SONARJAVA-5730 S1301 should report on small but non-exhaustive switch over enum (#5538)

tomasz-tylenda-sonarsource · web-flow · commit 1f730dd89e97 · 2026-03-27T15:57:55.000+01:00
diff --git a/java-checks-test-sources/default/src/test/java/checks/tests/SwitchAtLeastThreeCasesCheckSample.java b/java-checks-test-sources/default/src/test/java/checks/tests/SwitchAtLeastThreeCasesCheckSample.java
@@ -122,4 +122,59 @@ public int switchOverSmallEnum3(SmallEnum smallEnum) {
     }
     return ret;
   }
+
+  public enum LargeEnum {
+    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
+  };
+
+  public String switchOverLargeEnum(LargeEnum largeEnum) {
+    String mood = "excited";
+    switch (largeEnum) { // Noncompliant
+      case FRIDAY:
+        mood = "love";
+        break;
+    }
+    return mood;
+  }
+
+  public enum SmallEnumWithMethods {
+    PUBLIC("pub"),
+    PRIVATE("prv");
+
+    enum Weird {A, B, C}
+
+    private final String label;
+
+    SmallEnumWithMethods(String label) {
+      this.label = label;
+    }
+
+    public String getLabel() {
+      return label;
+    }
+
+    public int spaceRequired() {
+      return label.length();
+    }
+  }
+
+  public int switchSmallEnumWithMethods1(SmallEnumWithMethods largeEnum) {
+    int ret = -1;
+    switch (largeEnum) { // Compliant
+      case PRIVATE:
+        ret = 1;
+        break;
+      case PUBLIC:
+        ret = 2;
+        break;
+    }
+    return ret;
+  }
+
+  public void switchSmallEnumWithMethods2(SmallEnumWithMethods largeEnum) {
+    switch (largeEnum) { // Compliant
+      case PRIVATE, PUBLIC:
+        System.out.println("Same, Same");
+    }
+  }
 }
diff --git a/java-checks/src/main/java/org/sonar/java/checks/SwitchAtLeastThreeCasesCheck.java b/java-checks/src/main/java/org/sonar/java/checks/SwitchAtLeastThreeCasesCheck.java
@@ -56,10 +56,11 @@ public void visitNode(Tree tree) {
       return;
     }
 
-    // Switching over an enum without a default case will cause a compilation error
-    // if a new enum constant is added. Therefore, using if-then should not be recommended.
+    // Do not suggest replacing exhaustive switches over small enums.
+    // It does not aid readability and can lead to error-prone code when
+    // "->" switch is used (adding new enum constant would cause compilation error).
     Symbol.TypeSymbol typeSymbol = switchStatementTree.expression().symbolType().symbol();
-    if (typeSymbol.isEnum() && !hasDefault) {
+    if (typeSymbol.isEnum() && !hasDefault && enumConstantCount(typeSymbol) == count) {
       return;
     }
 
@@ -94,6 +95,15 @@ private static boolean containsDefaultLabel(CaseGroupTree caseGroup) {
     return false;
   }
 
+  /**
+   * Number of constants declared in the enum. Note, that it excludes fields and methods.
+   */
+  private static long enumConstantCount(Symbol.TypeSymbol typeSymbol) {
+    return typeSymbol.memberSymbols().stream()
+      .filter(s -> s.isVariableSymbol() && s.isEnum())
+      .count();
+  }
+
   private static boolean hasLabelWithAllowedPattern(CaseGroupTree caseGroupTree) {
     return caseGroupTree.labels().stream()
       .flatMap(label -> label.expressions().stream())
