The rest of the updater functionality

src/main/java/com/gtnewhorizons/gtnhgradle/PropertiesConfiguration.java

@@ -18,6 +18,8 @@
 import java.util.Map;
 import java.util.Properties;
 import java.util.function.BiConsumer;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 /**
  * A helper for accessing gradle Properties entries configuring the GTNH plugins.
@@ -765,11 +767,27 @@ public void initFromProperties(Map<?, ?> props, BiConsumer<String, Object> onMis
         }
     }
 
+    private static final Pattern BLOWDRYER_SETTINGS_PATTERN = Pattern
+        .compile("'GTNewHorizons/ExampleMod1\\.7\\.10'\\s*,\\s*'tag'\\s*,\\s*'([^']+)'\\s*\\)");
+
     /**
+     * @param settingsPath   Path to the settings.gradle file
      * @param originalValues The old parsed properties
      * @return An updated properties file contents
+     * @throws Throwable for convenience
      */
-    public String generateUpdatedProperties(Map<String, String> originalValues) {
+    public String generateUpdatedProperties(Path settingsPath, Map<String, String> originalValues) throws Throwable {
+        final String settingsContents = new String(Files.readAllBytes(settingsPath), StandardCharsets.UTF_8);
+
+        // Migrate from pre-GTNHGradle buildscript
+        final Matcher blowdryerMatch = BLOWDRYER_SETTINGS_PATTERN.matcher(settingsContents);
+        if (blowdryerMatch.find()) {
+            final String group = blowdryerMatch.group(1);
+            originalValues.put("gtnh.settings.blowdryerTag", group);
+            System.out
+                .println("Found old settings blowdryer tag pointing to " + group + ", migrating to gradle.properties");
+        }
+
         final StringBuilder sb = new StringBuilder();
         final String newline = System.lineSeparator();
 

src/main/java/com/gtnewhorizons/gtnhgradle/tasks/SettingsUpdater.java

@@ -0,0 +1,55 @@
+package com.gtnewhorizons.gtnhgradle.tasks;
+
+import com.gtnewhorizons.gtnhgradle.BuildConfig;
+
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/** The settings update task, loaded as an isolated class from the future when updating the buildscript. */
+public class SettingsUpdater {
+
+    private static final Pattern BLOWDRYER_BLOCK_PATTERN = Pattern.compile("blowdryerSetup\\s*\\{[^}]*}");
+    private static final Pattern PLUGIN_VERSION_PATTERN = Pattern.compile(
+        "(['\"]com\\.gtnewhorizons\\.gtnhsettingsconvention['\"]\\s*\\)?\\s*version\\s*\\(?['\"])([^'\"]+)(['\"])");
+
+    /**
+     * Runs the update process
+     *
+     * @param settingsPath Path to the settings.gradle file
+     * @throws Throwable for convenience
+     */
+    @SuppressWarnings("unused") // used by reflection
+    public void update(Path settingsPath) throws Throwable {
+        final String oldSettings = new String(Files.readAllBytes(settingsPath), StandardCharsets.UTF_8);
+        String newSettings = oldSettings;
+
+        final Matcher blowdryerBlock = BLOWDRYER_BLOCK_PATTERN.matcher(newSettings);
+        if (blowdryerBlock.find()) {
+            System.out.println("Removed the old blowdryerSetup block from settings.gradle");
+            newSettings = blowdryerBlock.replaceAll("");
+        }
+
+        final Matcher versionMatcher = PLUGIN_VERSION_PATTERN.matcher(newSettings);
+        if (versionMatcher.find()) {
+            final String preVersion = versionMatcher.group(1);
+            final String oldVersion = versionMatcher.group(2);
+            final String postVersion = versionMatcher.group(3);
+            final String newVersion = BuildConfig.VERSION;
+            if (oldVersion.equals(newVersion)) {
+                System.out.println("Settings.gradle plugin already at the newest version of " + newVersion);
+            } else {
+                System.out.println("Found plugin version update " + newVersion + " from " + oldVersion + ", applying");
+            }
+            newSettings = newSettings.substring(0, versionMatcher.start(2)) + newVersion
+                + newSettings.substring(versionMatcher.end(2));
+        }
+
+        // noinspection StringEquality
+        if (newSettings != oldSettings) {
+            Files.write(settingsPath, newSettings.getBytes(StandardCharsets.UTF_8));
+        }
+    }
+}

src/main/java/com/gtnewhorizons/gtnhgradle/tasks/UpdateBuildscriptTask.java

@@ -95,16 +95,17 @@ public void doUpdate() throws Throwable {
         }
     }
 
-    private void updateSettings(URLClassLoader newJarLoader) throws Exception {
-        //
-    }
-
     private void updateProperties(URLClassLoader newJarLoader) throws Exception {
+        final Path settingsPath = getSettingsGradle().getAsFile()
+            .get()
+            .toPath();
+
         final Class<?> propsClass = Class
             .forName("com.gtnewhorizons.gtnhgradle.PropertiesConfiguration", true, newJarLoader);
         final Object propsObject = propsClass.getConstructor()
             .newInstance();
-        final Method generateUpdatedPropertiesMethod = propsClass.getMethod("generateUpdatedProperties", Map.class);
+        final Method generateUpdatedPropertiesMethod = propsClass
+            .getMethod("generateUpdatedProperties", Path.class, Map.class);
 
         final Properties p = new Properties();
         final Path propertiesPath = getPropertiesGradle().getAsFile()
@@ -122,7 +123,20 @@ private void updateProperties(URLClassLoader newJarLoader) throws Exception {
                     .toString());
         }
 
-        final String newProps = (String) generateUpdatedPropertiesMethod.invoke(propsObject, originalProps);
+        final String newProps = (String) generateUpdatedPropertiesMethod
+            .invoke(propsObject, settingsPath, originalProps);
         Files.write(propertiesPath, newProps.getBytes(StandardCharsets.UTF_8));
     }
+
+    private void updateSettings(URLClassLoader newJarLoader) throws Exception {
+        final Path settingsPath = getSettingsGradle().getAsFile()
+            .get()
+            .toPath();
+        final Class<?> upClass = Class
+            .forName("com.gtnewhorizons.gtnhgradle.tasks.SettingsUpdater", true, newJarLoader);
+        final Object upInstance = upClass.getConstructor()
+            .newInstance();
+        final Method update = upClass.getMethod("update", Path.class);
+        update.invoke(upInstance, settingsPath);
+    }
 }