MDEV-12441 Variables declared after cursors with parameters lose values

Parse context frames (sp_pcontext) can have holes in variable run-time offsets,
the missing offsets reside on the children contexts in such cases.

Example:

  CREATE PROCEDURE p1() AS
    x0 INT:=100;        -- context 0, position 0, run-time 0
    CURSOR cur(
      p0 INT,           -- context 1, position 0, run-time 1
      p1 INT            -- context 1, position 1, run-time 2
    ) IS SELECT p0, p1;
    x1 INT:=101;        -- context 0, position 1, run-time 3
  BEGIN
    ...
  END;

Fixing a few methods to take this into account:
- sp_pcontext::find_variable()
- sp_pcontext::retrieve_field_definitions()
- LEX::sp_variable_declarations_init()
- LEX::sp_variable_declarations_finalize()
- LEX::sp_variable_declarations_rowtype_finalize()
- LEX::sp_variable_declarations_with_ref_finalize()

Adding a convenience method:

  sp_pcontext::get_last_context_variable(uint offset_from_the_end);

to access variables from the end, rather than from the beginning.
This helps to loop through the context variable array (m_vars)
on the fragment that does not have any holes.

Additionally, renaming sp_pcontext::find_context_variable() to
sp_pcontext::get_context_variable(). This method simply returns
the variable by its index. So let's rename to avoid assumptions
that some heavy lookup is going on inside.

1 files changed, 10 insertions, 4 deletions

diff --git a/sql/sp_pcontext.h b/sql/sp_pcontext.h
index 98ab4955198..c6c8084fee2 100644
--- a/sql/sp_pcontext.h
+++ b/sql/sp_pcontext.h
@@ -440,15 +440,21 @@ public:
   { return m_vars.elements(); }
 
   /// return the i-th variable on the current context
-  sp_variable *find_context_variable(uint i) const
+  sp_variable *get_context_variable(uint i) const
   {
     DBUG_ASSERT(i < m_vars.elements());
     return m_vars.at(i);
   }
 
-  /// @return map index in this parsing context to runtime offset.
-  uint var_context2runtime(uint i) const
-  { return m_var_offset + i; }
+  /*
+    Return the i-th last context variable.
+    If i is 0, then return the very last variable in m_vars.
+  */
+  sp_variable *get_last_context_variable(uint i= 0) const
+  {
+    DBUG_ASSERT(i < m_vars.elements());
+    return m_vars.at(m_vars.elements() - i - 1);
+  }
 
   /// Add SP-variable to the parsing context.
   ///