MDEV-16094 Crash when using AS OF with a stored function

MDEV-16100 FOR SYSTEM_TIME erroneously resolves string user variables as transaction IDs

Problem:

Vers_history_point::resolve_unit() tested item->result_type() before
item->fix_fields() was called.

- Item_func_get_user_var::result_type() returned REAL_RESULT by default.
  This caused MDEV-16100.
- Item_func_sp::result_type() crashed on assert.
  This caused MDEV-16094

Changes:
1. Adding item->fix_fields() into Vers_history_point::resolve_unit()
   before using data type specific properties of the history point
   expression.

2. Adding a new virtual method Type_handler::Vers_history_point_resolve_unit()

3. Implementing type-specific
   Type_handler_xxx::Type_handler::Vers_history_point_resolve_unit()
    in the way to:
    a. resolve temporal and general purpose string types to TIMESTAMP
    b. resolve BIT and general purpose INT types to TRANSACTION
    c. disallow use of non-relevant data type expressions in FOR SYSTEM_TIME

    Note, DOUBLE and DECIMAL data types are disallowed intentionally.
    - DOUBLE does not have enough precision to hold huge BIGINT UNSIGNED values
    - DECIMAL rounds on conversion to INT
    Both lack of precision and rounding might potentionally lead to
    very unpredictable results when a wrong transaction ID would be chosen.
    If one really wants dangerous use of DOUBLE and DECIMAL, explicit CAST
    can be used:

      FOR SYSTEM_TIME AS OF CAST(double_or_decimal AS UNSIGNED)

    QQ: perhaps DECIMAL(N,0) could still be allowed.

4. Adding a new virtual method Item::type_handler_for_system_time(),
   to make HEX hybrids and bit literals work as TRANSACTION rather
   than TIMESTAMP.

5. sql_yacc.yy: replacing the rule temporal_literal to "TIMESTAMP TEXT_STRING".
   Other temporal literals now resolve to TIMESTAMP through the new
   Type_handler methods. No special grammar needed. This removed
   a few shift/resolve conflicts.
   (TIMESTAMP related conflicts in "history_point:" will be removed separately)

6. Removing the "timestamp_only" parameter from
   vers_select_conds_t::resolve_units() and Vers_history_point::resolve_unit().
   It was a hint telling that a table did not have any TRANSACTION-aware
   system time columns, so it's OK to resolve to TIMESTAMP in case of uncertainty.
   In the new reduction it works as follows:
   - the decision between TIMESTAMP and TRANSACTION is first made
     based only on the expression data type only
   - then, in case if the expression resolved to TRANSACTION, the table
     is checked if TRANSACTION-aware columns really exist.
   This way is safer against possible ALTER TABLE statements changing
   ROW START and ROW END columns from "BIGINT UNSIGNED" to "TIMESTAMP(x)"
   or the other way around.

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/sql_type.h b/sql/sql_type.h
index 16db421a4d3..1ddcef2da61 100644
--- a/sql/sql_type.h
+++ b/sql/sql_type.h
@@ -72,6 +72,7 @@ class handler;
 struct Schema_specification_st;
 struct TABLE;
 struct SORT_FIELD_ATTR;
+class Vers_history_point;
 
 
 /**
@@ -1409,6 +1410,9 @@ public:
   Item_func_div_fix_length_and_dec(Item_func_div *func) const= 0;
   virtual bool
   Item_func_mod_fix_length_and_dec(Item_func_mod *func) const= 0;
+
+  virtual bool
+  Vers_history_point_resolve_unit(THD *thd, Vers_history_point *point) const;
 };
 
 
@@ -2105,6 +2109,7 @@ public:
   virtual const Type_limits_int *
     type_limits_int_by_unsigned_flag(bool unsigned_flag) const= 0;
   uint32 max_display_length(const Item *item) const;
+  bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };
 
 
@@ -2174,6 +2179,7 @@ public:
   bool Item_func_mul_fix_length_and_dec(Item_func_mul *) const;
   bool Item_func_div_fix_length_and_dec(Item_func_div *) const;
   bool Item_func_mod_fix_length_and_dec(Item_func_mod *) const;
+  bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };
 
 
@@ -2298,6 +2304,7 @@ class Type_handler_general_purpose_string: public Type_handler_string_result
 {
 public:
   bool is_general_purpose_string_type() const { return true; }
+  bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };
 
 
@@ -2570,6 +2577,7 @@ public:
                           const Record_addr &addr,
                           const Type_all_attributes &attr,
                           TABLE *table) const;
+  bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };
 
 
@@ -3384,6 +3392,7 @@ public:
                                          const;
   void Item_param_set_param_func(Item_param *param,
                                  uchar **pos, ulong len) const;
+  bool Vers_history_point_resolve_unit(THD *thd, Vers_history_point *p) const;
 };