Commented by: @dyemanov

Solution for v3 Beta 2 and beyond: re-allow setting RDB$*_SOURCE to NULL (while protecting all other modifications).

Commented by: @pavel-zotov

Engine raises exception when 'UPDATE ... SET RDB$...SOURCE = NULL' tries to clear source of some object (proc/trigger) *again*, i.e. when this field already is NULL. This will borrow anyone who already has some units with NULL value in source and has added several units after it: one need to explicitly enumerate these units that has to be cleared.
Consider following sample:

=== begin of script ===

recreate table test(id int primary key, x int);
recreate table tlog(id int, x int);

recreate sequence g;

set term ^;
create or alter procedure sp_test1 as
declare c int;
begin
select count(*) from rdb$types into c;
end
^

create or alter function fn_test1 returns int as
begin
return 111;
end
^

create or alter trigger trg_test_1 active before insert on test as
begin
http://new.id = gen_id(g,1);
end
^

set term ;^
commit;

set blob all;
set list on;

------------------------------------------------------ [ 1 ] --------------------------------------------------
set echo on;

select rdb$procedure_name, rdb$procedure_source from rdb$procedures where rdb$system_flag is distinct from 1;

select rdb$function_name, rdb$function_source from rdb$functions where rdb$system_flag is distinct from 1;

select rdb$trigger_name, rdb$trigger_source from rdb$triggers where rdb$system_flag is distinct from 1;

set count on;

update rdb$procedures set rdb$procedure_source = null
where
rdb$system_flag is distinct from 1
;

update rdb$functions set rdb$function_source = null
where
rdb$system_flag is distinct from 1
;

update rdb$triggers set rdb$trigger_source = null
where
rdb$system_flag is distinct from 1
;

commit;

set echo off;
set count off;

set term ^;

create or alter procedure sp_test2 as
declare c int;
begin
select count(*) from rdb$types into c;
end
^

create or alter function fn_test2 returns int as
begin
return 222;
end
^

create or alter trigger trg_test_2 active after insert or update or delete on test as
begin
if ( not deleting ) then
insert into tlog(id, x) values( http://new.id, new.x );
else
insert into tlog(id, x) values( http://old.id, old.x );
end
^

set term ;^
commit;

set count on;

------------------------------------------------------ [ 2 ] --------------------------------------------------
set echo on;

update rdb$procedures set rdb$procedure_source = null
where
rdb$system_flag is distinct from 1
;

update rdb$functions set rdb$function_source = null
where
rdb$system_flag is distinct from 1
;

update rdb$triggers set rdb$trigger_source = null
where
rdb$system_flag is distinct from 1
;

commit;

set count off;

select rdb$procedure_name, rdb$procedure_source from rdb$procedures where rdb$system_flag is distinct from 1;

select rdb$function_name, rdb$function_source from rdb$functions where rdb$system_flag is distinct from 1;

select rdb$trigger_name, rdb$trigger_source from rdb$triggers where rdb$system_flag is distinct from 1;

=== end of script ===

Statements 'update ... set rdb$source = null' in block marked as [ 1 ] will execute without exceptions.
Statements in block marked as [ 2 ] will raise

Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$...

- and this mean that units that appear after 1st 'update ... set null' (i.e. 'SP_TEST2', 'FN_TEST2' and 'TRG_TEST_2') remain with source code: we have explicitly specify them in 2nd update serie.

Commented by: @pavel-zotov

PS. Of course, we can add in every UPDATE statement additional line like "and rdb$procedure_source is not null" but IMO it engine should allow to avoid this.

Commented by: @pavel-zotov

PPS.

update rdb$packages set rdb$package_body_source = null
where
rdb$system_flag is distinct from 1
and rdb$package_body_source is not null
;
Statement failed, SQLSTATE = 42000
UPDATE operation is not allowed for system table RDB$PACKAGES
After line 85 in file . . .
Records affected: 0

Not implemented yet ?

Commented by: @dyemanov

NULL->NULL changes are intentionally prohibited. The problem, AFAIR, is that it's impossible to distinguish between e.g. SET RDB$PROCEDURE_SOURCE = NULL and SET RDB$PROCEDURE_NAME = RDB$PROCEDURE_NAME or any other kind of dummy update. This may cause confusion as some direct system table updates (that do not actually change anything) become allowed, e.g.:

update rdb$relations set rdb$system_flag = 0

would succeed for records already having rdb$system_flag = 0 and fail for others, and this is impossible to predict without knowing what's actually stored inside rdb$system_flag.

Given that the SOURCE->NULL changes are allowed only temporarily, until something better is implemented, and given that the issue can be worked around using the WHERE clause, I tend to leave everything as is.

Commented by: @dyemanov

SET RDB$PACKAGE_BODY_SOURCE = NULL is allowed now.