SimplifyBooleanExpression: skip nullable boolean comparisons in Kotlin

src/main/java/org/openrewrite/staticanalysis/SimplifyBooleanExpression.java

@@ -19,10 +19,13 @@
 import org.jspecify.annotations.Nullable;
 import org.openrewrite.ExecutionContext;
 import org.openrewrite.Recipe;
+import org.openrewrite.SourceFile;
 import org.openrewrite.Tree;
 import org.openrewrite.TreeVisitor;
 import org.openrewrite.java.cleanup.SimplifyBooleanExpressionVisitor;
+import org.openrewrite.java.tree.Expression;
 import org.openrewrite.java.tree.J;
+import org.openrewrite.java.tree.JavaType;
 import org.openrewrite.kotlin.marker.IsNullSafe;
 
 import java.util.Set;
@@ -52,10 +55,21 @@ public TreeVisitor<?, ExecutionContext> getVisitor() {
 
             // Comparing Kotlin nullable type `?` with true/false can not be simplified,
             // e.g. `X?.fun() == true` is not equivalent to `X?.fun()`
+            // and `nullableBoolean == true` is not equivalent to `nullableBoolean`
             @Override
             protected boolean shouldSimplifyEqualsOn(@Nullable J j) {
-                return !(j instanceof J.MethodInvocation) ||
-                        !j.getMarkers().findFirst(IsNullSafe.class).isPresent();
+                if (j instanceof J.MethodInvocation) {
+                    return !j.getMarkers().findFirst(IsNullSafe.class).isPresent();
+                }
+                // For non-Java source files (e.g. Kotlin), only simplify when the
+                // expression type is primitive boolean to avoid changing semantics
+                // of nullable Boolean comparisons like `Boolean? == true`.
+                // Once the parent class includes this logic, this block can be
+                // replaced with just `super.shouldSimplifyEqualsOn(j)`.
+                if (!(getCursor().firstEnclosing(SourceFile.class) instanceof J.CompilationUnit)) {
+                    return j instanceof Expression && ((Expression) j).getType() == JavaType.Primitive.Boolean;
+                }
+                return super.shouldSimplifyEqualsOn(j);
             }
         };
     }

src/test/java/org/openrewrite/staticanalysis/kotlin/SimplifyBooleanExpressionTest.java

@@ -17,6 +17,7 @@
 
 import org.junit.jupiter.api.Test;
 import org.openrewrite.DocumentExample;
+import org.openrewrite.Issue;
 import org.openrewrite.staticanalysis.SimplifyBooleanExpression;
 import org.openrewrite.test.RecipeSpec;
 import org.openrewrite.test.RewriteTest;
@@ -111,4 +112,60 @@ fun main() {
           )
         );
     }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/303")
+    @Test
+    void nullableBooleanReceiverEqualsTrue() {
+        rewriteRun(
+          kotlin(
+            """
+              fun Boolean?.toLegacyFlag() = if (this == true) "1" else "0"
+              """
+          )
+        );
+    }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/303")
+    @Test
+    void nullableBooleanFieldEqualsTrue() {
+        rewriteRun(
+          kotlin(
+            """
+              data class Todo(val completed: Boolean?)
+              fun main() {
+                  val todo = Todo(null)
+                  val isCompleted: Boolean = todo.completed == true
+              }
+              """
+          )
+        );
+    }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/303")
+    @Test
+    void nullableBooleanParameterEqualsFalse() {
+        rewriteRun(
+          kotlin(
+            """
+              fun check(b: Boolean?) {
+                  if (b == false) println("false or null")
+              }
+              """
+          )
+        );
+    }
+
+    @Issue("https://github.com/openrewrite/rewrite-static-analysis/issues/303")
+    @Test
+    void nullableBooleanParameterNotEqualTrue() {
+        rewriteRun(
+          kotlin(
+            """
+              fun check(b: Boolean?) {
+                  if (b != true) println("not true")
+              }
+              """
+          )
+        );
+    }
 }