[[sec::declare_feature_variants]]
== Registering features

Features can be declared by applying the `java-library` plugin.
The following code illustrates how to declare a feature named `mongodbSupport`:

.Registering a feature
====

		check.error(ident, InvalidInitDecl, "cannot declare init - must be func")
		return
	}

	// spec: "The main package must have package name main and declare
	// a function main that takes no arguments and returns no value."
	if ident.Value == "main" && check.pkg.name == "main" {
		check.error(ident, InvalidMainDecl, "cannot declare main - must be func")
		return
	}

	check.declare(check.pkg.scope, ident, obj, nopos)

        true        | 'conflict fix applied'
    }

    /**
     * This test highlights the case where published module declares a relocation. This is the drop-in replacement
     * for "replacedBy" rules when a module has been relocated, and that the publisher uses Gradle. There's the
     * ability to declare, in a newer version of the module, that it actually provides the same capability as an

    }

    def "does not allow replacing with self"() {
        declaredReplacements 'a->a'
        expect:
        fails().assertHasCause("Cannot declare module replacement that replaces self: org:a->org:a")
    }

    def "when multiple replacement targets declared only the last one applies"() {
        publishedMavenModules 'c'
        declaredDependencies 'a', 'b', 'c'
        declaredReplacements 'a->b', 'a->c'

					// Keep imports.
				case token.VAR, token.CONST:
					// Blank the declared var/const names.
					for _, spec := range decl.Specs {
						spec := spec.(*ast.ValueSpec)
						for i := range spec.Names {
							spec.Names[i].Name = "_"
						}
					}
				}
			case *ast.FuncDecl:
				// Blank the declared func name.
				decl.Name.Name = "_"

				// Turn a method receiver:  func (T) f(P) R {...}

            """${intro}  - Problem: In version catalog ${catalog}, a bundle with name '${bundle}' declares a dependency on '${aliasRef}' which doesn't exist.

    Reason: Bundles can only contain references to existing library aliases.

    Possible solutions:
      1. Make sure that the library alias '${aliasRef}' is declared.
      2. Remove '${aliasRef}' from bundle '${bundle}'.

    ${documentation}"""
        }
    }

       - Configuration ':myElements' declares attribute 'color' with value 'blue':
           - Incompatible because this component declares attribute 'artifactType' with value 'jar' and the consumer needed attribute 'artifactType' with value 'dll'
       - Configuration ':myElements' variant secondary declares attribute 'color' with value 'blue':

====

By using the `belongsTo` with `false` (**not** virtual), we declare that all modules belong to the same _published platform_.
In this case, the platform is `com.fasterxml.jackson:jackson-bom` and Gradle will look for it, as for any other module, in the declared repositories.

.Making use of a dependency version alignment rule
====

   *
   * @return this method does not return; it always throws
   * @throws IOException when the given throwable is an IOException
   * @throws X1 when the given throwable is of the declared type X1
   * @throws X2 when the given throwable is of the declared type X2
   */
  public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow(
      Throwable e, Class<X1> declaredType1, Class<X2> declaredType2) throws IOException, X1, X2 {

   *
   * @return this method does not return; it always throws
   * @throws IOException when the given throwable is an IOException
   * @throws X1 when the given throwable is of the declared type X1
   * @throws X2 when the given throwable is of the declared type X2
   */
  public <X1 extends Exception, X2 extends Exception> RuntimeException rethrow(
      Throwable e, Class<X1> declaredType1, Class<X2> declaredType2) throws IOException, X1, X2 {