Improve error messages for CREATE OR REPLACE PROCEDURE

Change the hint to recommend DROP PROCEDURE instead of FUNCTION.  Also
make the error message when changing the return type more specific to
the case of procedures.
Reported-by: Jeremy Evans <code@jeremyevans.net>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>

src/backend/catalog/pg_proc.c

@@ -375,6 +375,7 @@ ProcedureCreate(const char *procedureName,
 		Form_pg_proc oldproc = (Form_pg_proc) GETSTRUCT(oldtup);
 		Datum		proargnames;
 		bool		isnull;
+		const char *dropcmd;
 
 		if (!replace)
 			ereport(ERROR,
@@ -400,16 +401,26 @@ ProcedureCreate(const char *procedureName,
 					  errdetail("\"%s\" is a window function.", procedureName) :
 					  0)));
 
+		dropcmd = (prokind == PROKIND_PROCEDURE ? "DROP PROCEDURE" : "DROP FUNCTION");
+
 		/*
 		 * Not okay to change the return type of the existing proc, since
 		 * existing rules, views, etc may depend on the return type.
+		 *
+		 * In case of a procedure, a changing return type means that whether
+		 * the procedure has output parameters was changed.  Since there is no
+		 * user visible return type, we produce a more specific error message.
 		 */
 		if (returnType != oldproc->prorettype ||
 			returnsSet != oldproc->proretset)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
-					 errmsg("cannot change return type of existing function"),
-					 errhint("Use DROP FUNCTION %s first.",
+					 prokind == PROKIND_PROCEDURE
+					 ? errmsg("cannot change whether a procedure has output parameters")
+					 : errmsg("cannot change return type of existing function"),
+					 /* translator: first %s is DROP FUNCTION or DROP PROCEDURE */
+					 errhint("Use %s %s first.",
+							 dropcmd,
 							 format_procedure(HeapTupleGetOid(oldtup)))));
 
 		/*
@@ -434,7 +445,9 @@ ProcedureCreate(const char *procedureName,
 						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
 						 errmsg("cannot change return type of existing function"),
 						 errdetail("Row type defined by OUT parameters is different."),
-						 errhint("Use DROP FUNCTION %s first.",
+						 /* translator: first %s is DROP FUNCTION or DROP PROCEDURE */
+						 errhint("Use %s %s first.",
+								 dropcmd,
 								 format_procedure(HeapTupleGetOid(oldtup)))));
 		}
 
@@ -477,7 +490,9 @@ ProcedureCreate(const char *procedureName,
 							(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
 							 errmsg("cannot change name of input parameter \"%s\"",
 									old_arg_names[j]),
-							 errhint("Use DROP FUNCTION %s first.",
+							 /* translator: first %s is DROP FUNCTION or DROP PROCEDURE */
+							 errhint("Use %s %s first.",
+									 dropcmd,
 									 format_procedure(HeapTupleGetOid(oldtup)))));
 			}
 		}
@@ -501,7 +516,9 @@ ProcedureCreate(const char *procedureName,
 				ereport(ERROR,
 						(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
 						 errmsg("cannot remove parameter defaults from existing function"),
-						 errhint("Use DROP FUNCTION %s first.",
+						 /* translator: first %s is DROP FUNCTION or DROP PROCEDURE */
+						 errhint("Use %s %s first.",
+								 dropcmd,
 								 format_procedure(HeapTupleGetOid(oldtup)))));
 
 			proargdefaults = SysCacheGetAttr(PROCNAMEARGSNSP, oldtup,
@@ -527,7 +544,9 @@ ProcedureCreate(const char *procedureName,
 					ereport(ERROR,
 							(errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
 							 errmsg("cannot change data type of existing parameter default value"),
-							 errhint("Use DROP FUNCTION %s first.",
+							 /* translator: first %s is DROP FUNCTION or DROP PROCEDURE */
+							 errhint("Use %s %s first.",
+									 dropcmd,
 									 format_procedure(HeapTupleGetOid(oldtup)))));
 				newlc = lnext(newlc);
 			}