Expose a few more PL/pgSQL functions to debugger plugins.

Add exec_assign_value, exec_eval_datum, and exec_cast_value
to the set of functions a PL/pgSQL debugger plugin can
conveniently call.  This allows more convenient manipulation
of the values of PL/pgSQL function variables.

Pavel Stehule, reviewed by Aleksander Alekseev and myself

Discussion: https://postgr.es/m/CAFj8pRD+dBPU0T-KrkP7ef6QNPDEsjYCejEsBe07NDq8TybOkA@mail.gmail.com

Author: tglsfdc

src/pl/plpgsql/src/pl_exec.c

@@ -4077,15 +4077,18 @@ plpgsql_estate_setup(PLpgSQL_execstate *estate,
 	plpgsql_create_econtext(estate);
 
 	/*
-	 * Let the plugin see this function before we initialize any local
-	 * PL/pgSQL variables - note that we also give the plugin a few function
-	 * pointers so it can call back into PL/pgSQL for doing things like
-	 * variable assignments and stack traces
+	 * Let the plugin, if any, see this function before we initialize local
+	 * PL/pgSQL variables.  Note that we also give the plugin a few function
+	 * pointers, so it can call back into PL/pgSQL for doing things like
+	 * variable assignments and stack traces.
 	 */
 	if (*plpgsql_plugin_ptr)
 	{
 		(*plpgsql_plugin_ptr)->error_callback = plpgsql_exec_error_callback;
 		(*plpgsql_plugin_ptr)->assign_expr = exec_assign_expr;
+		(*plpgsql_plugin_ptr)->assign_value = exec_assign_value;
+		(*plpgsql_plugin_ptr)->eval_datum = exec_eval_datum;
+		(*plpgsql_plugin_ptr)->cast_value = exec_cast_value;
 
 		if ((*plpgsql_plugin_ptr)->func_setup)
 			((*plpgsql_plugin_ptr)->func_setup) (estate, func);

src/pl/plpgsql/src/plpgsql.h

@@ -1120,9 +1120,17 @@ typedef struct PLpgSQL_execstate
  * statement.
  *
  * Also, immediately before any call to func_setup, PL/pgSQL fills in the
- * error_callback and assign_expr fields with pointers to its own
- * plpgsql_exec_error_callback and exec_assign_expr functions.  This is
- * a somewhat ad-hoc expedient to simplify life for debugger plugins.
+ * remaining fields with pointers to some of its own functions, allowing the
+ * plugin to invoke those functions conveniently.  The exposed functions are:
+ *		plpgsql_exec_error_callback
+ *		exec_assign_expr
+ *		exec_assign_value
+ *		exec_eval_datum
+ *		exec_cast_value
+ * (plpgsql_exec_error_callback is not actually meant to be called by the
+ * plugin, but rather to allow it to identify PL/pgSQL error context stack
+ * frames.  The others are useful for debugger-like plugins to examine and
+ * set variables.)
  */
 typedef struct PLpgSQL_plugin
 {
@@ -1135,8 +1143,20 @@ typedef struct PLpgSQL_plugin
 
 	/* Function pointers set by PL/pgSQL itself */
 	void		(*error_callback) (void *arg);
-	void		(*assign_expr) (PLpgSQL_execstate *estate, PLpgSQL_datum *target,
+	void		(*assign_expr) (PLpgSQL_execstate *estate,
+								PLpgSQL_datum *target,
 								PLpgSQL_expr *expr);
+	void		(*assign_value) (PLpgSQL_execstate *estate,
+								 PLpgSQL_datum *target,
+								 Datum value, bool isNull,
+								 Oid valtype, int32 valtypmod);
+	void		(*eval_datum) (PLpgSQL_execstate *estate, PLpgSQL_datum *datum,
+							   Oid *typeid, int32 *typetypmod,
+							   Datum *value, bool *isnull);
+	Datum		(*cast_value) (PLpgSQL_execstate *estate,
+							   Datum value, bool *isnull,
+							   Oid valtype, int32 valtypmod,
+							   Oid reqtype, int32 reqtypmod);
 } PLpgSQL_plugin;
 
 /*