Post-review fixes for BUG#14376: MySQL crash on scoped variable (re)initialization

sql/sp_pcontext.cc:
  Count boundary for variable visibility from the frame end instead.
sql/sp_pcontext.h:
  Count boundary for variable visibility from the frame end instead.
  Updated comments.
sql/sql_yacc.yy:
  Changed tabs to spaces.

sql/sp_pcontext.cc

@@ -150,7 +150,7 @@ sp_pcontext::diff_cursors(sp_pcontext *ctx)
 sp_pvar_t *
 sp_pcontext::find_pvar(LEX_STRING *name, my_bool scoped)
 {
-  uint i= m_pboundary;
+  uint i= m_pvar.elements - m_pboundary;
 
   while (i--)
   {
@@ -186,7 +186,6 @@ sp_pcontext::push_pvar(LEX_STRING *name, enum enum_field_types type,
     p->offset= current_pvars();
     p->dflt= NULL;
     insert_dynamic(&m_pvar, (gptr)&p);
-    m_pboundary= m_pvar.elements;
   }
 }
 

sql/sp_pcontext.h

@@ -164,7 +164,6 @@ class sp_pcontext : public Sql_alloc
   {
     while (num--)
       pop_dynamic(&m_pvar);
-    m_pboundary= m_pvar.elements;
   }
 
   // Find by name
@@ -184,12 +183,14 @@ class sp_pcontext : public Sql_alloc
     return p;
   }
 
-  // Set the current scope boundary (for default values)
-  // The argument is the number of variables to skip.
+  /*
+    Set the current scope boundary (for default values)
+    The argument is the number of variables to skip.   
+  */
   inline void
   declare_var_boundary(uint n)
   {
-    m_pboundary= m_pvar.elements-n;
+    m_pboundary= n;
   }
 
   //
@@ -297,10 +298,10 @@ private:
   uint m_poffset;		// Variable offset for this context
   uint m_coffset;		// Cursor offset for this context
   /*
-    Boundary for finding variables in this in this context.
-    This is normally the same as m_pvar.elements, but differs during
-    parsing of DECLARE ... DEFAULT, to get the scope right for DEFAULT
-    values.
+    Boundary for finding variables in this context. This is the number
+    of variables currently "invisible" to default clauses.
+    This is normally 0, but will be larger during parsing of
+    DECLARE ... DEFAULT, to get the scope right for DEFAULT values.
   */
   uint m_pboundary;