Use @Nullable from the Checker Framework and fix a few null-correct…

…ness issues.

RELNOTES= Use `@Nullable` from the Checker Framework and fix a few null-correctness issues.
PiperOrigin-RevId: 380043179

pom.xml

@@ -68,12 +68,6 @@
       <artifactId>guava</artifactId>
       <version>30.1.1-jre</version>
     </dependency>
-    <dependency>
-      <groupId>com.google.code.findbugs</groupId>
-      <artifactId>jsr305</artifactId>
-      <version>3.0.2</version>
-      <optional>true</optional>
-    </dependency>
     <dependency>
       <groupId>com.google.errorprone</groupId>
       <artifactId>error_prone_annotations</artifactId>
@@ -90,6 +84,11 @@
       <artifactId>auto-common</artifactId>
       <version>1.0.1</version>
     </dependency>
+    <dependency>
+      <groupId>org.checkerframework</groupId>
+      <artifactId>checker-qual</artifactId>
+      <version>3.14.0</version>
+    </dependency>
   </dependencies>
 
   <build>

src/main/java/com/google/testing/compile/Compiler.java

@@ -44,6 +44,7 @@
 import javax.tools.JavaCompiler.CompilationTask;
 import javax.tools.JavaFileObject;
 import javax.tools.StandardLocation;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** An object that can {@link #compile} Java source files. */
 @AutoValue
@@ -211,9 +212,10 @@ public final Compilation compile(Iterable<? extends JavaFileObject> files) {
     return compilation;
   }
 
-  @VisibleForTesting static final ClassLoader platformClassLoader = getPlatformClassLoader();
+  @VisibleForTesting
+  static final @Nullable ClassLoader platformClassLoader = getPlatformClassLoader();
 
-  private static ClassLoader getPlatformClassLoader() {
+  private static @Nullable ClassLoader getPlatformClassLoader() {
     try {
       // JDK >= 9
       return (ClassLoader) ClassLoader.class.getMethod("getPlatformClassLoader").invoke(null);
@@ -229,12 +231,14 @@ private static ClassLoader getPlatformClassLoader() {
    * @throws IllegalArgumentException if the given classloader had classpaths which we could not
    *     determine or use for compilation.
    */
-  private static ImmutableList<File> getClasspathFromClassloader(ClassLoader currentClassloader) {
+  private static ImmutableList<File> getClasspathFromClassloader(ClassLoader classloader) {
     ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
 
     // Concatenate search paths from all classloaders in the hierarchy 'till the system classloader.
     Set<String> classpaths = new LinkedHashSet<>();
-    while (true) {
+    for (ClassLoader currentClassloader = classloader;
+        ;
+        currentClassloader = currentClassloader.getParent()) {
       if (currentClassloader == systemClassLoader) {
         Iterables.addAll(
             classpaths,
@@ -263,7 +267,6 @@ private static ImmutableList<File> getClasspathFromClassloader(ClassLoader curre
                     + "since %s is not an instance of URLClassloader",
                 currentClassloader));
       }
-      currentClassloader = currentClassloader.getParent();
     }
 
     return classpaths.stream().map(File::new).collect(toImmutableList());

src/main/java/com/google/testing/compile/InMemoryJavaFileManager.java

@@ -42,6 +42,7 @@
 import javax.tools.SimpleJavaFileObject;
 import javax.tools.StandardJavaFileManager;
 import javax.tools.StandardLocation;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A file manager implementation that stores all output in memory.
@@ -90,8 +91,8 @@ public boolean isSameFile(FileObject a, FileObject b) {
   }
 
   @Override
-  public FileObject getFileForInput(Location location, String packageName,
-      String relativeName) throws IOException {
+  public @Nullable FileObject getFileForInput(
+      Location location, String packageName, String relativeName) throws IOException {
     if (location.isOutputLocation()) {
       return inMemoryOutputs.getIfPresent(uriForFileObject(location, packageName, relativeName));
     }
@@ -103,8 +104,8 @@ public FileObject getFileForInput(Location location, String packageName,
   }
 
   @Override
-  public JavaFileObject getJavaFileForInput(Location location, String className, Kind kind)
-      throws IOException {
+  public @Nullable JavaFileObject getJavaFileForInput(
+      Location location, String className, Kind kind) throws IOException {
     if (location.isOutputLocation()) {
       return inMemoryOutputs.getIfPresent(uriForJavaFileObject(location, className, kind));
     }

src/main/java/com/google/testing/compile/JavaFileObjectSubject.java

@@ -33,8 +33,8 @@
 import java.io.IOException;
 import java.nio.charset.Charset;
 import java.util.function.BiFunction;
-import javax.annotation.Nullable;
 import javax.tools.JavaFileObject;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** Assertions about {@link JavaFileObject}s. */
 public final class JavaFileObjectSubject extends Subject {
@@ -72,6 +72,7 @@ protected String actualCustomStringRepresentation() {
   public void isEqualTo(@Nullable Object other) {
     if (!(other instanceof JavaFileObject)) {
       super.isEqualTo(other);
+      return;
     }
 
     JavaFileObject otherFile = (JavaFileObject) other;

src/main/java/com/google/testing/compile/JavaSourcesSubject.java

@@ -57,12 +57,12 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import javax.annotation.Nullable;
 import javax.annotation.processing.Processor;
 import javax.tools.Diagnostic;
 import javax.tools.Diagnostic.Kind;
 import javax.tools.JavaFileManager;
 import javax.tools.JavaFileObject;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A <a href="https://github.com/truth0/truth">Truth</a> {@link Subject} that evaluates the result
@@ -213,7 +213,11 @@ public void parsesAs(JavaFileObject first, JavaFileObject... rest) {
         final CompilationUnitTree expectedTree = matchedTreePair.getKey();
         if (!matchedTreePair.getValue().isPresent()) {
           failNoCandidates(
-              expectedTreeTypes.get(expectedTree), expectedTree, actualTreeTypes, actualTrees);
+              // see comment above
+              requireNonNull(expectedTreeTypes.get(expectedTree)),
+              expectedTree,
+              actualTreeTypes,
+              actualTrees);
         } else {
           CompilationUnitTree actualTree = matchedTreePair.getValue().get();
           TreeDifference treeDifference = TreeDiffer.diffCompilationUnits(expectedTree, actualTree);

src/main/java/com/google/testing/compile/MoreTrees.java

@@ -35,7 +35,7 @@
 import com.sun.source.util.TreePathScanner;
 import java.util.Arrays;
 import java.util.Optional;
-import javax.annotation.Nullable;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A class containing methods which are useful for gaining access to {@code Tree} instances from
@@ -128,10 +128,8 @@ static TreePath findSubtreePath(CompilationUnitTree root, Tree.Kind treeKind,
     return res.get();
   }
 
-  /**
-   * A {@link TreePathScanner} to power the subtree searches in this class
-   */
-  static final class SearchScanner extends TreePathScanner<Optional<TreePath>, Void> {
+  /** A {@link TreePathScanner} to power the subtree searches in this class */
+  static final class SearchScanner extends TreePathScanner<Optional<TreePath>, @Nullable Void> {
     private final Optional<String> identifier;
     private final Tree.Kind kindSought;
 
@@ -178,7 +176,7 @@ private Optional<TreePath> absentIfNull(Optional<TreePath> ret) {
     }
 
     @Override
-    public Optional<TreePath> scan(Tree node, Void v) {
+    public Optional<TreePath> scan(Tree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       }
@@ -189,7 +187,7 @@ public Optional<TreePath> scan(Tree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> scan(Iterable<? extends Tree> nodes, Void v) {
+    public Optional<TreePath> scan(Iterable<? extends Tree> nodes, @Nullable Void v) {
       return absentIfNull(super.scan(nodes, v));
     }
 
@@ -200,7 +198,7 @@ public Optional<TreePath> reduce(Optional<TreePath> t1, Optional<TreePath> t2) {
     }
 
     @Override
-    public Optional<TreePath> visitBreak(@Nullable BreakTree node, Void v) {
+    public Optional<TreePath> visitBreak(@Nullable BreakTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       }
@@ -209,7 +207,7 @@ public Optional<TreePath> visitBreak(@Nullable BreakTree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> visitClass(@Nullable ClassTree node, Void v) {
+    public Optional<TreePath> visitClass(@Nullable ClassTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getSimpleName())) {
@@ -220,7 +218,7 @@ public Optional<TreePath> visitClass(@Nullable ClassTree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> visitContinue(@Nullable ContinueTree node, Void v) {
+    public Optional<TreePath> visitContinue(@Nullable ContinueTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getLabel())) {
@@ -231,7 +229,7 @@ public Optional<TreePath> visitContinue(@Nullable ContinueTree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> visitIdentifier(@Nullable IdentifierTree node, Void v) {
+    public Optional<TreePath> visitIdentifier(@Nullable IdentifierTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getName())) {
@@ -242,7 +240,8 @@ public Optional<TreePath> visitIdentifier(@Nullable IdentifierTree node, Void v)
     }
 
     @Override
-    public Optional<TreePath> visitLabeledStatement(@Nullable LabeledStatementTree node, Void v) {
+    public Optional<TreePath> visitLabeledStatement(
+        @Nullable LabeledStatementTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getLabel())) {
@@ -253,7 +252,7 @@ public Optional<TreePath> visitLabeledStatement(@Nullable LabeledStatementTree n
     }
 
     @Override
-    public Optional<TreePath> visitLiteral(@Nullable LiteralTree node, Void v) {
+    public Optional<TreePath> visitLiteral(@Nullable LiteralTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getValue())) {
@@ -264,7 +263,7 @@ public Optional<TreePath> visitLiteral(@Nullable LiteralTree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> visitMethod(@Nullable MethodTree node, Void v) {
+    public Optional<TreePath> visitMethod(@Nullable MethodTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getName())) {
@@ -275,7 +274,7 @@ public Optional<TreePath> visitMethod(@Nullable MethodTree node, Void v) {
     }
 
     @Override
-    public Optional<TreePath> visitMemberSelect(@Nullable MemberSelectTree node, Void v) {
+    public Optional<TreePath> visitMemberSelect(@Nullable MemberSelectTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getIdentifier())) {
@@ -286,7 +285,8 @@ public Optional<TreePath> visitMemberSelect(@Nullable MemberSelectTree node, Voi
     }
 
     @Override
-    public Optional<TreePath> visitTypeParameter(@Nullable TypeParameterTree node, Void v) {
+    public Optional<TreePath> visitTypeParameter(
+        @Nullable TypeParameterTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getName())) {
@@ -297,7 +297,7 @@ public Optional<TreePath> visitTypeParameter(@Nullable TypeParameterTree node, V
     }
 
     @Override
-    public Optional<TreePath> visitVariable(@Nullable VariableTree node, Void v) {
+    public Optional<TreePath> visitVariable(@Nullable VariableTree node, @Nullable Void v) {
       if (node == null) {
         return Optional.empty();
       } else if (isMatch(node, node.getName())) {

src/main/java/com/google/testing/compile/ProcessedCompileTesterFactory.java

@@ -16,7 +16,6 @@
 package com.google.testing.compile;
 
 import java.io.File;
-import javax.annotation.CheckReturnValue;
 import javax.annotation.processing.Processor;
 
 /**
@@ -25,7 +24,6 @@
  *
  * @author Gregory Kick
  */
-@CheckReturnValue
 public interface ProcessedCompileTesterFactory {
 
   /**