Bug 561167 - "Source > Cleanup" removes necessary cast of nullI20201115-1800I20201115-0600I20201114-1800I20201114-0740I20201114-0600I20201113-1800

- add setVarTypeDeclaration() method to CastExpression to
  indicate when CastExpression is the initialization of a var type
- add logic in CastExpression to disable unnecessary cast checks
  if we are initializing a var type variable and the type of the cast
  and expression are not equal
- add logic in LocalDeclaration to call
  CastExpression.setVarTypeDeclaration() when appropriate
- add new test to CastTest

Change-Id: I43ac031a69796a14be3a00fc2656becec5b38b81
Signed-off-by: Jeff Johnston <jjohnstn@redhat.com>

3 files changed, 49 insertions, 0 deletions

diff --git a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CastTest.java b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CastTest.java
index 45f4e9e41e..c979cdf012 100644
--- a/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CastTest.java
+++ b/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/CastTest.java
@@ -3532,6 +3532,44 @@ public void test472466() {
 	runner.runWarningTest();
 }
 
+public void testBug561167() {
+	if (this.complianceLevel < ClassFileConstants.JDK10)
+		return;
+	Map customOptions = getCompilerOptions();
+	customOptions.put(CompilerOptions.OPTION_ReportUnnecessaryTypeCheck, CompilerOptions.ERROR);
+	runNegativeTest(
+		// test directory preparation
+		true /* flush output directory */,
+		new String[] { /* test files */
+			"X.java",
+			"public class X {\n" +
+			"	public static void main(String[] args) {\n" +
+			"		var s = (String) null;	// Necessary\n" +
+			"		var t = (String) \"hello\";	// UNnecessary\n" +
+			"		var f = (float) 12;			// Necessary\n" +
+			"		var g = (float)f;			// UNnecessary\n" +
+			"	}\n" +
+			"}\n"
+		},
+		// compiler options
+		null /* no class libraries */,
+		customOptions /* custom options */,
+		// compiler results
+		"----------\n" +
+		"1. ERROR in X.java (at line 4)\n" +
+		"	var t = (String) \"hello\";	// UNnecessary\n" +
+		"	        ^^^^^^^^^^^^^^^^\n" +
+		"Unnecessary cast from String to String\n" +
+		"----------\n" +
+		"2. ERROR in X.java (at line 6)\n" +
+		"	var g = (float)f;			// UNnecessary\n" +
+		"	        ^^^^^^^^\n" +
+		"Unnecessary cast from float to float\n" +
+		"----------\n",
+		// javac options
+		JavacTestOptions.Excuse.EclipseWarningConfiguredAsError /* javac test options */);
+}
+
 public static Class testClass() {
 	return CastTest.class;
 }
diff --git a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/CastExpression.java b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/CastExpression.java
index 38fa4fccbe..034482324c 100644
--- a/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/CastExpression.java
+++ b/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/CastExpression.java
@@ -65,6 +65,7 @@ public class CastExpression extends Expression {
 	public TypeReference type;
 	public TypeBinding expectedType; // when assignment conversion to a given expected type: String s = (String) t;
 	public TypeBinding instanceofType; // set by InstanceofExpression to ensure we don't flag a necessary cast unnecessary
+	public boolean isVarTypeDeclaration; // set by LocalDeclaration to indicate we are initializing a var type declaration
 
 //expression.implicitConversion holds the cast for baseType casting
 public CastExpression(Expression expression, TypeReference type) {
@@ -646,6 +647,9 @@ public TypeBinding resolveType(BlockScope scope) {
 					&& expressionType.isProvablyDistinct(this.instanceofType)) {
 				this.bits |= ASTNode.DisableUnnecessaryCastCheck;
 			}
+			if (this.isVarTypeDeclaration && TypeBinding.notEquals(expressionType, castType)) {
+				this.bits |= ASTNode.DisableUnnecessaryCastCheck;
+			}
 			boolean isLegal = checkCastTypesCompatibility(scope, castType, expressionType, this.expression, true);
 			if (isLegal) {
 				this.expression.computeConversion(scope, castType, expressionType);
@@ -731,6 +735,10 @@ public void setInstanceofType(TypeBinding instanceofTypeBinding) {
 	this.instanceofType = instanceofTypeBinding;
 }
 
+public void setVarTypeDeclaration(boolean value) {
+	this.isVarTypeDeclaration = value;
+}
+
 @Override
 public void traverse(ASTVisitor visitor, BlockScope blockScope) {
 	if (visitor.visit(this, blockScope)) {
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 0b6454b354..64c1c9a7b3 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
@@ -340,6 +340,9 @@ public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, Fl
 
 		if (variableType == null) {
 			if (this.initialization != null) {
+				if (this.initialization instanceof CastExpression) {
+					((CastExpression)this.initialization).setVarTypeDeclaration(true);
+				}
 				this.initialization.resolveType(scope); // want to report all possible errors
 				if (isTypeNameVar && this.initialization.resolvedType != null) {
 					if (TypeBinding.equalsEquals(TypeBinding.NULL, this.initialization.resolvedType)) {