[DAPHNE-#492] Creating Subframe of Frame with zero rows (#496)

- Add test to check for crashes when creating sub-frame from Frame with zero rows.
- Add fix to enable creation of a sub-frame with zero rows from a Frame with zero rows, by excluding the assertions.
- Closes #492.

src/runtime/local/datastructures/Frame.h

@@ -264,9 +264,13 @@ class Frame : public Structure {
             Structure(rowUpperExcl - rowLowerIncl, numCols)
     {
         assert(src && "src must not be null");
-        assert((rowLowerIncl < src->numRows) && "rowLowerIncl is out of bounds");
-        assert((rowUpperExcl <= src->numRows) && "rowUpperExcl is out of bounds");
-        assert((rowLowerIncl < rowUpperExcl) && "rowLowerIncl must be lower than rowUpperExcl");
+
+        // Only check conditions, if input Frame has not zero rows and the expected output has not zero rows.
+        if(!(rowLowerIncl == rowUpperExcl && rowLowerIncl == 0 && src->numRows == 0)) {
+            assert((rowLowerIncl < src->numRows) && "rowLowerIncl is out of bounds");
+            assert((rowUpperExcl <= src->numRows) && "rowUpperExcl is out of bounds");
+            assert((rowLowerIncl < rowUpperExcl) && "rowLowerIncl must be lower than rowUpperExcl");
+        }
         for(size_t i = 0; i < numCols; i++)
             assert((colIdxs[i] < src->numCols) && "some colIdx is out of bounds");
 

test/runtime/local/datastructures/FrameTest.cpp

@@ -145,4 +145,41 @@ TEST_CASE("Frame column labels must be unique", TAG_DATASTRUCTURES) {
     ValueTypeCode schema[] = {ValueTypeCode::SI64, ValueTypeCode::F64, ValueTypeCode::UI8};
     const std::string labels[] = {"foo", "bar", "foo"};
     CHECK_THROWS(DataObjectFactory::create<Frame>(4, 3, schema, labels, false));
+}
+
+TEST_CASE("Frame sub-frame for empty source frame works properly", TAG_DATASTRUCTURES) {
+    const size_t numRowsOrig = 0;
+    const ValueTypeCode schemaOrig[] = {ValueTypeCode::SI8, ValueTypeCode::UI32, ValueTypeCode::F64};
+    const size_t numColsOrig = sizeof(schemaOrig) / sizeof(ValueTypeCode);
+
+    Frame * fOrig = DataObjectFactory::create<Frame>(numRowsOrig, numColsOrig, schemaOrig, nullptr, true);
+    const size_t colIdxsSub[] = {2, 0};
+    const size_t numColsSub = sizeof(colIdxsSub) / sizeof(size_t);
+    Frame * fSub = DataObjectFactory::create<Frame>(fOrig, 0, 0, numColsSub, colIdxsSub);
+
+    // Sub-frame dimensions are as expected.
+    CHECK(fSub->getNumRows() == 0);
+    CHECK(fSub->getNumCols() == numColsSub);
+
+    // Sub-frame schema is as expected.
+    CHECK(fSub->getColumnType(0) == ValueTypeCode::F64);
+    CHECK(fSub->getColumnType(1) == ValueTypeCode::SI8);
+
+    // Sub-frame shares data arrays with original.
+    int8_t * colOrig0 = fOrig->getColumn<int8_t>(0)->getValues();
+    double * colOrig2 = fOrig->getColumn<double>(2)->getValues();
+    double * colSub0 = fSub->getColumn<double>(0)->getValues();
+    int8_t * colSub1 = fSub->getColumn<int8_t>(1)->getValues();
+    CHECK(colSub0 == colOrig2);
+    CHECK(colSub1 == colOrig0);
+
+    // Freeing both frames does not result in double-free errors.
+    SECTION("Freeing the original frame first is fine") {
+        DataObjectFactory::destroy(fOrig);
+        DataObjectFactory::destroy(fSub);
+    }
+    SECTION("Freeing the sub-frame first is fine") {
+        DataObjectFactory::destroy(fSub);
+        DataObjectFactory::destroy(fOrig);
+    }
 }