`MissingMemberFailure::diagnoseInLiteralCollectionContext`
should verify that a parent (or parent of a parent) expression
is indeed a collection expression instead of checking types.
Resolves: rdar://91452726
Instead of failing constraint generation by returning `nullptr` for an `ErrorExpr` or returning a null type when a type fails to be resolved, return a fresh type variable. This allows the constraint solver to continue further and produce more meaningful diagnostics.
Most importantly, it allows us to produce a solution where previously constraint generation for a syntactic element had failed, which is required to type check multi-statement closures in result builders inside the constraint system.
The deepest expression is the one that introduced the ambiguity into
the chain, so depth and index should be deciding factors and number of
overloads - a tie-breaker, while choosing what to diagnose.
Resolves: rdar://94360230
Avoid mutating case label items while solving, instead let's use types
recorded in the constraint system for each pattern variable and use
that for var reference in the case body. This also helps to detect
and diagnose type conflicts while solving.
Fix an oversight where syntactic checking was not performed on
any statements in a body of a multi-statement after successful
solution application.
Resolves: rdar://94049113
`fallthrough` requires both source and destination `case`
"preambles" be type-checked before it could be validated,
which means that solution application for `case` statements
in a `switch` has to be split in two - preamble first and
bodies afterwards.
Resolves: https://github.com/apple/swift/issues/59035
Resolves: rdar://93796211
Type finder is still allowed to walk into closures to find any
referenced variables, but it should bring external result type
into scope only if a particular `return` belongs to the same
closure as the element.
If all solutions point to the same overload choice that needs
re-labeling it's safe to diagnose it as if there was no ambiguity
because the call site is static.
If a syntactic element references an external declaration (relative
to its own context), let's check whether it has any type variables,
and if so, replace them with errors to remove any possibility of
bringing external constraints into element's scope.
Resolves: rdar://92347054
Add ClosureExpr to the list of expressions we don't
walk into for the purposes of diagnosing trailing
closures in conditional initializers.
rdar://92521618
