Bug 545756 - Improve EvalBinding.isConstantExpression()

Previously, all variables with an initial value (even non-const)
were treated as constant expressions, now only constexpr variables,
static const members and global const variables are treated as constant expression.

Change-Id: I2acb4033a1f75110302ea25640afb070d025ec2b
Signed-off-by: Hannes Vogt <hannes@havogt.de>

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

@@ -13031,6 +13031,18 @@ public class AST2CPPTests extends AST2CPPTestBase {
 		parseAndCheckImplicitNameBindings();
 	}
 
+	//	struct A {
+	//	    int x;
+	//	};
+	//
+	//	template <typename T>
+	//	struct B {
+	//	    A a{sizeof(T)};
+	//	};
+	public void testAggregateInitNoNarrowingConversionInDependentConstContext_545756() throws Exception {
+		parseAndCheckImplicitNameBindings();
+	}
+
 	//  struct type{
 	//      int a;
 	//  };

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2TemplateTests.java

@@ -11282,4 +11282,20 @@ public class AST2TemplateTests extends AST2CPPTestBase {
 		helper.assertVariableValue("val1", 42);
 		helper.assertVariableValue("val2", 43);
 	}
+
+	//  template <typename T>
+	//  constexpr T id(T a) {
+	//      return a;
+	//  }
+	//
+	//  template <int> struct Waldo {using type = int;};
+	//
+	//  const int forty_two = 42;
+	//  using const_int_ref = int const&;
+	//  const_int_ref ref_forty_two = forty_two;
+	//
+	//  Waldo<id(ref_forty_two)>::type a;
+	public void testGlobalConstWorksAsConstExpression_545756() throws Exception {
+		parseAndCheckBindings();
+	}
 }

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/CPPVariable.java

@@ -202,7 +202,7 @@ public class CPPVariable extends PlatformObject implements ICPPInternalDeclaredV
 
 	@Override
 	public boolean isConstexpr() {
-		return VariableHelpers.isConstexpr(fDefinition);
+		return VariableHelpers.isConstexpr(fDefinition != null ? fDefinition : fDeclarations[0]);
 	}
 
 	@Override

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

@@ -103,8 +103,10 @@ class AggregateInitialization {
 			fIndex++;
 			// [dcl.init.aggr] If the initializer-clause is an expression and a narrowing conversion is
 			// required to convert the expression, the program is ill-formed.
-			if (!(initializer instanceof EvalInitList) && costWithoutElision.isNarrowingConversion()) {
-				return Cost.NO_CONVERSION;
+			if (!initializer.isConstantExpression()) {
+				if (!(initializer instanceof EvalInitList) && costWithoutElision.isNarrowingConversion()) {
+					return Cost.NO_CONVERSION;
+				}
 			}
 			if (costWithoutElision.compareTo(worstCost) > 0) {
 				worstCost = costWithoutElision;

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

@@ -32,6 +32,7 @@ import org.eclipse.cdt.core.dom.ast.IProblemBinding;
 import org.eclipse.cdt.core.dom.ast.IType;
 import org.eclipse.cdt.core.dom.ast.IValue;
 import org.eclipse.cdt.core.dom.ast.IVariable;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPField;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPFunction;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPParameter;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPParameterPackType;
@@ -257,8 +258,24 @@ public class EvalBinding extends CPPDependentEvaluation {
 	}
 
 	private boolean computeIsConstantExpression() {
-		return fBinding instanceof IEnumerator || fBinding instanceof ICPPFunction
-				|| (fBinding instanceof IVariable && isConstexprValue(((IVariable) fBinding).getInitialValue()));
+		if (fBinding instanceof IEnumerator || fBinding instanceof ICPPFunction)
+			return true;
+		else if (fBinding instanceof ICPPVariable) {
+			if (!isConstexprValue(((IVariable) fBinding).getInitialValue()))
+				return false;
+			ICPPVariable var = (ICPPVariable) fBinding;
+			if (var.isConstexpr())
+				return true;
+			IType type = SemanticUtil.getNestedType(var.getType(), SemanticUtil.TDEF | SemanticUtil.REF);
+			if (ExpressionTypes.isConst(type)) {
+				if (var instanceof ICPPField) {
+					if (var.isStatic())
+						return true;
+				} else
+					return true;
+			}
+		}
+		return false;
 	}
 
 	@Override

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

@@ -113,7 +113,7 @@ public class ExpressionTypes {
 		return type;
 	}
 
-	private static boolean isConst(IType type) {
+	public static boolean isConst(IType type) {
 		if (type instanceof IQualifierType) {
 			return ((IQualifierType) type).isConst();
 		} else if (type instanceof IPointerType) {