ast: result type propagation

src/dev/flang/ast/Call.java

@@ -27,6 +27,7 @@
 package dev.flang.ast;
 
 import java.util.ListIterator;
+import java.util.function.Supplier;
 
 import dev.flang.util.Errors;
 import dev.flang.util.FuzionConstants;
@@ -2337,6 +2338,15 @@ else if (e instanceof Block b)
    */
   boolean needsToInferTypeParametersFromArgs()
   {
+    if (_generics == NO_GENERICS &&
+        _propagatedType != null &&
+        _propagatedType.isNormalType() &&
+        // if features do not match we will get an error later (in checktypes)
+        _propagatedType.feature() == _calledFeature)
+      {
+        _generics = new List<>(_propagatedType.generics());
+      }
+
     return _calledFeature != null && (_generics == NO_GENERICS || _generics.stream().anyMatch(g -> g.containsUndefined(false))) && !_calledFeature.typeArguments().isEmpty();
   }
 
@@ -2354,6 +2364,12 @@ boolean needsToInferTypeParametersFromArgs()
   protected Context _resolvedFor;
 
 
+  /**
+   * The type this call should result in.
+   */
+  private AbstractType _propagatedType;
+
+
   /**
    * Has this call been resolved and if so, for which context?
    *
@@ -2677,6 +2693,34 @@ void propagateExpectedType(Resolution res, Context context)
   }
 
 
+  /**
+   * During type inference: Inform this expression that it is used in an
+   * environment that expects the given type.  In particular, if this
+   * expression's result is assigned to a field, this will be called with the
+   * type of the field.
+   *
+   * @param res this is called during type inference, res gives the resolution
+   * instance.
+   *
+   * @param context the source code context where this Expr is used
+   *
+   * @param t the expected type.
+   *
+   * @param from for error output: if non-null, produces a String describing
+   * where the expected type came from.
+   *
+   * @return either this or a new Expr that replaces thiz and produces the
+   * result. In particular, if the result is assigned to a temporary field, this
+   * will be replaced by the expression that reads the field.
+   */
+  @Override
+  Expr propagateExpectedType(Resolution res, Context context, AbstractType t, Supplier<String> from)
+  {
+    _propagatedType = t;
+    return super.propagateExpectedType(res, context, t, from);
+  }
+
+
   /**
    * During type inference: Wrap expressions that are assigned to lazy actuals
    * in functions.

src/dev/flang/ast/Feature.java

@@ -1432,6 +1432,23 @@ void resolveDeclarations(Resolution res)
   }
 
 
+  public void propagateResultType(Resolution res)
+  {
+    // NYI: BUG: this currently does not work here:
+    // since resultTypeIfPresentUrgent lets numliteral fix their types
+    //
+    // var a = resultTypeIfPresentUrgent(res, false);
+    if (isRoutine() &&
+        (_returnType instanceof FunctionReturnType frt) &&
+        frt.functionReturnType(false) != null &&
+        // NYI: BUG: without this, some issue in lock_free module
+        !featureName().isInternal())
+      {
+        _impl.propagateExpectedType(res, context(), _returnType.functionReturnType(false));
+      }
+  }
+
+
   /**
    * Perform an action as soon as this feature has reached
    * State.atLeast(State.RESOLVED_DECLARATIONS).  Perform the action immediately
@@ -1542,6 +1559,26 @@ void internalResolveTypes(Resolution res)
       {
         _state = State.RESOLVING_TYPES;
 
+
+        // NYI: BUG: does not work currently
+        // because propagateExpectedType is misused
+        // to add result field currently
+        //
+        // visit(new FeatureVisitor()
+        //   {
+        //   @Override
+        //     public Expr action(Feature f, AbstractFeature outer)
+        //     {
+        //       if (f.impl().hasInitialValue())
+        //         {
+        //           f.propagateResultType(res);
+        //         }
+        //       return super.action(f, outer);
+        //     }
+        //   });
+
+        propagateResultType(res);
+
         if (Contract.requiresPreConditionsFeature(this) && preFeature() == null)
           {
             Contract.addPreFeature(res, this, context(), false);

tests/reg_issue321/Makefile

@@ -0,0 +1,25 @@
+# This file is part of the Fuzion language implementation.
+#
+# The Fuzion language implementation is free software: you can redistribute it
+# and/or modify it under the terms of the GNU General Public License as published
+# by the Free Software Foundation, version 3 of the License.
+#
+# The Fuzion language implementation is distributed in the hope that it will be
+# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License along with The
+# Fuzion language implementation.  If not, see <https://www.gnu.org/licenses/>.
+
+
+# -----------------------------------------------------------------------
+#
+#  Tokiwa Software GmbH, Germany
+#
+#  Source code of Fuzion test Makefile
+#
+# -----------------------------------------------------------------------
+
+override NAME = reg_issue321
+include ../simple.mk

tests/reg_issue321/reg_issue321.fz

@@ -0,0 +1,31 @@
+# This file is part of the Fuzion language implementation.
+#
+# The Fuzion language implementation is free software: you can redistribute it
+# and/or modify it under the terms of the GNU General Public License as published
+# by the Free Software Foundation, version 3 of the License.
+#
+# The Fuzion language implementation is distributed in the hope that it will be
+# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License along with The
+# Fuzion language implementation.  If not, see <https://www.gnu.org/licenses/>.
+
+
+# -----------------------------------------------------------------------
+#
+#  Tokiwa Software GmbH, Germany
+#
+#  Source code of Fuzion test reg_issue321
+#
+# -----------------------------------------------------------------------
+
+reg_issue321 =>
+
+  a tuple i8 i8 => tuple 3 4
+  # NYI: BUG: does not yet work
+  # b tuple i8 i8 := tuple 3 4
+
+  say a
+  # say b

tests/reg_issue321/reg_issue321.fz.expected_out

@@ -0,0 +1 @@
+instance[tuple i8 i8]