Bug fix: Reads no longer fail after dropping a fixed attribute and ad…

…ding it back as var-sized.

test/src/unit-cppapi-schema-evolution.cc

@@ -808,7 +808,7 @@ TEST_CASE(
 
 TEST_CASE(
     "C++ API: SchemaEvolution, drop fixed attribute and add back as var-sized",
-    "[!mayfail][cppapi][schema][evolution][add][drop]") {
+    "[cppapi][schema][evolution][add][drop]") {
   test::VFSTestSetup vfs_test_setup;
   Context ctx{vfs_test_setup.ctx()};
   auto array_uri{

tiledb/sm/query/readers/reader_base.cc

@@ -130,6 +130,13 @@ bool ReaderBase::skip_field(
     return true;
   }
 
+  // If an attribute exists but has changed from fixed->var or var->fixed after
+  // schema evolution, ignore for this fragment's tile offsets
+  if ((array_schema_.var_size(name) && !schema->var_size(name)) ||
+      (!array_schema_.var_size(name) && schema->var_size(name))) {
+    return true;
+  }
+
   // If the fragment doesn't include timestamps
   if (timestamps_not_present(name, frag_idx)) {
     return true;
@@ -1135,7 +1142,14 @@ uint64_t ReaderBase::get_attribute_tile_size(
 
   tile_size += fragment_metadata_[f]->tile_size(name, t);
 
-  if (array_schema_.var_size(name)) {
+  /**
+   * Note: There is a distinct case in which a schema may evolve from
+   * fixed-sized to var-sized. In this scenario, the LoadedFragmentMetadata
+   * contains fixed tiles. The tile_var_size should be calculated iff
+   * both the current _and_ loaded attributes are var-sized.
+   */
+  if (array_schema_.var_size(name) &&
+      fragment_metadata_[f]->array_schema()->var_size(name)) {
     tile_size +=
         fragment_metadata_[f]->loaded_metadata()->tile_var_size(name, t);
   }