionStrategy code in settings.gradle, but I don’t know how to morph a specific binary file to a substitution rule.

I’d appreciate some help here. Thanks.

2

A ‘module’ in dependency substitution roughly corresponds to an ExternalModuleDependency, and ‘project’ corresponds to a ProjectDependency. More precisely they correspond to subtypes of ComponentSelector.

If you have a pre-built Jar file that you want to use instead of building a project dependency, then you need to treat that pre-built Jar file as an external module dependency. So you’d

  1. Define a file-backed repository containing the jar file and include that in the set of repositories for resolving: using a Flat Directory repository is probably the easiest way, but an standard file-backed Ivy repository will work too.
  2. Place your prebuilt-artifact in the flat-dir repository, making sure that your artifacts include a version number in their name.
  3. Use a substitution rule to replace the project dependency with the module dependency resolved from the local repository.

Hope that helps,
Daz

3

Thanks, but that won’t directly work for our case. We just got rid off all versions on jars (for reasons I won’t go into here). Also, although all jars exist under a common root dir (corresponding to our product installation layout, and directly corresponding to the ultimate target build locations of each module), they are not in a flat directory repo. Perhaps we could somehow map from an Ivy repo to what we have. Does that sound like the best approach?

4

Yep, you can configure a file-backed Ivy repository with pretty much any pattern you like: using the Pattern layout.

5

I’m making good progress with this, simply using a flatDir repo with multiple dirs for now just to try to flesh out other issues. I’ve hit one snag which I can’t figure out.

I have a number of places in the build, where I do something like this:

mod/a/b/c/build.gradle
configurations { aSpecialJar }
task buildSomeJar(type: Jar) {…}

artifacts {
aSpecialJar buildSomeJar
}

Then, in another module I make a reference to this configuration:

mod/d/e/f/build.gradle
configurations { mySpecialRefConfig }
dependencies {
mySpecialRefConfig project(path: ‘:a:b:c’, configuration: aSpecialJar)
}

Now, most of the time, when I have a dependency on project(‘:a:b:c’) is simply to the default configuration and not specified, as in compile(project(‘:a:b:c’)) as is typical. For dependencies like this, my DependencySubsitution rules work. However, for the case where the dependencies are of the mySpecialRefConfig project(path: ‘:a:b:c’, configuration: aSpecialJar) form, they fail with a message like:

Could not resolve all dependencies for configuration ‘:mySpecialRefConfg’.
Module version :mod:unspecified, configuration ‘mySpecialRefConfg’ declares a dependency on configuration ‘aSpecialJar’ which is not declared in the module descriptor for group-ignored:symName:1.0

My dependencySubsitution code in mod/build.gradle looks like this:

  configurations.all {
    resolutionStrategy {
      dependencySubstitution {
        all { DependencySubstitution dependency ->
            if (dependency.requested instanceof ProjectComponentSelector) {
              def symName = project(dependency.requested.getProjectPath()).symbolicName
              /*
                If we're running with -a, then substitute the pre-built jar, if one exists, for the
                requested dependency.  Otherwise, don't do a substitution
              */
              if (!project.gradle.startParameter.isBuildProjectDependencies()) { // i.e. "gradle -a"
                dependency.useTarget(module("group-ignored:${symName}:1.0")) // ignores group-ignored and version 1.0
              }
            }
          }
        }
      }
    }

The only thing I’ve been able to figure out so far is to not do the dependency substitution rule for modules which are referenced this way, but this is not a good solution at all for a number of reasons, the main one being that it will defeat the potential performance gains of substituting a pre-built jar for those modules that have lots of references.
How can I either (a) construct the substitution rules to account for this, or (2) override the rules when an alternative configuration is specified on the dependency?

Thanks

6

By using a flatDir repository you are losing the ability to describe multiple configurations for a module, and there’s no way to replace the configuration value using a dependency substitution rule. So the only way forward that I can see is to use a local ivy repository, which will allow you to more accurately represent the project artifacts.

7

I’ve switched to an ivy repository, but the same question remains: How can I define a different way of handling dependencies on a project when those dependencies reference named external configurations on the project. Ideally, what I would like to do is define the dependency substitution only for the default configuration, but not otherwise or if. To use the example above:

For normal dependencies such as:
compile(project(’:a:b:c’)) I want my substitution to be applied/used,

however if the dependency is of this form:
special(project(path: ‘:a:b:c’, configuration: aSpecialJar), I do not want to my substitution to be applied/used

Even using ivy, I am no closer to figuring out how at resolution time, I can circumvent the substitution so that the original/unaltered dependency is used in this special case.

It seems to me that the substitution rules would be more powerful if they would allow substitution on a designated set of configurations and not simply apply to all configurations.

Thanks again,
Jim