[java switch resolve] IDEA-277110 Compilation error not highlighted when using Pattern Matching for switch

Fallthrough to default is not acceptable according to JEP 406. This patch eliminates the default cases from a special case rules and leaves only `case null` as the only special case rule.

GitOrigin-RevId: 06c865f92fed01a41c5c87e1aa0a852acb3e7ee0

java/java-psi-impl/src/com/intellij/psi/impl/source/tree/java/PsiSwitchLabelStatementImpl.java

@@ -107,7 +107,7 @@ public class PsiSwitchLabelStatementImpl extends PsiSwitchLabelStatementBaseImpl
         immediateSwitchLabel = PsiTreeUtil.getPrevSiblingOfType(currentScope, PsiSwitchLabelStatementBase.class);
       }
 
-      while (immediateSwitchLabel != null && isFallthrough(immediateSwitchLabel) && isSpecialCaseLabel(immediateSwitchLabel)) {
+      while (immediateSwitchLabel != null && isFallthrough(immediateSwitchLabel) && isCaseNull(immediateSwitchLabel)) {
         immediateSwitchLabel = PsiTreeUtil.getPrevSiblingOfType(immediateSwitchLabel, PsiSwitchLabelStatementBase.class);
       }
 
@@ -136,18 +136,12 @@ public class PsiSwitchLabelStatementImpl extends PsiSwitchLabelStatementBaseImpl
     }
   }
 
-  private static boolean isSpecialCaseLabel(@NotNull PsiSwitchLabelStatementBase switchCaseLabel) {
-    return isCase(switchCaseLabel, JavaTokenType.NULL_KEYWORD) ||
-           isCase(switchCaseLabel, JavaTokenType.DEFAULT_KEYWORD) ||
-           switchCaseLabel.isDefaultCase();
-  }
+  private static boolean isCaseNull(@NotNull PsiSwitchLabelStatementBase switchCaseLabel) {
+    if (switchCaseLabel.getCaseLabelElementList() == null) return false;
 
-  private static boolean isCase(@NotNull PsiSwitchLabelStatementBase item, @NotNull IElementType keyword) {
-    if (item.getCaseLabelElementList() == null) return false;
-
-    final PsiCaseLabelElement[] elements = item.getCaseLabelElementList().getElements();
+    final PsiCaseLabelElement[] elements = switchCaseLabel.getCaseLabelElementList().getElements();
     if (elements.length != 1) return false;
 
-    return elements[0].getNode().getFirstChildNode().getElementType() == keyword;
+    return elements[0].getNode().getFirstChildNode().getElementType() == JavaTokenType.NULL_KEYWORD;
   }
 }

java/java-psi-impl/src/com/intellij/psi/impl/source/tree/java/PsiSwitchLabeledRuleStatementImpl.java

@@ -5,7 +5,9 @@ import com.intellij.psi.*;
 import com.intellij.psi.impl.source.tree.JavaElementType;
 import com.intellij.psi.scope.PsiScopeProcessor;
 import com.intellij.psi.tree.TokenSet;
+import com.intellij.psi.util.PsiUtil;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public class PsiSwitchLabeledRuleStatementImpl extends PsiSwitchLabelStatementBaseImpl implements PsiSwitchLabeledRuleStatement {
   private static final TokenSet BODY_STATEMENTS =
@@ -47,8 +49,37 @@ public class PsiSwitchLabeledRuleStatementImpl extends PsiSwitchLabelStatementBa
     // Do not resolve references that come from the list of elements in this case rule
     if (lastParent instanceof PsiCaseLabelElementList) return true;
 
+    if (!shouldProcess()) return true;
+
     final PsiCaseLabelElementList patternsInCaseLabel = getCaseLabelElementList();
     if (patternsInCaseLabel == null) return true;
     return patternsInCaseLabel.processDeclarations(processor, state, null, place);
   }
+
+  private boolean shouldProcess() {
+    final PsiCaseLabelElementList elementList = getCaseLabelElementList();
+    if (elementList == null) return false;
+
+    final PsiCaseLabelElement[] elements = elementList.getElements();
+    if (elements.length == 1) return true;
+    else if (elements.length > 2 || elements.length == 0) return false;
+
+    final PsiElement first = stripParensIfNecessary(elements[0]);
+    final PsiElement second = stripParensIfNecessary(elements[1]);
+
+    if (first == null || second == null) return true;
+
+    return firstPatternVariableSecondNull(first, second) || firstPatternVariableSecondNull(second, first);
+  }
+
+  private static boolean firstPatternVariableSecondNull(PsiElement first, @NotNull PsiElement second) {
+    return first instanceof PsiTypeTestPattern &&
+           second.getNode().getFirstChildNode().getElementType() == JavaTokenType.NULL_KEYWORD;
+  }
+
+  private static @Nullable PsiElement stripParensIfNecessary(@NotNull PsiCaseLabelElement element) {
+    return element instanceof PsiExpression
+           ? PsiUtil.skipParenthesizedExprDown((PsiExpression)element)
+           : element;
+  }
 }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlightingPatternsInSwitch/BreakAndOtherStopWords.java

@@ -4,9 +4,9 @@ class Main {
     switch (o) {
       case Integer i :
         System.out.println();
-      case default:
       case null:
         System.out.println(i);
+      case default:
     };
   }
 

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlightingPatternsInSwitch/FallthroughDefault.java

@@ -0,0 +1,38 @@
+
+class Main {
+  void f(Object o) {
+    switch (o) {
+      case Integer i :
+        System.out.println(i);
+        break;
+      case String s:
+      default:
+        System.out.println(<error descr="Cannot resolve symbol 's'">s</error>);
+    }
+  }
+
+  void g(Object o) {
+    switch (o) {
+      case Integer i :
+        System.out.println(i);
+        break;
+      case String s:
+      case default:
+        System.out.println(<error descr="Cannot resolve symbol 's'">s</error>);
+    }
+  }
+
+  void ff(Object o) {
+    switch (o) {
+      case Integer i -> System.out.println(i);
+      case String s, default -> System.out.println(<error descr="Cannot resolve symbol 's'">s</error>);
+    }
+  }
+
+  void gg(Object o) {
+    switch (o) {
+      case Integer i -> System.out.println(i);
+      case default, String s -> System.out.println(<error descr="Cannot resolve symbol 's'">s</error>);
+    }
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlightingPatternsInSwitch/PatternMatchingInSwitch.java

@@ -21,17 +21,17 @@ class Main {
     };
 
     int i4 = switch(o) {
-      case String s, <error descr="Illegal fall-through to a pattern">X x</error> -> x.f();
+      case String s, X x -> <error descr="Cannot resolve symbol 'x'">x</error>.f();
       default -> 1;
     };
 
     int i5 = switch(o) {
-      case String s, <error descr="Illegal fall-through to a pattern">X x</error> -> x.f();
+      case String s, X x -> <error descr="Cannot resolve symbol 'x'">x</error>.f();
       default -> 1;
     };
 
     int i6 = switch(o) {
-      case X x, <error descr="Illegal fall-through to a pattern">String s</error> -> x.f();
+      case X x, String s -> <error descr="Cannot resolve symbol 'x'">x</error>.f();
       default -> 1;
     };
     return i1 + i2 + i3 + i4 + i5 + i6;

java/java-tests/testData/codeInsight/gotoDeclaration/CaseNullAfterPatternMatching.java

@@ -4,9 +4,6 @@ class Main {
     switch (o) {
       case Integer i :
         System.out.println();
-      case null:
-      default: {}
-      case default:
       case null:
         System.out.println(i<caret>);
     };

java/java-tests/testData/codeInsight/gotoDeclaration/CaseNullAfterPatternMatchingExpr.java

@@ -0,0 +1,8 @@
+class Main {
+  private static final int i = 0;
+  private void f(Object o) {
+    switch (o) {
+      case Integer i, null -> System.out.println(i<caret>);
+    };
+  }
+}

java/java-tests/testData/codeInsight/gotoDeclaration/DefaultAfterPatternMatching.java

@@ -0,0 +1,11 @@
+class Main {
+  private static final int i = 0;
+  private void f(Object o) {
+    switch (o) {
+      case Integer i :
+        System.out.println();
+      default:
+        System.out.println(i<caret>);
+    };
+  }
+}

java/java-tests/testData/codeInsight/gotoDeclaration/DefaultAfterPatternMatchingExpr.java

@@ -0,0 +1,8 @@
+class Main {
+  private static final int i = 0;
+  private void f(Object o) {
+    switch (o) {
+      case Integer i, default -> System.out.println(i<caret>);
+    };
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInsight/daemon/LightPatternsForSwitchHighlightingTest.java

@@ -99,6 +99,10 @@ public class LightPatternsForSwitchHighlightingTest extends LightJavaCodeInsight
     doTest();
   }
 
+  public void testFallthroughDefault() {
+    doTest();
+  }
+
   public void testUnusedPatternVariable() {
     myFixture.enableInspections(new UnusedDeclarationInspection());
     doTest();

java/java-tests/testSrc/com/intellij/java/codeInsight/navigation/GotoDeclarationTest.java

@@ -121,38 +121,47 @@ public class GotoDeclarationTest extends LightJavaCodeInsightTestCase {
   }
 
   public void testPatternMatchingGuardInSwitchExpression() {
-    doTestPatternMatchingGuard();
+    doTestGoToField();
   }
 
   public void testPatternMatchingGuardInSwitchStatement() {
-    doTestPatternMatchingGuard();
+    doTestGoToField();
   }
 
   public void testPatternMatchingWithParensAroundReference() {
-    doTestPatternMatchingGuard();
+    doTestGoToField();
   }
 
 
   public void testReferenceFieldInPatternMatchingInSwitchStatement() {
-    doTestPatternMatchingGuard();
+    doTestGoToField();
   }
 
-  public void testCaseNullDefaultAfterPatternMatching() {
-    configure();
-    final PsiElement patternVariable = PsiTreeUtil.findChildOfType(getFile(), PsiPatternVariable.class);
-    final PsiElement element = GotoDeclarationAction.findTargetElement(getProject(), getEditor(), getEditor().getCaretModel().getOffset());
-    assertThat(element).isEqualTo(patternVariable);
+  public void testCaseNullAfterPatternMatching() {
+    doTestGoToPatternVariable();
+  }
+
+  public void testCaseNullAfterPatternMatchingExpr() {
+    doTestGoToPatternVariable();
+  }
+
+  public void testDefaultAfterPatternMatching() {
+    doTestGoToField();
+  }
+
+  public void testDefaultAfterPatternMatchingExpr() {
+    doTestGoToField();
   }
 
   public void testGuardWithInstanceOfPatternMatchingInIf() {
-    doTestGoToPatternVariable();
+    doTestGoToSecondPatternVariable();
   }
 
   public void testGuardWithInstanceOfPatternMatchingInSwitch() {
-    doTestGoToPatternVariable();
+    doTestGoToSecondPatternVariable();
   }
 
-  private void doTestPatternMatchingGuard() {
+  private void doTestGoToField() {
     configure();
     final PsiField field = PsiTreeUtil.findChildOfType(getFile(), PsiField.class);
     final PsiElement element = GotoDeclarationAction.findTargetElement(getProject(), getEditor(), getEditor().getCaretModel().getOffset());
@@ -160,6 +169,13 @@ public class GotoDeclarationTest extends LightJavaCodeInsightTestCase {
   }
 
   private void doTestGoToPatternVariable() {
+    configure();
+    final PsiPatternVariable patternVariable = PsiTreeUtil.findChildOfType(getFile(), PsiPatternVariable.class);
+    final PsiElement element = GotoDeclarationAction.findTargetElement(getProject(), getEditor(), getEditor().getCaretModel().getOffset());
+    assertThat(element).isEqualTo(patternVariable);
+  }
+
+  private void doTestGoToSecondPatternVariable() {
     configure();
     final Iterator<PsiPatternVariable> iterator = PsiTreeUtil.findChildrenOfType(getFile(), PsiPatternVariable.class).iterator();
     iterator.next();