## Summary
If a package lacks a source distribution, and we can't find a compatible
wheel for the current platform, we need to just _assume_ that the
package will have a valid wheel on all platforms on which it's
requested; if not, we raise an error at install time.
It's possible that we can be smarter about this over time. For example,
if the package was requested _only_ for macOS, we could verify that
there's at least one macOS-compatible wheel. See the linked issue for
more details.
Closes https://github.com/astral-sh/uv/issues/4139.
The basic idea here is to make it so forking can only ever result in a
resolution that, for a particular marker environment, will only install
at most one version of a package. We can guarantee this by ensuring we
only fork on conflicting dependency specifications only when their
corresponding markers are completely disjoint. If they aren't, then
resolution _must_ find a single version of the package in the
intersection of the two dependency specifications.
A test for this case has been added to packse here:
https://github.com/astral-sh/packse/pull/182. Previously, that test
would result in a resolution with two different unconditional versions
of the same package. With this change, resolution fails (as it should).
A commit-by-commit review should be helpful here, since the first commit
is a refactor to make the second commit a bit more digestible.
## Summary
I think we should be able to model PubGrub such that this isn't
necessary (at least for the case described in the issue), but for now,
let's just avoid attempting to build very old distributions in
prefetching.
Closes https://github.com/astral-sh/uv/issues/4136.
## Summary
This PR adds a lowering similar to that seen in
https://github.com/astral-sh/uv/pull/3100, but this time, for markers.
Like `PubGrubPackageInner::Extra`, we now have
`PubGrubPackageInner::Marker`. The dependencies of the `Marker` are
`PubGrubPackageInner::Package` with and without the marker.
As an example of why this is useful: assume we have `urllib3>=1.22.0` as
a direct dependency. Later, we see `urllib3 ; python_version > '3.7'` as
a transitive dependency. As-is, we might (for some reason) pick a very
old version of `urllib3` to satisfy `urllib3 ; python_version > '3.7'`,
then attempt to fetch its dependencies, which could even involve
building a very old version of `urllib3 ; python_version > '3.7'`. Once
we fetch the dependencies, we would see that `urllib3` at the same
version is _also_ a dependency (because we tack it on). In the new
scheme though, as soon as we "choose" the very old version of `urllib3 ;
python_version > '3.7'`, we'd then see that `urllib3` (the base package)
is also a dependency; so we see a conflict before we even fetch the
dependencies of the old variant.
With this, I can successfully resolve the case in #4099.
Closes https://github.com/astral-sh/uv/issues/4099.
## Summary
This PR modifies our `Requires-Python` handling to treat
`Requires-Python` as a lower bound. There's extensive discussion around
this in https://github.com/astral-sh/uv/issues/4022 and the references
linked therein. I think it's an experiment worth trying. Even in my own
small projects, I'm running into issues whereby I'm being "forced" to
add a `<4` upper bound to my `Requires-Python` due to these caps.
Separately, we should explore adding a mechanism that's distinct from
`Requires-Python` to enable users to declare a supported range for
locking.
Closes https://github.com/astral-sh/uv/issues/4022.
## Summary
Externally, development dependencies are currently structured as a flat
list of PEP 580-compatible requirements:
```toml
[tool.uv]
dev-dependencies = ["werkzeug"]
```
When locking, we lock all development dependencies; when syncing, users
can provide `--dev`.
Internally, though, we model them as dependency groups, similar to
Poetry, PDM, and [PEP 735](https://peps.python.org/pep-0735). This
enables us to change out the user-facing frontend without changing the
internal implementation, once we've decided how these should be exposed
to users.
A few important decisions encoded in the implementation (which we can
change later):
1. Groups are enabled globally, for all dependencies. This differs from
extras, which are enabled on a per-requirement basis. Note, however,
that we'll only discover groups for uv-enabled packages anyway.
2. Installing a group requires installing the base package. We rely on
this in PubGrub to ensure that we resolve to the same version (even
though we only expect groups to come from workspace dependencies anyway,
which are unique). But anyway, that's encoded in the resolver right now,
just as it is for extras.
## Summary
This PR adds the `Requires-Python` range to the user's lockfile. This
will enable us to validate it when installing.
For now, we repeat the `Requires-Python` back to the user;
alternatively, though, we could detect the supported Python range
automatically.
See: https://github.com/astral-sh/uv/issues/4052
## Summary
Thankfully this is pretty rare since `pip sync` is usually run on `pip
compile` output, and `pip compile` never outputs markers.
Closes https://github.com/astral-sh/uv/issues/4044
## Summary
Instead of checking if the target and installed version are the same, we
model the data such that the target version is only present if it was
specified by the user. This also means that we correctly say "requested
version" even if the two happen to be the same.
## Summary
I believe this is no longer necessary. Part of the problem here is that
we can't _know_ the full set of available Python versions, especially
once we start resolving against a `Requires-Python` rather than a fixed
set of two versions.
## Summary
Once we use a _range_ rather than a precise version, it won't actually
make sense to return a version here. It's no longer required, so I'm
removing it.
## Summary
Running a resolution that required forking was failing due to breaking
an invariant in PubGrub. It looks like we were adding the same
incompatibility multiple times, or something like that. The issue
appears to be that when forking, we modify the current state, then clone
it as the "next state", then push to the "forked states" -- but that
means we're cloning the _modified_ state.
This PR changes the order of operations such that we clone, then modify.
It shouldn't introduce any additional clones though.
## Summary
This PR removes the static resolver map:
```rust
static RESOLVED_GIT_REFS: Lazy<Mutex<FxHashMap<RepositoryReference, GitSha>>> =
Lazy::new(Mutex::default);
```
With a `GitResolver` struct that we now pass around on the
`BuildContext`. There should be no behavior changes here; it's purely an
internal refactor with an eye towards making it cleaner for us to
"pre-populate" the list of resolved SHAs.
With the change, we remove the special casing of workspace dependencies
and resolve `tool.uv` for all git and directory distributions. This
gives us support for non-editable workspace dependencies and path
dependencies in other workspaces. It removes a lot of special casing
around workspaces. These changes are the groundwork for supporting
`tool.uv` with dynamic metadata.
The basis for this change is moving `Requirement` from
`distribution-types` to `pypi-types` and the lowering logic from
`uv-requirements` to `uv-distribution`. This changes should be split out
in separate PRs.
I've included an example workspace `albatross-root-workspace2` where
`bird-feeder` depends on `a` from another workspace `ab`. There's a
bunch of failing tests and regressed error messages that still need
fixing. It does fix the audited package count for the workspace tests.
We significantly regressed performance in some cases because we were
cloning the resolver state one more time than we needed to. That doesn't
sound like a lot, but in the case where there are no forks, it implies
we were cloning the state for every `get_dependencies` called when we
shouldn't have been cloning it at all.
Avoiding the clone results in somewhat tortured code. This can probably
be refactored by moving bits out to a helper routine, but that also
seemed non-trivial. So we let this suffice for now.
This addresses the lack of marker support in prior commits.
Specifically, we add them as a new field to `AnnotatedDist`, and from
there, they get added to a `Distribution` in a `Lock`.
This commit is a pretty invasive change that implements the merging
of resolutions created by each fork of the resolver.
The main idea here is that each `SolveState` is converted into a
`Resolution` (a new type) and stored on the heap after its fork
completes. When all forks complete, they are all merged into a single
`Resolution`. This `Resolution` is then used to build a `ResolutionGraph`.
Construction of `ResolutionGraph` mostly stays the same (despite the
gnarly diff due to an indent change) with one exception: the code to
extract dependency edges out of PubGrub's state has been moved to
`SolveState::into_resolution`. The idea here is that once a fork
completes, we extract what we need from the PubGrub state and then
throw it away. We store these edges in our own intermediate type which
is then converted into petgraph edges in the `ResolutionGraph`
constructor.
One interesting change we make here is that our edge
data is now a `Version` instead of a `Range<Version>`. I don't think
`Range<Version>` was actually being used anywhere, so this seems okay?
In any case, I think `Version` here is correct because a resolution
corresponds to specific dependencies of each package. Moreover, I didn't
see an easy way to make things work with `Range<Version>`. Notably,
since we no longer have the guarantee that there is only one version of
each package, we need to use `(PackageName, Version)` instead of just
`PackageName` for inverted lookups in `ResolutionGraph::from_state`.
Finally, the main resolver loop itself is changed a bit to track all
forked resolutions and then merge them at the end.
Note that we don't really have any dealings with markers in this commit.
We'll get to that in a subsequent commit.
This changes the constructor to just take an `InMemoryIndex`
directly instead of the constituent parts. No real reason other
than it seems a little simpler.
There are still some TODOs/FIXMEs here, but this makes represents a
chunk of the resolver refactoring to enable forking. We don't do any
merging of resolutions yet, so crucially, this code is broken when no
marker environment is provided. But when a marker environment is
provided, this should behave the same as a non-forking resolver. In
particular, `get_dependencies_forking` is just `get_dependencies`
whenever there's a marker environment.
## Summary
This PR adds extras to the lockfile, and enables users to selectively
sync extras in `uv sync` and `uv run`. The end result here was fairly
simple, though it required a few refactors to get here. The basic idea
is that `DistributionId` now includes `extra: Option<ExtraName>`, so we
effectively treat extras as separate packages. Generating the lockfile,
and generating the resolution from the lockfile, fall out of this
naturally with no special-casing or additional changes.
The main downside here is that it bloats the lockfile significantly.
Specifically:
- We include _all_ distribution URLs and hashes for _every_ extra
variant.
- We include all dependencies for the extra variant, even though that
are dependencies of the base package.
We could normalize this representation by changing each distribution
have an `optional-dependencies` hash map that keys on extras, but we
actually don't have the information we need to create that right now
(specifically, we can't differentiate between dependencies that
_require_ the extra and dependencies on the base package).
Closes#3700.
## Summary
There are a few behavior changes in here:
- We now enforce `--require-hashes` for editables, like pip. So if you
use `--require-hashes` with an editable requirement, we'll reject it. I
could change this if it seems off.
- We now treat source tree requirements, editable or not (e.g., both `-e
./black` and `./black`) as if `--refresh` is always enabled. This
doesn't mean that we _always_ rebuild them; but if you pass
`--reinstall`, then yes, we always rebuild them. I think this is an
improvement and is close to how editables work today.
Closes#3844.
Closes#2695.
When parsing requirements from any source, directly parse the url parts
(and reject unsupported urls) instead of parsing url parts at a later
stage. This removes a bunch of error branches and concludes the work
parsing url parts once and passing them around everywhere.
Many usages of the assembled `VerbatimUrl` remain, but these can be
removed incrementally.
Please review commit-by-commit.
Pubgrub stores incompatibilities as (package name, version range)
tuples, meaning it needs to clone the package name for each
incompatibility, and each non-borrowed operation on incompatibilities.
https://github.com/astral-sh/uv/pull/3673 made me realize that
`PubGrubPackage` has gotten large (expensive to copy), so like `Version`
and other structs, i've added an `Arc` wrapper around it.
It's a pity clippy forbids `.deref()`, it's less opaque than `&**` and
has IDE support (clicking on `.deref()` jumps to the right impl).
## Benchmarks
It looks like this matters most for complex resolutions which, i assume
because they carry larger `PubGrubPackageInner::Package` and
`PubGrubPackageInner::Extra` types.
```bash
hyperfine --warmup 5 "./uv-main pip compile -q ./scripts/requirements/jupyter.in" "./uv-branch pip compile -q ./scripts/requirements/jupyter.in"
hyperfine --warmup 5 "./uv-main pip compile -q ./scripts/requirements/airflow.in" "./uv-branch pip compile -q ./scripts/requirements/airflow.in"
hyperfine --warmup 5 "./uv-main pip compile -q ./scripts/requirements/boto3.in" "./uv-branch pip compile -q ./scripts/requirements/boto3.in"
```
```
Benchmark 1: ./uv-main pip compile -q ./scripts/requirements/jupyter.in
Time (mean ± σ): 18.2 ms ± 1.6 ms [User: 14.4 ms, System: 26.0 ms]
Range (min … max): 15.8 ms … 22.5 ms 181 runs
Benchmark 2: ./uv-branch pip compile -q ./scripts/requirements/jupyter.in
Time (mean ± σ): 17.8 ms ± 1.4 ms [User: 14.4 ms, System: 25.3 ms]
Range (min … max): 15.4 ms … 23.1 ms 159 runs
Summary
./uv-branch pip compile -q ./scripts/requirements/jupyter.in ran
1.02 ± 0.12 times faster than ./uv-main pip compile -q ./scripts/requirements/jupyter.in
```
```
Benchmark 1: ./uv-main pip compile -q ./scripts/requirements/airflow.in
Time (mean ± σ): 153.7 ms ± 3.5 ms [User: 165.2 ms, System: 157.6 ms]
Range (min … max): 150.4 ms … 163.0 ms 19 runs
Benchmark 2: ./uv-branch pip compile -q ./scripts/requirements/airflow.in
Time (mean ± σ): 123.9 ms ± 4.6 ms [User: 152.4 ms, System: 133.8 ms]
Range (min … max): 118.4 ms … 138.1 ms 24 runs
Summary
./uv-branch pip compile -q ./scripts/requirements/airflow.in ran
1.24 ± 0.05 times faster than ./uv-main pip compile -q ./scripts/requirements/airflow.in
```
```
Benchmark 1: ./uv-main pip compile -q ./scripts/requirements/boto3.in
Time (mean ± σ): 327.0 ms ± 3.8 ms [User: 344.5 ms, System: 71.6 ms]
Range (min … max): 322.7 ms … 334.6 ms 10 runs
Benchmark 2: ./uv-branch pip compile -q ./scripts/requirements/boto3.in
Time (mean ± σ): 311.2 ms ± 3.1 ms [User: 339.3 ms, System: 63.1 ms]
Range (min … max): 307.8 ms … 317.0 ms 10 runs
Summary
./uv-branch pip compile -q ./scripts/requirements/boto3.in ran
1.05 ± 0.02 times faster than ./uv-main pip compile -q ./scripts/requirements/boto3.in
```
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This is split out from workspaces support, which needs editables in the
bluejay commands. It consists mainly of refactorings:
* Move the `editable` module one level up.
* Introduce a `BuiltEditableMetadata` type for `(LocalEditable,
Metadata23, Requirements)`.
* Add editables to `InstalledPackagesProvider` so we can use
`EmptyInstalledPackages` for them.
## Summary
Uncertain about this, but we don't actually need the full
`SourceDistFilename`, only the name and version -- and we often have
that information already (as in the lockfile routines). So by flattening
the fields onto `RegistrySourceDist`, we can avoid re-parsing for
information we already have.
## Summary
This PR introduces parallelism to the resolver. Specifically, we can
perform PubGrub resolution on a separate thread, while keeping all I/O
on the tokio thread. We already have the infrastructure set up for this
with the channel and `OnceMap`, which makes this change relatively
simple. The big change needed to make this possible is removing the
lifetimes on some of the types that need to be shared between the
resolver and pubgrub thread.
A related PR, https://github.com/astral-sh/uv/pull/1163, found that
adding `yield_now` calls improved throughput. With optimal scheduling we
might be able to get away with everything on the same thread here.
However, in the ideal pipeline with perfect prefetching, the resolution
and prefetching can run completely in parallel without depending on one
another. While this would be very difficult to achieve, even with our
current prefetching pattern we see a consistent performance improvement
from parallelism.
This does also require reverting a few of the changes from
https://github.com/astral-sh/uv/pull/3413, but not all of them. The
sharing is isolated to the resolver task.
## Test Plan
On smaller tasks performance is mixed with ~2% improvements/regressions
on both sides. However, on medium-large resolution tasks we see the
benefits of parallelism, with improvements anywhere from 10-50%.
```
./scripts/requirements/jupyter.in
Benchmark 1: ./target/profiling/baseline (resolve-warm)
Time (mean ± σ): 29.2 ms ± 1.8 ms [User: 20.3 ms, System: 29.8 ms]
Range (min … max): 26.4 ms … 36.0 ms 91 runs
Benchmark 2: ./target/profiling/parallel (resolve-warm)
Time (mean ± σ): 25.5 ms ± 1.0 ms [User: 19.5 ms, System: 25.5 ms]
Range (min … max): 23.6 ms … 27.8 ms 99 runs
Summary
./target/profiling/parallel (resolve-warm) ran
1.15 ± 0.08 times faster than ./target/profiling/baseline (resolve-warm)
```
```
./scripts/requirements/boto3.in
Benchmark 1: ./target/profiling/baseline (resolve-warm)
Time (mean ± σ): 487.1 ms ± 6.2 ms [User: 464.6 ms, System: 61.6 ms]
Range (min … max): 480.0 ms … 497.3 ms 10 runs
Benchmark 2: ./target/profiling/parallel (resolve-warm)
Time (mean ± σ): 430.8 ms ± 9.3 ms [User: 529.0 ms, System: 77.2 ms]
Range (min … max): 417.1 ms … 442.5 ms 10 runs
Summary
./target/profiling/parallel (resolve-warm) ran
1.13 ± 0.03 times faster than ./target/profiling/baseline (resolve-warm)
```
```
./scripts/requirements/airflow.in
Benchmark 1: ./target/profiling/baseline (resolve-warm)
Time (mean ± σ): 478.1 ms ± 18.8 ms [User: 482.6 ms, System: 205.0 ms]
Range (min … max): 454.7 ms … 508.9 ms 10 runs
Benchmark 2: ./target/profiling/parallel (resolve-warm)
Time (mean ± σ): 308.7 ms ± 11.7 ms [User: 428.5 ms, System: 209.5 ms]
Range (min … max): 287.8 ms … 323.1 ms 10 runs
Summary
./target/profiling/parallel (resolve-warm) ran
1.55 ± 0.08 times faster than ./target/profiling/baseline (resolve-warm)
```
Our current flow of data from "simple registry package" to "final
resolved distribution" goes through a number of types:
* `SimpleMetadata` is the API response from a registry that includes all
published versions for a package. Each version has an assortment of
metadata
associated with it.
* `VersionFiles` is the aforementioned metadata. It is split in two: a
group of files for source distributions and a group of files for wheels.
* `PrioritizedDist` collects a subset of the files from `VersionFiles`
to form a selection of the "best" sdist and the "best" wheel for the
current environment.
* `CompatibleDist` is created from a borrowed `PrioritizedDist` that,
perhaps among other things, encapsulates the decision of whether to pick
an sdist or a wheel. (This decision depends both on compatibility and
the action being performed. e.g., When doing installation, a
`CompatibleDist` will sometimes select an sdist over a wheel.)
* `ResolvedDistRef` is like a `ResolvedDist`, but borrows a `Dist`.
* `ResolvedDist` is the almost-final-form of a distribution in a
resolution and is created from a `ResolvedDistRef`.
* `AnnotatedResolvedDist` is a new data type that is the actual final
form of a distribution that a universal lock file cares about. It
bundles a `ResolvedDist` with some metadata needed to generate a lock
file.
One of the requirements of a universal lock file is that we include all
wheels (and maybe all source distributions? but at least one if it's
present) associated with a distribution. But the above flow of data (in
the step from `VersionFiles` to `PrioritizedDist`) drops all wheels
except for the best one.
To remedy this, in this PR, we rejigger `PrioritizedDist`,
`CompatibleDist` and `ResolvedDistRef` so that all wheel data is
preserved. And when a `ResolvedDistRef` is finally turned into a
`ResolvedDist`, we copy all of the wheel data. And finally, we adjust
the `Lock` constructor to read this new data and include it in the lock
file. To make this work, we also modify `RegistryBuiltDist` so that it
can contain one or more wheels instead of just one.
One shortcoming here (called out in the code as a FIXME) is that if a
source distribution is selected as the "best" thing to use (perhaps
there are no compatible wheels), then the wheels won't end up in the
lock file. I plan to fix this in a follow-up PR.
We also aren't totally consistent on source distribution naming.
Sometimes we use `sdist`. Sometimes `source`. Sometimes `source_dist`.
I think it'd be nice to just use `sdist` everywhere, but I do prefer
the type names to be `SourceDist`. And sometimes you want function
names to match the type names (i.e., `from_source_dist`), which in turn
leads to an appearance of inconsistency. I'm open to ideas.
Closes#3351
## Summary
In `ResolutionGraph::from_state`, we have mechanisms to grab the hashes
and metadata for all distributions -- but we then throw that information
away. This PR preserves it on a new `AnnotatedDist` (yikes, open to
suggestions) that wraps `ResolvedDist` and includes (1) the hashes
(computed or from the registry) and (2) the `Metadata23`, which lets us
extract the version.
Closes https://github.com/astral-sh/uv/issues/3356.
Closes https://github.com/astral-sh/uv/issues/3357.
## Summary
It's confusing that we use `constraints` here because constraints mean
something else for us (e.g., `--constraint constraints.txt`). These are
really the dependencies of a given `PubGrubPackage` -- the type is even
called `PubGrubDependencies`.
## Summary
I think this is overall good change because it explicitly encodes (in
the type system) something that was previously implicit. I'm not a huge
fan of the names here, open to input.
It covers some of https://github.com/astral-sh/uv/issues/3506 but I
don't think it _closes_ it.
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## Summary
Just fix typos.
While `alpha-numeric` is not really a misspelling:
- it is missing from mainstream curated dictionaries, all of them
suggest `alphanumeric`;
- it is less used than `alphanumeric` (more than ⨉10 less) according to
the Google [Ngram
Viewer](https://books.google.com/ngrams/graph?content=alpha-numeric%2Calphanumeric&year_start=1900&year_end=2019&corpus=en-2019);
- it is [missing from
SCOWL](http://app.aspell.net/lookup?dict=en_US-large;words=alpha-numeric).
## Test Plan
CI jobs.
## Summary
This PR consolidates the concurrency limits used throughout `uv` and
exposes two limits, `UV_CONCURRENT_DOWNLOADS` and
`UV_CONCURRENT_BUILDS`, as environment variables.
Currently, `uv` has a number of concurrent streams that it buffers using
relatively arbitrary limits for backpressure. However, many of these
limits are conflated. We run a relatively small number of tasks overall
and should start most things as soon as possible. What we really want to
limit are three separate operations:
- File I/O. This is managed by tokio's blocking pool and we should not
really have to worry about it.
- Network I/O.
- Python build processes.
Because the current limits span a broad range of tasks, it's possible
that a limit meant for network I/O is occupied by tasks performing
builds, reading from the file system, or even waiting on a `OnceMap`. We
also don't limit build processes that end up being required to perform a
download. While this may not pose a performance problem because our
limits are relatively high, it does mean that the limits do not do what
we want, making it tricky to expose them to users
(https://github.com/astral-sh/uv/issues/1205,
https://github.com/astral-sh/uv/issues/3311).
After this change, the limits on network I/O and build processes are
centralized and managed by semaphores. All other tasks are unbuffered
(note that these tasks are still bounded, so backpressure should not be
a problem).
This still keeps the resolver state on the stack, but it organizes it
into a more structured representation. This is a precursor to
implementing resolver forking, where we will ultimately put this state
on the heap. The idea is that this will let us maintain multiple
independent resolver states that will all produce their own resolution
(and potentially other forked states).
Closes#3354
This commit touches a lot of code, but the conceptual change here is
pretty simple: make it so we can run the resolver without providing a
`MarkerEnvironment`. This also indicates that the resolver should run in
universal mode. That is, the effect of a missing marker environment is
that all marker expressions that reference the marker environment are
evaluated to `true`. That is, they are ignored. (The only markers we
evaluate in that context are extras, which are the only markers that
aren't dependent on the environment.)
One interesting change here is that a `Resolver` no longer needs an
`Interpreter`. Previously, it had only been using it to construct a
`PythonRequirement`, by filling in the installed version from the
`Interpreter` state. But we now construct a `PythonRequirement`
explicitly since its `target` Python version should no longer be tied to
the `MarkerEnvironment`. (Currently, the marker environment is mutated
such that its `python_full_version` is derived from multiple sources,
including the CLI, which I found a touch confusing.)
The change in behavior can now be observed through the
`--unstable-uv-lock-file` flag. First, without it:
```
$ cat requirements.in
anyio>=4.3.0 ; sys_platform == "linux"
anyio<4 ; sys_platform == "darwin"
$ cargo run -qp uv -- pip compile -p3.10 requirements.in
anyio==4.3.0
exceptiongroup==1.2.1
# via anyio
idna==3.7
# via anyio
sniffio==1.3.1
# via anyio
typing-extensions==4.11.0
# via anyio
```
And now with it:
```
$ cargo run -qp uv -- pip compile -p3.10 requirements.in --unstable-uv-lock-file
x No solution found when resolving dependencies:
`-> Because you require anyio>=4.3.0 and anyio<4, we can conclude that the requirements are unsatisfiable.
```
This is expected at this point because the marker expressions are being
explicitly ignored, *and* there is no forking done yet to account for
the conflict.
Pubgrub got a new feature where all unavailability is a custom, instead
of the reasonless `UnavailableDependencies` and our custom `String` type
previously (https://github.com/pubgrub-rs/pubgrub/pull/208). This PR
introduces a `UnavailableReason` that tracks either an entire version
being unusable, or a specific version. The error messages now also track
this difference properly.
The pubgrub commit is our main rebased onto the merged
https://github.com/pubgrub-rs/pubgrub/pull/208, i'll push
`konsti/main-rebase-generic-reason` to `main` after checking for rebase
problems.
