improved error message

added debug info about constraint system status

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

@@ -24,6 +24,8 @@ import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
 import org.jetbrains.jet.lang.types.*;
 import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
 
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
 import java.util.*;
 
 public class ConstraintsUtil {
@@ -110,4 +112,32 @@ public class ConstraintsUtil {
         }
         return true;
     }
+    
+    public static String getDebugMessageForStatus(@NotNull ConstraintSystemStatus status) {
+        StringBuilder sb = new StringBuilder();
+        List<Method> interestingMethods = Lists.newArrayList();
+        for (Method method : status.getClass().getMethods()) {
+            String name = method.getName();
+            boolean isInteresting = name.startsWith("is") || name.startsWith("has") && !name.equals("hashCode");
+            if (method.getParameterTypes().length == 0 && isInteresting) {
+                interestingMethods.add(method);
+            }
+        }
+        for (Iterator<Method> iterator = interestingMethods.iterator(); iterator.hasNext(); ) {
+            Method method = iterator.next();
+            try {
+                sb.append("-").append(method.getName()).append(": ").append(method.invoke(status));
+                if (iterator.hasNext()) {
+                    sb.append("\n");
+                }
+            }
+            catch (IllegalAccessException e) {
+                sb.append(e.getMessage());
+            }
+            catch (InvocationTargetException e) {
+                sb.append(e.getMessage());
+            }
+        }
+        return sb.toString();
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/ControlStructureTypingUtils.java

@@ -35,6 +35,7 @@ import org.jetbrains.jet.lang.resolve.calls.autocasts.DataFlowInfo;
 import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintPosition;
 import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintSystem;
 import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintSystemStatus;
+import org.jetbrains.jet.lang.resolve.calls.inference.ConstraintsUtil;
 import org.jetbrains.jet.lang.resolve.calls.inference.InferenceErrorData;
 import org.jetbrains.jet.lang.resolve.calls.model.MutableDataFlowInfoForArguments;
 import org.jetbrains.jet.lang.resolve.calls.model.ResolvedCall;
@@ -345,13 +346,13 @@ public class ControlStructureTypingUtils {
                 if (status.hasErrorInConstrainingTypes()) {
                     return;
                 }
+                JetExpression expression = call.getCalleeExpression();
+                if (expression == null) return;
                 if (status.hasOnlyErrorsFromPosition(ConstraintPosition.EXPECTED_TYPE_POSITION) || status.hasConflictingConstraints()) {
-                    JetExpression expression = call.getCalleeExpression();
-                    if (expression != null) {
-                        expression.accept(checkTypeVisitor, new CheckTypeContext(trace, data.expectedType));
-                    }
+                    expression.accept(checkTypeVisitor, new CheckTypeContext(trace, data.expectedType));
                     return;
                 }
+                throwError("Expression: " + expression.getText() + ".\nConstraint system status: \n" + ConstraintsUtil.getDebugMessageForStatus(status));
                 super.typeInferenceFailed(trace, data);
             }
         };
@@ -365,7 +366,15 @@ public class ControlStructureTypingUtils {
         }
 
         private void throwError() {
-            throw new IllegalStateException("Resolution error of this type shouldn't occur for " + debugName);
+            throwError(null);
+        }
+
+        protected void throwError(@Nullable String additionalInformation) {
+            String errorMessage = "Resolution error of this type shouldn't occur for " + debugName;
+            if (additionalInformation != null) {
+                errorMessage += ".\n" + additionalInformation;
+            }
+            throw new IllegalStateException(errorMessage);
         }
 
         @Override

core/descriptors/src/org/jetbrains/jet/lang/resolve/calls/inference/ConstraintSystemImpl.java

@@ -59,6 +59,8 @@ public class ConstraintSystemImpl implements ConstraintSystem {
     private boolean hasErrorInConstrainingTypes;
 
     private final ConstraintSystemStatus constraintSystemStatus = new ConstraintSystemStatus() {
+        // for debug ConstraintsUtil.getDebugMessageForStatus might be used
+
         @Override
         public boolean isSuccessful() {
             return !hasContradiction() && !hasUnknownParameters();