C#: Add extractor support for the allows ref struct general type parameter constraint.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/TypeParameterConstraints.cs

@@ -43,6 +43,9 @@ public override void Populate(TextWriter trapFile)
             if (Symbol.HasNotNullConstraint)
                 trapFile.general_type_parameter_constraints(this, 6);
 
+            if (Symbol.AllowsRefLikeType)
+                trapFile.general_type_parameter_constraints(this, 7);
+
             foreach (var abase in Symbol.GetAnnotatedTypeConstraints())
             {
                 var t = Type.Create(Context, abase.Symbol);

csharp/ql/lib/semmle/code/csharp/Generics.qll

@@ -290,6 +290,9 @@ class TypeParameterConstraints extends Element, @type_parameter_constraints {
   /** Holds if these constraints include a notnull type constraint. */
   predicate hasNotNullTypeConstraint() { general_type_parameter_constraints(this, 6) }
 
+  /** Holds if these constraints include a `allows ref struct` constraint. */
+  predicate hasAllowRefLikeTypeConstraint() { general_type_parameter_constraints(this, 7) }
+
   /** Gets a textual representation of these constraints. */
   override string toString() { result = "where " + this.getTypeParameter().getName() + ": ..." }
 

csharp/ql/test/library-tests/typeparameterconstraints/typeParameterConstraints.expected

@@ -20,3 +20,5 @@ hasUnmanagedTypeConstraint
 hasNullableRefTypeConstraint
 hasNotNullConstraint
 | TypeParameterConstraints.cs:14:20:14:21 | T5 | file://:0:0:0:0 | where T5: ... |
+hasAllowRefLikeTypeConstraint
+| TypeParameterConstraints.cs:18:20:18:21 | T7 | file://:0:0:0:0 | where T7: ... |

csharp/ql/test/library-tests/typeparameterconstraints/typeParameterConstraints.ql

@@ -33,3 +33,7 @@ query predicate hasNullableRefTypeConstraint(TypeParameter tp, TypeParameterCons
 query predicate hasNotNullConstraint(TypeParameter tp, TypeParameterConstraints tpc) {
   typeParameterContraints(tp, tpc) and tpc.hasNotNullTypeConstraint()
 }
+
+query predicate hasAllowRefLikeTypeConstraint(TypeParameter tp, TypeParameterConstraints tpc) {
+  typeParameterContraints(tp, tpc) and tpc.hasAllowRefLikeTypeConstraint()
+}