From f7dabfa2f2914e0c720b1929119690df736c6514 Mon Sep 17 00:00:00 2001
From: Liam Miller-Cushon <cushon@google.com>
Date: Sun, 23 Aug 2026 07:11:17 -0700
Subject: [PATCH] Include `GeneratedMessageLite.ExtendableMessage` in
 `ImpossibleNullComparison` flag guard

PiperOrigin-RevId: 969381879
---
 .../bugpatterns/ImpossibleNullComparison.java | 27 +++++++++++-
 .../ImpossibleNullComparisonTest.java         | 44 +++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java b/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
index 0caece85abc..929a217f0c9 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java
@@ -122,12 +122,33 @@ public final class ImpossibleNullComparison extends BugChecker
   private static final ImmutableSet<Kind> COMPARISON_OPERATORS =
       Sets.immutableEnumSet(Kind.EQUAL_TO, Kind.NOT_EQUAL_TO);
 
+  private static final Matcher<ExpressionTree> EXTENSION_METHODS_WITH_FIX_LEGACY =
+      instanceMethod()
+          .onDescendantOf(EXTENDABLE_MESSAGE_CLASS)
+          .named("getExtension")
+          .withParameters(EXTENSION_LITE_CLASS);
+
   private static final Matcher<ExpressionTree> EXTENSION_METHODS_WITH_FIX =
       instanceMethod()
           .onDescendantOfAny(EXTENDABLE_MESSAGE_CLASS, EXTENDABLE_MESSAGE_LITE_CLASS)
           .named("getExtension")
           .withParameters(EXTENSION_LITE_CLASS);
 
+  private static final Matcher<ExpressionTree> EXTENSION_METHODS_WITH_NO_FIX_LEGACY =
+      anyOf(
+          instanceMethod()
+              .onDescendantOf(MESSAGE_OR_BUILDER_CLASS)
+              .named("getRepeatedField")
+              .withParameters(FIELD_DESCRIPTOR_CLASS, "int"),
+          instanceMethod()
+              .onDescendantOf(EXTENDABLE_MESSAGE_CLASS)
+              .named("getExtension")
+              .withParameters(EXTENSION_LITE_CLASS, "int"),
+          instanceMethod()
+              .onDescendantOf(MESSAGE_OR_BUILDER_CLASS)
+              .named("getField")
+              .withParameters(FIELD_DESCRIPTOR_CLASS));
+
   private static final Matcher<ExpressionTree> EXTENSION_METHODS_WITH_NO_FIX =
       anyOf(
           instanceMethod()
@@ -572,10 +593,12 @@ private String generateFix(
         if (!protoReceiver(checkOrBuilder).matches(tree, state)) {
           return null;
         }
-        if (EXTENSION_METHODS_WITH_NO_FIX.matches(tree, state)) {
+        if ((checkOrBuilder ? EXTENSION_METHODS_WITH_NO_FIX : EXTENSION_METHODS_WITH_NO_FIX_LEGACY)
+            .matches(tree, state)) {
           return GetterTypes::emptyFix;
         }
-        if (EXTENSION_METHODS_WITH_FIX.matches(tree, state)) {
+        if ((checkOrBuilder ? EXTENSION_METHODS_WITH_FIX : EXTENSION_METHODS_WITH_FIX_LEGACY)
+            .matches(tree, state)) {
           // If the extension represents a repeated field (i.e.: it's an ExtensionLite<T, List<R>>),
           // the suggested fix from get->has isn't appropriate,so we shouldn't suggest a replacement
 
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/ImpossibleNullComparisonTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/ImpossibleNullComparisonTest.java
index 80ed912d692..b4fa6fad017 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/ImpossibleNullComparisonTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/ImpossibleNullComparisonTest.java
@@ -689,4 +689,48 @@ public void test(TestProtoMessageOrBuilder orBld) {
             """)
         .doTest();
   }
+
+  @Test
+  public void liteExtendableMessage_flagEnabled() {
+    compilationHelper
+        .addSourceLines(
+            "Test.java",
+            """
+            import com.google.protobuf.ExtensionLite;
+            import com.google.protobuf.GeneratedMessageLite;
+
+            public class Test {
+              public static <MessageType extends GeneratedMessageLite.ExtendableMessage<MessageType, ?>, Type>
+                  void test(
+                      GeneratedMessageLite.ExtendableMessage<MessageType, ?> msg,
+                      ExtensionLite<MessageType, Type> extension) {
+                // BUG: Diagnostic contains: msg.hasExtension(extension)
+                if (msg.getExtension(extension) != null) {}
+              }
+            }
+            """)
+        .doTest();
+  }
+
+  @Test
+  public void liteExtendableMessage_flagDisabled() {
+    compilationHelper
+        .setArgs("-XepOpt:ImpossibleNullComparison:CheckOrBuilder=false")
+        .addSourceLines(
+            "Test.java",
+            """
+            import com.google.protobuf.ExtensionLite;
+            import com.google.protobuf.GeneratedMessageLite;
+
+            public class Test {
+              public static <MessageType extends GeneratedMessageLite.ExtendableMessage<MessageType, ?>, Type>
+                  void test(
+                      GeneratedMessageLite.ExtendableMessage<MessageType, ?> msg,
+                      ExtensionLite<MessageType, Type> extension) {
+                if (msg.getExtension(extension) != null) {}
+              }
+            }
+            """)
+        .doTest();
+  }
 }