- Allow an if/switch expression to become an
implicit return of a function that has a `#if`
body with a single active element that is an `if`
or `switch`.
- Allow `#if` branches of an if/switch expression,
as long as there is a single active expression
element.
rdar://107487977
the main things still left behind the experimental flag(s) are
- move-only classes (guarded by MoveOnlyClasses feature)
- noimplicitcopy
- the _borrow operator
Unify the duplicate pattern var checking in
pattern resolution such that it is always called
no matter how we end up type-checking the pattern.
This avoids incorrectly allowing duplicate pattern
vars to compile for patterns as a part of
multi-statement closures.
It's possible for out-of-scope type variable to be the type of
declaration if such declaration is recursively referenced in
the body of a closure located in its initializer expression.
In such cases type of the variable declaration cannot be connected
to the closure because its not known in advance (determined by the
initializer itself).
Resolves: https://github.com/apple/swift/issues/63455
Look through `try`/`await` markers when looking for
out of place if/switch expressions, and customize
the effect checking diagnostic such that we error
that `try`/`await` are redundant on `if`/`switch`
expressions.
Introduce SingleValueStmtExpr, which allows the
embedding of a statement in an expression context.
This then allows us to parse and type-check `if`
and `switch` statements as expressions, gated
behind the `IfSwitchExpression` experimental
feature for now. In the future,
SingleValueStmtExpr could also be used for e.g
`do` expressions.
For now, only single expression branches are
supported for producing a value from an
`if`/`switch` expression, and each branch is
type-checked independently. A multi-statement
branch may only appear if it ends with a `throw`,
and it may not `break`, `continue`, or `return`.
The placement of `if`/`switch` expressions is also
currently limited by a syntactic use diagnostic.
Currently they're only allowed in bindings,
assignments, throws, and returns. But this could
be lifted in the future if desired.
Member chains with leading-dot syntax can infer the base type
only from context, so optionality mismatch with the contextual
type should propagate object type down the chain.
If a placeholder appears on one of the side of tuple element matching
conversion, consider that conversion to be solved, because the actual
error is related to the placeholder.
Currently solver picks the first conjunction it can find,
which means - the earliest resolved closure. This is not
always correct because when calls are chained closures
passed to the lower members could be resolved sooner
than the ones higher up but at the same time they depend
on types inferred from members higher in the chain.
Let's make sure that multi-statement closures are always
solved in order they appear in the AST to make sure that
types are available to members lower in the chain.
These were replaced by `#file`, `#line`, etc. with SE-0028, prior to
Swift 3. We don't need this custom error message any more, and they
shouldn't be keywords. Stop treating them as keywords in the lexer.
