/**
     * Returns the modules required by this module.
     */
    Set<Module> getRequiredModules();

    /**
     * Returns the transitive closure of all modules required by this module, including the module itself.
     */
    Set<Module> getAllRequiredModules();

    /**
     * Returns the implementation + runtime classpath of the transitive closure of all modules required by this module, including the module itself.

                { "module": "m5", "version": { "prefers": "v5", "rejects": ["v6", "v7"] }, "group": "g5"},
                { "module": "m6", "version": { "rejects": ["v8"] }, "group": "g6"},
                { "module": "m7", "version": { "rejects": ["v7"] }, "group": "g7", "reason": "v7 is buggy"},
                { "module": "m8", "version": { "strictly": "v8" }, "group": "g8"},

            return false;
        }
        Module module = (Module) o;
        return Objects.equal(dependencies, module.dependencies)
            && Objects.equal(excludeFolders, module.excludeFolders)
            && Objects.equal(outputDir, module.outputDir)
            && Objects.equal(sourceFolders, module.sourceFolders)
            && Objects.equal(generatedSourceFolders, module.generatedSourceFolders)

        given: "3 modules, where there are dependency relations such that module1 depends on module2 and module2 depends on module3"
        mavenRepo.module('org.test', 'module1', '1.0').publish()
        mavenRepo.module('org.test', 'module2', '1.0')
            .dependsOn('org.test', 'module1', '1.0')
            .publish()
        mavenRepo.module('org.test', 'module3', '1.0')

        def module2 = registry.getModule("gradle-module-2")
        module1.allRequiredModules as List == [module1, module2]
        module2.allRequiredModules as List == [module2, module1]
    }

    def "supports cycles between optional modules"() {
        given:
        def module1Dir = createModule("module-1", properties(optional: 'gradle-optional-module,gradle-module-2'))

    "variants": [
        {
            "name": "api",
            "attributes": { "usage": "compile" },
            "files": [ { "name": "a.zip", "url": "a.zop" } ],
            "dependencies": [ { "group": "g1", "module": "m1", "version": { "prefers": "v1" } } ]
        }
    ]

    }
    retrieve.dependsOn(':a:retrieve')
}
"""

        when:
        module1.ivy.expectGet()
        module1.jar.expectGet()

        module2.ivy.expectHead()
        module2.ivy.sha1.expectGet()
        module2.ivy.expectGet()
        module2.jar.expectHead()
        module2.jar.sha1.expectGet()
        module2.jar.expectGet()

        then:
        succeeds 'retrieve'

        and:

        dependenciesMetadata[0].selector.version == "1.0"
    }

    def "add via map id propagate to the underlying dependency list"() {
        when:
        adapter.add group: "org.gradle.test", name: "module1", version: "1.0"

        then:
        dependenciesMetadata.size() == 1
        dependenciesMetadata[0].selector.group == "org.gradle.test"
        dependenciesMetadata[0].selector.module == "module1"

    void "transitive external dependency substituted with project dependency"() {
        mavenRepo.module("org.gradle", "module1").dependsOnModules("module2").publish()
        mavenRepo.module("org.gradle", "module2").publish()

        createDirs("project1", "project2")
        runTask("idea", "include 'project1', 'project2'", """
allprojects {
    apply plugin: "java"
    apply plugin: "idea"
}

    def resolve = new ResolveTestFixture(buildFile, "conf")

    def setup() {
        mavenRepo.module("myorg", "ModuleC", "2.0").publish()
        mavenRepo.module("myorg", "ModuleD", "2.0").publish()
        mavenRepo.module("myorg", "ModuleB", '1.0').dependsOn("myorg", "ModuleC", "2.0").publish()
        settingsFile << """
            rootProject.name = 'test'
        """
        resolve.prepare()
    }