Introduce method for getting element with context for better error reports

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetPsiUtil.java

@@ -20,6 +20,7 @@ import com.google.common.base.Function;
 import com.google.common.base.Predicate;
 import com.google.common.collect.Lists;
 import com.intellij.lang.ASTNode;
+import com.intellij.openapi.util.Condition;
 import com.intellij.psi.*;
 import com.intellij.psi.impl.CheckUtil;
 import com.intellij.psi.impl.source.codeStyle.CodeEditUtil;
@@ -946,4 +947,28 @@ public class JetPsiUtil {
         }
         return element;
     }
+
+    @NotNull
+    public static String getElementTextWithContext(@NotNull JetElement element) {
+        if (element instanceof JetFile) {
+            return element.getContainingFile().getText();
+        }
+
+        // Find parent for element among file children
+        PsiElement inFileParent = PsiTreeUtil.findFirstParent(element, new Condition<PsiElement>() {
+            @Override
+            public boolean value(PsiElement parentCandidate) {
+                return parentCandidate != null && parentCandidate.getParent() instanceof JetFile;
+            }
+        });
+
+        assert inFileParent != null : "For non-file element we should always be able to find parent in file children";
+
+        int startContextOffset = inFileParent.getTextRange().getStartOffset();
+        int elementContextOffset = element.getTextRange().getStartOffset();
+
+        int inFileParentOffset = elementContextOffset - startContextOffset;
+
+        return new StringBuilder(inFileParent.getText()).insert(inFileParentOffset, "<caret>").toString();
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/ResolveSession.java

@@ -341,7 +341,8 @@ public class ResolveSession implements KotlinCodeAnalyzer {
 
             @Override
             public DeclarationDescriptor visitJetElement(JetElement element, Void data) {
-                throw new IllegalArgumentException("Unsupported declaration type: " + element + " " + element.getText());
+                throw new IllegalArgumentException("Unsupported declaration type: " + element + " " +
+                                                   JetPsiUtil.getElementTextWithContext(element));
             }
         }, null);
         if (result == null) {