Additionally, refactor some of the logic for the original add $ diagnostic
so that a lot of logic can be shared between the two. Also rename the
original fix and diagnostic to better reflect their purpose.
For the purposes of fix deduplication, we want to use the simplified
locator. However for the purposes of diagnostics, preserve the full
locator, which gives us more information to work with.
Add `llvm_unreachable` to mark covered switches which MSVC does not
analyze correctly and believes that there exists a path through the
function without a return value.
Introduce a fix to detect and diagnose situations when omitted
generic arguments couldn't be deduced by the solver based on
the enclosing context.
Example:
```swift
struct S<T> {
}
_ = S() // There is not enough context to deduce `T`
```
Resolves: rdar://problem/51203824
All places where `invalid member ref` fix/diagnostic is used already
have a reference to the potential member choice declaration, which
diagnostic could take advantage of.
Extend use of `missing protocol conformance` fix to cover contextual
failures, such as:
- Assignment mismatches, where destination requires source to conform
to certain protocol (or protocol composition);
- Incorrect returns where returned type doesn't conform to the
protocol specified in the signature.
Extend use of `missing protocol conformance` fix to cover contextual
failures, such as:
- Assignment mismatches, where destination requires source to conform
to certain protocol (or protocol composition);
- Incorrect returns where returned type doesn't conform to the
protocol specified in the signature.
Detect and diagnose a contextual mismatch between expected
collection element type and the one provided (e.g. source
of the assignment or argument to a call) e.g.:
```swift
let _: [Int] = ["hello"]
func foo(_: [Int]) {}
foo(["hello"])
```
Diagnose extraneous use of address of (`&`) which could only be
associated with arguments to `inout` parameters e.g.
```swift
struct S {}
var a: S = ...
var b: S = ...
a = &b
```
Detect situations where key path doesn't have capability required
by the context e.g. read-only vs. writable, or either root or value
types are incorrect e.g.
```swift
struct S { let foo: Int }
let _: WritableKeyPath<S, Int> = \.foo
```
Here context requires a writable key path but `foo` property is
read-only.
Referencing (instance or static) methods in the key path is not
currently allowed, solver should be responsible for early detection
and diagnosis of both standalone e.g. `\.foo` and chained
e.g. `\.foo.bar` (where foo is a method) references in key path
components.
```swift
struct S {
func foo() -> Int { return 42 }
}
let _: KeyPath<S, Int> = \.foo
```
Resolves: rdar://problem/49413561
Previously it was possible to create an invalid solution where
static members would be referenced in a key path, which is not
currently supported and would only be diagnosed while applying
such solution to AST e.g.
```swift
struct S {
static var foo: Int = 42
}
_ = \S.Type.foo
```
