From ed35fdafea8dff1f4dcfcb94b28d25d483d361f5 Mon Sep 17 00:00:00 2001
From: Liam Miller-Cushon <cushon@google.com>
Date: Fri, 15 Apr 2022 11:15:21 -0700
Subject: [PATCH] Fix a crash in `UnnecessaryBoxedVariable`

Don't assume that return statements are enclosed by a method with a return
type, to handle statement lambdas inside constructors.

Fixes https://github.com/google/error-prone/issues/3115

PiperOrigin-RevId: 442056569
---
 .../bugpatterns/UnnecessaryBoxedVariable.java  | 12 +++++++-----
 .../UnnecessaryBoxedVariableTest.java          | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariable.java b/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariable.java
index 25b8b9a986e..9dad59d75fa 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariable.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariable.java
@@ -21,6 +21,7 @@
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.method.MethodMatchers.instanceMethod;
 import static com.google.errorprone.matchers.method.MethodMatchers.staticMethod;
+import static com.google.errorprone.util.ASTHelpers.findEnclosingMethod;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 
 import com.google.common.collect.ArrayListMultimap;
@@ -429,11 +430,12 @@ public Void visitReturn(ReturnTree node, Void unused) {
       // Don't count a return value as a boxed usage, except if we are returning a parameter, and
       // the method's return type is boxed.
       if (nodeSymbol.getKind() == ElementKind.PARAMETER) {
-        MethodTree enclosingMethod =
-            ASTHelpers.findEnclosingNode(getCurrentPath(), MethodTree.class);
-        Type returnType = ASTHelpers.getType(enclosingMethod.getReturnType());
-        if (!returnType.isPrimitive()) {
-          boxedUsageFound.add((VarSymbol) nodeSymbol);
+        MethodTree enclosingMethod = findEnclosingMethod(state.withPath(getCurrentPath()));
+        if (enclosingMethod != null) {
+          Type returnType = ASTHelpers.getType(enclosingMethod.getReturnType());
+          if (!returnType.isPrimitive()) {
+            boxedUsageFound.add((VarSymbol) nodeSymbol);
+          }
         }
       }
       return null;
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariableTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariableTest.java
index 26629b25957..0309d9912b7 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariableTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryBoxedVariableTest.java
@@ -69,4 +69,22 @@ public void lambdas() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void lambdaReturn() {
+    compilationTestHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  interface F {",
+            "    int f(Integer i);",
+            "  }",
+            "  Test() {",
+            "    F f = (Integer i) -> {",
+            "      return i;",
+            "    };",
+            "  }",
+            "}")
+        .doTest();
+  }
 }