From ccfb971dc54cb77522d70f1ecbf1e9080e7ba0ca Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Sun, 28 Aug 2022 03:45:45 +0300 Subject: fix(tvix/eval): correctly thread through dynamic upvalues This puts together the puzzle pieces for threading dynamic upvalues (that is, upvalues resolved from the `with`-stack) all the way through. Reading the test case enclosed in this commit and walking through it is recommended to understand what problem is being tackled here. In short, because the compiler can not statically know *which* with-scope a dynamic argument is resolved from it needs to lay the groundwork for resolving from *all* possible scopes. There are multiple different approaches to doing this. The approach chosen in this commit is that if a dynamic upvalue is detected, the compiler will emit instructions to close over this dynamic value in *all* enclosing lambda contexts. It uses a new instruction for this that will leave around a sentinel value in case an identifier could not be resolved, and wire the location of this found value (or sentinel) up through the upvalues to the next level of nesting. In this tradeoff, tvix potentially closes over more upvalues than are needed (but in practice, how often do people create *really* deep `with`-stacks? and in *this* kind of code situation? maybe we should even warn for this!) but avoids keeping the entire attribute sets themselves around. Looking at the test case, each surrounding closure will close over *all* dynamic identifiers that are referenced later on visible to it, but only the last one for each identifier will actually end up being used. This also covers our bases for an additional edge-case this creates, in which an identifier potentially resolves to a dynamic upvalue *and* to a dynamic value within the function's own scope (again, would anyone really do this?) by introducing a resolution instruction for that particular case. There is likely some potential for cleaning up this code which is quite ugly in some parts, but as this implementation is now carefully calibrated to work I decided it is time to commit it and clean it up in subsequent commits. Change-Id: Ib701e3e6da39bd2c95938d1384036ff4f9fb3749 Reviewed-on: https://cl.tvl.fyi/c/depot/+/6322 Tested-by: BuildkiteCI Reviewed-by: sterni --- tvix/eval/src/value/mod.rs | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'tvix/eval/src/value') diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs index eb23605bd0b2..54211e8ba313 100644 --- a/tvix/eval/src/value/mod.rs +++ b/tvix/eval/src/value/mod.rs @@ -34,6 +34,7 @@ pub enum Value { // are never returned to or created directly by users. AttrPath(Vec), AttrNotFound, + DynamicUpvalueMissing(NixString), } impl Value { @@ -54,7 +55,9 @@ impl Value { Value::Closure(_) | Value::Builtin(_) => "lambda", // Internal types - Value::AttrPath(_) | Value::AttrNotFound => "internal", + Value::AttrPath(_) | Value::AttrNotFound | Value::DynamicUpvalueMissing(_) => { + "internal" + } } } @@ -163,6 +166,9 @@ impl Display for Value { // internal types Value::AttrPath(path) => write!(f, "internal[attrpath({})]", path.len()), Value::AttrNotFound => f.write_str("internal[not found]"), + Value::DynamicUpvalueMissing(name) => { + write!(f, "internal[no_dyn_upvalue({name})]") + } } } } -- cgit 1.4.1