From e489a52bc2d737b70ba741990cec5f48f4bd9238 Mon Sep 17 00:00:00 2001
From: Liam Miller-Cushon <cushon@google.com>
Date: Sun, 3 Nov 2024 21:00:57 -0800
Subject: [PATCH] DuplicateBranches: don't crash on empty blocks

PiperOrigin-RevId: 692822985
---
 .../bugpatterns/DuplicateBranches.java        |  8 ++++--
 .../bugpatterns/DuplicateBranchesTest.java    | 25 +++++++++++++++++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/DuplicateBranches.java b/core/src/main/java/com/google/errorprone/bugpatterns/DuplicateBranches.java
index 3936c3fc9ad..297c57de3df 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/DuplicateBranches.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/DuplicateBranches.java
@@ -76,8 +76,12 @@ private Description match(Tree tree, Tree thenTree, Tree elseTree, VisitorState
     if (elseTree instanceof BlockTree) {
       needsBraces = !state.getPath().getParentPath().getLeaf().getKind().equals(Kind.BLOCK);
       var statements = ((BlockTree) elseTree).getStatements();
-      start = getStartPosition(statements.get(0));
-      end = state.getEndPosition(getLast(statements));
+      if (statements.isEmpty()) {
+        start = end;
+      } else {
+        start = getStartPosition(statements.get(0));
+        end = state.getEndPosition(getLast(statements));
+      }
     }
     String comments =
         ErrorProneTokens.getTokens(
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/DuplicateBranchesTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/DuplicateBranchesTest.java
index bf9c8eb87bb..c8b0c42c124 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/DuplicateBranchesTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/DuplicateBranchesTest.java
@@ -215,4 +215,29 @@ boolean g(boolean a, boolean b) {
             """)
         .doTest(TestMode.TEXT_MATCH);
   }
+
+  @Test
+  public void negativeEmpty() {
+    BugCheckerRefactoringTestHelper.newInstance(DuplicateBranches.class, getClass())
+        .addInputLines(
+            "Test.java",
+            """
+            class Test {
+              void f(boolean a) {
+                if (a) {
+                } else {
+                }
+              }
+            }
+            """)
+        .addOutputLines(
+            "Test.java",
+            """
+            class Test {
+              void f(boolean a) {
+              }
+            }
+            """)
+        .doTest();
+  }
 }