From 42f43778e2baff715e452efb1d9231d689aedbfc Mon Sep 17 00:00:00 2001
From: Tagir Valeev <tagir.valeev@jetbrains.com>
Date: Wed, 18 May 2022 09:50:17 +0200
Subject: [PATCH] [java-dfa] Do not report unreachable switch branches if they
 are throwing

GitOrigin-RevId: 5164e1b5f86abb797f7aa1a33b61fd28d85ca1d5
---
 .../dataFlow/DataFlowInspectionBase.java      | 22 +++++++++++++++++++
 .../dataFlow/fixture/SwitchStatements.java    | 16 ++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
index 5996d82a33ad..7943b5610e00 100644
--- a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
+++ b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DataFlowInspectionBase.java
@@ -369,6 +369,7 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
       unreachableLabels.put(label, switchBlock);
     }
     unreachableLabels.forEach((label, switchBlock) -> {
+      if (isThrowing(label)) return;
       // 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)) {
@@ -378,6 +379,27 @@ public abstract class DataFlowInspectionBase extends AbstractBaseJavaLocalInspec
     });
   }
 
+  private static boolean isThrowing(PsiCaseLabelElement label) {
+    PsiCaseLabelElementList caseLabelList = tryCast(label.getParent(), PsiCaseLabelElementList.class);
+    if (caseLabelList == null) return false;
+    PsiSwitchLabelStatementBase labelStatement = tryCast(caseLabelList.getParent(), PsiSwitchLabelStatementBase.class);
+    if (labelStatement == null) return false;
+    if (labelStatement instanceof PsiSwitchLabeledRuleStatement) {
+      return ControlFlowUtils.stripBraces(((PsiSwitchLabeledRuleStatement)labelStatement).getBody()) instanceof PsiThrowStatement;
+    }
+    if (labelStatement instanceof PsiSwitchLabelStatement) {
+      PsiElement cur = labelStatement;
+      while(true) {
+        PsiElement next = cur.getNextSibling();
+        if (!(next instanceof PsiComment) && !(next instanceof PsiWhiteSpace) && !(next instanceof PsiSwitchLabelStatement)) {
+          return next instanceof PsiThrowStatement;
+        }
+        cur = next;
+      }
+    }
+    return false;
+  }
+
   private static boolean canRemoveUnreachableBranches(PsiSwitchLabelStatementBase labelStatement, PsiSwitchBlock statement) {
     if (Objects.requireNonNull(labelStatement.getCaseLabelElementList()).getElementCount() != 1) return true;
     List<PsiSwitchLabelStatementBase> allBranches =
diff --git a/java/java-tests/testData/inspection/dataFlow/fixture/SwitchStatements.java b/java/java-tests/testData/inspection/dataFlow/fixture/SwitchStatements.java
index dac6aba5cb56..4b9451c79775 100644
--- a/java/java-tests/testData/inspection/dataFlow/fixture/SwitchStatements.java
+++ b/java/java-tests/testData/inspection/dataFlow/fixture/SwitchStatements.java
@@ -54,4 +54,20 @@ public class SwitchStatements {
       case 2 -> System.out.println("two");
     }
   }
+
+  enum X {A, B, C}
+
+  void testThrowingBranch(X x) {
+    if (x == X.A) return;
+    switch(x) {
+      case A -> throw new AssertionError();
+      case B -> System.out.println(1);
+      case C -> System.out.println(2);
+    }
+    switch(x) {
+      case B: System.out.println(1);break;
+      case C: System.out.println(2);break;
+      case A: default: throw new AssertionError();
+    }
+  }
 }