I think everything compiles

gradle-palantir-java-format/build.gradle

@@ -13,6 +13,7 @@ dependencies {
     testImplementation 'org.junit.jupiter:junit-jupiter'
     testImplementation 'org.junit.vintage:junit-vintage-engine'
     testImplementation 'org.assertj:assertj-core'
+    testImplementation project(':palantir-java-format')
 }
 
 gradlePlugin {

gradle-palantir-java-format/src/main/java/com/palantir/javaformat/gradle/FormatDiff.java

@@ -21,15 +21,16 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import com.google.common.base.Splitter;
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Range;
 import com.google.common.collect.RangeSet;
 import com.google.common.collect.Streams;
 import com.google.common.collect.TreeRangeSet;
 import com.google.common.io.ByteStreams;
 import com.palantir.javaformat.Utils;
-import com.palantir.javaformat.java.Formatter;
 import com.palantir.javaformat.java.FormatterException;
-import com.palantir.javaformat.java.JavaFormatterOptions;
+import com.palantir.javaformat.java.FormatterService;
+import com.palantir.javaformat.java.Replacement;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.file.Files;
@@ -52,10 +53,8 @@ public final class FormatDiff {
     private static final Pattern HUNK =
             Pattern.compile("^@@.*\\+(?<startLineOneIndexed>\\d+)(,(?<numLines>\\d+))?", Pattern.MULTILINE);
 
-    public static void formatDiff(Path dirToFormat) throws IOException, InterruptedException {
-        Formatter formatter = Formatter.createFormatter(
-                JavaFormatterOptions.builder().style(JavaFormatterOptions.Style.PALANTIR).build());
-
+    public static void formatDiff(Path dirToFormat, FormatterService formatter)
+            throws IOException, InterruptedException {
         String gitOutput = gitDiff(dirToFormat);
         Path gitTopLevelDir = gitTopLevelDir(dirToFormat);
 
@@ -90,7 +89,7 @@ static Stream<SingleFileDiff> parseGitDiffOutput(String gitOutput) {
         });
     }
 
-    private static void format(Formatter formatter, SingleFileDiff diff) {
+    private static void format(FormatterService formatter, SingleFileDiff diff) {
         String input;
         try {
             input = new String(Files.readAllBytes(diff.path), UTF_8);
@@ -104,7 +103,8 @@ private static void format(Formatter formatter, SingleFileDiff diff) {
 
         try {
             System.err.println("Formatting " + diff.path);
-            String output = formatter.formatSource(input, charRanges.asRanges());
+            ImmutableList<Replacement> replacements = formatter.getFormatReplacements(input, charRanges.asRanges());
+            String output = Utils.applyReplacements(input, replacements);
             Files.write(diff.path, output.getBytes(UTF_8));
         } catch (IOException | FormatterException e) {
             System.err.println("Failed to format file " + diff.path);

gradle-palantir-java-format/src/main/java/com/palantir/javaformat/gradle/PalantirJavaFormatPlugin.java

@@ -16,7 +16,12 @@
 
 package com.palantir.javaformat.gradle;
 
+import com.google.common.collect.Iterables;
+import com.palantir.javaformat.java.FormatterService;
 import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.ServiceLoader;
 import org.gradle.api.DefaultTask;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
@@ -43,7 +48,20 @@ public static class FormatDiffTask extends DefaultTask {
 
         @TaskAction
         public final void formatDiff() throws IOException, InterruptedException {
-            FormatDiff.formatDiff(getProject().getProjectDir().toPath());
+            URL[] jarUris = getProject()
+                    .getRootProject()
+                    .getConfigurations()
+                    .getByName(PalantirJavaFormatProviderPlugin.CONFIGURATION_NAME)
+                    .getFiles()
+                    .stream()
+                    .map(file -> file.toURI())
+                    .toArray(URL[]::new);
+
+            ClassLoader classLoader = new URLClassLoader(jarUris, PalantirJavaFormatPlugin.class.getClassLoader());
+            FormatterService formatter =
+                    Iterables.getOnlyElement(ServiceLoader.load(FormatterService.class, classLoader));
+
+            FormatDiff.formatDiff(getProject().getProjectDir().toPath(), formatter);
         }
     }
 }

gradle-palantir-java-format/src/test/groovy/com/palantir/javaformat/gradle/FormatDiffTest.java

@@ -22,6 +22,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.io.ByteStreams;
+import com.palantir.javaformat.java.FormatterServiceImpl;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
@@ -73,7 +74,7 @@ void reformat_a_subpath_of_a_git_directory_for_only_changed_lines() throws IOExc
 
         runCommandInRepo("git", "add", "-N", ".");
 
-        FormatDiff.formatDiff(subdir);
+        FormatDiff.formatDiff(subdir, new FormatterServiceImpl());
 
         assertThat(reformatMe).hasContent("class ReformatMe {}");
         assertThat(dontTouchMe).hasContent("                                 class DontTouchMe {}");