It isn't possible to implement PartialEq properly for Value, because
any sensible implementation needs to force() thunks, which cannot be
done without a `&mut VM`.
The existing derive(PartialEq) has false negatives, which caused the
bug which cl/7142 fixed. Fortunately that bug was easy to find, but
a silent false negative deep within the bowels of nixpkgs could be a
real nightmare to hunt down.
Let's just remove the PartialEq impl for Value, and the other
derive(PartialEq)'s that depend on it.
Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: Iacd3726fefc7fc1edadcd7e9b586e04cf8466775
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7144
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
This commit deduplicates the Thunk-like functionality from Closure
and unifies it with Thunk.
Specifically, we now have one and only one way of breaking reference
cycles in the Value-graph: Thunk. No other variant contains a
RefCell. This should make it easier to reason about the behavior of
the VM. InnerClosure and UpvaluesCarrier are no longer necessary.
This refactoring allowed an improvement in code generation:
`Rc<RefCell<>>`s are now created only for closures which do not have
self-references or deferred upvalues, instead of for all closures.
OpClosure has been split into two separate opcodes:
- OpClosure creates non-recursive closures with no deferred
upvalues. The VM will not create an `Rc<RefCell<>>` when executing
this instruction.
- OpThunkClosure is used for closures with self-references or
deferred upvalues. The VM will create a Thunk when executing this
opcode, but the Thunk will start out already in the
`ThunkRepr::Evaluated` state, rather than in the
`ThunkRepr::Suspeneded` state.
To avoid confusion, OpThunk has been renamed OpThunkSuspended.
Thanks to @sterni for suggesting that all this could be done without
adding an additional variant to ThunkRepr. This does however mean
that there will be mutating accesses to `ThunkRepr::Evaluated`,
which was not previously the case. The field `is_finalised:bool`
has been added to `Closure` to ensure that these mutating accesses
are performed only on finalised Closures. Both the check and the
field are present only if `#[cfg(debug_assertions)]`.
Change-Id: I04131501029772f30e28da8281d864427685097f
Signed-off-by: Adam Joseph <adam@westernsemico.com>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7019
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
This commit adds a comment for the benefit of non-Lua-users
explaining what an upvalue is. It also adds a comment explaining
what `with_stack` does, including a brief reminder of nix's
slightly-unusual-but-well-justified handling of this construct.
Signed-off-by: Adam Joseph <adam@westernsemico.com>
Change-Id: If6d0e133292451af906e1c728e34010f99be8c7c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7007
Reviewed-by: j4m3s <james.landrein@gmail.com>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Using rust's PartialEq trait to implement Nix equality semantics is
reasonably fraught with peril, both because the actual laws are
different than what nix expects, and (more importantly) because certain
things actually require extra context to compare for equality (for
example, thunks need to be forced). This converts the manual PartialEq
impl for Value (and all its descendants) to a *derived* PartialEq
impl (which requires a lot of extra PartialEq derives on miscellanious
other types within the codebase), and converts the previous
nix-semantics equality comparison into a new `nix_eq` method. This
returns an EvalResult, even though it can't currently return an error,
to allow it to fail when eg forcing thunks (which it will do soon).
Since the PartialEq impls for Value and NixAttrs are now quite boring,
this converts the generated proptests for those into handwritten ones
that cover `nix_eq` instead
Change-Id: If3da7171f88c22eda5b7a60030d8b00c3b76f672
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6650
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
This completely rewrites the handling of "dynamic upvalues" to,
instead of resolving them at thunk/closure instantiation time (which
forces some values too early), capture the entire with stack of parent
contexts if it exists.
There are a couple of things in here that could be written more
efficiently, but I'm first working through this to get to a bug
related to with + recursion and the code complexity of some of the
optimisations is distracting.
Change-Id: Ia538e06c9146e3bf8decb9adf02dd726d2c651cf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6486
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
This struct will be responsible for tracking upvalues (and is a
convenient place to introduce optimisations for reducing value clones)
instead of a plain value vector.
The main motivation for this is that the upvalues will have to capture
the `with`-stack fully and I want to avoid duplicating the logic for
this between the two capturing types.
Change-Id: I6654f8739fc2e04ca046e6667d4a015f51724e99
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6485
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
This trait abstracts over the commonalities of upvalue handling
between closures and thunks.
It allows the VM to simplify the code used for setting up upvalues,
without duplicating between the two different types.
Note that this does not yet refactor the VM code to optimally make use
of this.
Change-Id: If8de5181f26ae1fa00d554f1ae6ea473ee4b6070
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6347
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
