Added argument to tell only which files have changed

README.md

@@ -65,6 +65,11 @@ Optional system properties:
   retrolambda.outputDir
       Output directory into where the generated class files are written.
       Defaults to same as retrolambda.inputDir
+
+  retrolambda.changed
+      A list of all the files that have changed since last run.
+      This is useful for a build tool to support incremental compilation.
+
 ```
 
 

retrolambda/src/main/java/net/orfjackal/retrolambda/Config.java

@@ -6,8 +6,11 @@
 
 import org.objectweb.asm.Opcodes;
 
-import java.nio.file.*;
+import java.io.File;
+import java.nio.file.Path;
+import java.nio.file.Paths;
 import java.util.*;
+import java.util.stream.Collectors;
 
 public class Config {
 
@@ -16,6 +19,7 @@ public class Config {
     private static final String INPUT_DIR = PREFIX + "inputDir";
     private static final String OUTPUT_DIR = PREFIX + "outputDir";
     private static final String CLASSPATH = PREFIX + "classpath";
+    private static final String CHANGED = PREFIX + "changed";
 
     private static final List<String> requiredProperties = new ArrayList<>();
     private static final List<String> requiredProperitesHelp = new ArrayList<>();
@@ -119,6 +123,20 @@ private String getRequiredProperty(String key) {
         return value;
     }
 
+    // incremental files
+
+    static {
+        optionalParameterHelp(CHANGED,
+                "A list of all the files that have changed since last run.",
+                "This is useful for a build tool to support incremental compilation.");
+    }
+
+    public List<Path> getChangedFiles() {
+        String files = p.getProperty(CHANGED);
+        if (files == null) return null;
+        return Arrays.asList(files.split(File.pathSeparator)).stream()
+                .map(Paths::get).collect(Collectors.toList());
+    }
 
     // help
 

retrolambda/src/main/java/net/orfjackal/retrolambda/Main.java

@@ -4,10 +4,19 @@
 
 package net.orfjackal.retrolambda;
 
-import java.io.*;
-import java.net.*;
-import java.nio.file.*;
-import java.util.*;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.MalformedURLException;
+import java.net.URI;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Properties;
 
 public class Main {
 
@@ -23,10 +32,14 @@ public static void main(String[] args) {
         Path inputDir = config.getInputDir();
         Path outputDir = config.getOutputDir();
         String classpath = config.getClasspath();
+        List<Path> changedFiles = config.getChangedFiles();
         System.out.println("Bytecode version: " + bytecodeVersion + " (" + config.getJavaVersion() + ")");
         System.out.println("Input directory:  " + inputDir);
         System.out.println("Output directory: " + outputDir);
         System.out.println("Classpath:        " + classpath);
+        if (changedFiles != null) {
+            System.out.println("Changed:          " + changedFiles.size() + " files");
+        }
 
         if (!Files.isDirectory(inputDir)) {
             System.out.println("Nothing to do; not a directory: " + inputDir);
@@ -35,12 +48,21 @@ public static void main(String[] args) {
 
         try {
             Thread.currentThread().setContextClassLoader(new URLClassLoader(asUrls(classpath)));
-            Files.walkFileTree(inputDir, new BytecodeTransformingFileVisitor(inputDir, outputDir) {
+
+            BytecodeTransformingFileVisitor visitor = new BytecodeTransformingFileVisitor(inputDir, outputDir) {
+                @Override
                 protected byte[] transform(byte[] bytecode) {
                     return LambdaUsageBackporter.transform(bytecode, bytecodeVersion);
                 }
-            });
+            };
 
+            if (changedFiles == null) {
+                Files.walkFileTree(inputDir, visitor);
+            } else {
+                for (Path inputFile : changedFiles) {
+                    visitor.visitFile(inputFile, Files.readAttributes(inputFile, BasicFileAttributes.class));
+                }
+            }
         } catch (Throwable t) {
             System.out.println("Error! Failed to transform some classes");
             t.printStackTrace(System.out);