Added support for using model transformers with mixins.

picocli-codegen/src/main/java/picocli/codegen/annotation/processing/TypedMember.java

@@ -114,6 +114,15 @@ public String getMixinName() {
         return empty(annotationName) ? getName() : annotationName;
     }
 
+    @Override
+    public Class<? extends CommandLine.IModelTransformer> getModelTransformer() {
+        if (isMixin()) {
+            return getAnnotation(CommandLine.Mixin.class).modelTransformer();
+        } else {
+            return null;
+        }
+    }
+
     static String propertyName(String methodName) {
         if (methodName.length() > 3 && (methodName.startsWith("get") || methodName.startsWith("set"))) { return decapitalize(methodName.substring(3)); }
         return decapitalize(methodName);

src/main/java/picocli/CommandLine.java

@@ -4467,6 +4467,10 @@ public enum ScopeType {
          * If not specified the name of the annotated field is used.
          * @return a String to register the mixin object with, or an empty String if the name of the annotated field should be used */
         String name() default "";
+
+        /** Returns the model transformer for this mixin.
+         **/
+        Class<? extends IModelTransformer> modelTransformer() default NoOpModelTransformer.class;
     }
     /**
      * Fields annotated with {@code @Spec} will be initialized with the {@code CommandSpec} for the command the field is part of. Example usage:
@@ -7464,6 +7468,7 @@ public void updateCommandAttributes(Command cmd, IFactory factory) {
 
             void initAliases(String[] aliases)          { if (aliases != null) { this.aliases.addAll(Arrays.asList(aliases));}}
             void initName(String value)                 { if (initializable(name, value, DEFAULT_COMMAND_NAME))                           {name = value;} }
+            void resetName()                 {name = null;}
             void initHelpCommand(boolean value)         { if (initializable(isHelpCommand, value, DEFAULT_IS_HELP_COMMAND))               {isHelpCommand = value;} }
             void initVersion(String[] value)            { if (initializable(version, value, UsageMessageSpec.DEFAULT_MULTI_LINE))         {version = value.clone();} }
             void initVersionProvider(IVersionProvider value) { if (versionProvider == null) { versionProvider = value; } }
@@ -11347,6 +11352,7 @@ public interface IAnnotatedElement {
             <T extends Annotation> T getAnnotation(Class<T> annotationClass);
             String getName();
             String getMixinName();
+            Class<? extends IModelTransformer> getModelTransformer();
             boolean isArgSpec();
             boolean isOption();
             boolean isParameter();
@@ -11539,6 +11545,13 @@ public String getMixinName()    {
                 String annotationName = getAnnotation(Mixin.class).name();
                 return empty(annotationName) ? getName() : annotationName;
             }
+            public Class<? extends IModelTransformer> getModelTransformer() {
+                if (isMixin()) {
+                    return getAnnotation(Mixin.class).modelTransformer();
+                } else {
+                  return NoOpModelTransformer.class;
+                }
+            }
             static String propertyName(String methodName) {
                 if (methodName.length() > 3 && (methodName.startsWith("get") || methodName.startsWith("set"))) { return decapitalize(methodName.substring(3)); }
                 return decapitalize(methodName);
@@ -12058,6 +12071,15 @@ private static CommandSpec buildMixinForMember(IAnnotatedElement member, IFactor
                         member.setter().set(userObject);
                     }
                     CommandSpec result = CommandSpec.forAnnotatedObject(userObject, factory);
+                    IModelTransformer modelTransformer = DefaultFactory.create(factory, member.getModelTransformer());
+                    String oldName = result.name;
+                    result.initName(member.getMixinName());
+                    result = modelTransformer.transform(result);
+                    if (oldName != null && !oldName.equals(CommandSpec.DEFAULT_COMMAND_NAME)) {
+                        result.initName(oldName);
+                    } else {
+                        result.resetName();
+                    }
                     return result.withToString(member.getToString());
                 } catch (InitializationException ex) {
                     throw ex;

src/test/java/picocli/MixinTest.java

@@ -27,6 +27,8 @@
 import java.io.File;
 import java.io.PrintStream;
 import java.io.UnsupportedEncodingException;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
 
 import static org.junit.Assert.*;
@@ -1100,4 +1102,51 @@ public void testIssue1836CommandAliasOnMixin() {
         Help help = new Help(new App_Issue1836());
         assertEquals("list, ls", help.commandList().trim());
     }
+
+    public static class MixinReuseModelTransformer implements IModelTransformer {
+        @Override
+        public CommandSpec transform(CommandSpec commandSpec) {
+            String prefix = commandSpec.name();
+            ArrayList<OptionSpec> options = new ArrayList<OptionSpec>(commandSpec.options());
+            for (OptionSpec option : options) {
+                commandSpec.remove(option);
+                OptionSpec.Builder optionBuilder = option.toBuilder();
+                String[] names = optionBuilder.names();
+                String[] newNames = new String[names.length];
+                for (int i = 0; i < names.length; i++) {
+                    String name = names[i];
+                    String newName = "--" + prefix + name.substring(2, 3).toUpperCase() + name.substring(3);
+                    newNames[i] = newName;
+                }
+                optionBuilder.names(newNames);
+                String defaultValue = optionBuilder.defaultValue();
+                if (defaultValue.startsWith("${env:")) {
+                    optionBuilder.defaultValue("${env:" + prefix.toUpperCase() + "_" + defaultValue.substring(6, defaultValue.length() - 1).toUpperCase() + "}");
+                }
+                commandSpec.add(optionBuilder.build());
+            }
+            return commandSpec;
+        }
+    }
+
+    @Test
+    public void testModelTransformation() {
+        class ReusableMixin {
+            @Option(names = "--url", defaultValue = "${env:URL}")
+            String  url;
+        }
+        class Application {
+            @Mixin(modelTransformer = MixinReuseModelTransformer.class)
+            ReusableMixin first;
+            @Mixin(modelTransformer = MixinReuseModelTransformer.class)
+            ReusableMixin second;
+        }
+        Application application = new Application();
+        CommandLine commandLine = new CommandLine(application, new InnerClassFactory(this));
+        List<OptionSpec> options = commandLine.getCommandSpec().options();
+        assertArrayEquals(new String[]{"--firstUrl"}, options.get(0).names());
+        assertEquals("${env:FIRST_URL}", options.get(0).defaultValueString());
+        assertArrayEquals(new String[]{"--secondUrl"}, options.get(1).names());
+        assertEquals("${env:SECOND_URL}", options.get(1).defaultValueString());
+    }
 }

src/test/java/picocli/ModelArgSpecTest.java

@@ -243,6 +243,7 @@ private static class AnnotatedImpl implements CommandLine.Model.IAnnotatedElemen
         public <T extends Annotation> T getAnnotation(Class<T> annotationClass) { return null;}
         public String getName() {return name;}
         public String getMixinName() {return null;}
+        public Class<? extends CommandLine.IModelTransformer> getModelTransformer() { return null; }
         public boolean isArgSpec() {return false;}
         public boolean isOption() {return false;}
         public boolean isParameter() {return false;}