fix: Minor update to DictionaryVector toString (facebookincubator#12025)

Summary:

Fixes error raised in Github issue 10594 (facebookincubator#10594)

Error details blindspot in toString function for lazy vectors where they are able to be logged; however they still show as unitialized as setInternalState was never executed.

I propose that function loadedVector be called to start the method as it will quit early for initialized vectors and serve virtually no additional overhead, while unloaded vectors will be properly initialized

Differential Revision: D67870420

velox/vector/DictionaryVector.h

@@ -186,6 +186,9 @@ class DictionaryVector : public SimpleVector<T> {
   }
 
   std::string toString(vector_size_t index) const override {
+    VELOX_CHECK(
+        initialized_,
+        "Cannot convert to string because current DictionaryVector is not properly initialized yet.");
     if (BaseVector::isNullAt(index)) {
       return "null";
     }

velox/vector/tests/VectorTest.cpp

@@ -3932,6 +3932,30 @@ TEST_F(VectorTest, testFlatteningOfRedundantDictionary) {
   }
 }
 
+TEST_F(
+    VectorTest,
+    verifyOuterDictionaryLayersInitalizedWhenLoggingLazyLoadedVector) {
+  // Tester function verifies proper behavior when outer dictionary layers of a
+  // lazy vector are not properly initalized and user calls toString. Expected
+  // behavior should be a runtime error noting user to properly load vector
+  // prior to invoking toString.
+  auto doubleVector = makeFlatVector<double>({1.0, 2.0, 3.0});
+  auto doubleInDictionary = BaseVector::wrapInDictionary(
+      nullptr, makeIndices({0, 1, 2}), 3, doubleVector);
+  auto doubleInNestedDictionary = BaseVector::wrapInDictionary(
+      nullptr, makeIndices({0, 1, 2}), 3, doubleInDictionary);
+  auto doubleInLazyDictionary =
+      VectorFuzzer::wrapInLazyVector(doubleInNestedDictionary);
+
+  auto rowVector = makeRowVector({doubleVector, doubleInLazyDictionary});
+
+  // Log vector; in doing so, we should trigger our VELOX_CHECK error as
+  // dictionary is not properly initialized.
+  for (vector_size_t i = 0; i < rowVector->size(); ++i) {
+    EXPECT_THROW(rowVector->toString(i), VeloxRuntimeError);
+  }
+}
+
 TEST_F(VectorTest, hasOverlappingRanges) {
   auto test = [this](
                   vector_size_t length,