Fix #2543 CardinalityEqualsZero equality comparison check

baseline-error-prone/src/main/java/com/palantir/baseline/errorprone/CardinalityEqualsZero.java

@@ -31,7 +31,9 @@
 import com.sun.source.tree.ExpressionTree;
 import com.sun.source.tree.IdentifierTree;
 import com.sun.source.tree.MemberSelectTree;
+import com.sun.source.tree.Tree.Kind;
 import java.util.Collection;
+import java.util.Objects;
 import java.util.Optional;
 import org.immutables.value.Value.Immutable;
 
@@ -58,8 +60,11 @@ public Description matchBinary(BinaryTree tree, VisitorState state) {
 
         EqualsZeroExpression equalsZeroExpression = maybeEqualsZeroExpression.get();
         ExpressionTree operand = equalsZeroExpression.operand();
-        ExpressionTree collectionInstance = ASTHelpers.getReceiver(operand);
+        if (!Objects.equals(operand.getKind(), Kind.METHOD_INVOCATION)) {
+            return Description.NO_MATCH;
+        }
 
+        ExpressionTree collectionInstance = ASTHelpers.getReceiver(operand);
         if (collectionInstance == null || isExpressionThis(collectionInstance)) {
             return Description.NO_MATCH;
         }

baseline-error-prone/src/test/java/com/palantir/baseline/errorprone/CardinalityEqualsZeroTest.java

@@ -266,6 +266,28 @@ public void test_size_on_non_collection() {
                 .doTest();
     }
 
+    @Test
+    public void test_equals_on_non_collection() {
+        fix().addInputLines(
+                        "TestNonCollection.java",
+                        "class TestNonCollection {",
+                        "  public int size() {",
+                        "    return 0;",
+                        "  }",
+                        "  public boolean foo(String key) {",
+                        "    String current = \"x\";",
+                        "    int comparisonResult = current.compareTo(key);",
+                        "    if (comparisonResult == 0) {",
+                        "         return true;",
+                        "    } else {",
+                        "         return false;",
+                        "    }",
+                        "  }",
+                        "}")
+                .expectUnchanged()
+                .doTest();
+    }
+
     @Test
     public void test_qualified_this() {
         fix().addInputLines(

changelog/@unreleased/pr-2544.v2.yml

@@ -0,0 +1,5 @@
+type: fix
+fix:
+  description: 'Fix #2543 CardinalityEqualsZero equality comparison check'
+  links:
+  - https://github.com/palantir/gradle-baseline/pull/2544