From f181737c2baeab7ba64095249b4b2a3ba03671d2 Mon Sep 17 00:00:00 2001
From: Henry Coles <henry@pitest.org>
Date: Thu, 5 Jan 2023 14:49:54 +0000
Subject: [PATCH] do not mutate fall through switch cases

---
 README.md                                     |  4 ++
 .../experimental/RemoveSwitchMutator.java     |  6 +-
 .../experimental/RemoveSwitchMutatorTest.java | 55 +++++++++++++++++++
 .../verifier/mutants/MutatorVerifier.java     |  4 +-
 4 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 7fe479fb9..0cdabaee8 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,10 @@ Read all about it at http://pitest.org
 
 ## Releases
 
+## 1.10.5 (unreleased)
+
+* #1138 Do not mutate redundant fall through to default switch cases
+
 ## 1.10.4
 
 * #1134 Add `excludedRunners` parameter to command line interface and Ant
diff --git a/pitest/src/main/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutator.java b/pitest/src/main/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutator.java
index 4624af8a3..3f5a3ed4c 100644
--- a/pitest/src/main/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutator.java
+++ b/pitest/src/main/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutator.java
@@ -16,7 +16,7 @@
  * default label. We change each label to the default label, thus removing it
  */
 public class RemoveSwitchMutator implements MethodMutatorFactory {
-  // EXPERIMENTAL_REMOVE_SWITCH_MUTATOR;
+
   private static final String REMOVE_SWITCH_MUTATOR_NAME = "EXPERIMENTAL_REMOVE_SWITCH_MUTATOR_";
   private static final int GENERATE_FROM_INCLUDING = 0;
   private static final int GENERATE_UPTO_EXCLUDING = 100;
@@ -69,7 +69,7 @@ private final class RemoveSwitchMethodVisitor extends MethodVisitor {
     @Override
     public void visitTableSwitchInsn(final int min, final int max,
         final Label defaultLabel, final Label... labels) {
-      if ((labels.length > RemoveSwitchMutator.this.key) && shouldMutate(value(min,max))) {
+      if ((labels.length > RemoveSwitchMutator.this.key) && labels[key] != defaultLabel && shouldMutate(value(min,max))) {
         final Label[] newLabels = labels.clone();
         newLabels[RemoveSwitchMutator.this.key] = defaultLabel;
         super.visitTableSwitchInsn(min, max, defaultLabel, newLabels);
@@ -81,7 +81,7 @@ public void visitTableSwitchInsn(final int min, final int max,
     @Override
     public void visitLookupSwitchInsn(final Label defaultLabel,
         final int[] ints, final Label[] labels) {
-      if ((labels.length > RemoveSwitchMutator.this.key) && shouldMutate(ints[key])) {
+      if ((labels.length > RemoveSwitchMutator.this.key) && labels[key] != defaultLabel && shouldMutate(ints[key])) {
         final Label[] newLabels = labels.clone();
         newLabels[RemoveSwitchMutator.this.key] = defaultLabel;
         super.visitLookupSwitchInsn(defaultLabel, ints, newLabels);
diff --git a/pitest/src/test/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutatorTest.java b/pitest/src/test/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutatorTest.java
index 23224d453..fd2fca531 100644
--- a/pitest/src/test/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutatorTest.java
+++ b/pitest/src/test/java/org/pitest/mutationtest/engine/gregor/mutators/experimental/RemoveSwitchMutatorTest.java
@@ -255,4 +255,59 @@ public void shouldNotTouchIt() {
     v.forClass(HasFewerLabelsWithDefault.class)
                     .noMutantsCreated();
   }
+
+
+  private static class FallThroughLookupSwitch implements IntFunction<Integer> {
+
+    @Override
+    public Integer apply(int value) {
+      int i = 0;
+      switch (value) {
+        case 1:
+          i = 1;
+          break;
+        case 200:
+          i = 4;
+          break;
+        case 300:
+        case 400:
+        default:
+          i = 0;
+      }
+      return i;
+    }
+  }
+
+  @Test
+  public void doesNotReplaceLookupSwitchCasesThatFallThroughToDefault() {
+    v.forClass(FallThroughLookupSwitch.class)
+            .noMutantsCreated();
+  }
+
+  private static class FallThroughTableSwitch implements Function<TimeUnit,Integer> {
+
+    @Override
+    public Integer apply(TimeUnit value) {
+      switch (value) {
+        case NANOSECONDS:
+          return 1;
+        case MICROSECONDS:
+          return 2;
+        case MILLISECONDS:
+        case SECONDS:
+        default:
+          return -1;
+      }
+    }
+  }
+
+  @Test
+  public void doesNotReplaceTableSwitchCasesThatFallThroughToDefault() {
+    v.forClass(FallThroughTableSwitch.class)
+            .noMutantsCreated();
+  }
+
+
 }
+
+
diff --git a/pitest/src/test/java/org/pitest/verifier/mutants/MutatorVerifier.java b/pitest/src/test/java/org/pitest/verifier/mutants/MutatorVerifier.java
index 8f73bf5ff..37dd6510f 100644
--- a/pitest/src/test/java/org/pitest/verifier/mutants/MutatorVerifier.java
+++ b/pitest/src/test/java/org/pitest/verifier/mutants/MutatorVerifier.java
@@ -51,7 +51,9 @@ public void createsNMutants(int n) {
     }
 
     public void noMutantsCreated() {
-        assertThat(findMutations()).isEmpty();
+        assertThat(findMutations())
+                .as(() -> "Expecting no mutants to be generated for " + printClass(clazz))
+                .isEmpty();
     }
 
     public final StringAssert firstMutantDescription() {