Previously we could allow some invalid coercions to
sneak past Sema. In most cases these would either
cause crashes later down the pipeline or
miscompiles. However, for coercions between
collections, we emitted somewhat reasonable code
that performed a force cast.
This commit aims to preserve compatibility with
those collection coercions that previously
compiled, and emits a warning telling the user to
use either 'as?' or 'as!' instead.
New name is more consistent with existing `getOverloadChoiceIfAvailable`
and allows us to clean up a couple of places where `getCalleeLocator` was
used directly before.
This helps to avoid allocating new type variables (which shouldn't be done regardless)
to store parameter indices when `missing arguments` diagnostic is used by other diagnostics.
Make diagnostics stateless by providing them with a solution
instead of applying a solution back to constraint system and
using constraint system. Latter doesn't work well when there
is an ambiguity and multiple solutions are available instead
of one.
This is something I noticed by inspection while working on
<https://bugs.swift.org/browse/SR-75>.
Inside a static method, 'self' is a metatype value, so
'self.instanceMethod' produces an unbound reference of type
(Self) -> (Args...) -> Results.
You might guess that 'super.instanceMethod' can similarly
be used to produce an unbound method reference that calls
the superclass method given any 'self' value, but unfortunately
it doesn't work.
Instead, 'super.instanceMethod' would produce the same
result as 'self.instanceMethod'. Maybe we can implement this
later, but for now, let's just diagnose the problem.
Note that partially-applied method references with 'super.'
-- namely, 'self.staticMethod' inside a static context, or
'self.instanceMethod' inside an instance context, continue
to work as before.
They have the type (Args...) -> Result; since the self value
has already been applied we don't hit the representational
issue.
Diagnose an attempt to reference a top-level name shadowed by
a local member e.g.
```swift
extension Sequence {
func test() -> Int {
return max(1, 2)
}
}
```
Here `min` refers to a global function `min<T>(_: T, _: T)` in `Swift`
module and can only be accessed by adding `Swift.` to it, because `Sequence`
has a member named `min` which accepts a single argument.
When requesting information about the contextual type of a constraint
system, do so using a given expression rather than treating it like
the global state that it is.
This is useful in some situations where access to type variable(s)
helps to diagnose the problem properly e.g. if it's a conversion
to generic parameter.
Rather than maintaining a linked list of overload
choices, which must be linearly searched each time
we need to lookup an overload at a given callee
locator, use a MapVector which can be rolled back
at the end of a scope.
Remove ResolvedOverloadSetListItem in favor of
using SelectedOverload, which avoids the need to
convert between them when moving from
ConstraintSystem to Solution.
If none of the candidates produce expected contextual type, record
all of the posibilities to produce a note per and diagnose this as
contextual type mismatch instead of a reference ambiguity.
Record both sides of conversion where a form of force unwrap is
necessary to be able to produce tailored diagnostics such as for
an attempt to use optional type as a boolean.
We're still using the root expression to find the parent map, but we're not
falling back to it indiscriminately. Use the parent of the anchor (or
appropriate substitute) instead so we have a better handle on which
expression we're diagnosing for.
