Nanopasses

Motivation and Context

Put an end to the monolithic compilers we had, namely the "abstractors".

Description

Generated code

• folds/unfolds are written using the generated ppx.map (see recursion schemes )
• there is no printers (very annoying to maintain). We use deriving.sexp

New AST

Ast_unified (produced by unification)

• written in a style suitable for generated fold
• some node can't be emited by unification and only be emited by a nanopass. Those are tagged with [@is_initial]

New flow

When compiling, things happen in this way:

1. Unification (CST_<syntax> --> AST_unified) @ src/passes/03-unification/
2. Nanopasses (AST_unified --> AST_unified) @ src/passes/04-nanopasses/
3. Trivial (Ast_unified --> AST_core) @ src/passes/04-nanopasses/

A pass is define here, should be able to compile/decompile an expression/pattern/program

Each nanopass have a run-time check (reduction_check) making sure that node that are considered reduced are not present in the AST anymore (we could remove those from LIGO release binary?)

Notes:

• it is not yet due to annoying CST differences, but (1) should be trivial. Sometimes, some constructs in one syntax use a slightly different type from another syntax. To not create a dummy nanopasses just for that, I do the translation directly in unification (see module TODO_in_parsing / TODO_unifiy_in_cst)
• the last transformation (3) is trivial already. The only things being done there is handling the warnings on attributes (TODO?)

Side-effects

• locs have changed (for the best, at least in the tests)
• errors text might have change a little bit
• closes https://gitlab.com/ligolang/ligo/-/issues/1583
• closes https://gitlab.com/ligolang/ligo/-/issues/1717
• closes https://gitlab.com/ligolang/ligo/-/issues/1719 (added a pass single_switch_block)
• closes #1418 (closed)

Unit test

unit testing is made possible. A small example here.
But this needs to be improved

Future

• generated recursion schemes [trivial]
• generated sexp_of to_sexp [trivial]
• using anomorphism for pass 3 unification [trivial but long]
• define new type for each nanopasses, [complex: require ppx to generate new type (see existing ocaml nanopass framework)]
• if CSTs would share more types, write a ppx to generated unification [complex / need work]

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

frontend: syntax unification and nanopasses (replacing old abstraction)

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).