Type of UnresolvedSymbol is Function (#6284)

`Meta.is_a` and `Meta.type_of` now recognize UnresolvedSymbol.
Closes #6277.

engine/runtime-with-instruments/src/test/scala/org/enso/interpreter/test/instrument/RuntimeServerTest.scala

@@ -3622,7 +3622,7 @@ class RuntimeServerTest
           contextId,
           Seq(
             Api.ExecutionResult.Diagnostic.error(
-              "Type error: expected `that` to be Number, but got quux (Unresolved_Symbol).",
+              "Type error: expected `that` to be Number, but got Function.",
               Some(mainFile),
               Some(model.Range(model.Position(11, 8), model.Position(11, 17))),
               None,

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/meta/IsValueOfTypeNode.java

@@ -12,6 +12,7 @@ import com.oracle.truffle.api.profiles.ConditionProfile;
 import org.enso.interpreter.epb.runtime.PolyglotExceptionProxy;
 import org.enso.interpreter.epb.runtime.PolyglotProxy;
 import org.enso.interpreter.runtime.EnsoContext;
+import org.enso.interpreter.runtime.callable.UnresolvedSymbol;
 import org.enso.interpreter.runtime.callable.atom.AtomConstructor;
 import org.enso.interpreter.runtime.data.Type;
 import org.enso.interpreter.runtime.library.dispatch.TypesLibrary;
@@ -66,6 +67,12 @@ public abstract class IsValueOfTypeNode extends Node {
     return checkParentTypes(numbers.getBigInteger(), expectedType);
   }
 
+  @Specialization
+  boolean doUresolvedSymbol(Type expectedType, UnresolvedSymbol value) {
+    var funTpe = EnsoContext.get(this).getBuiltins().function();
+    return expectedType == funTpe;
+  }
+
   @ExplodeLoop
   private boolean checkParentTypes(Type actual, Type expected) {
     for (; ; ) {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/meta/TypeOfNode.java

@@ -13,6 +13,7 @@ import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.epb.runtime.PolyglotProxy;
 import org.enso.interpreter.runtime.EnsoContext;
 import org.enso.interpreter.runtime.builtin.Builtins;
+import org.enso.interpreter.runtime.callable.UnresolvedSymbol;
 import org.enso.interpreter.runtime.data.text.Text;
 import org.enso.interpreter.runtime.error.DataflowError;
 import org.enso.interpreter.runtime.error.PanicException;
@@ -36,6 +37,11 @@ public abstract class TypeOfNode extends Node {
     return TypeOfNodeGen.create();
   }
 
+  @Specialization
+  Object doUnresolvedSymbol(UnresolvedSymbol value) {
+    return EnsoContext.get(this).getBuiltins().function();
+  }
+
   @Specialization
   Object doDouble(double value) {
     return EnsoContext.get(this).getBuiltins().number().getDecimal();

test/Tests/src/Semantic/Case_Spec.enso

@@ -301,4 +301,9 @@ spec = Test.group "Pattern Matches" <|
             _ : Any -> Nothing
             _ -> Test.fail "Expected to match on Any."
 
+    Test.specify "should allow for pattern matching on unresolved symbol" <|
+        case (.name) of
+            _ : Function -> Nothing
+            _ -> Test.fail "Expected to match on Function type."
+
 main = Test_Suite.run_main spec

test/Tests/src/Semantic/Meta_Spec.enso

@@ -1,4 +1,5 @@
 from Standard.Base import all
+from Standard.Base.Function import Function
 import Standard.Base.Errors.File_Error.File_Error
 import Standard.Base.Errors.Illegal_Argument.Illegal_Argument
 from Standard.Base.Errors.Common import Uninitialized_State
@@ -358,5 +359,10 @@ spec =
             case atom.bar of
                 n : Number -> Test.fail "Not changed to number: "+n
                 _ -> Nothing
-
+    Test.group "Unresolved symbol"
+        Test.specify "should be treated as a Function" <|
+            (_.is_nothing) . is_a Function . should_equal True
+            (.is_nothing) . is_a Function . should_equal True
+            Meta.type_of (_.is_nothing) . should_equal Function
+            Meta.type_of (.is_nothing) . should_equal Function
 main = Test_Suite.run_main spec