add generateDiff task (not yet used in generate-diff.yml)

buildSrc/src/main/java/quilt/internal/QuiltMappingsPlugin.java

@@ -53,6 +53,7 @@
 import quilt.internal.tasks.diff.DownloadTargetMappingJarTask;
 import quilt.internal.tasks.diff.DownloadTargetMetaFileTask;
 import quilt.internal.tasks.diff.ExtractTargetMappingJarTask;
+import quilt.internal.tasks.diff.DiffDirectoriesTask;
 import quilt.internal.tasks.diff.RemapTargetMinecraftJarTask;
 import quilt.internal.tasks.diff.RemapTargetUnpickDefinitionsTask;
 import quilt.internal.tasks.diff.TargetVersionConsumingTask;
@@ -845,7 +846,7 @@ public void apply(@NotNull Project project) {
             }
         );
 
-        tasks.register(
+        final var decompileVineflower = tasks.register(
             DecompileVineflowerTask.DECOMPILE_VINEFLOWER_TASK_NAME,
             DecompileVineflowerTask.class,
             task -> {
@@ -859,7 +860,7 @@ public void apply(@NotNull Project project) {
                     insertAutoGeneratedMappings.flatMap(AddProposedMappingsTask::getOutputMappings)
                 ));
 
-                // TODO move this once generateDiff task eliminates magic strings
+                // TODO move this to build/ once generate-diff.yml uses generateDiff
                 task.getOutput().convention(projectDir.dir("namedSrc"));
             }
         );
@@ -1002,7 +1003,7 @@ public void apply(@NotNull Project project) {
             }
         );
 
-        tasks.register(
+        final var decompileTargetVineflower = tasks.register(
             DecompileTargetVineflowerTask.DECOMPILE_TARGET_VINEFLOWER_TASK_NAME,
             DecompileTargetVineflowerTask.class,
             task -> {
@@ -1017,12 +1018,25 @@ public void apply(@NotNull Project project) {
                         .map(dest -> dest.dir("mappings").file("mappings.tiny"))
                 ));
 
-            // TODO move this once generateDiff task eliminates magic strings
-            task.getOutput().convention(projectDir.dir("namedTargetSrc"));
-        });
+                // TODO move this to build/ once generate-diff.yml uses generateDiff
+                task.getOutput().convention(projectDir.dir("namedTargetSrc"));
+            }
+        );
+
+        // TODO use this in generate-diff.yml
+        tasks.register(
+            DiffDirectoriesTask.GENERATE_DIFF_TASK_NAME,
+            DiffDirectoriesTask.class,
+            task -> {
+                task.getAdditionalArgs().add("-bur");
+
+                task.getFirst().convention(decompileTargetVineflower.flatMap(DecompileTargetVineflowerTask::getOutput));
 
-        // TODO add generateDiff task,
-        //  allow passing its output location on command line and pass it in generate-diff.yml
+                task.getSecond().convention(decompileVineflower.flatMap(DecompileVineflowerTask::getOutput));
+
+                task.getDest().convention(buildDir.file("target.diff"));
+            }
+        );
 
         // sources are added in build.gradle because they're from a project source set
         tasks.register(SourcesJarTask.SOURCES_JAR_TASK_NAME, SourcesJarTask.class);

buildSrc/src/main/java/quilt/internal/tasks/diff/DiffDirectoriesTask.java

@@ -0,0 +1,121 @@
+package quilt.internal.tasks.diff;
+
+import org.gradle.api.GradleException;
+import org.gradle.api.file.Directory;
+import org.gradle.api.file.DirectoryProperty;
+import org.gradle.api.file.RegularFileProperty;
+import org.gradle.api.provider.ListProperty;
+import org.gradle.api.specs.Specs;
+import org.gradle.api.tasks.Exec;
+import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.InputDirectory;
+import org.gradle.api.tasks.Optional;
+import org.gradle.api.tasks.OutputFile;
+import org.gradle.api.tasks.TaskAction;
+import org.gradle.api.tasks.options.Option;
+import quilt.internal.Constants.Groups;
+import quilt.internal.tasks.MappingsTask;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import static quilt.internal.util.ProviderUtil.toOptional;
+
+public abstract class DiffDirectoriesTask extends Exec implements MappingsTask {
+    public static final String GENERATE_DIFF_TASK_NAME = "generateDiff";
+
+    public static final String DIFF_COMMAND = "diff";
+
+    private static final String EXIT_VALUE_1_ERROR =
+        "Process 'command '" + DIFF_COMMAND + "'' finished with non-zero exit value 1";
+
+    @Option(
+        option = "args",
+        description = "Additional args passed to the " + DIFF_COMMAND + " command."
+    )
+    @Optional
+    @Input
+    public abstract ListProperty<String> getAdditionalArgs();
+
+    @Option(
+        option = "first",
+        description = "The first file passed to the " + DIFF_COMMAND + " command."
+    )
+    @InputDirectory
+    public abstract DirectoryProperty getFirst();
+
+    @Option(
+        option = "second",
+        description = "The second file passed to the " + DIFF_COMMAND + " command."
+    )
+    @InputDirectory
+    public abstract DirectoryProperty getSecond();
+
+    @Option(
+        option = "dest",
+        description = "The location to save the " + DIFF_COMMAND + " command output to."
+    )
+    @OutputFile
+    public abstract RegularFileProperty getDest();
+
+    public DiffDirectoriesTask() {
+        this.setGroup(Groups.DIFF);
+
+        this.setExecutable(DIFF_COMMAND);
+
+        this.getOutputs().cacheIf(
+            "Re-enable caching because Exec has @DisableCachingByDefault",
+            Specs.satisfyAll()
+        );
+
+        this.getArgumentProviders().add(() -> {
+            // require neither directory is empty so the diff isn't just the full contents of one of them
+            final Directory first = this.getFirst().get();
+            if (first.getAsFileTree().isEmpty()) {
+                throw new GradleException("first directory is empty");
+            }
+
+            final Directory second = this.getSecond().get();
+            if (second.getAsFileTree().isEmpty()) {
+                throw new GradleException("second directory is empty");
+            }
+
+            final List<String> args = new ArrayList<>();
+
+            toOptional(this.getAdditionalArgs()).ifPresent(args::addAll);
+
+            args.add(first.getAsFile().getAbsolutePath());
+            args.add(second.getAsFile().getAbsolutePath());
+
+            return args;
+        });
+    }
+
+    @Override
+    @TaskAction
+    public void exec() {
+        try {
+            final File dest = this.getDest().get().getAsFile();
+
+            dest.getParentFile().mkdirs();
+
+            dest.createNewFile();
+
+            this.setStandardOutput(new FileOutputStream(dest.getAbsolutePath()));
+        } catch (IOException e) {
+            throw new GradleException("Failed to access destination file", e);
+        }
+
+        try {
+            super.exec();
+        } catch (GradleException e) {
+            // ignore exit value 1 which just means there was a difference between the inputs
+            if (!e.getMessage().equals(EXIT_VALUE_1_ERROR)) {
+                throw new GradleException("Error executing " + DIFF_COMMAND, e);
+            }
+        }
+    }
+}