[java-dfa] Report unreachable switch branches after 100% reachable branch

Fixes IDEA-294215 Inspection "Constant conditions & exceptions" does not report all unreachable switch labels

GitOrigin-RevId: 6f1e493b6a665221c1978a5c918028638ec23c09

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java

@@ -325,6 +325,7 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
   private void reportUnreachableSwitchBranches(Map<PsiCaseLabelElement, ThreeState> labelReachability, ProblemsHolder holder) {
     if (labelReachability.isEmpty()) return;
     Set<PsiSwitchBlock> coveredSwitches = new HashSet<>();
+    Map<PsiCaseLabelElement, PsiSwitchBlock> unreachableLabels = new HashMap<>();
 
     for (Map.Entry<PsiCaseLabelElement, ThreeState> entry : labelReachability.entrySet()) {
       if (entry.getValue() != ThreeState.YES) continue;
@@ -338,6 +339,14 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
         .nonNull().flatArray(PsiCaseLabelElementList::getElements)
         .append(StreamEx.iterate(label, Objects::nonNull, l -> PsiTreeUtil.getPrevSiblingOfType(l, PsiCaseLabelElement.class)).skip(1))
         .allMatch(l -> labelReachability.get(l) == ThreeState.NO)) {
+
+        // Add all labels after always-reachable one as unreachable
+        StreamEx.iterate(labelStatement, Objects::nonNull, l -> PsiTreeUtil.getNextSiblingOfType(l, PsiSwitchLabelStatementBase.class))
+          .remove(SwitchUtils::isDefaultLabel)
+          .skip(1).map(PsiSwitchLabelStatementBase::getCaseLabelElementList)
+          .nonNull().flatArray(PsiCaseLabelElementList::getElements)
+          .append(StreamEx.iterate(label, Objects::nonNull, l -> PsiTreeUtil.getNextSiblingOfType(l, PsiCaseLabelElement.class)).skip(1))
+          .forEach(l -> unreachableLabels.put(l, switchBlock));
         continue;
       }
       coveredSwitches.add(switchBlock);
@@ -357,13 +366,16 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
       PsiSwitchLabelStatementBase labelStatement = Objects.requireNonNull(PsiImplUtil.getSwitchLabel(label));
       PsiSwitchBlock switchBlock = labelStatement.getEnclosingSwitchBlock();
       if (switchBlock == null || coveredSwitches.contains(switchBlock)) continue;
+      unreachableLabels.put(label, switchBlock);
+    }
+    unreachableLabels.forEach((label, switchBlock) -> {
       // duplicate case label is a compilation error so no need to highlight by the inspection
       Set<PsiElement> suspiciousElements = SwitchBlockHighlightingModel.findSuspiciousLabelElements(switchBlock);
       if (!suspiciousElements.contains(label)) {
         holder.registerProblem(label, JavaAnalysisBundle.message("dataflow.message.unreachable.switch.label"),
                                new DeleteSwitchLabelFix(label));
       }
-    }
+    });
   }
 
   private static boolean canRemoveUnreachableBranches(PsiSwitchLabelStatementBase labelStatement, PsiSwitchBlock statement) {

java/java-tests/testData/inspection/dataFlow/fixture/SwitchExpressions.java

@@ -30,7 +30,7 @@ public class SwitchExpressionsJava12 {
     int i1 = switch(x) {
       case A -> 1;
       case B -> 2;
-      case C -> 3;
+      case <warning descr="Switch label 'C' is unreachable">C</warning> -> 3;
     };
 
     if (<warning descr="Condition 'i1 == 0' is always 'false'">i1 == 0</warning>) {} // exhaustive

java/java-tests/testData/inspection/dataFlow/fixture/SwitchStatementUnreachableBranches.java

@@ -0,0 +1,18 @@
+class Test {
+  enum Colors {
+    RED,
+    GREEN,
+    BLUE,
+    YELLOW,
+  }
+  public Test(Colors color) {
+    if (color == Colors.RED || color == Colors.GREEN) {
+      switch (color) {
+        case RED -> System.out.println("Red");
+        case <warning descr="Switch label 'BLUE' is unreachable">BLUE</warning> -> System.out.println("Blue");
+        case GREEN -> System.out.println("Green");
+        case <warning descr="Switch label 'YELLOW' is unreachable">YELLOW</warning> -> System.out.println("Yellow");
+      }
+    }
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspection16Test.java

@@ -19,6 +19,7 @@ public class DataFlowInspection16Test extends DataFlowInspectionTestCase {
 
   public void testInstanceOfPattern() { doTest(); }
   public void testSwitchStatements() { doTest(); }
+  public void testSwitchStatementUnreachableBranches() { doTest(); }
   public void testSwitchExpressions() { doTest(); }
   public void testSwitchExpressionsNullability() { doTest(); }
   public void testConstantDescAsWrapperSupertype() {