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fix(tvix/eval): wrap dynamic resolution in an extra thunk

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Without this change it was possible to cause situations (see the new
test) in which a `with`-namespace was forced prematurely.

Change-Id: I879ea7763b43edc693feace2c73c890d426fafd3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7031
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: Adam Joseph <adam@westernsemico.com>
This commit is contained in:
Vincent Ambo 2022-10-17 17:51:38 +03:00 committed by clbot
parent 0063e7e913
commit 13a5e7dd5b
4 changed files with 16 additions and 3 deletions
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11
tvix/eval/src/compiler/bindings.rs
View file

@ -694,9 +694,16 @@ impl Compiler<'_> {
// If there is a non-empty `with`-stack (or a parent context
// with one), emit a runtime dynamic resolution instruction.
//
// Since it is possible for users to e.g. assign a variable to a
// dynamic resolution without actually using it, this operation
// is wrapped in an extra thunk.
if self.has_dynamic_ancestor() {
self.emit_constant(Value::String(SmolStr::new(ident).into()), node);
self.push_op(OpCode::OpResolveWith, node);
self.thunk(slot, node, |c, _| {
c.context_mut().captures_with_stack = true;
c.emit_constant(Value::String(SmolStr::new(ident).into()), node);
c.push_op(OpCode::OpResolveWith, node);
});
return;
}

1
tvix/eval/src/tests/tvix_tests/eval-okay-lazy-with-nested.exp Normal file
View file

@ -0,0 +1 @@
42

5
tvix/eval/src/tests/tvix_tests/eval-okay-lazy-with-nested.nix Normal file
View file

@ -0,0 +1,5 @@
# The 'namespace' of a with should only be evaluated if an identifier
# from it is actually accessed.
with (abort "should not be evaluated");
let a = dynamic; in 42

2
tvix/eval/src/tests/tvix_tests/eval-okay-lazy-with.nix
View file

@ -1,6 +1,6 @@
# The 'namespace' of a with should only be evaluated if an identifier
# from it is actually accessed.
with (builtins.throw "should not occur");
with (abort "should not be evaluated");
42