C#: Add extractor support for the not null general type parameter constraint.

Author: michaelnebel

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

@@ -40,6 +40,9 @@ public override void Populate(TextWriter trapFile)
             if (Symbol.ReferenceTypeConstraintNullableAnnotation == NullableAnnotation.Annotated)
                 trapFile.general_type_parameter_constraints(this, 5);
 
+            if (Symbol.HasNotNullConstraint)
+                trapFile.general_type_parameter_constraints(this, 6);
+
             foreach (var abase in Symbol.GetAnnotatedTypeConstraints())
             {
                 var t = Type.Create(Context, abase.Symbol);

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

@@ -287,6 +287,9 @@ class TypeParameterConstraints extends Element, @type_parameter_constraints {
   /** Holds if these constraints include a nullable reference type constraint. */
   predicate hasNullableRefTypeConstraint() { general_type_parameter_constraints(this, 5) }
 
+  /** Holds if these constraints include a not-null type constraint. */
+  predicate hasNotNullTypeConstraint() { general_type_parameter_constraints(this, 6) }
+
   /** Gets a textual representation of these constraints. */
   override string toString() { result = "where " + this.getTypeParameter().getName() + ": ..." }
 

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

@@ -18,3 +18,5 @@ hasValueTypeConstraint
 hasUnmanagedTypeConstraint
 | TypeParameterConstraints.cs:10:20:10:21 | T3 | file://:0:0:0:0 | where T3: ... |
 hasNullableRefTypeConstraint
+hasNotNullConstraint
+| TypeParameterConstraints.cs:14:20:14:21 | T5 | file://:0:0:0:0 | where T5: ... |

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

@@ -29,3 +29,7 @@ query predicate hasUnmanagedTypeConstraint(TypeParameter tp, TypeParameterConstr
 query predicate hasNullableRefTypeConstraint(TypeParameter tp, TypeParameterConstraints tpc) {
   typeParameterContraints(tp, tpc) and tpc.hasNullableRefTypeConstraint()
 }
+
+query predicate hasNotNullConstraint(TypeParameter tp, TypeParameterConstraints tpc) {
+  typeParameterContraints(tp, tpc) and tpc.hasNotNullTypeConstraint()
+}