Prevent memory copy of list of Jar/Aar file entries. (#404)

See #403 discussion, credit for this optimization goes to @Stephan202.

Note the comment edit for the AAR case. ZipFile is just surprisingly
hostile to copy-free for-each iteration.

jar-infer/jar-infer-lib/src/main/java/com/uber/nullaway/jarinfer/BytecodeAnnotator.java

@@ -15,7 +15,6 @@
  */
 package com.uber.nullaway.jarinfer;
 
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Sets;
 import java.io.BufferedReader;
@@ -24,6 +23,7 @@
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.jar.JarEntry;
@@ -280,7 +280,7 @@ public static void annotateBytecodeInJar(
     // Reference: https://bugs.openjdk.java.net/browse/JDK-8215788
     // Note: we can't just put the code below inside stream().forach(), because it can throw
     // IOException.
-    for (JarEntry jarEntry : inputJar.stream().collect(ImmutableList.toImmutableList())) {
+    for (JarEntry jarEntry : (Iterable<JarEntry>) inputJar.stream()::iterator) {
       InputStream is = inputJar.getInputStream(jarEntry);
       copyAndAnnotateJarEntry(
           jarEntry,
@@ -317,10 +317,13 @@ public static void annotateBytecodeInAar(
     LOG(debug, "DEBUG", "nullableReturns: " + nullableReturns);
     LOG(debug, "DEBUG", "nonnullParams: " + nonnullParams);
     // Error Prone doesn't like usages of the old Java Enumerator APIs. ZipFile does not implement
-    // Iterable, and likely
-    // never will (see  https://bugs.openjdk.java.net/browse/JDK-6581715). So this seems like the
+    // Iterable, and likely never will (see  https://bugs.openjdk.java.net/browse/JDK-6581715).
+    // Additionally, inputZip.stream() returns a Stream<? extends ZipEntry>, and a for-each loop
+    // has trouble handling the corresponding ::iterator  method reference. So this seems like the
     // best remaining way:
-    for (ZipEntry zipEntry : inputZip.stream().collect(ImmutableList.toImmutableList())) {
+    Iterator<? extends ZipEntry> zipIterator = inputZip.stream().iterator();
+    while (zipIterator.hasNext()) {
+      ZipEntry zipEntry = zipIterator.next();
       InputStream is = inputZip.getInputStream(zipEntry);
       zipOS.putNextEntry(new ZipEntry(zipEntry.getName()));
       if (zipEntry.getName().equals("classes.jar")) {

jar-infer/jar-infer-lib/src/test/java/com/uber/nullaway/jarinfer/AnnotationChecker.java

@@ -16,9 +16,9 @@
 package com.uber.nullaway.jarinfer;
 
 import com.google.common.base.Preconditions;
-import com.google.common.collect.ImmutableList;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.jar.JarEntry;
@@ -54,7 +54,9 @@ public static boolean checkMethodAnnotationsInAar(
       String aarFile, Map<String, String> expectedToActualAnnotations) throws IOException {
     Preconditions.checkArgument(aarFile.endsWith(".aar"), "invalid aar file: " + aarFile);
     ZipFile zip = new ZipFile(aarFile);
-    for (ZipEntry zipEntry : zip.stream().collect(ImmutableList.toImmutableList())) {
+    Iterator<? extends ZipEntry> zipIterator = zip.stream().iterator();
+    while (zipIterator.hasNext()) {
+      ZipEntry zipEntry = zipIterator.next();
       if (zipEntry.getName().equals("classes.jar")) {
         JarInputStream jarIS = new JarInputStream(zip.getInputStream(zipEntry));
         JarEntry jarEntry = jarIS.getNextJarEntry();
@@ -87,7 +89,7 @@ public static boolean checkMethodAnnotationsInJar(
       String jarFile, Map<String, String> expectedToActualAnnotations) throws IOException {
     Preconditions.checkArgument(jarFile.endsWith(".jar"), "invalid jar file: " + jarFile);
     JarFile jar = new JarFile(jarFile);
-    for (JarEntry entry : jar.stream().collect(ImmutableList.toImmutableList())) {
+    for (JarEntry entry : (Iterable<JarEntry>) jar.stream()::iterator) {
       if (entry.getName().endsWith(".class")
           && !checkMethodAnnotationsInClass(
               jar.getInputStream(entry), expectedToActualAnnotations)) {