Fix indexing of directory classpath entries

xtext-gradle-builder/src/main/java/org/xtext/gradle/builder/XtextGradleBuilder.xtend

@@ -1,6 +1,8 @@
 package org.xtext.gradle.builder
 
+import com.google.common.hash.Funnels
 import com.google.common.hash.HashCode
+import com.google.common.hash.Hasher
 import com.google.common.hash.Hashing
 import com.google.common.io.Files
 import com.google.inject.Guice
@@ -101,7 +103,7 @@ class XtextGradleBuilder implements IncrementalXtextBuilder {
 	private def indexChangedClasspathEntries(GradleBuildRequest gradleRequest) {
 		val registry = IResourceServiceProvider.Registry.INSTANCE
 		gradleRequest.dirtyClasspathEntries.filter[exists].forEach[dirtyClasspathEntry|
-			val hash = Files.hash(dirtyClasspathEntry, Hashing.md5)
+			val hash = hash(dirtyClasspathEntry)
 			if (dependencyHashes.get(dirtyClasspathEntry) != hash) {
 				val containerHandle = dirtyClasspathEntry.path
 				val request = new BuildRequest => [
@@ -131,6 +133,20 @@ class XtextGradleBuilder implements IncrementalXtextBuilder {
 		]
 	}
 
+	private def HashCode hash(File file) {
+		val hasher = Hashing.md5.newHasher
+		hash(file, hasher)
+		hasher.hash
+	}
+
+	private def void hash(File file, Hasher hasher) {
+		if (file.isDirectory) {
+			file.listFiles.forEach[hash(hasher)]
+		} else {
+			Files.asByteSource(file).copyTo(Funnels.asOutputStream(hasher))
+		}
+	}
+
 	private def preparResourceSet(BuildRequest it, String containerHandle, ResourceDescriptionsData indexChunk, GradleBuildRequest gradleRequest) {
 		resourceSet = sharedInjector.getInstance(XtextResourceSet) => [
 			classpathURIContext = gradleRequest.jvmTypesLoader

xtext-gradle-plugin/src/integTest/java/org/xtext/gradle/test/BuildingASimpleXtendProject.xtend

@@ -267,5 +267,18 @@ class BuildingASimpleXtendProject extends AbstractXtendIntegrationTest {
 		build("build")
 	}
 
+ 	@Test
+	def void theIndexerCanHandleDirectoryClasspathEntries() {
+		file('src/main/java/com/example/Foo.xtend').content = '''
+			package com.example
+			class Foo {}
+		'''
+		file('src/test/java/com/example/HelloWorld.xtend').content = '''
+			package com.example
+			class HelloWorld {}
+		'''
+
+		build("build")
+	}
 }