`TrailingClosureAmbiguityFailure::diagnoseAsNote()` is used by
`diagnoseAmbiguity` opportunistically, which means that anchor
could be a pattern or a statement condition element.
Referencing a member in pattern context is not a regular member reference,
it should use only enum element declarations, just like leading-dot syntax
does, so both locators should end with `pattern matching` element to indicate
that to the member lookup.
Resolves: rdar://90347159
Solution application target can have its declaration context differ
from one used for constraint system, since target could be e.g. a
pattern associated with pattern binding declaration, a statement or
a sub-element of one (e.g. where clause) used in a closure etc.
`one-way` constraints disable some optimizations related to component
selection because they imply strict ordering. This is a problem for
multi-statement closures because variable declarations could involve
complex operator expressions that rely on aforementioned optimizations.
In order to fix that, let's move away from solving whole pattern binding
declaration into scheme that explodes such declarations into indvidual
elements and inlines them into a conjunction.
For example:
```
let x = 42, y = x + 1, z = (x, test())
```
Would result in a conjunction of three elements:
```
x = 42
y = x + 1
z = (x, test())
```
Each element is solved indepedently, which eliminates the need for
`one-way` constraints and re-enables component selection optimizations.
A local function can capture a variable that has been declared after it,
which means that type-checking such declaration in-order would trigger
sub-typecheck that would corrupt AST underness the solution application
walker.
Augment the constraint solver to fallback to implicit `~=` application
when member couldn't be found for `EnumElement` patterns because
`case` statement should be able to match enum member directly, as well
as through an implicit `~=` operator application.
Source compatibility workaround.
func test<T>(_: () -> T?) {
...
}
A multi-statement closure passed to `test` that has an optional
`Void` result type inferred from the body allows:
- empty `return`(s);
- to skip `return nil` or `return ()` at the end.
Implicit `return ()` has to be inserted as the last element
of the body if there is none. This wasn't needed before SE-0326
because result type was (incorrectly) inferred as `Void` due to
the body being skipped.
Resolves: rdar://85840941
With the argument list refactoring, it's no
longer sufficient to stop walking when we encounter
an explicit tuple or paren. Add an additional
check to stop walking when we encounter an explicit
argument list.
rdar://85343171
We've always emitted an error if we saw an implicit use of a self
parameter of class type from an escaping closure. In PR #35898, I fixed
this to also emit an error if the reference was to an explicit capture
of self that wasn't made in the current closure. That was causing
some source incompatibilities that we decided were too severe, so in
PR #38947 I weakened that to a warning when the diagnostic walk was
within multiple levels of closures, because I have always thought of
this as a fix to nested closures. However, this was the wrong condition
in two ways.
First, the diagnostic walk does not always start from the outermost
function declaration; it can also start from a multi-statement closure.
In that case, we'll still end up emitting an error when we see uses
of explicit captures from the closure when we walk it, and so we still
have a source incompatibility. That is rdar://82545600.
Second, the old diagnostic did actually fire correctly in nested
closures as long as the code was directly referring to the original
self parameter and not any intervening captures. Therefore, #38947
actually turned some things into warnings that had always been errors.
The fix is to produce a warning exactly when the referenced declaration
was an explicit capture.
Swift has diagnosed implicit uses of class-reference `self` in
escaping closures for a long time as potentially leading to reference
cycles. PR #35898 fixed a bug where we failed to diagnose this
condition in nested closures. Unfortunately, treating this as an
error has proven problematic because there's a lot of code doing
it. Requiring that code to be thoroughly stamped out before we
ship a compiler is just too much to ask. Stage the fix in by
treating it as a warning in Swift versions prior to 6.
As with the non-nested case, this warning can be suppressed by
explicitly either capturing `self` or spelling out `self.` in the
access.
Fixes rdar://80847025.
Instead of failing constraint generation upon encountering
an invalid declaration, let's turn that declaration into a
potential hole and keep going. Doing so enables the solver
to reach a solution and diagnose any other issue with
expression.
I created a second copy of each test where the output changes
after disabling parser lookup. The primary copy now explicitly
calls the frontend with -disable-parser-lookup and expects the
new diagnostics; the *_parser_lookup.swift version calls the
frontend with -enable-parser-lookup and has the old expectations.
This allows us to turn parser lookup on and off by default
without disturbing tests. Once parser lookup is completely
removed we can remove the *_parser_lookup.swift variants.
We'll need this to get the right 'selfDC' when name lookup
finds a 'self' declaration in a capture list, eg
class C {
func bar() {}
func foo() {
_ = { [self] in bar() }
}
}
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.
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.
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.
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.
