Bug#18761: constant expression as UDF parameters not passed in as constant

The code that set up data to be passed to user-defined functions was very
old and analyzed the "Type" of the data that was passed into the UDF, when
it really should analyze the "return_type", which is hard-coded for simple
Items and works correctly for complex ones like functions.
---
Added test at Sergei's behest.


mysql-test/r/udf.result:
  Verify that various arguments work.
  ---
  Added test at Sergei's behest.
mysql-test/t/udf.test:
  Verify that various arguments work.
  ---
  Added test at Sergei's behest.
sql/item_func.cc:
  For function-Items, test whether it is constant and set the struct members 
  for the UDF parameter appropriately.
  
  Replace tabs with spaces in affected code.
sql/udf_example.c:
  Include a simple function that is useful in testing.

1 files changed, 30 insertions, 0 deletions

diff --git a/sql/udf_example.c b/sql/udf_example.c
index 2fa7474eb16..a4f7eddd302 100644
--- a/sql/udf_example.c
+++ b/sql/udf_example.c
@@ -165,6 +165,9 @@ void avgcost_reset( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error
 void avgcost_clear( UDF_INIT* initid, char* is_null, char *error );
 void avgcost_add( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
 double avgcost( UDF_INIT* initid, UDF_ARGS* args, char* is_null, char *error );
+my_bool is_const_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
+char *is_const(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long
+               *length, char *is_null, char *error);
 
 
 /*************************************************************************
@@ -1075,4 +1078,31 @@ char *myfunc_argument_name(UDF_INIT *initid __attribute__((unused)),
   return result;
 }
 
+
+
+my_bool is_const_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
+{
+  if (args->arg_count != 1)
+  {
+    strmov(message, "IS_CONST accepts only one argument");
+    return 1;
+  }
+  initid->ptr= (args->args[0] != NULL) ? 1 : 0;
+  return 0;
+}
+
+char * is_const(UDF_INIT *initid, UDF_ARGS *args, char *result, unsigned long
+                *length, char *is_null, char *error)
+{
+  if (initid->ptr != 0) {
+    sprintf(result, "const");
+  } else {
+    sprintf(result, "not const");
+  }
+  *is_null= 0;
+  *length= strlen(result);
+  return result;
+}
+
+
 #endif /* HAVE_DLOPEN */