Pattern variable rejected as not in scope after a labeled block exited via break <label> #5172

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/ast/LabeledStatement.java

@@ -21,6 +21,7 @@
 import org.eclipse.jdt.internal.compiler.flow.LabelFlowContext;
 import org.eclipse.jdt.internal.compiler.flow.UnconditionalFlowInfo;
 import org.eclipse.jdt.internal.compiler.lookup.BlockScope;
+import org.eclipse.jdt.internal.compiler.lookup.LocalVariableBinding;
 
 public class LabeledStatement extends Statement {
 
@@ -154,6 +155,16 @@ public void traverse(
 		visitor.endVisit(this, blockScope);
 	}
 
+	@Override
+	public LocalVariableBinding[] bindingsWhenComplete() {
+		// If control can reach past this labeled statement via a break to our own
+		// label, the pattern variable(s) may not be matched at that exit point,
+		// so nothing may be treated as definitely matched on completion.
+		if (this.statement.breaksOut(this.label))
+			return NO_VARIABLES;
+		return this.statement.bindingsWhenComplete();
+	}
+
 	@Override
 	public boolean doesNotCompleteNormally() {
 		if (this.statement.breaksOut(this.label))
@@ -165,4 +176,4 @@ public boolean doesNotCompleteNormally() {
 	public boolean completesByContinue() {
 		return this.statement instanceof ContinueStatement; // NOT this.statement.continuesAtOuterLabel
 	}
-}
+}

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/ast/Statement.java

@@ -340,6 +340,9 @@ public boolean visit(Block block, BlockScope scope) {
 
 		@Override
 		public boolean visit(BreakStatement breakStatement, BlockScope skope) {
+			if (breakStatement.label != null && !CharOperation.equals(label, breakStatement.label)) {
+				return false;
+			}
 			if (label == null || CharOperation.equals(label,  breakStatement.label))
 				this.breaksOut = true;
 	    	return false;

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PatternMatching16Test.java

@@ -1,4 +1,4 @@
-/*******************************************************************************
+/*******************************************************************************
  * Copyright (c) 2020, 2025 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
@@ -4871,4 +4871,158 @@ public static void main(String [] args) {
 				+ "false\n"
 				+ "true");
 	}
+	// A pattern variable declared in a while-condition must remain in scope after the
+	// loop when the only exit from the loop body is a 'break' to an *enclosing* label
+	// (here 'break X' leaves the block X, not the while), so normal loop completion is
+	// the only way to reach 'a2 = s;' and 's' is definitely matched there.
+	public void testLabeledBreakOutOfEnclosingBlock() {
+		runConformTest(
+				new String[] {
+						"X.java",
+						"""
+						public class X {
+							public static void foo(Object obj) {
+								Object obj1 = obj;
+								Object obj2 = null;
+								X: {
+									while (!(obj1 instanceof String s)) {
+										break X;
+									}
+									obj2 = s;
+								}
+								System.out.println(obj2);
+							}
+							public static void main(String[] argv) {
+								foo("a");
+							}
+						}
+						""",
+				},
+				"a");
+	}
+	// A pattern variable from a labeled while-condition must be in scope after the loop
+	// when the body cannot break out at all (it always throws), so the loop can only be
+	// left by normal completion where the pattern is matched.
+	public void testLabeledWhileNoBreak() {
+		runConformTest(
+				new String[] {
+						"X.java",
+						"""
+						public class X {
+							public static void foo(Object obj) {
+								Object obj1 = obj;
+								Object obj2 = null;
+								X: while (!(obj1 instanceof String s)) {
+									throw new RuntimeException("no match");
+								}
+								obj2 = s;
+								System.out.println(obj2);
+							}
+							public static void main(String[] argv) {
+								foo("a");
+							}
+						}
+						""",
+				},
+				"a");
+	}
+	// When 'break X' targets the while loop's own label, the loop may be left with the
+	// pattern *unmatched*, so the pattern variable must NOT be in scope afterwards and a
+	// subsequent 'String s' is a legal fresh declaration (must not clash).
+	public void testLabeledWhileBreakThenRedeclare() {
+		runConformTest(
+				new String[] {
+						"X.java",
+						"""
+						public class X {
+							public static void foo(Object obj) {
+								Object obj1 = obj;
+								X: while (!(obj1 instanceof String s)) {
+									break X;
+								}
+								String s = "foo";
+								System.out.println(s);
+							}
+							public static void main(String[] argv) {
+								foo("a");
+							}
+						}
+						""",
+				},
+				"foo");
+	}
+	// When 'break X' targets the while loop's own label, the loop can complete with the
+	// pattern unmatched, so the pattern variable must not be resolvable after the loop.
+	public void testLabeledWhileBreakExitsLoop() {
+		Map<String, String> options = getCompilerOptions(true);
+		runNegativeTest(
+				new String[] {
+						"X.java",
+						"""
+						public class X {
+							public static void foo(Object obj) {
+								Object obj1 = obj;
+								Object obj2 = null;
+								X: while (!(obj1 instanceof String s)) {
+									break X;
+								}
+								obj2 = s;
+								System.out.println(obj2);
+							}
+							public static void main(String[] argv) {
+								foo("a");
+							}
+						}
+						""",
+				},
+				"----------\n" +
+				"1. ERROR in X.java (at line 8)\n" +
+				"	obj2 = s;\n" +
+				"	       ^\n" +
+				"s cannot be resolved to a variable\n" +
+				"----------\n",
+				"",
+				null,
+				true,
+				options);
+	}
+	// An inner 'break' that targets the while loop (not the enclosing label X) can leave
+	// the loop with the pattern unmatched, so the pattern variable must not be resolvable
+	// after the loop even though control also reaches there via 'break X'.
+	public void testInnerBreakExitsWhile() {
+		Map<String, String> options = getCompilerOptions(true);
+		runNegativeTest(
+				new String[] {
+						"X.java",
+						"""
+						public class X {
+							public static void foo(Object obj) {
+								Object obj1 = obj;
+								Object obj2 = null;
+								X: {
+									while (!(obj1 instanceof String s)) {
+										if (obj1 == null) break;
+										break X;
+									}
+									obj2 = s;
+								}
+								System.out.println(obj2);
+							}
+							public static void main(String[] argv) {
+								foo("a");
+							}
+						}
+						""",
+				},
+				"----------\n" +
+				"1. ERROR in X.java (at line 10)\n" +
+				"	obj2 = s;\n" +
+				"	       ^\n" +
+				"s cannot be resolved to a variable\n" +
+				"----------\n",
+				"",
+				null,
+				true,
+				options);
+	}
 }