chore: use dynamic default value for delimiter

Author: simschla

app/src/main/java/com/diffplug/spotless/cli/steps/LicenseHeader.java

@@ -18,6 +18,7 @@
 import java.io.File;
 import java.nio.file.Files;
 import java.util.List;
+import java.util.Map;
 
 import org.jetbrains.annotations.NotNull;
 
@@ -36,10 +37,20 @@
 
 import picocli.CommandLine;
 
-@CommandLine.Command(name = "license-header", description = "Runs license header")
+@CommandLine.Command(
+        name = "license-header",
+        description = "Runs license header",
+        defaultValueProvider = LicenseHeader.OptionDefaultProvider.class)
 @SupportedFileTypes("any")
 @AdditionalInfoLinks("https://github.com/diffplug/spotless/tree/main/plugin-gradle#license-header")
 public class LicenseHeader extends SpotlessFormatterStep {
+
+    static class OptionDefaultProvider extends OptionDefaultValueProvider {
+        OptionDefaultProvider() {
+            super(Map.of(OPTION_YEAR_SEPARATOR_LONG, LicenseHeaderStep::defaultYearDelimiter));
+        }
+    }
+
     @CommandLine.ArgGroup(exclusive = true, multiplicity = "1")
     LicenseHeaderSourceOption licenseHeaderSourceOption;
 
@@ -73,10 +84,13 @@ static class LicenseHeaderSourceOption {
                     + OptionConstants.VALID_AND_DEFAULT_VALUES_SUFFIX)
     LicenseHeaderStep.YearMode yearMode;
 
+    private static final String OPTION_YEAR_SEPARATOR_LONG = "--year-separator";
+    private static final String OPTION_YEAR_SEPARATOR_SHORT = "-Y";
+
     @CommandLine.Option(
-            names = {"--year-separator", "-Y"},
+            names = {OPTION_YEAR_SEPARATOR_LONG, OPTION_YEAR_SEPARATOR_SHORT},
             required = false,
-            defaultValue = "-" /* TODO simschla: Make accessible: LicenseHeaderStep.DEFAULT_YEAR_DELIMITER*/,
+            // defaultValue from DefaultValueProvider (because is dynamic)
             description = "The separator to use for the year range in the license header."
                     + OptionConstants.DEFAULT_VALUE_SUFFIX)
     String yearSeparator;

app/src/main/java/com/diffplug/spotless/cli/steps/OptionDefaultValueProvider.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless.cli.steps;
+
+import java.util.Map;
+import java.util.function.Supplier;
+
+import picocli.CommandLine;
+
+abstract class OptionDefaultValueProvider implements CommandLine.IDefaultValueProvider {
+    private final Map<String, Supplier<String>> optionsToDefaults;
+
+    protected OptionDefaultValueProvider(Map<String, Supplier<String>> optionsToDefaults) {
+        this.optionsToDefaults = Map.copyOf(optionsToDefaults);
+    }
+
+    @Override
+    public String defaultValue(CommandLine.Model.ArgSpec argSpec) throws Exception {
+        if (!argSpec.isOption()) {
+            return null;
+        }
+        if (!(argSpec instanceof CommandLine.Model.OptionSpec optionSpec)) {
+            return null;
+        }
+        Supplier<String> supplier = optionsToDefaults.get(optionSpec.longestName());
+        return supplier != null ? supplier.get() : null;
+    }
+}