We previously were not properly handling the diagnostics for using an rvalue implicit member on the left hand side of an assignment. This adds the proper handling and extends it for member chains.
Instead of creating the type variable for the unresolved member chain at the location of the last member, we now create it at the associated UnresolvedMemberChainResultExpr.
Previously, when the final element of a chain was a ForceValueExpr, the chain result type got caught up in the logic used to allow ForceValueExprs to properly infer lvalue types. By separating the result type variable from the last member of the chain, we make sure to keep that logic focused only on ForceValueExpr.
If reference collection discovered at least `ErrorExpr` in the body
of a closure, let's fail constraint generation only if it's a
single-statement closure, decision about multi-statement closures
should be delayed until body is opened.
This helps code completion because `ErrorExpr` could belong to
a statement unrelated to a completion, so it wouldn't affect
its correctness in any way.
Fix a regression introduced by moving the type checking of closure
captures into the constraint system. The pattern-type optimization for
initializations was causing inference of a double-optional where there
shouldn't be one, manifesting in a failure involving implicitly
unwrapped optionals and `weak self` captures.
Fixes rdar://problem/67351438.
Allow async calls and await expressions within @asyncHandler functions.
If we see an async call or await expression in a function that is not
an async context, also suggest adding @asyncHandler if the function
meets the semantic constraints.
Replace the uglified '__await' keyword with a contextual keyword
'await'. This is more of what we would actually want for the
concurrency model.
When concurrency is enabled, this will be a source-breaking change,
because this is valid Swift code today:
```swift
struct MyFuture<T> {
func await() -> }
func doSomething() {
let result = await()
}
}
```
but the call to `await()` will be parsed as an await expression when
concurrency is enabled. The source break is behind the experimental
concurrency flag, but this way we can see how much of an issue it is
in practice.
Closurea can become 'async' in one of two ways:
* They can be explicitly marked 'async' prior to the 'in'
* They can be inferred as 'async' if they include 'await' in the body
Implement missing restrictions on calls to 'async':
* Diagnose async calls/uses of await in illegal contexts (such as
default arguments)
* Diagnose async calls/uses of await in functions/closures that are not
asynchronous themselves
* Handle autoclosure arguments as their own separate contexts (so
'await' has to go on the argument), which differs from error handling
(where the 'try' can go outside) because we want to be more particular
about marking the specific suspension points.
when we have an optional type. This uncovered an error with unresolved member lookup where we allowed an unresolved value member constraint to fail if lookup failed in an optional type wrapping a type variable.
This resolves SR-13357.
The change to resolve ObjC #keyPath expression components caused some source
breakage as they are now being checked for availability issues. This change
updates availability checking to demote error diagnostics to warnings
within #keyPath expressions. There were cases in the source compat suite where
unavailble properites were used in #keyPath expressions, but they caused no
issues at runtime because the properties' ObjC runtime name was still correct
(e.g. the same as its renamed-to property in Swift).
Unlike \keypath expressions, only the property components of #keypath
expressions were being resolved, so index wouldn't pick up references for their
qualifying types.
Also fixes a code completion bug where it was reporting members from the Swift
rather than ObjC side of bridged types.
Resolves rdar://problem/61573935
Unlike \keypath expressions, only the property components of #keypath
expressions were being resolved, so index wouldn't pick up references for their
qualifying types.
Also fixes a code completion bug where it was reporting members from the Swift
rather than ObjC side of bridged types.
Resolves rdar://problem/61573935
Similar to `try`, await expressions have no specific semantics of their
own except to indicate that the subexpression contains calls to `async`
functions, which are suspension points. In this design, there can be
multiple such calls within the subexpression of a given `await`.
Note that we currently use the keyword `__await` because `await` in
this position introduces grammatical ambiguities. We'll wait until
later to sort out the specific grammar we want and evaluate
source-compatibility tradeoffs. It's possible that this kind of prefix
operator isn't what we want anyway.
Rather than type-checking captures as separate declarations during
pre-check, generate constraints and apply solutions to captures in
the same manner as other pattern bindings within a constraint
system.
Fixes SR-3186 / rdar://problem/64647232.
This approach, suggested by Xiaodi Wu, provides better source
compatibility for existing Swift code, by breaking ties in favor of the
existing Swift semantics. Each time the backward-scan rule is needed
(and differs from the forward-scan result), we will produce a warning
+ Fix-It to prepare for Swift 6 where the backward rule can be
removed.
My experiment to improve source compatibility by also performing a
backward scan removed the SE-0286 heuristic that skipped binding
the unlabeled trailing closure to a defaulted parameter when that
would fail. Reinstate that heuristic, which makes more existing code
work with the forward-scan behavior.
This makes my source-compatibility improvements a quality-of-implementation
Whenever we form a call that relies on the deprecated "backward" scan,
produce a warning to note the deprecation along with a Fix-It to label
the parameter appropriately (and suppress the warning). For example:
warning: backward matching of the unlabeled trailing closure is
deprecated; label the argument with 'g' to suppress this warning
trailingClosureEitherDirection { $0 * $1 }
^
(g: )
To better preserve source compatibility, teach the constraint
solver to try both the new forward scanning rule as well as the
backward scanning rule when matching a single, unlabeled trailing
closure. In the extreme case, where the unlabeled trailing closure
matches different parameters with the different rules, and yet both
produce a potential match, introduce a disjunction to explore both
possibilities.
Prefer solutions that involve forward scans to those that involve
backward scans, so we only use the backward scan as a fallback.
SE-0248 changes the backward-scan matching behavior for the unlabeled
trailing closure into a forward scan. In circumstances where this
could silently change the meaning of a call to a particular
function, i.e., when there are two defaulted closure parameters such
that a given closure to match either one of them, produce an warning
that describes the change in behavior. For example:
t4.swift:2:24: warning: since Swift 5.3, unlabeled trailing
closure argument matches parameter 'x' rather than parameter 'z'
trailingClosureSingle2 { $0 }
^
t4.swift:2:24: note: label the argument with 'z' to retain the
pre-Swift 5.3 behavior
trailingClosureSingle2 { $0 }
^
(z: )
t4.swift:2:24: note: label the argument with 'x' to silence this
warning for Swift 5.3 and newer
trailingClosureSingle2 { $0 }
^
(x: )
t4.swift:1:6: note: 'trailingClosureSingle2(x:y:z:)' contains
defaulted closure parameters 'x' and 'z'
func trailingClosureSingle2(x: (Int) -> Int = { $0 } , y: (Int) ->
Int = { $0 }, z: (Int) -> Int = { $0 }) {}
^ ~
This explains the (rare) case where SE-0286 silently changes the
meaning of a program, offering Fix-Its to either restore the
pre-SE-0286 behavior or silence the warning, as appropriate.
The change to the forward-scanning rule regressed some diagnostics,
because we no longer generated the special "trailing closure mismatch"
diagnostic. Reinstate the special-case "trailing closure mismatch"
diagnostic, but this time do so as part of the normal argument
mismatch diagnostics so it is based on type information.
While here, clean up the handling of missing-argument diagnostics to
deal with (multiple) trailing closures properly, so that we can (e.g)
suggest adding a new labeled trailing closure at the end, rather than
producing nonsensical Fix-Its.
And, note that SR-12291 is broken (again) by the forward-scan matching
rules.
Once the first argument for a variadic function-typed parameter has been
matched, allow an unlabeled trailing closure to match, rather than
banning all uses of the unlabeled trailing closure with variadic
parameters.
The "fuzzy" forward scan matching algorithm was only applied when there
was a single, unlabeled trailing closure, but was disabled in the
presence of multiple trailing closures. Extend the "fuzzy" match to
account for multiple trailing closures, by restricting the search for
"a later parameter that needs an argument" to stop when we find a
parameter that matches the first (labeled) trailing closure.
Introsuce a new "forward" algorithm for trailing closures where
the unlabeled trailing closure argument matches the next parameter in
the parameter list that can accept an unlabeled trailing closure.
The "can accept an unlabeled trailing closure" criteria looks at the
parameter itself. The parameter accepts an unlabeled trailing closure
if all of the following are true:
* The parameter is not 'inout'
* The adjusted type of the parameter (defined below) is a function type
The adjusted type of the parameter is the parameter's type as
declared, after performing two adjustments:
* If the parameter is an @autoclosure, use the result type of the
parameter's declared (function) type, before performing the second
adjustment.
* Remove all outer "optional" types.
For example, the following function illustrates both adjustments to
determine that the parameter "body" accepts an unlabeled trailing
closure:
func doSomething(body: @autoclosure () -> (((Int) -> String)?))
This is a source-breaking change. However, there is a "fuzzy" matching
rule that that addresses the source break we've observed in practice,
where a defaulted closure parameter precedes a non-defaulted closure
parameter:
func doSomethingElse(
onError: ((Error) -> Void)? = nil,
onCompletion: (Int) -> Void
) { }
doSomethingElse { x in
print(x)
}
With the existing "backward" scan rule, the trailing closure matches
onCompletion, and onError is given the default of "nil". With the
forward scanning rule, the trailing closure matches onError, and there
is no "onCompletion" argument, so the call fails.
The fuzzy matching rule proceeds as follows:
* if the call has a single, unlabeled trailing closure argument, and
* the parameter that would match the unlabeled trailing closure
argument has a default, and
* there are parameters *after* that parameter that require an argument
(i.e., they are not variadic and do not have a default argument)
then the forward scan skips this parameter and considers the next
parameter that could accept the unlabeled trailing closure.
Note that APIs like doSomethingElse(onError:onCompletion:) above
should probably be reworked to put the defaulted parameters at the
end, which works better with the forward scan and with multiple
trailing closures:
func doSomethingElseBetter(
onCompletion: (Int) -> Void,
onError: ((Error) -> Void)? = nil
) { }
doSomethingElseBetter { x in
print(x)
}
doSomethingElseBetter { x in
print(x)
} onError: { error in
throw error
}
