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feat(tvix/eval): nonrecursive coerce_to_string()

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After this commit, the only non-builtins uses of generators are:

  - coerce_to_string() uses generators::request_enter_lambda()
  - Thunk::force() uses generators::request_enter_lambda()

That's it!  Once those two are taken care of, GenCo can become an
implementation detail of `builtins::BuiltinGen`.  No more crazy
nonlocal flow control within the interpreter: if you've got a GenCo
floating around in your code it's because you're writing a builtin,
which isn't part of the core interpreter.  The interpreter won't
need GenCos to talk to itself anymore.

Technically generators::request_path_import() is also used by
coerce_to_string(), but that's just because the io_handle happens to
be part of the VM.  There's no recursion-depth issue there, so the
call doesn't need to go through the generator mechanism
(request_path_import() doesn't call back to the interpreter!)

Change-Id: I83ce5774d49b88fdafdd61160975b4937a435bb0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10256
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: Adam Joseph <adam@westernsemico.com>
This commit is contained in:
Adam Joseph 2023-12-11 03:57:22 -08:00 • committed by clbot
parent 3701379745
commit 1ac57b0d1c
6 changed files with 139 additions and 122 deletions
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26
tvix/eval/src/value/attrs.rs
View file

@ -14,11 +14,9 @@ use serde::Deserialize;
use super::string::NixString;
use super::thunk::ThunkSet;
use super::CoercionKind;
use super::TotalDisplay;
use super::Value;
use crate::errors::ErrorKind;
use crate::generators::{self, GenCo};
lazy_static! {
static ref NAME_S: NixString = "name".into();
@ -370,30 +368,6 @@ impl NixAttrs {
pub(crate) fn from_kv(name: Value, value: Value) -> Self {
NixAttrs(AttrsRep::KV { name, value })
}
/// Attempt to coerce an attribute set with a `__toString`
/// attribute to a string.
pub(crate) async fn try_to_string(&self, co: &GenCo, kind: CoercionKind) -> Option<NixString> {
if let Some(to_string) = self.select("__toString") {
let callable = generators::request_force(co, to_string.clone()).await;
// Leave the attribute set on the stack as an argument
// to the function call.
generators::request_stack_push(co, Value::Attrs(Box::new(self.clone()))).await;
// Call the callable ...
let result = generators::request_call(co, callable).await;
// Recurse on the result, as attribute set coercion
// actually works recursively, e.g. you can even return
// /another/ set with a __toString attr.
let s = generators::request_string_coerce(co, result, kind).await;
return s.ok();
}
None
}
}
impl IntoIterator for NixAttrs {