to `Sendable`.
The unavailability check was not using the root conformance, which is where
the extension declaration with the unavailability attribute is for inherited
conformances, leading to bogus warnings about re-stating unchecked conformances
to `Sendable`.
When diagnosing a concurrency-unsafe global or static variable, provide
Fix-Its with specific guidance and advice. This is intended to aid the
workflow for folks enabling strict concurrency checking or Swift 6.
There are up to three Fix-Its attached to a diagnostic about
concurrency-unsafe global/static variables:
* convert 'global' to a 'let' constant to make the shared state
immutable, which replaces `var` with `let`
* restrict 'global' to the main actor if it will only be accessed from the
main thread, which adds `@MainActor`
* unsafely mark %0 as concurrency-safe if all accesses are protected
by an external synchronization mechanism, which adds `nonisolated(unsafe)`
I fretted over two things before deciding on this path:
1. For the second note, the reality is that any global actor will
suffice, but `@MainActor` is orders of magnitude more common than any
other global actor, so "common case convenience" wins over "precise
but less useful.
2. For the third note, `nonisolated(unsafe)` should only be used
sparingly, and surfacing it via Fix-It could cause overuse. However,
developers need to know about it, and this is how we do that. It comes
last in the list of notes (after the better options) and says "unsafe"
in not one but two places.
I added a disable flag -disable-region-based-isolation-with-strict-concurrency
so that we do not need to update the current tests. It is only available when
asserts are enabled to ensure users cannot use it.
rdar://125918028
This means that:
1. In test cases where minimal is the default (swift 5 without
-warn-concurrency), I added RUN lines for targeted, complete, and complete +
sns.
2. In test cases where complete is the default (swift 6, -warn-concurrency,
specified complete with -strict-concurrency), I added a send non-sendable run
line.
In each of these cases, I added additional expected-* lines as appropriate so
the tests can compile in each mode successfully.
Isolation checking for calls had two separate implementation places:
one that looked at the declaration being called (for member
declarations) and one that worked on the actual call expression. Unify
on the latter implementation, which is more general and has access to
the specific call arguments. Improve diagnostics here somewher so we
don't regress in that area.
This refactoring shouldn't change the actual semantics, but it makes
upcoming semantic changes easier.
This is possible because actors do not support inheritance. There
is one specific exception to that rule, which is that an actor
can inherit from `NSObject` just to support ObjC interop.
This means an actor is effectively a final class.
resolves rdar://87568153
`isConcurrencyChecked()` was being used as a proxy for
`-warn-concurrency` that didn't account for Swift 6. Replace
checks against it within the current module with checks against the
strict concurrency level, which subsumes the Swift 6 check and can
account for the difference between "limited" and "on".
`isConcurrencyChecked()` is used now used exclusively to mean "treat a
missing Sendable conformance as an explicitly-non-Sendable type".
There were some tests that relied on the top-level code not being an
asynchronous context to emit certain error messages. Now that it is,
those tests weren't emitting the expected error message.
In other cases, the issue was that they were trying to initialize a
global variable and weren't really using top-level code as top-level
code, so adding `-parse-as-library` was sufficient for the testing
purposes.
To fix the objc_async test, parsing as a library was nearly sufficient.
Unfortunately, the little `if #available` trick that I was using stopped
working since it relied on being in top-level code. So that we emit the
unavailableFromAsync error message, I had to set the availability on
everything correctly because we can't just disable availability
checking.
This is a combination of fixes:
- inject hops in self-isolated delegating actor initializers
after self becomes initialized.
- fix sendable and isolation for convenience inits
- fix bug in distributed actor inits that I introduced when
implementing flow-isolation.
- fix / add test coverage.
Flow-isolation is a diagnostic SIL pass that finds
unsafe accesses to properties in initializers and
deinitializers that cannot gain isolation to otherwise
protect those accesses from concurrent modifications.
See SE-327 for more details about how and why it exists.
This commit includes changes and features like:
- The removal of the escaping-use restriction
- Flow-isolation that works properly with `defer` statements
- Flow-isolation with an emphasis on helpful diagnostics.
It also includes known issues like:
- Local / nonescaping functions are not analyzed by
flow-isolation, despite it being technically possible.
The main challenge in supporting it efficiently is that
such functions do not have a single exit-point, like
a `defer`. In particular, arbitrary functions can throw
so there are points where nonisolation should _not_ flow
out of the function at a call-site in the initializer, etc.
- The implementation of the flow-isolation pass is not
particularly memory efficient; it relies on BitDataflow
even though the particular flow problem is simple.
So, a more efficient implementation would be specialized for
this particular problem, etc.
There are also some changes to the Swift language itself: defer
will respect its context when deciding its property access kind.
Previously, a defer in an initializer would always access a stored
property through its accessor methods, instead of doing so directly
like its enclosing function might. This inconsistency is unfortunate,
so for Swift 6+ we make this consistent. For Swift 5, only a defer
in a function that is a member of the following kinds of types
will gain this consistency:
- an actor type
- any nominal type that is actor-isolated, excluding UnsafeGlobalActor.
These types are still rather new, so there is much less of a chance of
breaking expected behaviors around defer. In particular, the danger is
that users are relying on the behavior of defer triggering a property
observer within an init or deinit, when it would not be triggering it
without the defer.
Introduce the `@preconcurrency` attribute name for `@_predatesConcurrency`,
which has been the favored name in the pitch thread so far. Retain the
old name for now to help smooth migration.
Rather than only checking the sendability of captures at the point of
use, diagnose captures uniformly for the closure as a whole. Fixes a
case where we were missing a diagnostic due to an explicit capture,
rdar://85988937.
Non-isolated declarations in general do not require Sendable
diagnostics. However, we do need to make sure that `nonisolated let`
accesses to actor-isolated state are always cross-actor.
Fixes rdar://83371627.
