Commit graph

298 commits

Author SHA1 Message Date
Vincent Ambo
ec8ff79aee feat(tvix/eval): track source spans for function calls
Change-Id: If1bb463026414597acd561dc2032549fdb70f986
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6397
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 20:04:17 +00:00
Vincent Ambo
e590b585e7 feat(tvix/eval): track source spans for lambdas
Change-Id: I2f420fc915b6bfc5b197e9d0c128b539c4bc7467
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6396
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 20:04:17 +00:00
Vincent Ambo
20996601ea feat(tvix/eval): track source spans for with expressions
Change-Id: I1d58ce548b5b47e967928e85bb64acf5ed69ecc8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6395
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 20:04:17 +00:00
Vincent Ambo
9f5f85a1c1 feat(tvix/eval): track source spans for identifier access
Change-Id: I8e6ec0a84430d6e417fc7fd3e722a588913e4d18
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6394
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:23:22 +00:00
Vincent Ambo
f37e4a0b9c feat(tvix/eval): track source spans for let bindings
Change-Id: I9457917277a7fdd8bdbe227a567b28969312d06e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6393
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:23:22 +00:00
Vincent Ambo
7f687f0e99 feat(tvix/eval): track source spans for if expressions
These are again a bit tricky in terms of emitted errors. The main
error is that the condition is not a boolean, which means that the
jump inspecting the condition must derive from the condition itself to
return an error at the correct position.

For other parts of the expression, it is simply the node itself.

Change-Id: I72411630e5d57dfc199f4c3c48afe443fe966322
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6392
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
baa012d5a3 feat(tvix/eval): track source spans for assert
Change-Id: I5415f63ddde388847a261da4ce9a8d8235657535
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6391
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
805c1870ee feat(tvix/eval): track source spans for or operator
This one is tricky, specifically the span used for the final jump. I
decided that it makes sense to use the attrpath node, as the final
jump is the one that jumps *over* the default value, so the effect of
this is more closely related to the selector than the default.

It might be more correct to pass through the `or` token itself and
point to this for the jumps, but it depends a bit on what shape of
errors we could end up producing from this.

Change-Id: I29fbc97ba6b9e14e1a0e5f3a7759ddc299dd9c0c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6390
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
2b1468dde3 feat(tvix/eval): track source spans for attribute selects
Change-Id: Ifa8b0e7905f9d2746f83d6503ef0e8d42ce20f9c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6389
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
d1e0c6f680 feat(tvix/eval): track source spans for attrsets
Change-Id: I0fcb07146b5a38c67bc46ed3f67533b056858390
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6388
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
eb169c51a7 feat(tvix/eval): track source spans for lists
Change-Id: Icfd057ee29180cac17264bb3299c67eae0051aee
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6387
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
d8f494b50b feat(tvix/eval): track source spans for literal identifiers
Change-Id: I7ca08c6c0124f653e55fcc86413a847f0a4c50c5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6386
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
2ad89a00fb feat(tvix/eval): track source spans for ? operator
Change-Id: Idb842fb20fab14150455a81ea6c947e75b314d8a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6385
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
c417a084cc feat(tvix/eval): track source spans for binary operators
Change-Id: I43e433ff3094232b244d38335d31e56a79ca70c1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6384
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
176e729556 feat(tvix/eval): track source spans for unary operators
Change-Id: I79034a4aa04aea66ec598e33e6eab35e1e19c0d0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6383
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
f14b368514 feat(tvix/eval): track source spans for strings
Change-Id: I29e6c7f9e25d1b2e6bafa602c463eb9ccee2131b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6382
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
3c4eed9b76 feat(tvix/eval): track source spans for paths
Change-Id: I42fbd0bb6c2a8feb520e262a25f59ff27dcd035c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6381
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
eaf7af18be feat(tvix/eval): track source spans for literals
Change-Id: Icfe77f85c4f65b6bf28b8752c2795419e8e396ce
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6380
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
72adcdf965 feat(tvix/eval): add methods for emitting code with tracked spans
These are not actually used yet; this is in preparation for a
multi-commit chain for emitting all the right spans in the right
locations.

Change-Id: Ie99d6add2696c1cc0acb9ab928917a10237159de
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6379
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:23:22 +00:00
Vincent Ambo
c5a8b93eaf chore(tvix/eval): thread a codemap::File reference to the compiler
This instantiates a codemap outside of the compiler and passes a
reference to the file currently under compilation to it. Note that the
"file" might just be a REPL line.

Change-Id: I131ae1ddb6d718e1374750da9ba0b99608c6058d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6378
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:10:40 +00:00
Vincent Ambo
b9566da5c9 refactor(tvix/eval): add and use Compiler::push_op method
This is currently just a wrapper around Chunk::push_op, but will gain
the span resolution logic in a moment.

Change-Id: I862bf9ecff0932f8da6708401ea044b9442c5d5b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6377
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:08:56 +00:00
Vincent Ambo
6f6bbc12f8 feat(tvix/eval): add data structures for tracking spans in chunks
This adds a new vector to the chunk data structure which tracks spans
into a codemap. The compiler will emit this information to the chunk
when adding instructions.

The internal representation of the spans is slightly optimised to
avoid storing duplicate spans, as there are cases where many
instructions might be derived from the same span.

Change-Id: I336f8c912e7eb50ea02ed71e6164f651ca3ca790
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6376
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:08:56 +00:00
Vincent Ambo
18f8fecba4 chore(tvix/eval): bump all dependencies
Updated the rnix hash manually, and ran `cargo update` for the rest.

Change-Id: I457262625d648e25d745efa4d33ae44cb8f21326
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6375
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:08:56 +00:00
Vincent Ambo
39e960daa6 chore(tvix/eval): add codemap dependency
This will be used to track source spans when emitting bytecode.

The codemap is a data structure which tracks *all* the source files
visited by an evaluation, and makes it possible to represent locations
across all of the files using a simple span (i.e. pair of offsets).

When reporting errors, this even contains enough information to
reconstruct the rnix AST to create fancier reporting in certain cases
if desired.

Change-Id: I4ae98620b9b150fb5a389bd7f1e12670e3192c62
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6374
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 19:08:56 +00:00
Vincent Ambo
f8919dbcd6 fix(tvix/eval): address current clippy lints
Note that I've allowed `needless_lifetimes` for the attribute set
iterator, as I find the type easier to understand with these
annotations present.

Change-Id: I33abb17837ee4813076cdb9a87f54bac4a37044e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6373
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:08:56 +00:00
Vincent Ambo
afcfa78364 feat(tvix/eval): semi-strictly evaluate output values of the VM
This essentially makes the VM behave like `nix-instantiate --eval
--strict`, i.e. data structures are traversed strictly and thunks are
forced. Thunks embedded in closures are not forced.

This allows us to re-enable tests that were disabled because they
needed to output nested thunk contents, but is overall a behaviour
that must be configurable later on, as it is not cmopatible with e.g.
an evaluation of nixpkgs.

Change-Id: I5303a5c8e4322feab1384fdb7712fecb950afca5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6372
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:08:56 +00:00
Vincent Ambo
6c6f9ae661 feat(tvix/eval): implement NixList::iter
This does not require a custom iterator type (for now?)

Change-Id: I5beb194bd8629571bd4040c69c977c27149807fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6371
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:08:56 +00:00
Vincent Ambo
fea7f90a7f fix(tvix/eval): thread Display & PartialEq through to thunk values
If a thunk is already evaluated, there are cases where due to the
memoisation implementation something might observe a value wrapped in
a thunk.

In these cases, the implementation of `Display` and `PartialEq` must
delegate to the underlying value.

Note that there are a handful of other cases like these which we need
to cover.

It is a little tricky to write integration tests for these directly,
especially as some of the open-upvalue optimisations coming down the
pipe will reduce the number of observable thunks.

One test that covers a part of this behaviour is currently
disabled (needs some more machinery), but it's being brought back in
the next commits.

Change-Id: Iaa8cd338c12236af844bbc99d8cec2205f0d0095
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6370
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
2022-09-07 19:08:56 +00:00
Vincent Ambo
38d3db5fb8 feat(tvix/eval): implement NixAttrs::iter()
Implementing iteration over NixAttrs requires a custom iterator type
in order to encapsulate the different representations. The BTreeMap
for example has its own iterator type which needs to be encapsulated.

This is mostly boilerplate code, but for a change some simple unit
tests have been added in.

Change-Id: Ie13b063241d461b810876f95f53878388e918ef2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6367
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
7d5dca7ba3 chore(tvix/eval): provide 'static references to "name"/"value"
These static strings show up a bunch when dealing with the internals
of attribute sets, and having them available as static references is
required.

Due to the way const expressions are evaluated, taking a reference to
the existing NixString::NAME / NixString::VALUE items does not work
and the references themselves need to be const-evaluated.

Change-Id: If6e75847af978118a3b266fe6a3242321722434d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6366
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
80713f207e refactor(tvix/eval): encapsulate all thunk-forcing logic in module
The VM previously took care of repeatedly forcing a thunk until it
reached an evaluated state. This logic is now encapsulated inside of
the `Thunk::force` implementation.

In addition, force no longer returns a reference to the value by
default, leaving it up to callers to decide whether they want to
borrow the value or not (a helper is provided for this).

Change-Id: I2aa7da922058ad1c57fbf8bfc7785aab7971c02b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6365
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
23a5caabec feat(tvix/eval): construct attribute sets lazily
This thunks the construction of attribute sets. Because Tvix does not
currently have a "strict output" mode, a test had to be disabled that
now displays a thunk representation.

The test will be re-enabled once that is available.

Change-Id: I360332be64cd5c154f9caea21828f6f1b37a265c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6363
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
727845645d chore(tvix/eval): add release-with-debug cargo profile
This lets us create a release build with debug info, for use with e.g.
perf + hotspot

Change-Id: I03897de36c872d318abf1332ca0c1aeabe344ec6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6362
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
79a2ba5175 fix(tvix/eval): avoid recomputing width in disassemble_op constantly
As noticed by sterni in cl/6195

Change-Id: Ie9c1e80e2e709284fa8412334af9188d999f64dc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6361
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
a8b2ba07df fix(tvix/eval): correctly resolve identifiers in inherit
This should not have grown a second implementation of the identifier
resolution logic, but it somehow did.

This implementation ended up being incorrect because it did not
account for upvalues inside of thunks.

Change-Id: Ieb1364d8fe43c96aaf4b125fd4b8a522aedff167
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6360
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
17dfb92a9f chore(tvix/eval): implement Debug for compiler::scope::Scope
Change-Id: I112b0119bd0511f26bb72f7e73d867d1b7144a36
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6359
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
9420a3b53d feat(tvix/eval): insert strictness points for attribute set keys
All attribute set *key* related operations strictly evaluate all key
fragments, including during construction of an attribute set.

Change-Id: I3519e5e9b0886c2cdc8615ea7dcb5f7be0c59b3f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6358
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
5b4f3811e6 feat(tvix/eval): insert strictness points for unary/binary operators
The arguments of all unary/binary operators that are built in to Nix
are forced when encountered. This emits the necessary OpForce operations.

Change-Id: I691fcdbebfe7586cfe217c68d44b10b1192f82d1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6357
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
6a42d9bddf chore(tvix/eval): thread slot value through all compiler methods
With this change any compilation of an expression is aware of its own
stack slot if it is leaving identifiers on the stack.

Change-Id: I0c9f148ae06b078a46b25180c4961686d5f2e166
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6356
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
50c33989dc chore(tvix/eval): thread slot value through Compiler:compile_attr
This threads the current local slot through the `compile_attr`
function and all of its callers. At the moment this does not improve
any user-facing behaviour, just internally changes the way in which
some correct expressions would fail to run.

Eventually this slot will need to reach everywhere ...

Change-Id: Iba73123dd1ced421093d8fc18ebeeffc16efacf8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6355
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
372bf4a0b7 test(tvix/eval): test very simple late-bound identifier access
This is the simplest kind of thunk that can be created (and so far the
only one the compiler knows how to create), in which an identifier
inside a `let` encounters a value that is bound *after* it is
initialised.

Change-Id: I6ea4408a3baef1e7d5137365d70804283f2dbf8e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6354
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
786e12a738 feat(tvix/eval): always emit OpForce as the last instruction
Change-Id: Id70c987f654dc5d9b47db74e395281309762b468
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6353
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
9a783e50a4 feat(tvix/eval): implement OpForce in VM
This operation forces the evaluation of a thunk.

There is some potential here for making an implementation that avoids
some copies, but the thunk machinery is tricky to get right so the
first priority is to make sure it is correct by keeping the
implementation simple.

Change-Id: Ib381455b02f42ded717faff63f55afed4c8fb7e3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6352
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-07 15:25:59 +00:00
Vincent Ambo
a8c13a5ce1 fix(tvix/eval): allocate Thunk::upvalues with known capacity
The capacity (i.e. number of builtins) is known from the lambda, so we
can size it correctly right away.

Change-Id: Iab0b5a3f47d450fa9866c091ebbbed935b934907
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6351
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 16:54:42 +00:00
Vincent Ambo
6c895d4b28 feat(tvix/eval): implement OpThunk for runtime thunk construction
Implements an operation very similar to `OpClosure` which populates a
thunk's upvalues and leaves it on the stack.

Change-Id: I753b4dfeeaae6919316c7028ec361aaa13d87646
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6350
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 16:54:42 +00:00
Vincent Ambo
6c4b9bdce9 refactor(tvix/eval): extract VM::populate_upvalues function
This function is reusable between thunks & closures.

Change-Id: I44d5f9897b087a385c8e75027d2ff39c48a096f0
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6349
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 16:36:46 +00:00
Vincent Ambo
ce498052e6 refactor(tvix/eval): Carry lambda & upvalues directly in CallFrame
CallFrame has to work for both thunks & closures (as a thunk is
basically a "weird 0-argument closure").

We opt to store the common, relevant fields directly in the frame to
avoid having to dereference through the nested structures
constantly (which would be especially annoying in the case of thunks).

Change-Id: I47781597b84ec5cd55502dba1713e92cf2592af3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6348
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 14:58:52 +00:00
Vincent Ambo
25c62dd0ef refactor(tvix/eval): introduce UpvalueCarrier trait
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>
2022-09-06 14:58:52 +00:00
Vincent Ambo
8033a7abae refactor(tvix/eval): simplify thunk representations
For now, do not distinguish between closing and non-closing thunks, it
will make the initial implementation easier. See Knuth etc.

Change-Id: I0bd51e0f89f2c77e90bac63b507e5027b649e3d8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6346
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 14:58:52 +00:00
Vincent Ambo
28a9847c65 feat(tvix/eval): emit thunks for recursive local scope resolution
When resolving a value on the same level that is known but not yet
defined, emit a thunk.

Consider for example:

    let
      #       v--- requires a thunk
      a = 1 * b;
      b = 10;
    in a

Change-Id: I922cb50973ebe05e335a7bc7cb851960cf34733b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6345
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>
2022-09-06 14:58:52 +00:00