From fed5957f686d3538b3eb87b5a1e484541f02f455 Mon Sep 17 00:00:00 2001
From: Liam Miller-Cushon <cushon@google.com>
Date: Sat, 29 May 2021 12:29:47 -0700
Subject: [PATCH] Handle arrow switches in `MissingDefault`

Fixes https://github.com/google/error-prone/issues/2256

PiperOrigin-RevId: 376482444
---
 .../bugpatterns/MissingDefault.java           | 11 ++++--
 .../bugpatterns/MissingDefaultTest.java       | 38 +++++++++++++++++++
 2 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/MissingDefault.java b/core/src/main/java/com/google/errorprone/bugpatterns/MissingDefault.java
index f633a4b231d..c7b610913cb 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/MissingDefault.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/MissingDefault.java
@@ -30,8 +30,10 @@
 import com.google.errorprone.util.ASTHelpers;
 import com.google.errorprone.util.Reachability;
 import com.sun.source.tree.CaseTree;
+import com.sun.source.tree.StatementTree;
 import com.sun.source.tree.SwitchTree;
 import com.sun.tools.javac.code.Type;
+import java.util.List;
 import java.util.Optional;
 import javax.lang.model.element.ElementKind;
 
@@ -62,8 +64,10 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
         // for the switch statement. Hopefully we don't often see switches with zero cases.
         CaseTree lastCase = getLast(tree.getCases());
         String replacement;
-        if (lastCase.getStatements().isEmpty()
-            || Reachability.canCompleteNormally(Iterables.getLast(lastCase.getStatements()))) {
+        List<? extends StatementTree> statements = lastCase.getStatements();
+        if (statements == null
+            || statements.isEmpty()
+            || Reachability.canCompleteNormally(Iterables.getLast(statements))) {
           replacement = "\nbreak;\ndefault: // fall out\n";
         } else {
           replacement = "\ndefault: // fall out\n";
@@ -73,7 +77,8 @@ public Description matchSwitch(SwitchTree tree, VisitorState state) {
       return description.build();
     }
     CaseTree defaultCase = maybeDefault.get();
-    if (!defaultCase.getStatements().isEmpty()) {
+    List<? extends StatementTree> statements = defaultCase.getStatements();
+    if (statements != null && !statements.isEmpty()) {
       return NO_MATCH;
     }
     // If `default` case is empty, and last in switch, add `// fall out` comment
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/MissingDefaultTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/MissingDefaultTest.java
index ac77bfad793..05f77cab6c8 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/MissingDefaultTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/MissingDefaultTest.java
@@ -17,9 +17,11 @@
 package com.google.errorprone.bugpatterns;
 
 import static com.google.errorprone.BugCheckerRefactoringTestHelper.TestMode.TEXT_MATCH;
+import static org.junit.Assume.assumeTrue;
 
 import com.google.errorprone.BugCheckerRefactoringTestHelper;
 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;
@@ -225,4 +227,40 @@ public void multipleStatementsInGroup() {
             "}")
         .doTest(TEXT_MATCH);
   }
+
+  @Test
+  public void arrowSwitch() {
+    assumeTrue(RuntimeVersion.isAtLeast14());
+    compilationHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  void m(int i) {",
+            "    // BUG: Diagnostic contains:",
+            "    switch (i) {",
+            "      case 1 -> {}",
+            "      case 2 -> {}",
+            "    }",
+            "  }",
+            "}")
+        .doTest();
+  }
+
+  @Test
+  public void arrowSwitchNegative() {
+    assumeTrue(RuntimeVersion.isAtLeast14());
+    compilationHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  void m(int i) {",
+            "    switch (i) {",
+            "      case 1 -> {}",
+            "      case 2 -> {}",
+            "      default -> {} // fall out",
+            "    }",
+            "  }",
+            "}")
+        .doTest();
+  }
 }