allow some way to specify type-aliases for elemental types

[goyalyashpal]

summary

allow some way to specify type-aliases for elemental types

details

current situation:

• kaitai allows specifying subtypes, but not "type aliases"
• with type-alias, i mean the parsing specification (e.g. type, size, enum, valid, encoding, etc.) for single field value as against the subtype (defined in types.<id>.seq) which is for multiple fields

use scenario:

• on using types construct to define single-field type-aliases,

• ... it gets needlessly parsed as a subtype (thus, redundant sub-attribute / children node etc) with name _unnamedX

• this looks ugly, increases output's size, & require meaningless unfolding / exapnding

• screenshots:

  

.ksy samples:

• small example: types: {my_type_alias: {seq: [{type: u1, enum: my_enum}]}}

• working sample with multiple aliases:

  types:
  
    my_type_alias_a:
      seq:
        - {type: u1, enum: my_enum}
    
    my_file_name:  # alias for elemental type "string"
      seq:
        - {type: str, size: 10, encoding: utf-8}  # why does ksc complain about utf-8's lower-case?
    
    my_validation:
      seq:
        - {type: u4le, valid: {min: 10}}
  

additional info:
type aliases are used in a lot of places:

• as above schema example shows: for specifying enum, size, valid, or any myriad of attributes
• for reusing same specification at multiple places i.e. DRY

for these uses, there really is no need of any sequence, as all the definition is for single value only.

also, these two features (type-alias, and sequence-def) are fairly orthogonal i think, and can be easily composed on user's end if the need arises.

solutions

• i am not sure at the moment regarding what the details of implementation (even for syntax) can be, considering the cross-language exports.
• i thought about instances, but it seems it requires explicitly specifying pos, and it's purpose seems something else too.

versions

Kaitai WebIDE version: 0.1-SNAPSHOT-a02d396 (2025-09-06 13:13:49, license)
Kaitai compiler version: 0.11.0 (2025-09-07T18:59:46Z)

meta

i tried searching for existing duplicates with following queries:

• is:issue type alias
• is:issue typedef
• is:issue element type

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[generalmimon]

I'm inclined to close this in favor of #88, since it solves the ergonomic issues you mentioned...

• ... it gets needlessly parsed as a subtype (thus, redundant sub-attribute / children node etc) with name _unnamedX

• require meaningless unfolding / exapnding

... but it's much more versatile and fits better with what the Kaitai Struct language already supports.