feat(tvix/eval): add builtins to builtins

This is a somewhat terrifying hack that enables us to support
`builtins.builtins`, by running a "fake compilation" inside of a
suspended native thunk that can resolve the weak pointer to the
globals.

With this implementation, the thunk at `builtins.builtins` actually
resolves to the "real" `builtins` (verified with a new test).

This is kind of ugly, and it's something users shouldn't use, but
bubbling a warning out of this is difficult at the moment due to a
little bit of trickery with how the spans in suspended native thunks
work (they don't) (see b/237, b/238)

Change-Id: I67d0e93246dd5b279c960aeda00402031aa12af3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7748
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
This commit is contained in:
Vincent Ambo 2023-01-04 17:12:33 +03:00 committed by tazjin
parent 79e54f46ce
commit b9646ab40c
3 changed files with 34 additions and 2 deletions

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@ -28,7 +28,7 @@ use std::sync::Arc;
use crate::chunk::Chunk;
use crate::errors::{Error, ErrorKind, EvalResult};
use crate::observer::CompilerObserver;
use crate::observer::{CompilerObserver, NoOpObserver};
use crate::opcode::{CodeIdx, Count, JumpOffset, OpCode, UpvalueIdx};
use crate::spans::LightSpan;
use crate::spans::ToSpan;
@ -1261,7 +1261,7 @@ pub fn prepare_globals(
// to instantiate its compiler, the `Weak` reference is passed
// here.
if enable_import {
let import = Value::Builtin(import::builtins_import(weak, source));
let import = Value::Builtin(import::builtins_import(weak, source.clone()));
builtins_under_construction.insert("import", import);
}
@ -1278,6 +1278,36 @@ pub fn prepare_globals(
}
}
// builtins contain themselves (`builtins.builtins`), which we
// can resolve by manually constructing a suspended thunk that
// dereferences the same weak pointer as above.
//
// This is an inefficient hack, but *if* anyone was to use
// `builtins.builtins`, it would only happen once as the thunk
// is then resolved.
let weak_globals = weak.clone();
builtins_under_construction.insert(
"builtins",
Value::Thunk(Thunk::new_suspended_native(Rc::new(Box::new(move |_| {
let file = source.add_file("builtins-dot-builtins.nix".into(), "builtins".into());
let span = file.span;
let mut observer = NoOpObserver::default();
let mut compiler = Compiler::new(
None,
file,
weak_globals
.upgrade()
.expect("globals dropped while still in use"),
&mut observer,
)?;
weak_globals.upgrade().unwrap().get("builtins").unwrap()(&mut compiler, span);
Ok(compiler.chunk().constants[0].clone())
})))),
);
// This is followed by the actual `builtins` attribute set
// being constructed and inserted in the global scope.
let builtins_set =

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@ -0,0 +1 @@
true

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@ -0,0 +1 @@
[ builtins ] == [ builtins.builtins ]