From b84b80c2624219894ea67ee6beee97d1ec01860b Mon Sep 17 00:00:00 2001
From: Liam Miller-Cushon <cushon@google.com>
Date: Tue, 19 Jan 2021 10:39:04 -0800
Subject: [PATCH] Don't crash on 'arrow' switches in `FallThrough`

arrow switches don't fall through, so this check doesn't apply to them,
just exiting gracefully is all we need to do here.

Fixes https://github.com/google/error-prone/issues/2118

PiperOrigin-RevId: 352602004
---
 .../errorprone/bugpatterns/FallThrough.java   |  6 +++--
 .../bugpatterns/FallThroughTest.java          | 22 +++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/FallThrough.java b/core/src/main/java/com/google/errorprone/bugpatterns/FallThrough.java
index 2f519bb026c..0a5284ccae7 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/FallThrough.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/FallThrough.java
@@ -35,6 +35,7 @@
 import com.sun.source.tree.SwitchTree;
 import com.sun.tools.javac.tree.JCTree;
 import com.sun.tools.javac.util.Position;
+import java.util.List;
 import java.util.regex.Pattern;
 
 /** A {@link BugChecker}; see the associated {@link BugPattern} annotation for details. */
@@ -57,13 +58,14 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
         break;
       }
       CaseTree next = it.peek();
-      if (caseTree.getStatements().isEmpty()) {
+      List<? extends StatementTree> statements = caseTree.getStatements();
+      if (statements == null || statements.isEmpty()) {
         continue;
       }
       // We only care whether the last statement completes; javac would have already
       // reported an error if that statement wasn't reachable, and the answer is
       // independent of any preceding statements.
-      boolean completes = Reachability.canCompleteNormally(getLast(caseTree.getStatements()));
+      boolean completes = Reachability.canCompleteNormally(getLast(statements));
       int endPos = caseEndPosition(state, caseTree);
       if (endPos == Position.NOPOS) {
         break;
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/FallThroughTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/FallThroughTest.java
index 95ff8396fb0..203f5c40e1c 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/FallThroughTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/FallThroughTest.java
@@ -16,7 +16,10 @@
 
 package com.google.errorprone.bugpatterns;
 
+import static org.junit.Assume.assumeTrue;
+
 import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.util.RuntimeVersion;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -95,4 +98,23 @@ public void emptyBlock() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void arrowSwitch() {
+    assumeTrue(RuntimeVersion.isAtLeast14());
+    testHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  enum Case { ONE, TWO }",
+            "  void m(Case c) {",
+            "    switch (c) {",
+            "      case ONE -> {}",
+            "      case TWO -> {}",
+            "      default -> {}",
+            "    }",
+            "  }",
+            "}")
+        .doTest();
+  }
 }