Fix handling of unnamed packages in getPackageElement

PiperOrigin-RevId: 836134198

Author: cushon

java/com/google/turbine/binder/Binder.java

@@ -257,6 +257,7 @@ private static BindPackagesResult bindPackages(
     }
     CompoundScope topLevel = CompoundScope.base(tli.scope()).append(javaLang);
     for (PreprocessedCompUnit unit : units) {
+      // omitEmptyStrings() to return an empty Iterable for the default package
       ImmutableList<String> packagename =
           ImmutableList.copyOf(Splitter.on('/').omitEmptyStrings().split(unit.packageName()));
       Scope packageScope = tli.lookupPackage(packagename);

java/com/google/turbine/binder/lookup/SimpleTopLevelIndex.java

@@ -170,6 +170,9 @@ public Scope scope() {
   public @Nullable PackageScope lookupPackage(Iterable<String> packagename) {
     Node curr = root;
     for (String bit : packagename) {
+      if (bit.isEmpty()) {
+        throw new IllegalArgumentException("Empty package name");
+      }
       curr = curr.lookup(bit);
       if (curr == null || curr.sym != null) {
         return null;

java/com/google/turbine/processing/TurbineElement.java

@@ -1059,7 +1059,9 @@ public Element getEnclosingElement() {
     @Override
     public List<TurbineTypeElement> getEnclosedElements() {
       ImmutableSet.Builder<TurbineTypeElement> result = ImmutableSet.builder();
-      PackageScope scope = factory.tli().lookupPackage(Splitter.on('/').split(sym.binaryName()));
+      // omitEmptyStrings() to return an empty Iterable for the default package
+      PackageScope scope =
+          factory.tli().lookupPackage(Splitter.on('/').omitEmptyStrings().split(sym.binaryName()));
       requireNonNull(scope); // the current package exists
       for (ClassSymbol key : scope.classes()) {
         if (key.binaryName().contains("$") && factory.getSymbol(key).owner() != null) {

java/com/google/turbine/processing/TurbineElements.java

@@ -76,7 +76,8 @@ private static Symbol asSymbol(Element element) {
 
   @Override
   public PackageElement getPackageElement(CharSequence name) {
-    ImmutableList<String> packageName = ImmutableList.copyOf(Splitter.on('.').split(name));
+    ImmutableList<String> packageName =
+        name.isEmpty() ? ImmutableList.of() : ImmutableList.copyOf(Splitter.on('.').split(name));
     if (factory.tli().lookupPackage(packageName) == null) {
       return null;
     }

javatests/com/google/turbine/processing/ProcessingIntegrationTest.java

@@ -69,6 +69,7 @@
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.Element;
 import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.PackageElement;
 import javax.lang.model.element.RecordComponentElement;
 import javax.lang.model.element.TypeElement;
 import javax.lang.model.element.VariableElement;
@@ -1163,6 +1164,49 @@ class T {
             "field h with annotations [], type '@A int[]' with annotations []");
   }
 
+  @SupportedAnnotationTypes("*")
+  public static class UnnamedPackageProcessor extends AbstractProcessor {
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+      return SourceVersion.latestSupported();
+    }
+
+    private boolean first = true;
+
+    @Override
+    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
+      if (!first) {
+        return false;
+      }
+      first = false;
+      PackageElement p = processingEnv.getElementUtils().getPackageElement("");
+      for (Element e : p.getEnclosedElements()) {
+        processingEnv
+            .getMessager()
+            .printMessage(
+                Diagnostic.Kind.ERROR, String.format("package '%s' contains %s", p, e), e);
+      }
+      return false;
+    }
+  }
+
+  @Test
+  public void unnamedPackage() {
+    ImmutableList<Tree.CompUnit> units =
+        parseUnit(
+            """
+            === T.java ===
+            class A {}
+            class B {}
+            """);
+    TurbineError e = runProcessors(units, new UnnamedPackageProcessor());
+    assertThat(
+            e.diagnostics().stream()
+                .filter(d -> d.severity().equals(Diagnostic.Kind.ERROR))
+                .map(d -> d.message()))
+        .containsExactly("package '' contains A", "package '' contains B");
+  }
+
   private TurbineError runProcessors(ImmutableList<Tree.CompUnit> units, Processor... processors) {
     return assertThrows(
         TurbineError.class,