Package constants

[Noremos]

Package Constants

This PR adds a new database object - Package Constant (#1036). It is a constant value located in a package header (public visibility) or a package body (private visibility). See README.packages.txt for more information.

SYNTAX

Creation:

CREATE PACKAGE <package_name>
AS
BEGIN
    CONSTANT <constant_name> <type> = <constant_expr>; -- public constant
    -- package routines
END

CREATE PACKAGE BODY <package_name>
AS
BEGIN
    CONSTANT <constant_name> <type> = <constant_expr>; -- private constant
    -- package routines
END

<constant_expr> is an expression that remains unchanged after recompilation.

Package constants can be queried using the expression <package_name>.<consatnt_name> outside the package (<consatnt_name> must be a public constant) and using the expression <consatnt_name> inside the package.
To query a constant, the user/role must have USAGE permission on the package.

Other SQL extensions:

COMMENT ON CONSTANT [<schema>.]<package>.<const_name> IS <text>
GRANT USAGE ON PACKAGE  [<schema>.]<package_name> to [<user|role>] <name> [<grant_option>] [<granted_by>]
REVOKE USAGE ON PACKAGE  [<schema>.]<package_name> FROM <user|role> <name> [<granted_by>]
SHOW CONST[ANTS]  [ [<schema>.]<package_name> ] -- isql only

Usage examples:

set autoterm;
CREATE PACKAGE MY_PACKAGE
AS
BEGIN
    CONSTANT PUBLIC_CONST INTEGER = 10;
    FUNCTION MY_SECRET_PRINT() RETURNS INT;
END;

CREATE PACKAGE BODY MY_PACKAGE
AS
BEGIN
    CONSTANT SECRET_1 INTEGER = 15;
    CONSTANT SECRET_2 INTEGER = 30;

    FUNCTION MY_SECRET_PRINT() RETURNS INT
    AS
    BEGIN
        RETURN SECRET_1 * SECRET_2;
    END
END;
commit;

select MY_PACKAGE.PUBLIC_CONST from rdb$database ;
select MY_PACKAGE.MY_SECRET_PRINT() from rdb$database;

System Constants

As an exmaple, 3 consatnts have been added to the RDB$BLOB_UTIL package

FROM_BEGIN  : INTEGER = 0
FROM_CURRENT : INTEGER = 1
FROM_END : INTEGER = 2

System metadata changes

New system table - RDB$CONSTANTS

Table: SYSTEM.RDB$CONSTANTS
RDB$CONSTANT_NAME               (SYSTEM.RDB$FIELD_NAME) CHAR(63) CHARACTER SET SYSTEM.UTF8 Nullable 
RDB$CONSTANT_ID                 (SYSTEM.RDB$CONSTANT_ID) INTEGER Nullable 
RDB$PACKAGE_NAME                (SYSTEM.RDB$PACKAGE_NAME) CHAR(63) CHARACTER SET SYSTEM.UTF8 Nullable 
RDB$FIELD_SOURCE                (SYSTEM.RDB$FIELD_NAME) CHAR(63) CHARACTER SET SYSTEM.UTF8 Nullable 
RDB$PRIVATE_FLAG                (SYSTEM.RDB$SYSTEM_NULLFLAG) SMALLINT Nullable 
RDB$CONSTANT_BLR                (SYSTEM.RDB$CONSTANT_BLR) BLOB segment 80, subtype BLR Nullable 
RDB$CONSTANT_SOURCE             (SYSTEM.RDB$SOURCE) BLOB segment 80, subtype TEXT CHARACTER SET SYSTEM.UTF8 Nullable 
RDB$SCHEMA_NAME                 (SYSTEM.RDB$SCHEMA_NAME) CHAR(63) CHARACTER SET SYSTEM.UTF8 Nullable 
RDB$DESCRIPTION                 (SYSTEM.RDB$DESCRIPTION) BLOB segment 80, subtype TEXT CHARACTER SET SYSTEM.UTF8 Nullable 
CONSTRAINT RDB$INDEX_98:
  Unique key (RDB$SCHEMA_NAME, RDB$PACKAGE_NAME, RDB$CONSTANT_NAME)
CONSTRAINT RDB$INDEX_99:
  Unique key (RDB$CONSTANT_ID)

A new field has been added to RDB$PACKAGES - RDB$PACKAGE_ID

New indexes:

Unique key SYSTEM.RDB$CONSTANTS  (RDB$SCHEMA_NAME, RDB$PACKAGE_NAME, RDB$CONSTANT_NAME)
Unique key SYSTEM.RDB$CONSTANTS (RDB$CONSTANT_ID)
Unique key SYSTEM.RDB$PACKAGES (RDB$PACKAGE_ID)

Implementation

Packages have been added to the metacaching system. Since it relies heavily on identifiers, a new ID field (RDB$PACKAGE_ID) has been added to the RDB$PACKAGES table. Constants are stored as an array in the package metacaching object, with a package_id-to-array_id and constant_name-to-array_id mappings.

There are also two important points:

1. All nodes now have an 'is constant' flag, similar to the 'is deterministic' flag. This is necessary to determine whether an expression can initialize a constant.
2. In the CreateAlterPackageNode node, a lot of code had to be copied and pasted, and adding constants led to complete chaos. Therefore, I decided to slightly refactor this node. All functionality remains the same; only code duplication was removed.

[sim1984]

Are comments supported for constants? I didn't see this in the documentation.
Let me clarify what I mean:

COMMENT ON CONSTANT [<schema>.]<package>.<const_name> IS 'Text'

Comments are simply supported for packaged procedures and functions. It would make sense to do the same for constants (and any package objects, for that matter).

COMMENT ON PROCEDURE [<schema>.]<package>.<proc_name> IS 'Text';
COMMENT ON FUNCTION [<schema>.]<package>.<func_name> IS 'Text';

[Noremos]

Are comments supported for constants?

No, I didn't plan to implement comments, but I think it's possible. I will take a look

[Noremos]

Is this check allowed or should I add the RDB$SYSTEM_FLAG field?

[Noremos]

I think this PR is ready to rereviw @AlexPeshkoff @asfernandes @dyemanov