Minor refactoring while working on prioritized constraints

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/ResolutionDebugInfo.java

@@ -5,7 +5,7 @@ import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.jet.lang.descriptors.CallableDescriptor;
 import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
-import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintSystemImpl;
+import org.jetbrains.jet.lang.resolve.calls.inference.BoundsOwner;
 import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintSystemSolution;
 import org.jetbrains.jet.lang.types.JetType;
 import org.jetbrains.jet.util.slicedmap.*;
@@ -22,8 +22,8 @@ public class ResolutionDebugInfo {
     public static final WritableSlice<One, ResolvedCall<? extends CallableDescriptor>> RESULT = Slices.createSimpleSlice();
     public static final WritableSlice<One, StringBuilder> ERRORS = Slices.createSimpleSlice();
     public static final WritableSlice<One, StringBuilder> LOG = Slices.createSimpleSlice();
-    public static final WritableSlice<One, Map<TypeParameterDescriptor, ConstraintSystemImpl.TypeValue>> BOUNDS_FOR_UNKNOWNS = Slices.createSimpleSlice();
+    public static final WritableSlice<One, Map<TypeParameterDescriptor, BoundsOwner>> BOUNDS_FOR_UNKNOWNS = Slices.createSimpleSlice();
-    public static final WritableSlice<One, Map<JetType, ConstraintSystemImpl.TypeValue>> BOUNDS_FOR_KNOWNS = Slices.createSimpleSlice();
+    public static final WritableSlice<One, Map<JetType, BoundsOwner>> BOUNDS_FOR_KNOWNS = Slices.createSimpleSlice();
     public static final WritableSlice<One, ConstraintSystemSolution> SOLUTION = Slices.createSimpleSlice();
     public static final WritableSlice<One, Collection<TypeParameterDescriptor>> UNKNOWNS = Slices.createSimpleSlice();
 

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/BoundsOwner.java

@@ -0,0 +1,16 @@
+package org.jetbrains.jet.lang.resolve.calls.inference;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Set;
+
+/**
+ * @author abreslav
+ */
+public interface BoundsOwner {
+    @NotNull
+    Set<TypeValue> getUpperBounds();
+
+    @NotNull
+    Set<TypeValue> getLowerBounds();
+}

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/ConstraintResolutionListener.java

@@ -12,11 +12,11 @@ public interface ConstraintResolutionListener {
 
     public static final ConstraintResolutionListener DO_NOTHING = new ConstraintResolutionListener() {
         @Override
-        public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, ConstraintSystemImpl.TypeValue typeValue) {
+        public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, BoundsOwner typeValue) {
         }
 
         @Override
-        public void constraintsForKnownType(JetType type, ConstraintSystemImpl.TypeValue typeValue) {
+        public void constraintsForKnownType(JetType type, BoundsOwner typeValue) {
         }
 
         @Override
@@ -24,18 +24,18 @@ public interface ConstraintResolutionListener {
         }
 
         @Override
-        public void log(Object message) {
+        public void log(Object... messageFragments) {
         }
 
         @Override
-        public void error(Object message) {
+        public void error(Object... messageFragments) {
         }
     };
 
-    void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, ConstraintSystemImpl.TypeValue typeValue);
+    void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, BoundsOwner typeValue);
-    void constraintsForKnownType(JetType type, ConstraintSystemImpl.TypeValue typeValue);
+    void constraintsForKnownType(JetType type, BoundsOwner typeValue);
     void done(ConstraintSystemSolution solution, Set<TypeParameterDescriptor> typeParameterDescriptors);
 
-    void log(Object message);
+    void log(Object... messageFragments);
-    void error(Object message);
+    void error(Object... messageFragments);
 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/ConstraintSystemImpl.java

@@ -143,7 +143,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
                                 }
                             }
 
-                            listener.log("minimal solution from lowerbounds for " + this + " is " + commonSupertype);
+                            listener.log("minimal solution from lowerbounds for ", this, " is ", commonSupertype);
                             value = new KnownType(commonSupertype);
                         }
                         else {
@@ -247,10 +247,10 @@ public class ConstraintSystemImpl implements ConstraintSystem {
         }
 
         @Override
-        public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, TypeCheckingProcedure typeCheckingProcedure) {
+        public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
             boolean result = delegate.assertEqualTypes(a, b, typeCheckingProcedure);
             if (!result) {
-                listener.error("-- Failed to equate " + a + " and " + b);
+                listener.error("-- Failed to equate ", a, " and ", b);
             }
             return result;
         }
@@ -259,16 +259,16 @@ public class ConstraintSystemImpl implements ConstraintSystem {
         public boolean assertEqualTypeConstructors(@NotNull TypeConstructor a, @NotNull TypeConstructor b) {
             boolean result = delegate.assertEqualTypeConstructors(a, b);
             if (!result) {
-                listener.error("-- Type constructors are not equal: " + a + " and " + b);
+                listener.error("-- Type constructors are not equal: ", a, " and ", b);
             }
             return result;
         }
 
         @Override
-        public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, TypeCheckingProcedure typeCheckingProcedure) {
+        public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
             boolean result = delegate.assertSubtype(subtype, supertype, typeCheckingProcedure);
             if (!result) {
-                listener.error("-- " + subtype + " can't be a subtype of " + supertype);
+                listener.error("-- ", subtype, " can't be a subtype of ", supertype);
             }
             return result;
         }
@@ -277,7 +277,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
         public boolean noCorrespondingSupertype(@NotNull JetType subtype, @NotNull JetType supertype) {
             boolean result = delegate.noCorrespondingSupertype(subtype, supertype);
             if (!result) {
-                listener.error("-- " + subtype + " has no supertype corresponding to " + supertype);
+                listener.error("-- ", subtype, " has no supertype corresponding to ", supertype);
             }
             return result;
         }
@@ -294,7 +294,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
     private TypeCheckingProcedure createConstraintExpander() {
         return new TypeCheckingProcedure(new TypeConstraintBuilderAdapter(new TypingConstraints() {
             @Override
-            public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, TypeCheckingProcedure typeCheckingProcedure) {
+            public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
                 TypeValue aValue = getTypeValueFor(a);
                 TypeValue bValue = getTypeValueFor(b);
 
@@ -309,7 +309,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
             }
 
             @Override
-            public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, TypeCheckingProcedure typeCheckingProcedure) {
+            public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
                 TypeValue subtypeValue = getTypeValueFor(subtype);
                 TypeValue supertypeValue = getTypeValueFor(supertype);
 
@@ -389,7 +389,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
     }
 
     private void addSubtypingConstraintOnTypeValues(TypeValue typeValueForLower, TypeValue typeValueForUpper) {
-        listener.log("Constraint added: " + typeValueForLower + " :< " + typeValueForUpper);
+        listener.log("Constraint added: ", typeValueForLower, " :< ", typeValueForUpper);
         if (typeValueForLower != typeValueForUpper) {
             typeValueForLower.addUpperBound(typeValueForUpper);
             typeValueForUpper.addLowerBound(typeValueForLower);
@@ -409,7 +409,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
                     KnownType knownBoundType = (KnownType) upperBound;
                     boolean ok = constraintExpander.isSubtypeOf(jetType, knownBoundType.getType());
                     if (!ok) {
-                        listener.error("Error while expanding '" + jetType + " :< " + knownBoundType.getType() + "'");
+                        listener.error("Error while expanding '", jetType, " :< ", knownBoundType.getType(), "'");
                         return new Solution().registerError("Mismatch while expanding constraints");
                     }
                 }
@@ -443,11 +443,11 @@ public class ConstraintSystemImpl implements ConstraintSystem {
         }
 
         for (UnknownType unknownType : unknownTypes.values()) {
-            listener.constraintsForUnknown(unknownType.getTypeParameterDescriptor(), unknownType);
+//            listener.constraintsForUnknown(unknownType.getTypeParameterDescriptor(), unknownType);
         }
 
         for (KnownType knownType : knownTypes.values()) {
-            listener.constraintsForKnownType(knownType.getType(), knownType);
+//            listener.constraintsForKnownType(knownType.getType(), knownType);
         }
 
         // Find inconsistencies
@@ -477,14 +477,14 @@ public class ConstraintSystemImpl implements ConstraintSystem {
                 JetType boundingType = solution.getSubstitutor().substitute(upperBound.getValue().getType(), Variance.INVARIANT);
                 if (!typeChecker.isSubtypeOf(type, boundingType)) { // TODO
                     solution.registerError("Constraint violation: " + type + " is not a subtype of " + boundingType);
-                    listener.error("Constraint violation: " + type + " :< " + boundingType);
+                    listener.error("Constraint violation: ", type, " :< ", boundingType);
                 }
             }
             for (TypeValue lowerBound : typeValue.getLowerBounds()) {
                 JetType boundingType = solution.getSubstitutor().substitute(lowerBound.getValue().getType(), Variance.INVARIANT);
                 if (!typeChecker.isSubtypeOf(boundingType, type)) {
                     solution.registerError("Constraint violation: " + boundingType + " is not a subtype of " + type);
-                    listener.error("Constraint violation: " + boundingType + " :< " + type);
+                    listener.error("Constraint violation: ", boundingType, " :< ", type);
                 }
             }
         }
@@ -542,7 +542,7 @@ public class ConstraintSystemImpl implements ConstraintSystem {
 
                     TypeProjection typeProjection = new TypeProjection(getValue(descriptor));
 
-                    listener.log(descriptor + " |-> " + typeProjection);
+                    listener.log(descriptor, " |-> ", typeProjection);
 
                     return typeProjection;
                 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/ConstraintSystemWithPriorities.java

@@ -0,0 +1,470 @@
+package org.jetbrains.jet.lang.resolve.calls.inference;
+
+import com.google.common.collect.Maps;
+import com.google.common.collect.Sets;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.jet.lang.descriptors.DeclarationDescriptor;
+import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
+import org.jetbrains.jet.lang.types.*;
+import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
+import org.jetbrains.jet.lang.types.checker.TypeCheckingProcedure;
+import org.jetbrains.jet.lang.types.checker.TypingConstraints;
+
+import java.util.*;
+
+import static org.jetbrains.jet.lang.resolve.calls.inference.ConstraintType.PARAMETER_BOUND;
+
+/**
+ * @author abreslav
+ */
+public class ConstraintSystemWithPriorities implements ConstraintSystem {
+
+    public static final Comparator<SubtypingConstraint> SUBTYPING_CONSTRAINT_ORDER = new Comparator<SubtypingConstraint>() {
+        @Override
+        public int compare(SubtypingConstraint o1, SubtypingConstraint o2) {
+            return o1.getType().compareTo(o2.getType());
+        }
+    };
+
+    private static class LoopInTypeVariableConstraintsException extends RuntimeException {
+        public LoopInTypeVariableConstraintsException() {}
+    }
+
+    //==========================================================================================================================================================
+
+    private final Map<JetType, TypeValue> knownTypes = Maps.newLinkedHashMap(); // linked - for easier debugging
+    private final Map<TypeParameterDescriptor, TypeValue> unknownTypes = Maps.newLinkedHashMap(); // linked - for easier debugging
+    private final Set<TypeValue> unsolvedUnknowns = Sets.newLinkedHashSet(); // linked - for easier debugging
+    private final PriorityQueue<SubtypingConstraint> constraintQueue = new PriorityQueue<SubtypingConstraint>(10, SUBTYPING_CONSTRAINT_ORDER);
+
+    private final JetTypeChecker typeChecker = JetTypeChecker.INSTANCE;
+    private final TypeCheckingProcedure constraintExpander;
+    private final ConstraintResolutionListener listener;
+
+    public ConstraintSystemWithPriorities(ConstraintResolutionListener listener) {
+        this.listener = listener;
+        this.constraintExpander = createConstraintExpander();
+    }
+
+    @NotNull
+    private TypeValue getTypeValueFor(@NotNull JetType type) {
+        DeclarationDescriptor declarationDescriptor = type.getConstructor().getDeclarationDescriptor();
+        if (declarationDescriptor instanceof TypeParameterDescriptor) {
+            TypeParameterDescriptor typeParameterDescriptor = (TypeParameterDescriptor) declarationDescriptor;
+            // Checking that this is not a T?, but exactly T
+            if (typeParameterDescriptor.getDefaultType().isNullable() == type.isNullable()) {
+                TypeValue unknownType = unknownTypes.get(typeParameterDescriptor);
+                if (unknownType != null) {
+                    return unknownType;
+                }
+            }
+        }
+
+        TypeValue typeValue = knownTypes.get(type);
+        if (typeValue == null) {
+            typeValue = new TypeValue(type);
+            knownTypes.put(type, typeValue);
+        }
+        return typeValue;
+    }
+
+    @Override
+    public void registerTypeVariable(@NotNull TypeParameterDescriptor typeParameterDescriptor, @NotNull Variance positionVariance) {
+        assert !unknownTypes.containsKey(typeParameterDescriptor);
+        TypeValue typeValue = new TypeValue(typeParameterDescriptor, positionVariance);
+        unknownTypes.put(typeParameterDescriptor, typeValue);
+        unsolvedUnknowns.add(typeValue);
+    }
+
+    @NotNull
+    private TypeValue getTypeVariable(TypeParameterDescriptor typeParameterDescriptor) {
+        TypeValue unknownType = unknownTypes.get(typeParameterDescriptor);
+        if (unknownType == null) {
+            throw new IllegalArgumentException("This type parameter is not an unknown in this constraint system: " + typeParameterDescriptor);
+        }
+        return unknownType;
+    }
+
+    @Override
+    public void addSubtypingConstraint(@NotNull SubtypingConstraint constraint) {
+        constraintQueue.add(constraint);
+    }
+
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    // Constraint expansion
+    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+    private TypeCheckingProcedure createConstraintExpander() {
+        return new TypeCheckingProcedure(new TypeConstraintBuilderAdapter(new TypingConstraints() {
+            @Override
+            public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
+                TypeValue aValue = getTypeValueFor(a);
+                TypeValue bValue = getTypeValueFor(b);
+
+                return expandEqualityConstraint(aValue, bValue);
+            }
+
+            @Override
+            public boolean assertEqualTypeConstructors(@NotNull TypeConstructor a, @NotNull TypeConstructor b) {
+                return a.equals(b)
+                       || unknownTypes.containsKey(a.getDeclarationDescriptor())
+                       || unknownTypes.containsKey(b.getDeclarationDescriptor());
+            }
+
+            @Override
+            public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
+                TypeValue subtypeValue = getTypeValueFor(subtype);
+                TypeValue supertypeValue = getTypeValueFor(supertype);
+
+                if (someUnknown(subtypeValue, supertypeValue)) {
+                    expandSubtypingConstraint(subtypeValue, supertypeValue);
+                }
+                return true; // For known types further expansion happens automatically
+            }
+
+            @Override
+            public boolean noCorrespondingSupertype(@NotNull JetType subtype, @NotNull JetType supertype) {
+                // If some of the types is an unknown, the constraint must be generated, and we should carry on
+                // otherwise there can be no solution, and we should fail
+                TypeValue subTypeValue = getTypeValueFor(subtype);
+                TypeValue superTypeValue = getTypeValueFor(supertype);
+                boolean someUnknown = someUnknown(subTypeValue, superTypeValue);
+                if (someUnknown) {
+                    expandSubtypingConstraint(subTypeValue, superTypeValue);
+                }
+                return someUnknown;
+            }
+
+            private boolean someUnknown(TypeValue subtypeValue, TypeValue supertypeValue) {
+                return !subtypeValue.isKnown() || !supertypeValue.isKnown();
+            }
+
+        }, listener));
+    }
+
+    private boolean assignValueTo(TypeValue unknown, JetType value) {
+        if (unknown.hasValue()) {
+            // If we have already assigned a value to this unknown,
+            // it is a conflict to assign another one, unless this new one is equal to the previous
+            return TypeUtils.equalTypes(unknown.getType(), value);
+        }
+        unsolvedUnknowns.remove(unknown);
+        unknown.setValue(value);
+        return true;
+    }
+
+    private boolean mergeUnknowns(@NotNull TypeValue a, @NotNull TypeValue b) {
+        assert !a.isKnown() && !b.isKnown();
+        listener.error("!!!mergeUnknowns() is not implemented!!!");
+        return false;
+    }
+
+    public boolean expandEqualityConstraint(TypeValue a, TypeValue b) {
+        if (a.isKnown() && b.isKnown()) {
+            return constraintExpander.equalTypes(a.getType(), b.getType());            
+        }
+
+        // At least one of them is unknown
+        if (a.isKnown()) {
+            TypeValue tmp = a;
+            a = b;
+            b = tmp;
+        }
+
+        // Now a is definitely unknown
+        if (b.isKnown()) {
+            return assignValueTo(a, b.getType());
+        }
+
+        // They are both unknown
+        return mergeUnknowns(a, b);
+    }
+
+    private boolean expandSubtypingConstraint(TypeValue lower, TypeValue upper) {
+        listener.log("Constraint added: ", lower, " :< ", upper);
+
+        if (lower == upper) return true;
+
+        // Remember for a later check
+        lower.addUpperBound(upper);
+        upper.addLowerBound(lower);
+
+        if (lower.isKnown() && upper.isKnown()) {
+            // Two known types: expand constraints
+            return constraintExpander.isSubtypeOf(lower.getType(), upper.getType());
+        }
+        else if (!lower.isKnown() && !upper.isKnown()) {
+            // Two unknown types: merge them into one variable
+            return mergeUnknowns(lower, upper);
+        }
+        else {
+            // One unknown and one known
+            if (upper.isKnown()) {
+                if (TypeUtils.canHaveSubtypes(typeChecker, upper.getType())) {
+                    // Upper bound is final -> we have to equate the lower bounds to it
+                    return expandEqualityConstraint(lower, upper);
+                }
+                if (lower.getLowerBounds().contains(upper)) {
+                    // upper :< lower :< upper
+                    return expandEqualityConstraint(lower, upper);
+                }
+            }
+            else {
+                if (upper.getUpperBounds().contains(lower)) {
+                    // lower :< upper :< lower
+                    return expandEqualityConstraint(lower, upper);
+                }
+            }
+        }
+        return true;
+    }
+
+    @Override
+    @NotNull
+    public ConstraintSystemSolution solve() {
+        Solution solution = new Solution();
+        // At this point we only have type values, no bounds added for them, no values computed for unknown types
+
+        // Generate low-priority constraints from bounds
+        for (Map.Entry<TypeParameterDescriptor, TypeValue> entry : Sets.newHashSet(unknownTypes.entrySet())) {
+            TypeParameterDescriptor typeParameterDescriptor = entry.getKey();
+            TypeValue typeValue = entry.getValue();
+            for (JetType upperBound : typeParameterDescriptor.getUpperBounds()) {
+                addSubtypingConstraint(PARAMETER_BOUND.assertSubtyping(typeValue.getOriginalType(), getTypeValueFor(upperBound).getOriginalType()));
+            }
+            for (JetType lowerBound : typeParameterDescriptor.getLowerBounds()) {
+                addSubtypingConstraint(PARAMETER_BOUND.assertSubtyping(getTypeValueFor(lowerBound).getOriginalType(), typeValue.getOriginalType()));
+            }
+        }
+
+        // Expand and solve constraints
+        while (!constraintQueue.isEmpty()) {
+            SubtypingConstraint constraint = constraintQueue.poll();
+
+            // Apply constraint
+            TypeValue lower = getTypeValueFor(constraint.getSubtype());
+            TypeValue upper = getTypeValueFor(constraint.getSupertype());
+            boolean success = expandSubtypingConstraint(lower, upper);
+            if (!success) {
+                solution.registerError(constraint.getErrorMessage());
+                break;
+            }
+
+            // (???) Propagate info
+
+            // Any unknowns left?
+            if (unsolvedUnknowns.isEmpty()) break;
+        }
+
+        // Now, let's check the rest of the constraints
+
+        // Expand custom bounds, e.g. List<T> <: List<Int>
+//        for (Map.Entry<JetType, TypeValue> entry : Sets.newHashSet(knownTypes.entrySet())) {
+//            JetType jetType = entry.getKey();
+//            TypeValue typeValue = entry.getValue();
+//
+//            for (TypeValue upperBound : typeValue.getUpperBounds()) {
+//                if (upperBound.isKnown()) {
+//                    boolean ok = constraintExpander.isSubtypeOf(jetType, upperBound.getType());
+//                    if (!ok) {
+//                        listener.error("Error while expanding '" + jetType + " :< " + upperBound.getType() + "'");
+//                        return new Solution().registerError("Mismatch while expanding constraints");
+//                    }
+//                }
+//            }
+//
+//            // Lower bounds. Probably not needed for known types, as everything is symmetrical anyway
+//        }
+
+        // effective bounds for each node
+//        Set<TypeValue> visited = Sets.newHashSet();
+//        for (TypeValue unknownType : unknownTypes.values()) {
+//            transitiveClosure(unknownType, visited);
+//        }
+
+        for (TypeValue unknownType : unknownTypes.values()) {
+            listener.constraintsForUnknown(unknownType.getTypeParameterDescriptor(), unknownType);
+        }
+        for (TypeValue knownType : knownTypes.values()) {
+            listener.constraintsForKnownType(knownType.getType(), knownType);
+        }
+
+        // Find inconsistencies
+
+        // Compute values and check that all bounds are respected by solutions:
+        // we have set some of them from equality constraints with known types
+        // and thus the bounds may be violated if some of the constraints conflict
+        for (TypeValue unknownType : unknownTypes.values()) {
+            check(unknownType, solution);
+        }
+        for (TypeValue knownType : knownTypes.values()) {
+            check(knownType, solution);
+        }
+
+        listener.done(solution, unknownTypes.keySet());
+
+        return solution;
+    }
+
+    private void transitiveClosure(TypeValue current, Set<TypeValue> visited) {
+        if (!visited.add(current)) {
+            return;
+        }
+
+        for (TypeValue upperBound : Sets.newHashSet(current.getUpperBounds())) {
+            if (upperBound.isKnown()) {
+                continue;
+            }
+            transitiveClosure(upperBound, visited);
+            Set<TypeValue> upperBounds = upperBound.getUpperBounds();
+            for (TypeValue transitiveBound : upperBounds) {
+                expandSubtypingConstraint(current, transitiveBound);
+            }
+        }
+    }
+
+    private void check(TypeValue typeValue, Solution solution) {
+        try {
+            JetType resultingType = typeValue.getType();
+            JetType type = solution.getSubstitutor().substitute(resultingType, Variance.INVARIANT); // TODO
+            for (TypeValue upperBound : typeValue.getUpperBounds()) {
+                JetType boundingType = solution.getSubstitutor().substitute(upperBound.getType(), Variance.INVARIANT);
+                if (!typeChecker.isSubtypeOf(type, boundingType)) { // TODO
+                    solution.registerError("Constraint violation: " + type + " is not a subtype of " + boundingType);
+                    listener.error("Constraint violation: ", type, " :< ", boundingType);
+                }
+            }
+            for (TypeValue lowerBound : typeValue.getLowerBounds()) {
+                JetType boundingType = solution.getSubstitutor().substitute(lowerBound.getType(), Variance.INVARIANT);
+                if (!typeChecker.isSubtypeOf(boundingType, type)) {
+                    solution.registerError("Constraint violation: " + boundingType + " is not a subtype of " + type);
+                    listener.error("Constraint violation: ", boundingType, " :< ", type);
+                }
+            }
+        }
+        catch (LoopInTypeVariableConstraintsException e) {
+            listener.error("Loop detected");
+            solution.registerError("[TODO] Loop in constraints");
+        }
+    }
+
+    private static class Error implements SolutionStatus {
+
+        private final String message;
+
+        private Error(String message) {
+            this.message = message;
+        }
+
+        @Override
+        public boolean isSuccessful() {
+            return false;
+        }
+
+        @Override
+        public String toString() {
+            return message;
+        }
+    }
+
+    public class Solution implements ConstraintSystemSolution {
+        private final TypeSubstitutor typeSubstitutor = TypeSubstitutor.create(new TypeSubstitutor.TypeSubstitution() {
+            @Override
+            public TypeProjection get(TypeConstructor key) {
+                DeclarationDescriptor declarationDescriptor = key.getDeclarationDescriptor();
+                if (declarationDescriptor instanceof TypeParameterDescriptor) {
+                    TypeParameterDescriptor descriptor = (TypeParameterDescriptor) declarationDescriptor;
+
+                    if (!unknownTypes.containsKey(descriptor)) return null;
+
+                    TypeProjection typeProjection = new TypeProjection(getValue(descriptor));
+
+                    listener.log(descriptor, " |-> ", typeProjection);
+
+                    return typeProjection;
+                }
+                return null;
+            }
+
+            @Override
+            public boolean isEmpty() {
+                return false;
+            }
+        });
+
+        private SolutionStatus status;
+
+        public Solution() {
+            this.status = SolutionStatus.SUCCESS;
+        }
+
+        private Solution registerError(String message) {
+            status = new Error(message);
+            return this;
+        }
+
+        @NotNull
+        @Override
+        public SolutionStatus getStatus() {
+            return status;
+        }
+
+        @Override
+        public JetType getValue(TypeParameterDescriptor typeParameterDescriptor) {
+            return getTypeVariable(typeParameterDescriptor).getType();
+        }
+
+        @NotNull
+        @Override
+        public TypeSubstitutor getSubstitutor() {
+            return typeSubstitutor;
+        }
+
+    }
+    private static final class TypeConstraintBuilderAdapter implements TypingConstraints {
+        private final TypingConstraints delegate;
+        private final ConstraintResolutionListener listener;
+
+        private TypeConstraintBuilderAdapter(TypingConstraints delegate, ConstraintResolutionListener listener) {
+            this.delegate = delegate;
+            this.listener = listener;
+        }
+
+        @Override
+        public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
+            boolean result = delegate.assertEqualTypes(a, b, typeCheckingProcedure);
+            if (!result) {
+                listener.error("-- Failed to equate ", a, " and ", b);
+            }
+            return result;
+        }
+
+        @Override
+        public boolean assertEqualTypeConstructors(@NotNull TypeConstructor a, @NotNull TypeConstructor b) {
+            boolean result = delegate.assertEqualTypeConstructors(a, b);
+            if (!result) {
+                listener.error("-- Type constructors are not equal: ", a, " and ", b);
+            }
+            return result;
+        }
+
+        @Override
+        public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
+            boolean result = delegate.assertSubtype(subtype, supertype, typeCheckingProcedure);
+            if (!result) {
+                listener.error("-- " + subtype + " can't be a subtype of " + supertype);
+            }
+            return result;
+        }
+
+        @Override
+        public boolean noCorrespondingSupertype(@NotNull JetType subtype, @NotNull JetType supertype) {
+            boolean result = delegate.noCorrespondingSupertype(subtype, supertype);
+            if (!result) {
+                listener.error("-- " + subtype + " has no supertype corresponding to " + supertype);
+            }
+            return result;
+        }
+    }
+
+}

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/DebugConstraintResolutionListener.java

@@ -23,9 +23,9 @@ public class DebugConstraintResolutionListener implements ConstraintResolutionLi
     }
 
     @Override
-    public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, ConstraintSystemImpl.TypeValue typeValue) {
+    public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, BoundsOwner typeValue) {
         if (!ResolutionDebugInfo.isResolutionDebugEnabled()) return;
-        Map<TypeParameterDescriptor, ConstraintSystemImpl.TypeValue> map = debugInfo.get(BOUNDS_FOR_UNKNOWNS);
+        Map<TypeParameterDescriptor, BoundsOwner> map = debugInfo.get(BOUNDS_FOR_UNKNOWNS);
         if (map == null) {
             map = Maps.newLinkedHashMap();
             debugInfo.set(BOUNDS_FOR_UNKNOWNS, map);
@@ -34,9 +34,9 @@ public class DebugConstraintResolutionListener implements ConstraintResolutionLi
     }
 
     @Override
-    public void constraintsForKnownType(JetType type, ConstraintSystemImpl.TypeValue typeValue) {
+    public void constraintsForKnownType(JetType type, BoundsOwner typeValue) {
         if (!ResolutionDebugInfo.isResolutionDebugEnabled()) return;
-        Map<JetType,ConstraintSystemImpl.TypeValue> map = debugInfo.get(BOUNDS_FOR_KNOWNS);
+        Map<JetType,BoundsOwner> map = debugInfo.get(BOUNDS_FOR_KNOWNS);
         if (map == null) {
             map = Maps.newLinkedHashMap();
             debugInfo.set(BOUNDS_FOR_KNOWNS, map);
@@ -52,24 +52,30 @@ public class DebugConstraintResolutionListener implements ConstraintResolutionLi
     }
 
     @Override
-    public void log(Object message) {
+    public void log(Object... messageFragments) {
         if (!ResolutionDebugInfo.isResolutionDebugEnabled()) return;
         StringBuilder stringBuilder = debugInfo.get(LOG);
         if (stringBuilder == null) {
             stringBuilder = new StringBuilder();
             debugInfo.set(LOG, stringBuilder);
         }
-        stringBuilder.append(message).append("\n");
+        for (Object m : messageFragments) {
+            stringBuilder.append(m);
+        }
+        stringBuilder.append("\n");
     }
 
     @Override
-    public void error(Object message) {
+    public void error(Object... messageFragments) {
         if (!ResolutionDebugInfo.isResolutionDebugEnabled()) return;
         StringBuilder stringBuilder = debugInfo.get(ERRORS);
         if (stringBuilder == null) {
             stringBuilder = new StringBuilder();
             debugInfo.set(ERRORS, stringBuilder);
         }
-        stringBuilder.append(message).append("\n");
+        for (Object m : messageFragments) {
+            stringBuilder.append(m);
+        }
+        stringBuilder.append("\n");
     }
 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/PrintingConstraintResolutionListener.java

@@ -12,13 +12,13 @@ import java.util.Set;
 public class PrintingConstraintResolutionListener implements ConstraintResolutionListener {
 
     @Override
-    public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, ConstraintSystemImpl.TypeValue typeValue) {
+    public void constraintsForUnknown(TypeParameterDescriptor typeParameterDescriptor, BoundsOwner typeValue) {
         println("Constraints for " + typeParameterDescriptor);
         printTypeValue(typeValue);
     }
 
     @Override
-    public void constraintsForKnownType(JetType type, ConstraintSystemImpl.TypeValue typeValue) {
+    public void constraintsForKnownType(JetType type, BoundsOwner typeValue) {
         println("Constraints for " + type);
         printTypeValue(typeValue);
     }
@@ -31,20 +31,24 @@ public class PrintingConstraintResolutionListener implements ConstraintResolutio
     }
 
     @Override
-    public void log(Object message) {
+    public void log(Object... messageFragments) {
-        println(message);
+        for (Object fragment : messageFragments) {
+            println(fragment);
+        }
     }
 
     @Override
-    public void error(Object message) {
+    public void error(Object... messageFragments) {
-        println(message);
+        for (Object fragment : messageFragments) {
+            println(fragment);
+        }
     }
 
-    private void printTypeValue(ConstraintSystemImpl.TypeValue typeValue) {
+    private void printTypeValue(BoundsOwner typeValue) {
-        for (ConstraintSystemImpl.TypeValue bound : typeValue.getUpperBounds()) {
+        for (BoundsOwner bound : typeValue.getUpperBounds()) {
             println(" :< " + bound);
         }
-        for (ConstraintSystemImpl.TypeValue bound : typeValue.getLowerBounds()) {
+        for (BoundsOwner bound : typeValue.getLowerBounds()) {
             println(" :> " + bound);
         }
     }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeValue.java

@@ -0,0 +1,82 @@
+package org.jetbrains.jet.lang.resolve.calls.inference;
+
+import com.google.common.collect.Sets;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
+import org.jetbrains.jet.lang.types.JetType;
+import org.jetbrains.jet.lang.types.Variance;
+
+import java.util.Set;
+
+/**
+* @author abreslav
+*/
+public class TypeValue implements BoundsOwner {
+    private final Set<TypeValue> upperBounds = Sets.newLinkedHashSet();
+    private final Set<TypeValue> lowerBounds = Sets.newLinkedHashSet();
+
+    private final Variance positionVariance;
+    private final TypeParameterDescriptor typeParameterDescriptor; // Null for known types
+    private final JetType originalType;
+    private JetType value; // For an unknown — the value found by constraint resolution, for a known — just it's value
+
+    // Unknown type
+    public TypeValue(@NotNull TypeParameterDescriptor typeParameterDescriptor, @NotNull Variance positionVariance) {
+        this.positionVariance = positionVariance;
+        this.typeParameterDescriptor = typeParameterDescriptor;
+        this.originalType = typeParameterDescriptor.getDefaultType();
+    }
+
+    // Known type
+    public TypeValue(@NotNull JetType knownType) {
+        this.positionVariance = null;
+        this.typeParameterDescriptor = null;
+        this.originalType = knownType;
+    }
+
+    public boolean isKnown() {
+        return typeParameterDescriptor == null;
+    }
+
+    public TypeParameterDescriptor getTypeParameterDescriptor() {
+        return typeParameterDescriptor;
+    }
+
+    @Override
+    @NotNull
+    public Set<TypeValue> getUpperBounds() {
+        return upperBounds;
+    }
+
+    @Override
+    @NotNull
+    public Set<TypeValue> getLowerBounds() {
+        return lowerBounds;
+    }
+
+    @NotNull
+    public JetType getType() {
+        return value;
+    }
+
+    @NotNull
+    public JetType getOriginalType() {
+        return originalType;
+    }
+
+    public void addUpperBound(@NotNull TypeValue bound) {
+        upperBounds.add(bound);
+    }
+
+    public void addLowerBound(@NotNull TypeValue bound) {
+        lowerBounds.add(bound);
+    }
+
+    public void setValue(@NotNull JetType value) {
+        this.value = value;
+    }
+
+    public boolean hasValue() {
+        return value != null;
+    }
+}

compiler/frontend/src/org/jetbrains/jet/lang/types/TypeSubstitutor.java

@@ -1,19 +1,41 @@
 package org.jetbrains.jet.lang.types;
 
+import com.google.common.collect.Sets;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
 import org.jetbrains.jet.lang.resolve.scopes.SubstitutingScope;
 
-import java.util.ArrayList;
+import java.util.*;
-import java.util.List;
-import java.util.Map;
 
 /**
  * @author abreslav
  */
 public class TypeSubstitutor {
 
+    public static TypeSubstitutor makeConstantSubstitutor(Collection<TypeParameterDescriptor> typeParameterDescriptors, JetType type) {
+        final Set<TypeConstructor> constructors = Sets.newHashSet();
+        for (TypeParameterDescriptor typeParameterDescriptor : typeParameterDescriptors) {
+            constructors.add(typeParameterDescriptor.getTypeConstructor());
+        }
+        final TypeProjection projection = new TypeProjection(type);
+
+        return create(new TypeSubstitution() {
+            @Override
+            public TypeProjection get(TypeConstructor key) {
+                if (constructors.contains(key)) {
+                    return projection;
+                }
+                return null;
+            }
+
+            @Override
+            public boolean isEmpty() {
+                return false;
+            }
+        });
+    }
+
     public interface TypeSubstitution {
         TypeSubstitution EMPTY = new TypeSubstitution() {
             @Override

compiler/frontend/src/org/jetbrains/jet/lang/types/checker/JetTypeChecker.java

@@ -46,7 +46,7 @@ public class JetTypeChecker {
 
     private static class TypeCheckerTypingConstraints implements TypingConstraints {
         @Override
-        public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, TypeCheckingProcedure typeCheckingProcedure) {
+        public boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
             return typeCheckingProcedure.equalTypes(a, b);
 //            return TypeUtils.equalTypes(a, b);
         }
@@ -57,7 +57,7 @@ public class JetTypeChecker {
         }
 
         @Override
-        public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, TypeCheckingProcedure typeCheckingProcedure) {
+        public boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure) {
             return typeCheckingProcedure.isSubtypeOf(subtype, supertype);
         }
 

compiler/frontend/src/org/jetbrains/jet/lang/types/checker/TypingConstraints.java

@@ -8,11 +8,11 @@ import org.jetbrains.jet.lang.types.TypeConstructor;
  * Methods of this class return true to continue type checking and false to fail
  */
 public interface TypingConstraints {
-    boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, TypeCheckingProcedure typeCheckingProcedure);
+    boolean assertEqualTypes(@NotNull JetType a, @NotNull JetType b, @NotNull TypeCheckingProcedure typeCheckingProcedure);
 
     boolean assertEqualTypeConstructors(@NotNull TypeConstructor a, @NotNull TypeConstructor b);
 
-    boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, TypeCheckingProcedure typeCheckingProcedure);
+    boolean assertSubtype(@NotNull JetType subtype, @NotNull JetType supertype, @NotNull TypeCheckingProcedure typeCheckingProcedure);
 
     boolean noCorrespondingSupertype(@NotNull JetType subtype, @NotNull JetType supertype);
 }

idea/src/org/jetbrains/jet/plugin/internal/resolvewindow/ResolveToolwindow.java

@@ -31,6 +31,7 @@ import org.jetbrains.jet.lang.resolve.BindingContext;
 import org.jetbrains.jet.lang.resolve.calls.ResolutionDebugInfo;
 import org.jetbrains.jet.lang.resolve.calls.ResolvedCall;
 import org.jetbrains.jet.lang.resolve.calls.ResolvedValueArgument;
+import org.jetbrains.jet.lang.resolve.calls.inference.BoundsOwner;
 import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintSystemImpl;
 import org.jetbrains.jet.lang.resolve.scopes.receivers.ReceiverDescriptor;
 import org.jetbrains.jet.lang.types.JetType;
@@ -190,9 +191,9 @@ public class ResolveToolwindow extends JPanel {
                 result.append("Log: \n").append(log).append(bar);
             }
 
-            Map<JetType, ConstraintSystemImpl.TypeValue> knowns = debugInfo.get(BOUNDS_FOR_KNOWNS);
+            Map<JetType, BoundsOwner> knowns = debugInfo.get(BOUNDS_FOR_KNOWNS);
             renderMap(knowns, result);
-            Map<TypeParameterDescriptor, ConstraintSystemImpl.TypeValue> unknowns = debugInfo.get(BOUNDS_FOR_UNKNOWNS);
+            Map<TypeParameterDescriptor, BoundsOwner> unknowns = debugInfo.get(BOUNDS_FOR_UNKNOWNS);
             renderMap(unknowns, result);
 
             result.append(bar);
@@ -205,17 +206,17 @@ public class ResolveToolwindow extends JPanel {
         return result.toString();
     }
     
-    private <K> void renderMap(Map<K, ConstraintSystemImpl.TypeValue> map, StringBuilder builder) {
+    private <K> void renderMap(Map<K, BoundsOwner> map, StringBuilder builder) {
         if (map == null) return;
 
-        for (Map.Entry<K, ConstraintSystemImpl.TypeValue> entry : map.entrySet()) {
+        for (Map.Entry<K, BoundsOwner> entry : map.entrySet()) {
             K key = entry.getKey();
-            ConstraintSystemImpl.TypeValue typeValue = entry.getValue();
+            BoundsOwner typeValue = entry.getValue();
             builder.append("Bounds for ").append(key).append("\n");
-            for (ConstraintSystemImpl.TypeValue bound : typeValue.getLowerBounds()) {
+            for (BoundsOwner bound : typeValue.getLowerBounds()) {
                 builder.append("    >: ").append(bound).append("\n");
             }
-            for (ConstraintSystemImpl.TypeValue bound : typeValue.getUpperBounds()) {
+            for (BoundsOwner bound : typeValue.getUpperBounds()) {
                 builder.append("    <: ").append(bound).append("\n");
             }
         }