C++: Deprecate ConversionConstructor.

cpp/ql/src/semmle/code/cpp/MemberFunction.qll

@@ -214,6 +214,9 @@ abstract class ImplicitConversionFunction extends MemberFunction {
 }
 
 /**
+ * DEPRECATED: as of C++11 this class does not correspond perfectly with the
+ * language definition of a converting constructor.
+ *
  * A C++ constructor that also defines an implicit conversion. For example the
  * function `MyClass` in the following code is a `ConversionConstructor`:
  * ```
@@ -225,7 +228,7 @@ abstract class ImplicitConversionFunction extends MemberFunction {
  * };
  * ```
  */
-class ConversionConstructor extends Constructor, ImplicitConversionFunction {
+deprecated class ConversionConstructor extends Constructor, ImplicitConversionFunction {
   ConversionConstructor() {
     strictcount(Parameter p | p = getAParameter() and not p.hasInitializer()) = 1 and
     not hasSpecifier("explicit")

cpp/ql/src/semmle/code/cpp/models/implementations/MemberFunction.qll

@@ -7,9 +7,18 @@ import semmle.code.cpp.models.interfaces.DataFlow
 import semmle.code.cpp.models.interfaces.Taint
 
 /**
- * Model for C++ conversion constructors.
+ * Model for C++ conversion constructors. As of C++11 this does not correspond
+ * perfectly with the language definition of a converting constructor, however,
+ * it does correspond with the constructors we are confident taint should flow
+ * through.
  */
-class ConversionConstructorModel extends ConversionConstructor, TaintFunction {
+class ConversionConstructorModel extends Constructor, TaintFunction {
+  ConversionConstructorModel()
+  {
+    strictcount(Parameter p | p = getAParameter() and not p.hasInitializer()) = 1 and
+    not hasSpecifier("explicit")
+  }
+
   override predicate hasTaintFlow(FunctionInput input, FunctionOutput output) {
     // taint flow from the first constructor argument to the returned object
     input.isParameter(0) and