Give formatDiff the formatter of its own project

With the Java-based formatter, formatDiff's classpath was the root
project's palantirJavaFormat, which a subproject's task cannot resolve
in a parallel build. It now takes openJavaFormatFormatterClasspath, as
the Spotless step does, resolved in the project the task belongs to.
The native image is left as it was: formatDiff already runs it in
parallel builds, this repository's among them.

Author: abashev

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

@@ -22,7 +22,6 @@
 import org.gradle.api.DefaultTask;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.file.FileCollection;
@@ -53,6 +52,7 @@ public void apply(Project project) {
         project.getPlugins().apply(PalantirJavaFormatSpotlessPlugin.class);
 
         project.getPlugins().withId("java", p -> {
+            var formatterClasspath = FormatterClasspath.of(project);
 
             // TODO(dfox): in the future we may want to offer a simple 'format' task so people don't need to use
             // spotless to try out our formatter
@@ -61,16 +61,12 @@ public void apply(Project project) {
                 if (getNativeImageSupport().isNativeImageConfigured()) {
                     task.getNativeImage().fileProvider(getNativeImplConfiguration(project));
                 } else {
-                    task.getFormatterClasspath().from(getImplConfiguration(project));
+                    task.getFormatterClasspath().from(formatterClasspath);
                 }
             });
         });
     }
 
-    private static Provider<Configuration> getImplConfiguration(Project project) {
-        return project.getRootProject().getConfigurations().named(PalantirJavaFormatProviderPlugin.CONFIGURATION_NAME);
-    }
-
     private static Provider<File> getNativeImplConfiguration(Project project) {
         return (project.getRootProject()
                 .getConfigurations()