Bug 470943 - Binding of rvalue reference to temporary (core issue 1138)

Change-Id: I9524816b279e3f791535b11b54d475cf657fe64b
Signed-off-by: Nathan Ridge <zeratul976@hotmail.com>

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPSpecTest.java

@@ -2389,39 +2389,95 @@ public class AST2CPPSpecTest extends AST2SpecTestBase {
 		parse(getAboveComment(), ParserLanguage.CPP, true, 0);
 	}
 
-	// double d = 2.0;
+	// Note: the examples for 8.5.3/5 are written slightly differently
-	// double& rd = d; // rd refers to d
+	// than they appear in the standard. In the standard, the examples
-	// const double& rcd = d; // rcd refers to d
+	// demonstrate the rules with variable initialiation, but CDT doesn't
-	// struct A { };
+	// currently issue problem bindings for variable initialization,
-	// struct B : public A { } b;
+	// so in the tests the examples are rewritten to use function calls.
-	// A& ra = b; // ra refers to A subobject in b
+	
-	// const A& rca = b; // rca refers to A subobject in b
+	//	void f1(double);
+	//	void f2(double&);
+	//	void f3(const double&);
+	//	struct A { };
+	//	struct B : public A { operator int&(); } b;
+	//	void f4(A&);
+	//	void f5(const A&);
+	//	void f6(int&);
+	//	int main() {
+	//		f1(2.0);
+	//		double d;
+	//		f2(d);
+	//		f3(d);
+	//		f4(b);
+	//		f5(b);
+	//		f6(B());
+	//	}
 	public void test8_5_3s5a() throws Exception {
 		parse(getAboveComment(), ParserLanguage.CPP, true, 0);
 	}
 
-	// double& rd2 = 2.0; // error: not an lvalue and reference not const
+	//	void f1(double&);
-	// int i = 2;
+	//	void f2(double&);
-	// double& rd3 = i; // error: type mismatch and reference not const
+	//	int main() {
+	//		f1(2.0);  // error: not an lvalue and reference not const
+	//		int i = 2;
+	//		f2(i);    // error: type mismatch and reference not const
+	//	}
 	public void test8_5_3s5b() throws Exception {
-		parse(getAboveComment(), ParserLanguage.CPP, true, 0);
+		BindingAssertionHelper helper = getAssertionHelper(ParserLanguage.CPP);
+		helper.assertProblem("f1(2", "f1");
+		helper.assertProblem("f2(i", "f2");
 	}
 
-	// struct A { };
+	//	struct A { };
-	// struct B : public A { } b;
+	//	struct B : public A { } b;
-	// extern B f();
+	//	extern B f();
-	// const A& rca = f(); // Either bound to the A subobject of the B rvalue,
+	//	void f1(const A&);
-	// // or the entire B object is copied and the reference
+	//	void f2(A&&);
-	// // is bound to the A subobject of the copy
+	//	struct X {
+	//		operator B();
+	//		operator int&();
+	//	} x;
+	//	void f3(int&&);
+	//	void f4(B&&);
+	//	int main() {
+	//		f1(f());  // bound to the A subobject of the B rvalue
+	//		f2(f());  // same as above
+	//		f1(x);    // bound to the A subobject of the result of the conversion
+	//		f3(static_cast<int&&>(i));  // bound directly to i
+	//		f4(x);    // bound directly to the result of operator B
+	//		f3(X());  // error: lvalue-to-rvalue conversion applied to result of operator int&
+	//	}
 	public void test8_5_3s5c() throws Exception {
-		parse(getAboveComment(), ParserLanguage.CPP, true, 0);
+		BindingAssertionHelper helper = getAssertionHelper(ParserLanguage.CPP);
+		helper.assertNonProblem("f1(f", "f1");
+		helper.assertNonProblem("f2(f", "f2");
+		helper.assertNonProblem("f1(x", "f1");
+		helper.assertNonProblem("f3(s", "f3");
+		helper.assertNonProblem("f4(x", "f4");
+		helper.assertProblem("f3(X", "f3");
 	}
 
-	// const double& rcd2 = 2; // rcd2 refers to temporary with value 2.0
+	//	void f1(const double&);
-	// const volatile int cvi = 1;
+	//	void f2(double&&);
-	// const int& r = cvi; // error: type qualifiers dropped
+	//	void f3(const int&);
+	//	int main() {
+	//		f1(2);
+	//		f2(2);
+	//		const volatile int cvi = 1;
+	//		f3(cvi);  // error: type qualifiers dropped
+	//		double d;
+	//		int i;
+	//		f2(d);    // error: copying lvalue of related type
+	//		f2(i);
+	//	}
 	public void test8_5_3s5d() throws Exception {
-		parse(getAboveComment(), ParserLanguage.CPP, true, 0);
+		BindingAssertionHelper helper = getAssertionHelper(ParserLanguage.CPP);
+		helper.assertNonProblem("f1(2", "f1");
+		helper.assertNonProblem("f2(2", "f2");
+		helper.assertProblem("f3(cv", "f3");
+		helper.assertProblem("f2(d)", "f2");
+		helper.assertNonProblem("f2(i", "f2");
 	}
 
 	// struct X { int a; };

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java

@@ -8281,7 +8281,7 @@ public class AST2CPPTests extends AST2TestBase {
 	//    caref(b);
 	//	  dref(2.0); // error: not an lvalue and reference not const
 	//	  dref(i);   // error: type mismatch and reference not const
-	//	  drref(i);  // error: rvalue reference cannot bind to lvalue
+	//	  drref(i);  // bound to temporary double object
 	//    caref(f());  // bound to the A subobject of the B rvalue.
 	//    carref(f()); // same as above
 	//    caref(x);    // bound to the A subobject of the result of the conversion
@@ -8298,7 +8298,7 @@ public class AST2CPPTests extends AST2TestBase {
 		bh.assertNonProblem("caref(b)", 5);
 		bh.assertProblem("dref(2.0)", 4);
 		bh.assertProblem("dref(i)", 4);
-		bh.assertProblem("drref(i)", 5);
+		bh.assertNonProblem("drref(i)", 5);
 		bh.assertNonProblem("caref(f())", 5);
 		bh.assertNonProblem("carref(f())", 6);
 		bh.assertNonProblem("caref(x)", 5);
@@ -11102,6 +11102,16 @@ public class AST2CPPTests extends AST2TestBase {
 		isParameterSignatureEqual(sd.getDeclarators()[0], "(int&&)");
 	}
 	
+	//	struct S { S(int); };
+	//	void find(S&&);
+	//	int main() {
+	//		int waldo = 42;
+	//		find(waldo);
+	//	}
+	public void testRValueReferenceBindingToTemporary_470943() throws Exception {
+		parseAndCheckBindings();
+	}
+	
 	//	constexpr int waldo1 = 42;
 	//	constexpr auto waldo2 = 43;
 	public void testConstexprVariableIsConst_451091() throws Exception {

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/Conversions.java

@@ -153,7 +153,7 @@ public class Conversions {
 				// 'cv3 T3' (this conversion is selected by enumerating the applicable conversion functions (13.3.1.6)
 				// and choosing the best one through overload resolution (13.3)),
 				if (T2 instanceof ICPPClassType && udc != UDCMode.FORBIDDEN && isReferenceRelated(T1, T2, point) < 0) {
-					Cost cost= initializationByConversionForDirectReference(cv1T1, cv2T2, (ICPPClassType) T2, true, ctx, point);
+					Cost cost= initializationByConversionForDirectReference(cv1T1, cv2T2, (ICPPClassType) T2, true, false, ctx, point);
 					if (cost != null) {
 						cost.setReferenceBinding(refBindingType);
 						return cost;
@@ -162,97 +162,65 @@ public class Conversions {
 			}
 
 			// Otherwise, the reference shall be an lvalue reference to a non-volatile const type (i.e., cv1
-			// shall be const), or the reference shall be an rvalue reference and the initializer expression
+			// shall be const), or the reference shall be an rvalue reference.
-			// shall be an rvalue or have function type.
+			if (isLValueRef && getCVQualifier(cv1T1) != CVQualifier.CONST) {
-			boolean ok;
-			if (isLValueRef) {
-				ok = getCVQualifier(cv1T1) == CVQualifier.CONST;
-			} else {
-				ok= valueCat.isRValue() || T2 instanceof IFunctionType;
-			}
-			if (!ok) {
 				return Cost.NO_CONVERSION;
 			}
-
+			
-			// If T1 is a function type, then
+			// If the initializer expression is an xvalue, class prvalue, array prvalue, or function lvalue 
-			if (T1 instanceof IFunctionType) {
+			// and 'cv1 T1' is reference-compatible with 'cv2 T2', then the reference is bound to the value
-				// if T2 is the same type as T1, the reference is bound to the initializer expression lvalue;
+			// of the initializer expression (or the appropriate base class subobject).
-				if (T2.isSameType(T1)) {
+			if (valueCat == ValueCategory.XVALUE
-					Cost cost= new Cost(T1, T2, Rank.IDENTITY);
+			    || (valueCat == ValueCategory.PRVALUE && (T2 instanceof ICPPClassType || T2 instanceof IArrayType))
-					cost.setReferenceBinding(refBindingType);
+			    || (valueCat == ValueCategory.LVALUE && T2 instanceof ICPPFunctionType)) {
-					return cost;
+				Cost cost = isReferenceCompatible(cv1T1, cv2T2, isImpliedObject, point);
-				}
-				// if T2 is a class type and the initializer expression can be implicitly converted to an lvalue of
-				// type T1 (this conversion is selected by enumerating the applicable conversion functions (13.3.1.6)
-				// and choosing the best one through overload resolution (13.3)), the reference is bound to the
-				// function lvalue that is the result of the conversion;
-				if (T2 instanceof ICPPClassType) {
-					Cost cost= initializationByConversionForDirectReference(cv1T1, cv2T2, (ICPPClassType) T2, true, ctx, point);
-					if (cost != null) {
-						cost.setReferenceBinding(refBindingType);
-						return cost;
-					}
-				}
-				// otherwise, the program is ill-formed.
-				return Cost.NO_CONVERSION;
-			}
-
-			// Otherwise, if T2 is a class type and
-			if (T2 instanceof ICPPClassType) {
-				// ... the initializer expression is an rvalue and 'cv1 T1' is reference-compatible with 'cv2 T2'
-				// ..., then the reference is bound to the initializer expression rvalue in the first case
-				if (valueCat.isRValue()) {
-					Cost cost= isReferenceCompatible(cv1T1, cv2T2, isImpliedObject, point);
-					if (cost != null) {
-						// [13.3.3.1.4-1] direct binding has either identity or conversion rank.
-						if (cost.getInheritanceDistance() > 0) {
-							cost.setRank(Rank.CONVERSION);
-						}
-						cost.setReferenceBinding(refBindingType);
-						return cost;
-					}
-				}
-
-				// or T1 is not reference-related to T2 and the initializer expression can be implicitly
-				// converted to an rvalue of type 'cv3 T3' (this conversion is selected by enumerating the
-				// applicable conversion functions (13.3.1.6) and choosing the best one through overload
-				// resolution (13.3)), then the reference is bound to the initializer expression rvalue in the
-				// first case and to the object that is the result of the conversion in the second case (or,
-				// in either case, to the appropriate base class sub-object of the object).
-				if (udc != UDCMode.FORBIDDEN && isReferenceRelated(T1, T2, point) < 0) {
-					Cost cost= initializationByConversionForDirectReference(cv1T1, cv2T2, (ICPPClassType) T2, false, ctx, point);
-					if (cost != null) {
-						cost.setReferenceBinding(refBindingType);
-						return cost;
-					}
-				}
-			}
-
-			// If the initializer expression is an rvalue, with T2 an array type, and 'cv1 T1' is
-			// reference-compatible with 'cv2 T2' the reference is bound to the object represented by the
-			// rvalue (see 3.10).
-			if (T2 instanceof IArrayType && valueCat.isRValue()) {
-				Cost cost= isReferenceCompatible(cv1T1, cv2T2, isImpliedObject, point);
 				if (cost != null) {
 					cost.setReferenceBinding(refBindingType);
 					return cost;
 				}
 			}
+			
+			// If the initializer expression has class type (i.e. T2 is a class type), where T1 is not
+			// reference-related to T2, and can be implicitly converted to an xvalue, class prvalue,
+			// or function lvalue of type 'cv3 T3', where 'cv1 T1' is reference-compatible with 'cv3 T3',
+			// then the reference is bound to the result of the conversion (or the appropriate base class
+			// subobject). If the reference is an rvalue reference and the second standard conversion
+			// sequence of the user-defined conversion sequence includes an lvalue-to-rvalue
+			// conversion, the program is ill-formed [this is why we pass illFormedIfLValue = true].
+			if (T2 instanceof ICPPClassType) {
+				if (udc != UDCMode.FORBIDDEN && isReferenceRelated(T1, T2, point) < 0) {
+					Cost cost= initializationByConversionForDirectReference(cv1T1, cv2T2, (ICPPClassType) T2, false, true, ctx, point);
+					if (cost != null) {
+						if (cost != Cost.NO_CONVERSION) {
+							cost.setReferenceBinding(refBindingType);
+						}
+						return cost;
+					}
+				}
+			}
 
 			// Otherwise, a temporary of type 'cv1 T1' is created and initialized from the initializer
 			// expression using the rules for a non-reference copy initialization (8.5). The reference is then
-			// bound to the temporary. If T1 is reference-related to T2, cv1 must be the same cv-qualification
+			// bound to the temporary.
-			// as, or greater cv-qualification than, cv2; otherwise, the program is ill-formed.
 
 			// 13.3.3.1.7 no temporary object when converting the implicit object parameter
 			if (!isImpliedObject && ctx != Context.REQUIRE_DIRECT_BINDING) {
-				if (isReferenceRelated(T1, T2, point) < 0 || compareQualifications(cv1T1, cv2T2) >= 0) {
+				Cost cost= nonReferenceConversion(valueCat, cv2T2, T1, udc, point);
-					Cost cost= nonReferenceConversion(valueCat, cv2T2, T1, udc, point);
+				if (cost.converts()) {
-					if (cost.converts()) {
+					cost.setReferenceBinding(refBindingType);
-						cost.setReferenceBinding(refBindingType);
-					}
-					return cost;
 				}
+				boolean referenceRelated = isReferenceRelated(T1, T2, point) >= 0;
+				// If T1 is reference-related to T2, cv1 shall be the same cv-qualification as,
+				// or greater cv-qualification than, cv2.
+				if (referenceRelated && compareQualifications(cv1T1, cv2T2) < 0) {
+					return Cost.NO_CONVERSION;
+				}
+				// if T1 is reference-related to T2 and the reference is an rvalue reference,
+				// the initializer expression shall not be an lvalue.
+				if (referenceRelated && !isLValueRef && valueCat == ValueCategory.LVALUE) {
+					return Cost.NO_CONVERSION;
+				}
+				return cost;
 			}
 			return Cost.NO_CONVERSION;
 		}
@@ -263,9 +231,15 @@ public class Conversions {
 
 	/**
 	 * C++0x: 13.3.1.6 Initialization by conversion function for direct reference binding
-	 * @param point
+	 * @param needLValue don't consider conversion functions that return rvalue references
+	 * @param illFormedIfLValue make the conversion ill-formed (by returning Cost.NO_CONVERSION)
+	 *                          if the best match is a conversion function that returns an
+	 *                          lvalue reference
+	 * Note that there's a difference between returning null and returning Cost.NO_CONVERSION:
+	 * in the former case, the caller will continue trying other conversion methods.
 	 */
-	private static Cost initializationByConversionForDirectReference(final IType cv1T1, final IType cv2T2, final ICPPClassType T2, boolean needLValue, Context ctx, IASTNode point)
+	private static Cost initializationByConversionForDirectReference(final IType cv1T1, final IType cv2T2, final ICPPClassType T2, 
+			boolean needLValue, boolean illFormedIfLValue, Context ctx, IASTNode point)
 			throws DOMException {
 		ICPPMethod[] fcns= SemanticUtil.getConversionOperators(T2, point);
 		Cost operatorCost= null;
@@ -281,21 +255,26 @@ public class Conversions {
 				final ICPPFunctionType ft = op.getType();
 				IType t= getNestedType(ft.getReturnType(), TDEF);
 				final boolean isLValueRef= t instanceof ICPPReferenceType && !((ICPPReferenceType) t).isRValueReference();
-				if (isLValueRef == needLValue) { // require an lvalue or rvalue
+				if (needLValue && !isLValueRef) {
-					IType implicitParameterType= CPPSemantics.getImplicitParameterType(op);
+					continue;
-					Cost udcCost= isReferenceCompatible(getNestedType(implicitParameterType, TDEF | REF), cv2T2, true, point); // expression type to implicit object type
+				}
-					if (udcCost != null) {
+				IType implicitParameterType= CPPSemantics.getImplicitParameterType(op);
-						// Make sure top-level cv-qualifiers are compared
+				Cost udcCost= isReferenceCompatible(getNestedType(implicitParameterType, TDEF | REF), cv2T2, true, point); // expression type to implicit object type
-						udcCost.setReferenceBinding(ReferenceBinding.LVALUE_REF);
+				if (udcCost != null) {
-						FunctionCost udcFuncCost= new FunctionCost(op, udcCost, point);
+					// Make sure top-level cv-qualifiers are compared
-						int cmp= udcFuncCost.compareTo(null, bestUdcCost);
+					udcCost.setReferenceBinding(ReferenceBinding.LVALUE_REF);
-						if (cmp <= 0) {
+					FunctionCost udcFuncCost= new FunctionCost(op, udcCost, point);
-							Cost cost= isReferenceCompatible(cv1T1, getNestedType(t, TDEF | REF), false, point); // converted to target
+					int cmp= udcFuncCost.compareTo(null, bestUdcCost);
-							if (cost != null) {
+					if (cmp <= 0) {
-								bestUdcCost= udcFuncCost;
+						Cost cost= isReferenceCompatible(cv1T1, getNestedType(t, TDEF | REF), false, point); // converted to target
-								ambiguousConversionOperator= cmp == 0;
+						if (cost != null) {
-								operatorCost= cost;
+							bestUdcCost= udcFuncCost;
-								operatorCost.setUserDefinedConversion(op);
+							ambiguousConversionOperator= cmp == 0;
+							operatorCost= cost;
+							operatorCost.setUserDefinedConversion(op);
+							
+							if (illFormedIfLValue && isLValueRef) {
+								operatorCost = Cost.NO_CONVERSION;
 							}
 						}
 					}