Add func<->constructor matching

src/org/rascalmpl/compiler/lang/rascalcore/check/ATypeInstantiation.rsc

@@ -192,6 +192,18 @@ public Bindings matchRascalTypeParams0(AType r, AType s, Bindings b) {
         return matchRascalTypeParams0(getFunctionReturnType(r), getFunctionReturnType(s), b);
     }
 
+    // A constructor can be used as a function (and vice versa during unification):
+    // match the parameter types with the fields, and the return type with the ADT
+    if ( isFunctionAType(r) && isConstructorAType(s) ) {
+        b = matchRascalTypeParams0(getFunctionArgumentTypesAsTuple(r), getConstructorArgumentTypesAsTuple(s), b);
+        return matchRascalTypeParams0(getFunctionReturnType(r), getConstructorResultType(s), b);
+    }
+
+    if ( isConstructorAType(r) && isFunctionAType(s) ) {
+        b = matchRascalTypeParams0(getConstructorArgumentTypesAsTuple(r), getFunctionArgumentTypesAsTuple(s), b);
+        return matchRascalTypeParams0(getConstructorResultType(r), getFunctionReturnType(s), b);
+    }
+
     // For tuples, check the arity then match the item types
     if ( isTupleAType(r) && isTupleAType(s) && getTupleFieldCount(r) == getTupleFieldCount(s) ) {
         rfields = getTupleFieldTypes(r);

src/org/rascalmpl/compiler/lang/rascalcore/check/tests/FunctionTCTests.rsc

@@ -111,4 +111,28 @@ test bool SyntaxConstructorAsArgNotOk(){
          void f(void(A) _) { }
 
       void main(){ f(a);  }");
-}
+}
+// https://github.com/usethesource/rascal/issues/2908
+test bool ADTConstructorAsArgToHigherOrderGenericFunctionOk(){
+   return checkModuleOK("
+      module ADTConstructorAsArgToHigherOrderGenericFunctionOk
+         data Msg = editField(str field, str val);
+
+         &T(&V) partial(&T(&U0, &V) f, &U0 u0) = &T(&V v) { return f(u0, v); };
+
+         void show(Msg(str) _) { }
+
+      void main(){ show(partial(editField, \"x\"));  }");
+}
+
+test bool ADTConstructorAsArgToHigherOrderGenericFunctionNotOk(){
+   return argumentMismatchInModule("
+      module ADTConstructorAsArgToHigherOrderGenericFunctionNotOk
+         data Msg = editField(str field, str val);
+
+         &T(&V) partial(&T(&U0, &V) f, &U0 u0) = &T(&V v) { return f(u0, v); };
+
+         void show(int(str) _) { }
+
+      void main(){ show(partial(editField, \"x\"));  }");
+}