Bug 531715: [14] JEP 305: Pattern Matching for instanceof (Preview)Y20200218-0315Y20200218-0120

Flow analysis looking good

Change-Id: Iec4e81d7379bdf97f18c62afc918ae46d66512d6
Signed-off-by: Jay Arthanareeswaran <jarthana@in.ibm.com>
Also-by: Stephan Herrmann <stephan.herrmann@berlin.de>

20 files changed, 234 insertions, 347 deletions

diff --git a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CompilerInvocationTests.java b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CompilerInvocationTests.java
index 37cdd0c7a6..45c96d788a 100644
--- a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CompilerInvocationTests.java
+++ b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CompilerInvocationTests.java
@@ -941,6 +941,7 @@ public void test011_problem_categories() {
 		expectedProblemAttributes.put("ParsingErrorOnKeywordNoSuggestion", new ProblemAttributes(CategorizedProblem.CAT_SYNTAX));
 		expectedProblemAttributes.put("ParsingErrorReplaceTokens", new ProblemAttributes(CategorizedProblem.CAT_SYNTAX));
 		expectedProblemAttributes.put("ParsingErrorUnexpectedEOF", new ProblemAttributes(CategorizedProblem.CAT_SYNTAX));
+		expectedProblemAttributes.put("PatternVariableNotInScope", new ProblemAttributes(CategorizedProblem.CAT_PREVIEW_RELATED));
 		expectedProblemAttributes.put("PolymorphicMethodNotBelow17", new ProblemAttributes(CategorizedProblem.CAT_MEMBER));
 		expectedProblemAttributes.put("PossibleAccidentalBooleanAssignment", new ProblemAttributes(CategorizedProblem.CAT_POTENTIAL_PROGRAMMING_PROBLEM));
 		expectedProblemAttributes.put("PotentialHeapPollutionFromVararg", new ProblemAttributes(CategorizedProblem.CAT_UNCHECKED_RAW));
@@ -1958,6 +1959,7 @@ public void test012_compiler_problems_tuning() {
 		expectedProblemAttributes.put("ParsingErrorOnKeywordNoSuggestion", SKIP);
 		expectedProblemAttributes.put("ParsingErrorReplaceTokens", SKIP);
 		expectedProblemAttributes.put("ParsingErrorUnexpectedEOF", SKIP);
+		expectedProblemAttributes.put("PatternVariableNotInScope", SKIP);
 		expectedProblemAttributes.put("PolymorphicMethodNotBelow17", SKIP);
 		expectedProblemAttributes.put("PossibleAccidentalBooleanAssignment", new ProblemAttributes(JavaCore.COMPILER_PB_POSSIBLE_ACCIDENTAL_BOOLEAN_ASSIGNMENT));
 		expectedProblemAttributes.put("PotentialHeapPollutionFromVararg", new ProblemAttributes(JavaCore.COMPILER_PB_UNCHECKED_TYPE_OPERATION));
diff --git a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PatternMatching14Test.java b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PatternMatching14Test.java
index d688bfaaf0..652efc5091 100644
--- a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PatternMatching14Test.java
+++ b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/PatternMatching14Test.java
@@ -24,11 +24,11 @@ import junit.framework.Test;
 
 public class PatternMatching14Test extends AbstractRegressionTest {
 
-	private static final JavacTestOptions JAVAC_OPTIONS = new JavacTestOptions("-source 14 --enable-preview");
+	private static final JavacTestOptions JAVAC_OPTIONS = new JavacTestOptions("-source 14 --enable-preview -Xlint:-preview");
 	static {
 //		TESTS_NUMBERS = new int [] { 40 };
 //		TESTS_RANGE = new int[] { 1, -1 };
-//		TESTS_NAMES = new String[] { "test022" };
+//		TESTS_NAMES = new String[] { "test005" };
 	}
 	
 	public static Class<?> testClass() {
@@ -89,7 +89,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"	                   ^^^^^^^^\n" + 
 				"Instanceof Pattern is a preview feature and disabled by default. Use --enable-preview to enable\n" + 
 				"----------\n",
-				"",
+				/* omit one arg to directly call super method without JAVA_OPTIONS */
 				null,
 				true,
 				options);
@@ -240,12 +240,12 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X6a.java (at line 8)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X6a.java (at line 11)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -278,12 +278,12 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X6b.java (at line 8)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X6b.java (at line 11)\n" + 
 				"	System.out.print(s);\n" + 
 				"	                 ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -313,7 +313,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X6c.java (at line 7)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -343,7 +343,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X6d.java (at line 7)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -373,7 +373,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X7.java (at line 7)\n" + 
 				"	System.out.print(i);\n" + 
 				"	                 ^\n" + 
-				"i cannot be resolved to a variable\n" + 
+				"The pattern variable i is not in scope in this location\n" + 
 				"----------\n",
 				"X7.java:4: warning: [preview] pattern matching in instanceof is a preview feature and may be removed in a future release.\n" + 
 				"		if (obj instanceof Integer i) {\n" + 
@@ -494,7 +494,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X11.java (at line 7)\n" + 
 				"	System.out.println(s);\n" + 
 				"	                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -509,11 +509,11 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"@SuppressWarnings(\"preview\")\n" +
 						"public class X12 {\n" +
 						"  	public static void foo(Object b) {\n" + 
-						"		Object c = null;\n" + 
+						"		Object c = new Object();\n" + 
 						"		if (b != c) {\n" + 
 						"			if (b == null && (b instanceof String s)) {\n" + 
 						"				System.out.println(\"s:\" + s);\n" + 
-						"			} else { " + 
+						"			} else {\n" + 
 						"				System.out.println(\"b:\" + b);\n" + 
 						"			}\n" + 
 						"			s = null;\n" +
@@ -526,10 +526,10 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X12.java (at line 10)\n" + 
+				"1. ERROR in X12.java (at line 11)\n" + 
 				"	s = null;\n" + 
 				"	^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -560,10 +560,15 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X13.java (at line 9)\n" + 
+				"1. WARNING in X13.java (at line 7)\n" + 
+				"	System.out.println(\"s:\" + s);\n" + 
+				"	^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n" + 
+				"Dead code\n" + 
+				"----------\n" + 
+				"2. ERROR in X13.java (at line 9)\n" + 
 				"	System.out.println(s);\n" + 
 				"	                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -593,7 +598,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X14.java (at line 5)\n" + 
 				"	System.out.print(\"then:\" + s);\n" + 
 				"	                           ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -604,9 +609,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 		Map<String, String> options = getCompilerOptions(true);
 		runNegativeTest(
 				new String[] {
-						"X14.java",
+						"X14a.java",
 						"@SuppressWarnings(\"preview\")\n" +
-						"public class X14 {\n" +
+						"public class X14a {\n" +
 						"  	public static void foo(Object o) {\n" + 
 						"		if (!(o instanceof String s)) {\n" + 
 						"			System.out.print(\"then:\" + s);\n" +
@@ -620,10 +625,10 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X14.java (at line 5)\n" + 
+				"1. ERROR in X14a.java (at line 5)\n" + 
 				"	System.out.print(\"then:\" + s);\n" + 
 				"	                           ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -634,9 +639,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 		Map<String, String> options = getCompilerOptions(true);
 		runNegativeTest(
 				new String[] {
-						"X14.java",
+						"X14b.java",
 						"@SuppressWarnings(\"preview\")\n" +
-						"public class X14 {\n" +
+						"public class X14b {\n" +
 						"  	public static void foo(Object o) {\n" + 
 						"		if (!!(o instanceof String s)) {\n" + 
 						"			System.out.print(\"then:\" + s);\n" +
@@ -650,10 +655,10 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X14.java (at line 7)\n" + 
+				"1. ERROR in X14b.java (at line 7)\n" + 
 				"	System.out.print(\"else:\" + s);\n" + 
 				"	                           ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -664,9 +669,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 		Map<String, String> options = getCompilerOptions(true);
 		runNegativeTest(
 				new String[] {
-						"X14.java",
+						"X14c.java",
 						"@SuppressWarnings(\"preview\")\n" +
-						"public class X14 {\n" +
+						"public class X14c {\n" +
 						"  	public static void foo(Object o) {\n" + 
 						"		if (o == null) {\n" + 
 						"			System.out.print(\"null\");\n" +
@@ -680,10 +685,10 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X14.java (at line 7)\n" + 
+				"1. ERROR in X14c.java (at line 7)\n" + 
 				"	System.out.print(\"else:\" + s);\n" + 
 				"	                           ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -694,9 +699,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 		Map<String, String> options = getCompilerOptions(true);
 		runConformTest(
 				new String[] {
-						"X14.java",
+						"X14d.java",
 						"@SuppressWarnings(\"preview\")\n" +
-						"public class X14 {\n" +
+						"public class X14d {\n" +
 						"  	public static void foo(Object o) {\n" + 
 						"		if (o == null) {\n" + 
 						"			System.out.print(\"null\");\n" +
@@ -813,7 +818,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X15b.java (at line 9)\n" + 
 				"	System.out.print(s);\n" + 
 				"	                 ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -859,7 +864,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X17.java (at line 5)\n" + 
 				"	System.out.print(s[0]);\n" + 
 				"	                 ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -914,6 +919,35 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"false,true",
 				options);
 	}
+	/* Test that we still detect duplicate pattern variable declarations
+	 */
+	public void test019b() {
+		Map<String, String> options = getCompilerOptions(true);
+		runNegativeTest(
+				new String[] {
+						"X19b.java",
+						"@SuppressWarnings(\"preview\")\n" +
+						"public class X19b {\n" +
+						"  public static void main(String[] obj) {\n" +
+						"		boolean a = true;\n" +
+						"		if (obj instanceof String[] s && s.length == 0) {\n" + 
+						"			boolean b = (obj instanceof String[] s && s.length == 0);\n" + 
+						"			System.out.print(b);\n" + 
+						"		}\n" + 
+						"	}\n" +
+						"}\n",
+				},
+				"----------\n" + 
+				"1. ERROR in X19b.java (at line 6)\n" + 
+				"	boolean b = (obj instanceof String[] s && s.length == 0);\n" + 
+				"	                                     ^\n" + 
+				"Duplicate local variable s\n" + 
+				"----------\n",
+				"",
+				null,
+				true,
+				options);
+	}
 	/* Test that we allow consequent pattern expressions in the same statement
 	 */
 	public void test020() {
@@ -952,12 +986,12 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X21.java (at line 5)\n" + 
 				"	System.out.print(s);\n" + 
 				"	                 ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X21.java (at line 6)\n" + 
 				"	System.out.print(s2);\n" + 
 				"	                 ^^\n" + 
-				"s2 cannot be resolved to a variable\n" + 
+				"The pattern variable s2 is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1011,12 +1045,12 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X23.java (at line 7)\n" + 
 				"	while (!(o instanceof String s) && s.length() > 0) {\n" + 
 				"	                                   ^\n" + 
-				"s cannot be resolved\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X23.java (at line 8)\n" + 
 				"	System.out.println(s);\n" + 
 				"	                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1029,9 +1063,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 		Map<String, String> options = getCompilerOptions(true);
 		runNegativeTest(
 				new String[] {
-						"X23.java",
+						"X23a.java",
 						"@SuppressWarnings(\"preview\")\n" +
-						"public class X23 {\n" +
+						"public class X23a {\n" +
 						"  public static void main(String[] o) {\n" +
 						"		foo(\"one\");\n" + 
 						"	}\n" +
@@ -1044,15 +1078,15 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X23.java (at line 7)\n" + 
+				"1. ERROR in X23a.java (at line 7)\n" + 
 				"	while (!(o instanceof String s) && s.length() > 0) {\n" + 
 				"	                                   ^\n" + 
-				"s cannot be resolved\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
-				"2. ERROR in X23.java (at line 8)\n" + 
+				"2. ERROR in X23a.java (at line 8)\n" + 
 				"	System.out.println(s);\n" + 
 				"	                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1080,8 +1114,9 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"one",
 				options);
 	}
-	/* Test that we reject two patter variables with same name in the same
-	 * equals expression
+	/* 
+	 * It's not a problem to define the same var in two operands of a binary expression,
+	 * but then it is not in scope below.
 	 */
 	public void test025() {
 		Map<String, String> options = getCompilerOptions(true);
@@ -1101,18 +1136,19 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X25.java (at line 7)\n" + 
-				"	if ((o instanceof String s) != p instanceof String s) {\n" + 
-				"	                                                   ^\n" + 
-				"Duplicate local variable s\n" + 
+				"1. ERROR in X25.java (at line 8)\n" + 
+				"	System.out.print(\"s:\" + s);\n" + 
+				"	                        ^\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
 				true,
 				options);
 	}
-	/* Test that we reject two patter variables with same name in the same
-	 * equals expression
+	/*
+	 * It's not a problem to define the same var in two operands of a binary expression,
+	 * but then it is not in scope below.
 	 */
 	public void test026() {
 		Map<String, String> options = getCompilerOptions(true);
@@ -1132,10 +1168,10 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"}\n",
 				},
 				"----------\n" + 
-				"1. ERROR in X26.java (at line 7)\n" + 
-				"	if ((o instanceof String s) == p instanceof String s) {\n" + 
-				"	                                                   ^\n" + 
-				"Duplicate local variable s\n" + 
+				"1. ERROR in X26.java (at line 8)\n" + 
+				"	System.out.print(\"s:\" + s);\n" + 
+				"	                        ^\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1200,12 +1236,11 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				getCompilerOptions(true));
 	}
 	/*
-	 * Test that pattern variables are accepted in initialization of
-	 * a for statement
-	 * TODO: Javac rejects this
+	 * Test that pattern variables are accepted in initialization of a for statement,
+	 * but unavailable in the body if uncertain which if instanceof check was true
 	 */
 	public void test030() {
-		runConformTest(
+		runNegativeTest(
 				new String[] {
 						"X30.java",
 						"@SuppressWarnings(\"preview\")\n" +
@@ -1220,7 +1255,15 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"	}\n" +
 						"}\n",
 				},
-				"one",
+				"----------\n" + 
+				"1. ERROR in X30.java (at line 8)\n" + 
+				"	System.out.print(s.charAt(i));\n" + 
+				"	                 ^\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
+				"----------\n",
+				"",
+				null,
+				true,
 				getCompilerOptions(true));
 	}
 	public void test031() {
@@ -1243,17 +1286,17 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X31.java (at line 7)\n" + 
 				"	for(int i = 0; !(obj instanceof String[] s) && s.length > 0 && i < s.length; i++) {\n" + 
 				"	                                               ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X31.java (at line 7)\n" + 
 				"	for(int i = 0; !(obj instanceof String[] s) && s.length > 0 && i < s.length; i++) {\n" + 
 				"	                                                                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
 				"3. ERROR in X31.java (at line 8)\n" + 
 				"	System.out.println(s[i]);\n" + 
 				"	                   ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1285,11 +1328,8 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"one",
 				getCompilerOptions(true));
 	}
-	/*
-	 * FAILURE: Javac rejects this code, but we accept.
-	 */
 	public void test033() {
-		runConformTest(
+		runNegativeTest(
 				new String[] {
 						"X33.java",
 						"@SuppressWarnings(\"preview\")\n" +
@@ -1311,7 +1351,15 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 						"	}\n" +
 						"}\n",
 				},
-				"ne",
+				"----------\n" + 
+				"1. ERROR in X33.java (at line 12)\n" + 
+				"	res = s.substring(1);\n" + 
+				"	      ^\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
+				"----------\n",
+				"",
+				null,
+				true,
 				getCompilerOptions(true));
 	}
 	public void test034() {
@@ -1377,12 +1425,12 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"1. ERROR in X35.java (at line 11)\n" + 
 				"	yield s;\n" + 
 				"	      ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n" + 
 				"2. ERROR in X35.java (at line 14)\n" + 
 				"	yield s;\n" + 
 				"	      ^\n" + 
-				"s cannot be resolved to a variable\n" + 
+				"The pattern variable s is not in scope in this location\n" + 
 				"----------\n",
 				"",
 				null,
@@ -1435,6 +1483,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"	                   ^^^^\n" + 
 				"The type of the expression must be an array type but it resolved to String\n" + 
 				"----------\n",
+				"",
 				null,
 				true,
 				getCompilerOptions(true));
@@ -1462,6 +1511,7 @@ public class PatternMatching14Test extends AbstractRegressionTest {
 				"	                   ^\n" + 
 				"s cannot be resolved to a variable\n" + 
 				"----------\n",
+				"",
 				null,
 				true,
 				getCompilerOptions(true));
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/core/compiler/IProblem.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/core/compiler/IProblem.java
index 1a89cf7759..ddcff78c6a 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/core/compiler/IProblem.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/core/compiler/IProblem.java
@@ -2315,5 +2315,9 @@ void setSourceStart(int sourceStart);
 	 * @noreference preview feature error */
 	int RecordIllegalVararg= PreviewRelated + 1754;
 	/* records - end */
+	/* instanceof pattern: */
+	/** @since 3.21 BETA_JAVA14
+	 * @noreference preview feature error */
+	int PatternVariableNotInScope = PreviewRelated + 1760;
 	/* Java14 errors - end */
 	}
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AND_AND_Expression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AND_AND_Expression.java
index 2bd0f31c60..66a6adb113 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AND_AND_Expression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AND_AND_Expression.java
@@ -282,7 +282,6 @@ public class AND_AND_Expression extends BinaryExpression {
 	 */
 	@Override
 	public TypeBinding resolveType(BlockScope scope) {
-		resolvePatternVariable(scope, true);
 		TypeBinding result = super.resolveType(scope);
 		// check whether comparing identical expressions
 		Binding leftDirect = Expression.getDirectBinding(this.left);
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AbstractMethodDeclaration.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AbstractMethodDeclaration.java
index 8f2086af01..33893e8756 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AbstractMethodDeclaration.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/AbstractMethodDeclaration.java
@@ -346,8 +346,6 @@ public abstract class AbstractMethodDeclaration
 			if (this.statements != null) {
 				for (Statement stmt : this.statements) {
 					stmt.generateCode(this.scope, codeStream);
-					if ((stmt.bits & ASTNode.HasInstancePatternExpression) != 0)
-						stmt.exitPatternVariableScope(codeStream);
 				}
 			}
 			// if a problem got reported during code gen, then trigger problem method creation
@@ -650,12 +648,7 @@ public abstract class AbstractMethodDeclaration
 		if (this.statements != null) {
  			for (int i = 0, length = this.statements.length; i < length; i++) {
  				Statement stmt = this.statements[i];
- 				stmt.lookForPatternVariables(this.scope);
- 				if ((stmt.bits & ASTNode.HasInstancePatternExpression) == 0) {
- 					stmt.resolve(this.scope);
- 				} else {
- 					stmt.resolve(stmt.patternScope);
- 				}
+ 				stmt.resolve(this.scope);
 			}
 		} else if ((this.bits & UndocumentedEmptyBlock) != 0) {
 			if (!this.isConstructor() || this.arguments != null) { // https://bugs.eclipse.org/bugs/show_bug.cgi?id=319626
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/BinaryExpression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/BinaryExpression.java
index 86033e1cf7..915b205026 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/BinaryExpression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/BinaryExpression.java
@@ -1812,16 +1812,6 @@ public void initializePatternVariables(BlockScope scope, CodeStream codeStream)
 	this.right.initializePatternVariables(scope, codeStream);
 }
 @Override
-public void resolvePatternVariable(BlockScope scope, boolean trueFalse) {
-	this.left.resolvePatternVariable(scope, trueFalse);
-	this.right.resolvePatternVariable(scope, trueFalse);
-}
-@Override
-public void generatePatternVariable(BlockScope currentScope, CodeStream codeStream) {
-	this.left.generatePatternVariable(currentScope, codeStream);
-	this.right.generatePatternVariable(currentScope, codeStream);
-}
-@Override
 public TypeBinding resolveType(BlockScope scope) {
 	// keep implementation in sync with CombinedBinaryExpression#resolveType
 	// and nonRecursiveResolveTypeUpwards
@@ -1929,6 +1919,7 @@ public TypeBinding resolveType(BlockScope scope) {
 	}
 	// compute the constant when valid
 	computeConstant(scope, leftTypeID, rightTypeID);
+	this.bits |= (this.left.bits | this.right.bits) & ASTNode.HasInstancePatternExpression;
 	return this.resolvedType;
 }
 
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Block.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Block.java
index ab8efa0069..de2a55f30f 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Block.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Block.java
@@ -90,8 +90,6 @@ public void generateCode(BlockScope currentScope, CodeStream codeStream) {
 	if (this.statements != null) {
 		for (Statement stmt : this.statements) {
 			stmt.generateCode(this.scope, codeStream);
-			if ((stmt.bits & ASTNode.HasInstancePatternExpression) != 0)
-				stmt.exitPatternVariableScope(codeStream);
 		}
 	} // for local variable debug attributes
 	if (this.scope != currentScope) { // was really associated with its own scope
@@ -134,12 +132,7 @@ public void resolve(BlockScope upperScope) {
 				: new BlockScope(upperScope, this.explicitDeclarations);
 		for (int i = 0, length = this.statements.length; i < length; i++) {
 			final Statement stmt = this.statements[i];
-			stmt.lookForPatternVariables(this.scope);
-			if ((stmt.bits & ASTNode.HasInstancePatternExpression) == 0) {
-				stmt.resolve(this.scope);
-			} else {
-				stmt.resolve(stmt.patternScope);
-			}
+			stmt.resolve(this.scope);
 		}
 	}
 }
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ConditionalExpression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ConditionalExpression.java
index 12fbf324ea..0d6abb2775 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ConditionalExpression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ConditionalExpression.java
@@ -451,9 +451,9 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext,
 
 	@Override
 	public void initializePatternVariables(BlockScope scope, CodeStream codeStream) {
-		this.condition.initializePatternVariables(this.patternScope, codeStream);
-		this.valueIfTrue.initializePatternVariables(this.patternScope, codeStream);
-		this.valueIfFalse.initializePatternVariables(this.patternScope, codeStream);
+		this.condition.initializePatternVariables(scope, codeStream);
+		this.valueIfTrue.initializePatternVariables(scope, codeStream);
+		this.valueIfFalse.initializePatternVariables(scope, codeStream);
 	}
 
 	@Override
@@ -475,7 +475,6 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext,
 		
 		if (this.constant != Constant.NotAConstant) {
 			this.constant = Constant.NotAConstant;
-			this.condition.resolvePatternVariable(scope, true);
 			TypeBinding conditionType = this.condition.resolveTypeExpecting(scope, TypeBinding.BOOLEAN);
 			this.condition.computeConversion(scope, TypeBinding.BOOLEAN, conditionType);
 
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Expression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Expression.java
index a6706b9286..6e572a300f 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Expression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Expression.java
@@ -778,15 +778,9 @@ public void generateCode(BlockScope currentScope, CodeStream codeStream, boolean
 		throw new ShouldNotImplement(Messages.ast_missingCode);
 	}
 }
-public void resolvePatternVariable(BlockScope scope, boolean trueFalse) {
-	// Nothing by default
-}
 public void initializePatternVariables(BlockScope scope, CodeStream codeStream) {
 	// Nothing by default
 }
-public void generatePatternVariable(BlockScope currentScope, CodeStream codeStream) {
-	// Nothing by default
-}
 /**
  * Default generation of a boolean value
  * @param currentScope
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ForStatement.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ForStatement.java
index 56a5c6aec0..298e92f5f6 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ForStatement.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/ForStatement.java
@@ -265,7 +265,7 @@ public class ForStatement extends Statement {
 				this.initializations[i].generateCode(this.scope, codeStream);
 			}
 		}
-		if (this.condition != null && (this.bits & ASTNode.HasInstancePatternExpression) != 0) {
+		if (this.condition != null && (this.condition.bits & ASTNode.HasInstancePatternExpression) != 0) {
 			this.condition.initializePatternVariables(currentScope, codeStream);
 		}
 		Constant cst = this.condition == null ? null : this.condition.optimizedBooleanConstant();
@@ -402,60 +402,21 @@ public class ForStatement extends Statement {
 	}
 
 	@Override
-	public void lookForPatternVariables(BlockScope outerScope) {
-		if (this.condition == null)
-			return;
-		this.condition.traverse(new ASTVisitor() {
-			@Override
-			public boolean visit(
-		    		InstanceOfExpression instanceOfExpression,
-		    		BlockScope sc) {
-				if (instanceOfExpression.elementVariable != null) {
-					ForStatement.this.bits |= ASTNode.HasInstancePatternExpression;
-				}
-				return false; // mission finished, exit
-			}
-		}, outerScope);
-		this.patternScope = new BlockScope(outerScope);
-	}
-
-	@Override
 	public void resolve(BlockScope upperScope) {
-		boolean hasPatternVariable = (this.bits & ASTNode.HasInstancePatternExpression) != 0;
-		if (hasPatternVariable)
-			upperScope = (BlockScope) upperScope.parent;
 		// use the scope that will hold the init declarations
 		this.scope = (this.bits & ASTNode.NeededScope) != 0 ? new BlockScope(upperScope) : upperScope;
 		if (this.initializations != null)
 			for (int i = 0, length = this.initializations.length; i < length; i++)
 				this.initializations[i].resolve(this.scope);
 		if (this.condition != null) {
-		 	if (hasPatternVariable) {
-		 	 	this.scope = this.patternScope = new BlockScope(this.scope);
-		 	 	this.condition.resolvePatternVariable(this.scope, true);
-		 	}
-		}
-
-		if (this.condition != null) {
 			TypeBinding type = this.condition.resolveTypeExpecting(this.scope, TypeBinding.BOOLEAN);
 			this.condition.computeConversion(this.scope, type, type);
 		}
 		if (this.increments != null)
 			for (int i = 0, length = this.increments.length; i < length; i++)
 				this.increments[i].resolve(this.scope);
-		if (this.action != null) {
-			BlockScope falseScope = null;
-			BlockScope trueScope = null;
-			if (hasPatternVariable) {
-				trueScope = this.patternScope;
-				if (this.action.doesNotCompleteNormally()) {
-					falseScope = upperScope;
-				}
-			}
-			this.action.resolve(hasPatternVariable ? trueScope : this.scope);
-			if (falseScope != null)
-				this.condition.resolvePatternVariable(falseScope, false);
-		}
+		if (this.action != null)
+			this.action.resolve(this.scope);
 	}
 
 	@Override
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/IfStatement.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/IfStatement.java
index 11aae31732..a75062fbef 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/IfStatement.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/IfStatement.java
@@ -202,10 +202,6 @@ public void generateCode(BlockScope currentScope, CodeStream codeStream) {
 		}
 		// generate then statement
 		this.thenStatement.generateCode(currentScope, codeStream);
-		boolean hasPatternVariable = (this.bits & ASTNode.HasInstancePatternExpression) != 0;
-		if (hasPatternVariable) {
-			this.exitPatternVariableScope(codeStream);
-		}
 		// jump around the else statement
 		if (hasElsePart) {
 			if ((this.bits & ASTNode.ThenExit) == 0) {
@@ -279,62 +275,13 @@ public StringBuffer printStatement(int indent, StringBuffer output) {
 	return output;
 }
 @Override
-public void lookForPatternVariables(BlockScope scope) {
-	this.condition.traverse(new ASTVisitor() {
-		@Override
-		public boolean visit(
-	    		InstanceOfExpression instanceOfExpression,
-	    		BlockScope sc) {
-			if (instanceOfExpression.elementVariable != null) {
-				IfStatement.this.bits |= ASTNode.HasInstancePatternExpression;
-				IfStatement.this.patternScope = new BlockScope(scope);
-			}
-			return false; // mission finished, exit
-		}
-	}, scope);
-}
-@Override
-public void resolve(BlockScope outerScope) {
-	boolean hasPatternVariable = (this.bits & ASTNode.HasInstancePatternExpression) != 0;
- 	BlockScope trueScope = null;
- 	if (hasPatternVariable) {
- 		trueScope = this.patternScope;
- 				//new BlockScope((BlockScope) outerScope.parent);
- 	 	this.condition.resolvePatternVariable(trueScope, true);
- 	}
-	TypeBinding type = this.condition.resolveTypeExpecting(hasPatternVariable ? trueScope : outerScope, TypeBinding.BOOLEAN);
- 	this.condition.computeConversion(hasPatternVariable ? trueScope : outerScope, type, type);
-	if (this.thenStatement != null) {
-		this.thenStatement.resolve(hasPatternVariable ? trueScope : outerScope);
-	}
-	if (hasPatternVariable) {
-		BlockScope falseScope = null;
-		if (this.thenStatement.doesNotCompleteNormally()) {
-			falseScope = (BlockScope) outerScope.parent;
-		} else {
-			falseScope = new BlockScope((BlockScope) outerScope.parent);
-		}
-		this.condition.resolvePatternVariable(falseScope, false);
-		outerScope = falseScope;
-	}
-	if (this.elseStatement != null) {
-		this.elseStatement.traverse(new ASTVisitor() {
-			@Override
-			public boolean visit(
-		    		InstanceOfExpression instanceOfExpression,
-		    		BlockScope sc) {
-				if (instanceOfExpression.elementVariable != null) {
-					IfStatement.this.elseStatement.bits |= ASTNode.HasInstancePatternExpression;
-				}
-				return false;
-			}
-		}, outerScope);
-		if ((this.elseStatement.bits & ASTNode.HasInstancePatternExpression) != 0) {
-			this.elseStatement.patternScope = new BlockScope(outerScope);
-			this.elseStatement.resolve(this.elseStatement.patternScope);
-		} else
-			this.elseStatement.resolve(outerScope);
-	}
+public void resolve(BlockScope scope) {
+	TypeBinding type = this.condition.resolveTypeExpecting(scope, TypeBinding.BOOLEAN);
+	this.condition.computeConversion(scope, type, type);
+	if (this.thenStatement != null)
+		this.thenStatement.resolve(scope);
+	if (this.elseStatement != null)
+		this.elseStatement.resolve(scope);
 }
 
 @Override
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java
index 559283e261..6b827df116 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java
@@ -63,9 +63,6 @@ public InstanceOfExpression(Expression expression, LocalDeclaration local) {
 
 @Override
 public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, FlowInfo flowInfo) {
-	if (this.elementVariable != null) {
-		flowInfo.markAsDefinitelyAssigned(this.elementVariable.binding);
-	}
 	LocalVariableBinding local = this.expression.localVariableBinding();
 	if (local != null && (local.type.tagBits & TagBits.IsBaseType) == 0) {
 		flowInfo = this.expression.analyseCode(currentScope, flowContext, flowInfo).
@@ -74,6 +71,12 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, Fl
 		initsWhenTrue.markAsComparedEqualToNonNull(local);
 		flowContext.recordUsingNullReference(currentScope, local,
 				this.expression, FlowContext.CAN_ONLY_NULL | FlowContext.IN_INSTANCEOF, flowInfo);
+		if (this.elementVariable != null) {
+			if (this.elementVariable.duplicateCheckObligation != null) {
+				this.elementVariable.duplicateCheckObligation.accept(flowInfo);
+			}
+			initsWhenTrue.markAsDefinitelyAssigned(this.elementVariable.binding);
+		}
 		// no impact upon enclosing try context
 		return FlowInfo.conditional(initsWhenTrue, flowInfo.copy());
 	}
@@ -86,28 +89,6 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, Fl
 	return this.expression.analyseCode(currentScope, flowContext, flowInfo).
 			unconditionalInits();
 }
-@Override
-public void generateOptimizedBoolean(BlockScope currentScope, CodeStream codeStream, BranchLabel trueLabel, BranchLabel falseLabel, boolean valueRequired) {
-	super.generateOptimizedBoolean(currentScope, codeStream, trueLabel, falseLabel, valueRequired);
-	generatePatternVariable(currentScope, codeStream);
-//	if (this.elementVariable != null) {
-//		int position = codeStream.position;
-//		codeStream.load(this.expression.localVariableBinding());
-//		codeStream.checkcast(this.type, this.type.resolvedType, position);
-//		codeStream.store(this.elementVariable.binding, false);
-//		codeStream.recordPositionsFrom(position, this.sourceEnd);
-//	}
-}
-@Override
-public void generatePatternVariable(BlockScope currentScope, CodeStream codeStream) {
-//	if (this.elementVariable != null) {
-//		int position = codeStream.position;
-//		codeStream.load(this.expression.localVariableBinding());
-//		codeStream.checkcast(this.type, this.type.resolvedType, position);
-//		codeStream.store(this.elementVariable.binding, false);
-//		codeStream.recordPositionsFrom(position, this.sourceEnd);
-//	}
-}
 /**
  * Code generation for instanceOfExpression
  *
@@ -161,33 +142,25 @@ public void initializePatternVariables(BlockScope currentScope, CodeStream codeS
 			this.isInitialized = true;
 			codeStream.aconst_null();
 			codeStream.store(this.elementVariable.binding, false);
-//			int position = codeStream.position;
-//			codeStream.addVisibleLocalVariable(this.elementVariable.binding);
-//			this.elementVariable.binding.recordInitializationStartPC(position);
 		}
 		int position = codeStream.position;
 		codeStream.addVisibleLocalVariable(this.elementVariable.binding);
 		this.elementVariable.binding.recordInitializationStartPC(position);
 	}
-	//generatePatternVariable(currentScope, codeStream);
 }
-@Override
-public void resolvePatternVariable(BlockScope scope, boolean inScope) {
-	if (!inScope) return;
+public void resolvePatternVariable(BlockScope scope) {
 	if (this.elementVariable != null && this.elementVariable.binding == null) {
-		this.patternScope = scope;
-		this.elementVariable.resolve(scope);
+		this.elementVariable.resolve(scope, true);
+		this.elementVariable.binding.modifiers |= ExtraCompilerModifiers.AccPatterVariable;
 		// Why cant this be done in the constructor?
 		this.type = this.elementVariable.type;
+		this.bits |= ASTNode.HasInstancePatternExpression;
 	}
 }
 @Override
 public TypeBinding resolveType(BlockScope scope) {
-//	resolvePatternVariable(scope, scope);
 	this.constant = Constant.NotAConstant;
-	if (this.type == null && this.elementVariable != null) {
-		this.type = this.elementVariable.type;
-	}
+	resolvePatternVariable(scope);
 	TypeBinding checkedType = this.type.resolveType(scope, true /* check bounds*/);
 	if (this.expression instanceof CastExpression) {
 		((CastExpression) this.expression).setInstanceofType(checkedType); // for cast expression we need to know instanceof type to not tag unnecessary when needed
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/LocalDeclaration.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/LocalDeclaration.java
index 57f81073df..e7f562d4e0 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/LocalDeclaration.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/LocalDeclaration.java
@@ -45,6 +45,7 @@ import static org.eclipse.jdt.internal.compiler.ast.ExpressionContext.VANILLA_CO
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.function.Consumer;
 
 import org.eclipse.jdt.internal.compiler.ASTVisitor;
 import org.eclipse.jdt.internal.compiler.impl.*;
@@ -60,6 +61,12 @@ public class LocalDeclaration extends AbstractVariableDeclaration {
 
 	public LocalVariableBinding binding;
 
+	/**
+	 * For pattern variable, resolve() may store here an obligation to be checked when we have
+	 * a flow info that tells us whether a potential duplicates is in fact in scope.
+	 */
+	Consumer<FlowInfo> duplicateCheckObligation;
+
 	public LocalDeclaration(
 		char[] name,
 		int sourceStart,
@@ -257,7 +264,9 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, Fl
 	
 	@Override
 	public void resolve(BlockScope scope) {
-
+		resolve(scope, false);
+	}
+	public void resolve(BlockScope scope, boolean isPatternVariable) {
 		// prescan NNBD
 		handleNonNullByDefault(scope, this.annotations, this);
 
@@ -296,13 +305,23 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, Fl
 
 		Binding existingVariable = scope.getBinding(this.name, Binding.VARIABLE, this, false /*do not resolve hidden field*/);
 		if (existingVariable != null && existingVariable.isValidBinding()){
-			boolean localExists = existingVariable instanceof LocalVariableBinding; 
-			if (localExists && (this.bits & ASTNode.ShadowsOuterLocal) != 0 && scope.isLambdaSubscope() && this.hiddenVariableDepth == 0) {
+			boolean localExists = existingVariable instanceof LocalVariableBinding;
+			if (localExists && isPatternVariable
+					&& (((LocalVariableBinding) existingVariable).modifiers & ExtraCompilerModifiers.AccPatterVariable) != 0)
+			{
+				this.duplicateCheckObligation = (flowInfo) -> {
+					if (flowInfo.isDefinitelyAssigned((LocalVariableBinding) existingVariable)) {
+						scope.problemReporter().redefineLocal(this);
+					}
+				};
+			} else {
+				if (localExists && (this.bits & ASTNode.ShadowsOuterLocal) != 0 && scope.isLambdaSubscope() && this.hiddenVariableDepth == 0) {
 					scope.problemReporter().lambdaRedeclaresLocal(this);
-			} else if (localExists && this.hiddenVariableDepth == 0) {
+				} else if (localExists && this.hiddenVariableDepth == 0) {
 					scope.problemReporter().redefineLocal(this);
-			} else {
-				scope.problemReporter().localVariableHiding(this, existingVariable, false);
+				} else {
+					scope.problemReporter().localVariableHiding(this, existingVariable, false);
+				}
 			}
 		}
 
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Statement.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Statement.java
index 1cf1230ac7..9d386d58a5 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Statement.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/Statement.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2020 IBM Corporation and others.
+ * Copyright (c) 2000, 2019 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -8,10 +8,6 @@
  *
  * SPDX-License-Identifier: EPL-2.0
  *
- * This is an implementation of an early-draft specification developed under the Java
- * Community Process (JCP) and is made available for testing and evaluation purposes
- * only. The code is not compatible with any specification of the JCP.
- *
  * Contributors:
  *     IBM Corporation - initial API and implementation
  *     Stephan Herrmann - Contributions for
@@ -107,7 +103,6 @@ public boolean doesNotCompleteNormally() {
 public boolean completesByContinue() {
 	return false;
 }
-	public BlockScope patternScope;
 
 	public static final int NOT_COMPLAINED = 0;
 	public static final int COMPLAINED_FAKE_REACHABLE = 1;
@@ -427,15 +422,6 @@ public void generateArguments(MethodBinding binding, Expression[] arguments, Blo
 }
 
 public abstract void generateCode(BlockScope currentScope, CodeStream codeStream);
-public void exitPatternVariableScope(CodeStream stream) {
-	if (this.patternScope != null && (this.bits & ASTNode.HasInstancePatternExpression) != 0) {
-		for (Scope s : this.patternScope.subscopes) {
-		 if (s == null) continue;
-			stream.exitUserScope((BlockScope) s);
-		}
-		stream.exitUserScope(this.patternScope);
-	}
-}
 
 public boolean isBoxingCompatible(TypeBinding expressionType, TypeBinding targetType, Expression expression, Scope scope) {
 	if (scope.isBoxingCompatibleWith(expressionType, targetType))
@@ -477,21 +463,6 @@ public abstract StringBuffer printStatement(int indent, StringBuffer output);
 
 public abstract void resolve(BlockScope scope);
 
-public void lookForPatternVariables(BlockScope scope) {
-	this.traverse(new ASTVisitor() {
-		@Override
-		public boolean visit(
-	    		InstanceOfExpression instanceOfExpression,
-	    		BlockScope sc) {
-			if (instanceOfExpression.elementVariable != null) {
-				Statement.this.bits |= ASTNode.HasInstancePatternExpression;
-			}
-			return false; // mission finished, exit
-		}
-	}, scope);
-	if ((this.bits & ASTNode.HasInstancePatternExpression) != 0)
-		this.patternScope = new BlockScope(scope);
-}
 /**
  * Returns case constant associated to this statement (NotAConstant if none)
  * parameter statement has to be either a SwitchStatement or a SwitchExpression
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/UnaryExpression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/UnaryExpression.java
index c1d0368878..b25157f635 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/UnaryExpression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/UnaryExpression.java
@@ -224,16 +224,6 @@ public FlowInfo analyseCode(
 	}
 
 	@Override
-	public void resolvePatternVariable(BlockScope scope, boolean trueFalse) {
-		if ((((this.bits & OperatorMASK) >> OperatorSHIFT) == NOT)) {
-			this.expression.resolvePatternVariable(scope, !trueFalse);
-		}
-	}
-	@Override
-	public void generatePatternVariable(BlockScope currentScope, CodeStream codeStream) {
-		this.expression.generatePatternVariable(currentScope, codeStream);
-	}
-	@Override
 	public TypeBinding resolveType(BlockScope scope) {
 		boolean expressionIsCast;
 		if ((expressionIsCast = this.expression instanceof CastExpression) == true) this.expression.bits |= DisableUnnecessaryCastCheck; // will check later on
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/WhileStatement.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/WhileStatement.java
index c0e5790e5c..09ef32e52e 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/WhileStatement.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/WhileStatement.java
@@ -194,6 +194,7 @@ public class WhileStatement extends Statement {
 		if ((this.bits & IsReachable) == 0) {
 			return;
 		}
+		// TODO: Do this at the appropriate point only
 		this.condition.initializePatternVariables(currentScope, codeStream);
 		int pc = codeStream.position;
 		Constant cst = this.condition.optimizedBooleanConstant();
@@ -236,7 +237,6 @@ public class WhileStatement extends Statement {
 		// generate the action
 		BranchLabel actionLabel = new BranchLabel(codeStream);
 		if (this.action != null) {
-			this.condition.generatePatternVariable(currentScope, codeStream);
 			actionLabel.tagBits |= BranchLabel.USED;
 			// Required to fix 1PR0XVS: LFRE:WINNT - Compiler: variable table for method appears incorrect
 			if (this.condIfTrueInitStateIndex != -1) {
@@ -275,42 +275,11 @@ public class WhileStatement extends Statement {
 	}
 
 	@Override
-	public void lookForPatternVariables(BlockScope scope) {
-		this.condition.traverse(new ASTVisitor() {
-			@Override
-			public boolean visit(
-		    		InstanceOfExpression instanceOfExpression,
-		    		BlockScope sc) {
-				if (instanceOfExpression.elementVariable != null) {
-					WhileStatement.this.bits |= ASTNode.HasInstancePatternExpression;
-				}
-				return false; // mission finished, exit
-			}
-		}, scope);
-		this.patternScope = new BlockScope(scope);
-	}
-
-	@Override
 	public void resolve(BlockScope scope) {
-		boolean hasPatternVariable = (this.bits & ASTNode.HasInstancePatternExpression) != 0;
-	 	BlockScope trueScope = null;
-	 	BlockScope falseScope = null;
-	 	if (hasPatternVariable) {
-	 		trueScope = this.patternScope;
-	 	 	this.condition.resolvePatternVariable(trueScope, true);
-	 	}
-		TypeBinding type = this.condition.resolveTypeExpecting(hasPatternVariable ? trueScope : scope, TypeBinding.BOOLEAN);
+		TypeBinding type = this.condition.resolveTypeExpecting(scope, TypeBinding.BOOLEAN);
 		this.condition.computeConversion(scope, type, type);
-		if (this.action != null) {
-			if (hasPatternVariable) {
-				if (this.action.doesNotCompleteNormally()) {
-					falseScope = (BlockScope) scope.parent;
-				}
-			}
-			this.action.resolve(hasPatternVariable ? trueScope : scope);
-			if (falseScope != null)
-				this.condition.resolvePatternVariable(falseScope, false);
-		}
+		if (this.action != null)
+			this.action.resolve(scope);
 	}
 
 	@Override
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/BlockScope.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/BlockScope.java
index 6980158b37..39d64e3762 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/BlockScope.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/BlockScope.java
@@ -134,7 +134,6 @@ public final void addLocalType(TypeDeclaration localType) {
 		methodScope = methodScope.enclosingMethodScope();
 	}
 }
-
 /* Insert a local variable into a given scope, updating its position
  * and checking there are not too many locals or arguments allocated.
  */
@@ -419,7 +418,7 @@ public LocalDeclaration[] findLocalVariableDeclarations(int position) {
 		} else {
 			// consider variable first
 			LocalVariableBinding local = this.locals[ilocal]; // if no local at all, will be locals[ilocal]==null
-			if (local != null) {
+			if (local != null && (local.modifiers & ExtraCompilerModifiers.AccPatterVariable) == 0) {
 				LocalDeclaration localDecl = local.declaration;
 				if (localDecl != null) {
 					if (localDecl.declarationSourceStart <= position) {
@@ -447,9 +446,20 @@ public LocalDeclaration[] findLocalVariableDeclarations(int position) {
 public LocalVariableBinding findVariable(char[] variableName) {
 	int varLength = variableName.length;
 	for (int i = this.localIndex-1; i >= 0; i--) { // lookup backward to reach latest additions first
-		LocalVariableBinding local;
+		LocalVariableBinding local = this.locals[i];
+		if ((local.modifiers & ExtraCompilerModifiers.AccPatterVariable) != 0)
+			continue;
+		char[] localName;
+		if ((localName = local.name).length == varLength && CharOperation.equals(localName, variableName))
+			return local;
+	}
+	// Look at the pattern variables now
+	for (int i = this.localIndex-1; i >= 0; i--) { // lookup backward to reach latest additions first
+		LocalVariableBinding local = this.locals[i];
+		if ((local.modifiers & ExtraCompilerModifiers.AccPatterVariable) == 0)
+			continue;
 		char[] localName;
-		if ((localName = (local = this.locals[i]).name).length == varLength && CharOperation.equals(localName, variableName))
+		if ((localName = local.name).length == varLength && CharOperation.equals(localName, variableName))
 			return local;
 	}
 	return null;
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ExtraCompilerModifiers.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ExtraCompilerModifiers.java
index fdba43ae5d..cc2f201db4 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ExtraCompilerModifiers.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/lookup/ExtraCompilerModifiers.java
@@ -57,4 +57,5 @@ public interface ExtraCompilerModifiers { // modifier constant
 	final int AccOverriding = ASTNode.Bit29; // record fact a method overrides another one
 	final int AccImplementing = ASTNode.Bit30; // record fact a method implements another one (it is concrete and overrides an abstract one)
 	final int AccGenericSignature = ASTNode.Bit31; // record fact a type/method/field involves generics in its signature (and need special signature attr)
+	final int AccPatterVariable = ASTNode.Bit29;
 }
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/ProblemReporter.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/ProblemReporter.java
index aa2193a718..74d5ef7c87 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/ProblemReporter.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/ProblemReporter.java
@@ -2102,12 +2102,20 @@ public void duplicateInitializationOfBlankFinalField(FieldBinding field, Referen
 }
 public void duplicateInitializationOfFinalLocal(LocalVariableBinding local, ASTNode location) {
 	String[] arguments = new String[] { new String(local.readableName())};
-	this.handle(
-		IProblem.DuplicateFinalLocalInitialization,
-		arguments,
-		arguments,
-		nodeSourceStart(local, location),
-		nodeSourceEnd(local, location));
+	if ((local.modifiers & ExtraCompilerModifiers.AccPatterVariable) == 0) {
+		this.handle(
+			IProblem.DuplicateFinalLocalInitialization,
+			arguments,
+			arguments,
+			nodeSourceStart(local, location),
+			nodeSourceEnd(local, location));
+	} else {
+		this.handle(IProblem.PatternVariableNotInScope,
+			arguments,
+			arguments,
+			nodeSourceStart(local, location),
+			nodeSourceEnd(local, location));
+	}
 }
 public void duplicateMethodInType(AbstractMethodDeclaration methodDecl, boolean equalParameters, int severity) {
     MethodBinding method = methodDecl.binding;
@@ -8716,14 +8724,25 @@ public void uninitializedNonNullField(FieldBinding field, ASTNode location) {
 		nodeSourceEnd(field, location));
 }
 public void uninitializedLocalVariable(LocalVariableBinding binding, ASTNode location, Scope scope) {
-	binding.markAsUninitializedIn(scope);
-	String[] arguments = new String[] {new String(binding.readableName())};
-	this.handle(
-		methodHasMissingSwitchDefault() ? IProblem.UninitializedLocalVariableHintMissingDefault : IProblem.UninitializedLocalVariable,
-		arguments,
-		arguments,
-		nodeSourceStart(binding, location),
-		nodeSourceEnd(binding, location));
+	if ((binding.modifiers & ExtraCompilerModifiers.AccPatterVariable) == 0) {
+		binding.markAsUninitializedIn(scope);
+		String[] arguments = new String[] {new String(binding.readableName())};
+		this.handle(
+				methodHasMissingSwitchDefault() ? IProblem.UninitializedLocalVariableHintMissingDefault : IProblem.UninitializedLocalVariable,
+						arguments,
+						arguments,
+						nodeSourceStart(binding, location),
+						nodeSourceEnd(binding, location));
+	} else {
+		String[] arguments = new String[] {new String(binding.readableName())};
+		this.handle(
+				IProblem.PatternVariableNotInScope,
+						arguments,
+						arguments,
+						nodeSourceStart(binding, location),
+						nodeSourceEnd(binding, location));
+		
+	}
 }
 private boolean methodHasMissingSwitchDefault() {
 	MethodScope methodScope = null;
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/messages.properties b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/messages.properties
index 61367457cf..05d990a28a 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/messages.properties
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/problem/messages.properties
@@ -1051,6 +1051,8 @@
 1753 = void is an invalid type for the component {0} of a record
 1754 = The variable argument type {0} of the record {1} must be the last parameter
 
+1760 = The pattern variable {0} is not in scope in this location
+
 # Java 14 Preview - end
 
 # Additional doc