UnresolvedSymbol is now accepted by Vector.sort (#6334)

`Vector.sort` does some custom method dispatch logic which always expected a function as `by` and `on` arguments. At the same time, `UnresolvedSymbol` is treated like a (to be resolved) `Function` and under normal circumstances there would be no difference between `_.foo` and `.foo` provided as arguments.

Rather than adding an additional phase that does some form of eta-expansion, to accomodate for this custom dispatch, this change only fixes the problem locally. We accept `Function` and `UnresolvedSymbol` and perform the resolution on the fly. Ideally, we would have a specialization on the latter but again, it would be dependent on the contents of the `Vector` so unclear if that is better.

Closes #6276,

# Important Notes
There was a suggestion to somehow modify our codegen to accomodate for this scenario but I went against it. In fact a lot of name literals have `isMethod` flag and that information is used in the passes but it should not control how (late) codegen is done. If we were to make this more generic, I would suggest maybe to add separate eta-expansion pass. But it could affect other things and could be potentially a significant change with limited potential initially, so potential future work item.

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/ordering/SortVectorNode.java

@@ -22,11 +22,13 @@ import java.util.stream.Collectors;
 import org.enso.interpreter.dsl.AcceptsError;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.node.callable.dispatch.CallOptimiserNode;
+import org.enso.interpreter.node.callable.resolver.MethodResolverNode;
 import org.enso.interpreter.node.expression.builtin.interop.syntax.HostValueToEnsoNode;
 import org.enso.interpreter.node.expression.builtin.meta.EqualsNode;
 import org.enso.interpreter.node.expression.builtin.meta.TypeOfNode;
 import org.enso.interpreter.node.expression.builtin.text.AnyToTextNode;
 import org.enso.interpreter.runtime.EnsoContext;
+import org.enso.interpreter.runtime.callable.UnresolvedSymbol;
 import org.enso.interpreter.runtime.callable.atom.Atom;
 import org.enso.interpreter.runtime.callable.function.Function;
 import org.enso.interpreter.runtime.data.Array;
@@ -39,6 +41,7 @@ import org.enso.interpreter.runtime.error.PanicException;
 import org.enso.interpreter.runtime.error.Warning;
 import org.enso.interpreter.runtime.error.WarningsLibrary;
 import org.enso.interpreter.runtime.error.WithWarnings;
+import org.enso.interpreter.runtime.library.dispatch.TypesLibrary;
 import org.enso.interpreter.runtime.state.State;
 
 /**
@@ -179,10 +182,12 @@ public abstract class SortVectorNode extends Node {
       long problemBehaviorNum,
       @CachedLibrary(limit = "10") InteropLibrary interop,
       @CachedLibrary(limit = "5") WarningsLibrary warningsLib,
+      @CachedLibrary(limit = "5") TypesLibrary typesLib,
       @Cached LessThanNode lessThanNode,
       @Cached EqualsNode equalsNode,
       @Cached TypeOfNode typeOfNode,
       @Cached AnyToTextNode toTextNode,
+      @Cached MethodResolverNode methodResolverNode,
       @Cached(value = "build()", uncached = "build()") HostValueToEnsoNode hostValueToEnsoNode,
       @Cached(value = "build()", uncached = "build()") CallOptimiserNode callNode) {
     var problemBehavior = ProblemBehavior.fromInt((int) problemBehaviorNum);
@@ -230,7 +235,9 @@ public abstract class SortVectorNode extends Node {
                   less,
                   equal,
                   greater,
-                  interop);
+                  interop,
+                  typesLib,
+                  methodResolverNode);
         }
         group.elems.sort(javaComparator);
         if (javaComparator.hasWarnings()) {
@@ -647,6 +654,94 @@ public abstract class SortVectorNode extends Node {
     }
   }
 
+  /**
+   * Helper class that returns the comparator function.
+   *
+   * The class is introduced to handle the presence of {@code UnresolvedSymbol},
+   * as the comparator function, which has to be first resolved before it
+   * can be used to compare values.
+   */
+  private abstract class Compare {
+
+    /**
+     * Test if the comparator function has self argument.
+     *
+     * @param definedOn the value on which the function is defined on.
+     * @return true if self argument is present, false otherwise.
+     */
+    abstract boolean hasFunctionSelfArgument(Object definedOn);
+
+    /**
+     * Return a comparator function.
+     *
+     * @param arg the value on which the function is defined on.
+     * @return a non-null comparator function.
+     */
+    abstract Function get(Object arg);
+
+  }
+
+  private final class CompareFromFunction extends Compare {
+
+    private final Function function;
+
+    private CompareFromFunction(Function function) {
+      this.function = function;
+    }
+
+    @Override
+    boolean hasFunctionSelfArgument(Object definedOn) {
+      if (function.getSchema().getArgumentsCount() > 0) {
+        return function.getSchema().getArgumentInfos()[0].getName().equals("self");
+      } else {
+        return false;
+      }
+    }
+
+    @Override
+    Function get(Object arg) {
+      return function;
+    }
+  }
+
+  private class CompareFromUnresolvedSymbol extends Compare {
+
+    private final UnresolvedSymbol unresolvedSymbol;
+    private final MethodResolverNode methodResolverNode;
+    private final TypesLibrary typesLibrary;
+
+    private @CompilerDirectives.CompilationFinal Function resolvedFunction;
+
+    private CompareFromUnresolvedSymbol(UnresolvedSymbol unresolvedSymbol,
+                                        MethodResolverNode methodResolvedNode,
+                                        TypesLibrary typesLibrary) {
+      this.unresolvedSymbol = unresolvedSymbol;
+      this.methodResolverNode = methodResolvedNode;
+      this.typesLibrary = typesLibrary;
+
+    }
+
+    @Override
+    boolean hasFunctionSelfArgument(Object definedOn) {
+      ensureSymbolIsResolved(definedOn);
+      return resolvedFunction.getSchema().getArgumentsCount() > 0 &&
+        resolvedFunction.getSchema().getArgumentInfos()[0].getName().equals("self");
+
+    }
+
+    @Override
+    Function get(Object arg) {
+      ensureSymbolIsResolved(arg);
+      return resolvedFunction;
+    }
+
+    private void ensureSymbolIsResolved(Object definedOn) {
+      if (resolvedFunction == null) {
+        resolvedFunction = methodResolverNode.expectNonNull(definedOn, typesLibrary.getType(definedOn), unresolvedSymbol);
+      }
+    }
+  }
+
   /**
    * Comparator for any values. This comparator compares the values by calling back to Enso (by
    * {@link #compareFunc}), rather than using compare nodes (i.e. {@link LessThanNode}). directly,
@@ -659,9 +754,9 @@ public abstract class SortVectorNode extends Node {
      * Either function from `by` parameter to the `Vector.sort` method, or the `compare` function
      * extracted from the comparator for the appropriate group.
      */
-    private final Function compareFunc;
+    private final Compare compareFunc;
 
-    private final Function onFunc;
+    private final Compare onFunc;
     private final boolean hasCustomOnFunc;
     private final Type comparator;
     private final CallOptimiserNode callNode;
@@ -682,20 +777,22 @@ public abstract class SortVectorNode extends Node {
         Atom less,
         Atom equal,
         Atom greater,
-        InteropLibrary interop) {
+        InteropLibrary interop,
+        TypesLibrary typesLibrary,
+        MethodResolverNode methodResolverNode) {
       super(toTextNode, problemBehavior, interop);
       assert compareFunc != null;
       assert comparator != null;
       this.comparator = comparator;
       this.state = state;
       this.ascending = ascending;
-      this.compareFunc = checkAndConvertByFunc(compareFunc);
+      this.compareFunc = checkAndConvertByFunc(compareFunc, typesLibrary, methodResolverNode);
       if (interop.isNull(onFunc)) {
         this.hasCustomOnFunc = false;
         this.onFunc = null;
       } else {
         this.hasCustomOnFunc = true;
-        this.onFunc = checkAndConvertOnFunc(onFunc);
+        this.onFunc = checkAndConvertOnFunc(onFunc, typesLibrary, methodResolverNode);
       }
       this.callNode = callNode;
       this.less = less;
@@ -709,19 +806,19 @@ public abstract class SortVectorNode extends Node {
       Object yConverted;
       if (hasCustomOnFunc) {
         // onFunc cannot have `self` argument, we assume it has just one argument.
-        xConverted = callNode.executeDispatch(onFunc, null, state, new Object[] {x});
-        yConverted = callNode.executeDispatch(onFunc, null, state, new Object[] {y});
+        xConverted = callNode.executeDispatch(onFunc.get(x), null, state, new Object[]{x});
+        yConverted = callNode.executeDispatch(onFunc.get(y), null, state, new Object[]{y});
       } else {
         xConverted = x;
         yConverted = y;
       }
       Object[] args;
-      if (hasFunctionSelfArgument(compareFunc)) {
+      if (compareFunc.hasFunctionSelfArgument(xConverted)) {
         args = new Object[] {comparator, xConverted, yConverted};
       } else {
         args = new Object[] {xConverted, yConverted};
       }
-      Object res = callNode.executeDispatch(compareFunc, null, state, args);
+      Object res = callNode.executeDispatch(compareFunc.get(xConverted), null, state, args);
       if (res == less) {
         return ascending ? -1 : 1;
       } else if (res == equal) {
@@ -738,43 +835,43 @@ public abstract class SortVectorNode extends Node {
       }
     }
 
-    private boolean hasFunctionSelfArgument(Function function) {
-      if (function.getSchema().getArgumentsCount() > 0) {
-        return function.getSchema().getArgumentInfos()[0].getName().equals("self");
-      } else {
-        return false;
-      }
-    }
-
     /**
      * Checks value given for {@code by} parameter and converts it to {@link Function}. Throw a
      * dataflow error otherwise.
      */
-    private Function checkAndConvertByFunc(Object byFuncObj) {
+    private Compare checkAndConvertByFunc(Object byFuncObj, TypesLibrary typesLibrary, MethodResolverNode methodResolverNode) {
       return checkAndConvertFunction(
-          byFuncObj, "Unsupported argument for `by`, expected a method with two arguments", 2, 3);
+          byFuncObj, "Unsupported argument for `by`, expected a method with two arguments", 2, 3,
+              typesLibrary, methodResolverNode);
     }
 
     /**
      * Checks the value given for {@code on} parameter and converts it to {@link Function}. Throws a
      * dataflow error otherwise.
      */
-    private Function checkAndConvertOnFunc(Object onFuncObj) {
+    private Compare checkAndConvertOnFunc(Object onFuncObj, TypesLibrary typesLibrary, MethodResolverNode methodResolverNode) {
       return checkAndConvertFunction(
-          onFuncObj, "Unsupported argument for `on`, expected a method with one argument", 1, 1);
+          onFuncObj, "Unsupported argument for `on`, expected a method with one argument", 1, 1,
+              typesLibrary, methodResolverNode);
     }
 
     /**
      * @param minArgCount Minimal count of arguments without a default value.
      * @param maxArgCount Maximal count of argument without a default value.
+     * @param methodResolverNode node for resolving unresolved symbols.
+     * @param typesLibrary types library for resolving the dispatch type for unresolved symbols.
      */
-    private Function checkAndConvertFunction(
-        Object funcObj, String errMsg, int minArgCount, int maxArgCount) {
+    private Compare checkAndConvertFunction(
+        Object funcObj, String errMsg, int minArgCount, int maxArgCount,
+        TypesLibrary typesLibrary, MethodResolverNode methodResolverNode) {
+      if (funcObj instanceof UnresolvedSymbol unresolved) {
+        return new CompareFromUnresolvedSymbol(unresolved, methodResolverNode, typesLibrary);
+      }
       var err = new IllegalArgumentException(errMsg + ", got " + funcObj);
       if (funcObj instanceof Function func) {
         var argCount = getNumberOfNonDefaultArguments(func);
         if (minArgCount <= argCount && argCount <= maxArgCount) {
-          return func;
+          return new CompareFromFunction(func);
         } else {
           throw err;
         }

test/Benchmarks/src/Vector/Sort.enso

@@ -49,6 +49,11 @@ make_partially_sorted_vec n =
                 run_length.put (run_length.get - 1)
                 num
 
+type Int
+    Value v
+
+    identity self = self
+
 
 # The Benchmarks ==============================================================
 
@@ -56,6 +61,7 @@ bench =
     sorted_vec = make_sorted_ascending_vec vector_size
     partially_sorted_vec = make_partially_sorted_vec vector_size
     random_vec = Utils.make_random_vec vector_size
+    random_vec_wrapped = random_vec.map (v -> Int.Value v)
     projection = x -> x % 10
     comparator = l -> r -> Ordering.compare l r
 
@@ -66,6 +72,8 @@ bench =
     Bench.measure (random_vec.sort) "Random Elements Ascending" iter_size num_iterations
     Bench.measure (random_vec.sort Sort_Direction.Descending) "Random Elements Descending" iter_size num_iterations
     Bench.measure (random_vec.sort on=projection) "Sorting with a Custom Projection" iter_size num_iterations
+    Bench.measure (random_vec_wrapped.sort on=(_.identity)) "Sorting with an identity function" iter_size num_iterations
+    Bench.measure (random_vec_wrapped.sort on=(.identity)) "Sorting with an (unresolved) identity function" iter_size num_iterations
     Bench.measure (random_vec.sort by=comparator) "Sorting with the Default_Ordered_Comparator" iter_size num_iterations
 
 main = bench

test/Tests/src/Data/Vector_Spec.enso

@@ -579,6 +579,7 @@ type_spec name alter = Test.group name <|
         small_vec = alter [T.Value 1 8, T.Value 1 3, T.Value -20 0, T.Value -1 1, T.Value -1 10, T.Value 4 0]
         small_expected = [T.Value -20 0, T.Value 4 0, T.Value -1 1, T.Value 1 3, T.Value 1 8, T.Value -1 10]
         small_vec.sort (on = _.b) . should_equal small_expected
+        small_vec.sort (on = .b) . should_equal small_expected
 
     Test.specify "should be able to use a custom compare function" <|
         small_vec = alter [2, 7, -3, 383, -392, 28, -90]