Preserve stable field refinements in lambdas

checker/tests/nullness/Issue771.java

@@ -0,0 +1,50 @@
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.checker.nullness.qual.RequiresNonNull;
+
+public class Issue771 {
+    private @MonotonicNonNull String value = null;
+
+    @RequiresNonNull("value")
+    void print() {
+        System.out.println(value);
+    }
+
+    void func() {
+        if (value == null) {
+            return;
+        }
+
+        Runnable r = () -> print();
+    }
+
+    private final @Nullable String finalValue;
+
+    Issue771(@Nullable String finalValue) {
+        this.finalValue = finalValue;
+    }
+
+    void finalField() {
+        if (finalValue == null) {
+            return;
+        }
+
+        Runnable r = () -> finalValue.toString();
+    }
+
+    private @Nullable String nullableValue;
+
+    void nullableField() {
+        if (nullableValue == null) {
+            return;
+        }
+
+        Runnable r =
+                () -> {
+                    // :: error: (dereference.of.nullable)
+                    nullableValue.toString();
+                };
+        nullableValue = null;
+        r.run();
+    }
+}

docs/CHANGELOG.md

@@ -231,7 +231,7 @@ median of four warm-daemon reps per side).
 
 **Closed issues:**
 
-eisop#433, eisop#792, eisop#863, eisop#1801.
+eisop#433, eisop#771, eisop#792, eisop#863, eisop#1801.
 
 
 Version 3.49.5-eisop1 (April 26, 2026)

framework/src/main/java/org/checkerframework/framework/flow/CFAbstractTransfer.java

@@ -418,10 +418,17 @@ public S initialStore(UnderlyingAST underlyingAST, List<LocalVariableNode> param
                 addFinalLocalValues(store, enclosingElement);
             }
 
-            // We want the initialization stuff, but need to throw out any refinements.
+            // We want the initialization stuff, but need to throw out refinements that might not
+            // still hold when the lambda is invoked later.
             // Update values in place; keys are unchanged.
             store.fieldValues.replaceAll(
                     (fieldAccess, currentValue) -> {
+                        V laterValue =
+                                store.newFieldValueAfterMethodCall(
+                                        fieldAccess, analysis.atypeFactory, currentValue);
+                        if (laterValue != null) {
+                            return laterValue;
+                        }
                         AnnotatedTypeMirror declaredType =
                                 atypeFactory.getAnnotatedType(fieldAccess.getField());
                         return analysis.createAbstractValue(declaredType)