Validate that package names do not contain Java keywords in Dagger.

This change adds a check in `DaggerSuperficialValidation` to ensure that no part of a type's package name is a Java keyword. This is necessary for KSP because Dagger generates Java code, and using Java keywords in package names can lead to compilation errors in the generated code. A new `ValidationException` type is introduced to handle these errors.

RELNOTES=N/A
PiperOrigin-RevId: 839405001

Author: trexem

dagger-compiler/main/java/dagger/internal/codegen/base/KeywordValidator.java

@@ -24,13 +24,16 @@
 import static dagger.internal.codegen.xprocessing.XElements.asField;
 import static dagger.internal.codegen.xprocessing.XElements.asMethod;
 import static dagger.internal.codegen.xprocessing.XElements.asMethodParameter;
+import static dagger.internal.codegen.xprocessing.XElements.asTypeElement;
 import static dagger.internal.codegen.xprocessing.XElements.getSimpleName;
 import static dagger.internal.codegen.xprocessing.XElements.isExecutable;
 import static dagger.internal.codegen.xprocessing.XTypes.isPrimitive;
 import static javax.lang.model.SourceVersion.isKeyword;
 
 import androidx.room3.compiler.processing.XElement;
 import androidx.room3.compiler.processing.XType;
+import androidx.room3.compiler.processing.XTypeElement;
+import com.google.common.base.Splitter;
 import java.util.Optional;
 import javax.annotation.Nullable;
 import javax.inject.Inject;
@@ -57,6 +60,7 @@ ValidationReport validateJavaKeyword(XElement element) {
     if (isTypeElement(element)) {
       keywordFromName(getSimpleName(element))
           .ifPresent(keyword -> report.addError(javaKeywordErrorMessage(keyword), element));
+      validatePackageName(asTypeElement(element), report);
       // For KAPT We need to validate the Kotlin metadata methods name for type elements.
       // TODO(emjich): Re-enable this validation once we figure out how to avoid false positives.
       // As of now, we are seeing false positives for this validation because KAPT stubs do not
@@ -84,6 +88,19 @@ ValidationReport validateJavaKeyword(XElement element) {
     return report.build();
   }
 
+  private void validatePackageName(XTypeElement element, ValidationReport.Builder report) {
+    String packageName = element.getPackageName();
+    if (packageName == null) {
+      return;
+    }
+    Iterable<String> names = Splitter.on('.').split(packageName);
+    for (String name : names) {
+      keywordFromName(name)
+          .ifPresent(
+              keyword -> report.addError(javaKeywordInPackageErrorMessage(keyword), element));
+    }
+  }
+
   private void validateJavaKeywordType(@Nullable XType type, ValidationReport.Builder report) {
     if (type == null || type.isError() || isPrimitive(type)) {
       return;
@@ -118,4 +135,11 @@ private String javaKeywordErrorMessage(String keyword) {
             + " Please use a different name.",
         keyword);
   }
+
+  private String javaKeywordInPackageErrorMessage(String keyword) {
+    return String.format(
+        "The name '%s' cannot be used as a package name because it is a Java keyword."
+            + " Please use a different package name.",
+        keyword);
+  }
 }

javatests/dagger/internal/codegen/KeywordValidatorTest.java

@@ -402,4 +402,34 @@ public void javaKeywordAsAssistedFactoryParameterName_doesNotFail() {
             "}");
     CompilerTests.daggerCompiler(source).compile(subject -> subject.hasErrorCount(0));
   }
+
+  @Test
+  public void javaKeywordAsPackageName_failsWithExpectedError() {
+    Source componentSrc =
+        CompilerTests.kotlinSource(
+            "test/TestComponent.kt",
+            "package test.default",
+            "",
+            "import dagger.Component",
+            "",
+            "@Component",
+            "interface TestComponent {}" // "default" is a Java keyword
+            );
+    CompilerTests.daggerCompiler(componentSrc)
+        .compile(
+            subject -> {
+              switch (CompilerTests.backend(subject)) {
+                case KSP:
+                  subject
+                      .hasErrorContaining(
+                          "The name 'default' cannot be used as a package name because")
+                      .onSource(componentSrc);
+                  break;
+                case JAVAC:
+                  // JAVAC does not generate stubs for this case, thus no error is reported.
+                  subject.hasErrorCount(0);
+                  break;
+              }
+            });
+  }
 }