Fix the lifetimeof encoder for system temp tables

Author: malone-at-work

mysql-test/suite/villagesql/select/r/select_union_literal_encode_complex.result

@@ -0,0 +1,9 @@
+CREATE TABLE t1 (val vsql_complex.COMPLEX);
+INSERT INTO t1 VALUES ('(1.0, 2.0)'), ('(3.0, 4.0)');
+# String literal unioned with COMPLEX column: encoder runs on tmp table field
+SELECT '(5.0, 6.0)' AS val UNION SELECT val FROM t1 ORDER BY val;
+val
+(1,2)
+(3,4)
+(5,6)
+DROP TABLE t1;

mysql-test/suite/villagesql/select/t/select_union_literal_encode_complex.test

@@ -0,0 +1,19 @@
+# Regression test: encoding a string literal into a UNION result tmp table's
+# COMPLEX field must not allocate the TypeEncoder on TABLE::mem_root.
+#
+# A UNION where one arm is a string literal and the other is a COMPLEX column
+# forces GetTypeEncoderFor() to run on the UNION result tmp table's Field.
+# With the bug, close_tmp_table() asserts table->mem_root.allocated_size() == 0
+# in debug builds because the encoder was allocated there.
+
+--source include/villagesql/install_complex_extension.inc
+
+CREATE TABLE t1 (val vsql_complex.COMPLEX);
+INSERT INTO t1 VALUES ('(1.0, 2.0)'), ('(3.0, 4.0)');
+
+--echo # String literal unioned with COMPLEX column: encoder runs on tmp table field
+SELECT '(5.0, 6.0)' AS val UNION SELECT val FROM t1 ORDER BY val;
+
+DROP TABLE t1;
+
+--source include/villagesql/uninstall_complex_extension.inc

villagesql/types/util.cc

@@ -238,14 +238,26 @@ bool HandleCustomColumnsForTableRename(THD &thd, const char *old_db,
   return false;
 }
 
-// Lazily allocate a TypeEncoder for field from TABLE::mem_root. The encoder
-// is reused for all subsequent encodes on the same Field within the TABLE's
-// lifetime.
+// Lazily allocate a TypeEncoder for field, reused for all subsequent encodes
+// within the table's lifetime.
+//
+// For any kind of tmp table, close_tmp_table() asserts TABLE::mem_root is
+// empty, so we use TABLE_SHARE::mem_root instead. This covers UNION result
+// tables and any other internal tmp table that may hold custom type fields
+// (e.g. when a string literal is unioned with a COMPLEX column and must be
+// encoded into the result tmp table's field).
+// free_tmp_table() frees the share's mem_root, cleaning up the encoder.
+//
+// For regular tables (NO_TMP_TABLE), TABLE::mem_root has the same lifetime as
+// the Field clone that caches the encoder pointer, so both are freed together
+// when the TABLE is evicted from the table open cache.
 static TypeEncoder *GetTypeEncoderFor(Field *field) {
   TypeEncoder *encoder = field->get_type_encoder();
   if (encoder == nullptr) {
-    encoder = new (&field->table->mem_root)
-        TypeEncoder(field->get_type_context(), field->table->mem_root);
+    MEM_ROOT &mem_root = (field->table->s->tmp_table == NO_TMP_TABLE)
+                             ? field->table->mem_root
+                             : field->table->s->mem_root;
+    encoder = new (&mem_root) TypeEncoder(field->get_type_context(), mem_root);
     if (encoder == nullptr) {
       my_error(ER_OUTOFMEMORY, MYF(ME_FATALERROR), sizeof(TypeEncoder));
       return nullptr;