Moved to [JuliaLowering](c42f/JuliaLowering.jl#10)
     instead (the data structure we need is defined there).

Moved to [JuliaLowering](c42f/JuliaLowering.jl#10)
     instead (the data structure we need is defined there).

This PR along with [the associated JuliaLowering
PR](c42f/JuliaLowering.jl#10) allow us to
experiment
with JuliaLowering as the core lowering implementation, mainly for JETLS
development at the moment (cc @aviatesk, @c42f).

## Changes

JuliaLowering works with `JuliaLowering.SyntaxTree` input instead of
Expr. This
change allows`SyntaxTree`s out of parsing and into lowering, hopefully
without
disturbing existing code expecting Expr.  The current design wraps
`x::SyntaxTree` like `Expr(:syntaxtree, x)` because otherwise
`toplevel_eval_flex` wouldn't know what `x` is, but once we're past the
experimental phase, it would only make sense for the compiler to
actually know
about the types it's operating on.

### New: `Core._lower`

It (a julia entrypoint), `jl_lower` (C entrypoint), `jl_fl_lower`, and
`fl_lower` all mirror the existing parsing API which was added in
#35243.


<details>

<summary>
Click for pre-PR call graph
</summary>


![graph(6)](https://github.com/user-attachments/assets/a993eb92-5668-4ee7-837f-801feb686cb4)

</details>

After this change:


![graph(7)](https://github.com/user-attachments/assets/697b93cf-b3df-47b2-bc0e-c358fb0a6dca)

Like `Core._parse`, `Core._lower` returns an `svec` with the first
element as
the expected result, and the remaining elements can hold extra
information like
the lowered SyntaxTree with provenance info (I've left the specification
of
extra return values for later, when JuliaLowering is more stable and
JETLS knows
what it needs, because we may opt to pack provenance into the lowered
CodeInfo
object instead). Parsing only uses the svec to return an offset, but it
could
actually make use of the the flexibility to return diagnostics in the
future.

It's unfortunately not clear what types we can expect to go into and
come out of
lowering (I got Expr, LineNumberNode, String, Symbol, and Nothing in
testing.)

### Remove `jl_lower_expr_mod`

I realize this isn't being called from C, and Core._lower is a more
sensible
entry point from julia. We could probably also remove some uncalled
parse and
jl_load functions.

## Limitations

These belong to JuliaLowering, but are listed here as known issues for
anyone
who wants to try it out.

- `(module ...)` forms don't go through JuliaLowering yet. Modules are
lowered
to a call to `JuliaLowering.eval_module(parentmod, modname,
syntaxtree)`,
which is currently a stub function that converts to Expr for lowering
and
  evaluation, which JuliaLowering can't use.
- Macros work differently.  Defining and calling macros should work, but
  invoking normal macros defined pre-JuliaLowering will not.
- Compilation is currently slow (~30 seconds for me).

Use the `aviatesk/JuliaLowering.jl#avi/JETLS` branch which
combines the following JL branches:
- [`mlechu:fix-nightly`](c42f/JuliaLowering.jl#10)
- [`aviatesk:avi/precompile`](c42f/JuliaLowering.jl#14)

This is a temporary solution until these branches are merged
into JL#master.

This enables JL precompilation and significantly improves
JETLS startup time (even when JETLS `precompile_workload` is
set to `false`).

Use the `aviatesk/JuliaLowering.jl#avi/JETLS` branch which
combines the following JL branches:
- [`mlechu:fix-nightly`](c42f/JuliaLowering.jl#10)
- [`aviatesk:avi/precompile`](c42f/JuliaLowering.jl#14)

This is a temporary solution until these branches are merged
into JL#master.

This enables JL precompilation and significantly improves
JETLS startup time (even when JETLS `precompile_workload` is
set to `false`).

* Update CodeInfo struct and handling

Co-authored-by: Claire Foster <[email protected]>

* Don't produce raw symbol from globalref

This used to implicitly refer to a module-level name, but lowering is now
expected to wrap it in a `globalref`. Part of #54772

* Updates to const and global lowering; add K"constdecl"; omit `wrap`

#54773, #56713, #57470. Some
     changes omitted from `expand-decls` and `expand-assignment`.

Note that the two-argument IR "const" is K"constdecl", whereas the one-argument
    K"const" only appears in the AST.

Also note that the `wrap` parameter is omitted throughout assignment desugaring.
      As far as I'm aware, all this plumbing was just to support `const a,b,c =
     1,2,3` having `b` and `c` inherit the `const`.  TODO: find a better way of
     doing the same thing (a ScopedValue might be a clean solution; we currently
     throw an error).

The check for `let; const x = 1; end`, (which should throw) is in scope
     analysis (lisp has it in `compile`).

Co-authored-by: Claire Foster <[email protected]>

* Add `isdefinedglobal` builtin

#54999, #56985

* :global no longer valid_ir_argument; rm `is_defined_nothrow_global`

#56746.  Also call :slot and :static_parameter valid (for now)

* Fix `is_defined_and_owned_global` (Core.Binding changes)

Adapt to bpart changes in #54788

* Struct desugaring: "Undo decision to publish incomplete types..."

#56497; Add self-referencing struct shim

I have doubts about how long this solution will stay in the base repository, and
     how complete it is (doesn't seem to work with M1.M2.S), but we are testing
     for it here.

Also change the expected value of a test changed in the same PR.

* Emit `latestworld` world age increments

For method defs, `latestworld` is produced in desugaring rather than closure
conversion for now (our closure conversion doesn't seem to cover the same
cases as lisp lowering yet).

Covers #56523, #56509, #57299.

Also includes changes from #57102 (bpart: Start enforcing minimum
world age for const bparts) and #57150 (bpart: Start enforcing
min_world for global variable definitions) since the lowering changes from those
appear to be amendments to the changes above (missing world age increments).

Co-authored-by: Claire Foster <[email protected]>

* bpart changes: `Core._typebody!` signature

`Core._typebody!` now takes a new "prev" argument, which we don't use yet here.
 Changes from #57253

* bpart changes: struct desugaring

Changes from #57253 (bpart: Fully switch to partitioned
     semantics).  This fixes one failing test and realigns struct desugaring to
     match lisp for now.

Also changed: the expected result of redefining a primitive type (now allowed).

* Additional argument in `new_opaque_closure`

Fix segfaulting test.  Thanks for the TODO

* Adapt to different `GeneratedFunctionStub` signature

Signature changed in #57230.  Thanks @aviatesk for the help!

* Fix `public` and `export`

As of #57765, `jl_module_public` is no longer exported.  Change
our runtime to handle it like `public` and `export` like we handle `import`
or `using` for now

* Fix modules.jl test

I believe this was a world age issue

* Regenerate IR tests

Too many to count.

* Update README to known-good julia, JuliaSyntax versions

Latest julia works.  Changes are needed to work with the latest JuliaSyntax, but
     that isn't in base julia yet, and more changes are likely to come.

* Fix small bug from JuliaLang/JuliaLowering.jl#16 so tests pass

The change lifted the scope of `note`, so it was being changed in the loop

* Changes from code review: const/global lowering

Ping me if you'd like this squashed into the original const/global commit!

Co-authored-by: Claire Foster <[email protected]>

* Remove a special case

No longer needed since we no longer put `global` or `local` forms back into the
     expand_forms machine.  Some error messages change slightly as a result.

* Changes from code review

Co-authored-by: Claire Foster <[email protected]>

* Fix + test for assignment in value but not tail position

* Disallow `static_parameter` as `valid_ir_argument`

See added comment, and discussion at
    c42f/JuliaLowering.jl#10 (comment)

Co-authored-by: Claire Foster <[email protected]>

* Change printing of `K"latestworld"`

Parens are nice, but it wasn't consistent.

Also make it a leaf (remaining non-leaves are deleted in the next commit.)

* Move most `latestworld`s to linearization

From the docs:
```
The following statements raise the current world age:
    1. An explicit invocation of Core.@latestworld
    2. The start of every top-level statement
    3. The start of every REPL prompt
    4. Any type or struct definition
    5. Any method definition
    6. Any constant declaration
    7. Any global variable declaration (but not a global variable assignment)
    8. Any using, import, export or public statement
    9. Certain other macros like eval (depends on the macro implementation)
```

This commit handles each case as follows:

```
    1. = 9
    2. I'm not sure this actually happens (or needs to happen, unless we're
       being defensive? Doing it after each world-changing operation should
       suffice).  But if we need it, this would just be emitting once at the
       beginning of every lowered output.
    3. = 2
    4. = 6
    5. Emit seeing `method` in linearize
    6. Emit seeing `constdecl` in linearize
    7. Emit seeing `global` or `globaldecl` in linearize
    8. We just defer to `eval`, but should probably go in desugaring later
       - using/import recently became builtin calls, and I haven't
         updated JL to use them yet.  Base._import_using has an expr-based
         API that may change, and our importpath destructuring is worth keeping.
       - export and public (special forms) are handled in toplevel.c
    9. Done for us
```

Other quirks:

- `JuliaLowering.eval_closure_type` calls eval to assign a const, so we still
    need to deal with that in closure conversion.

- The `include` hack isn't mentioned in the docs, but can stay in desugaring.
      I'm not certain why we don't do the same for non-macro `eval`.

---------

Co-authored-by: Claire Foster <[email protected]>