Follow-up to https://github.com/apple/swift/pull/70148
Just like with arrays it's advantageous to favor dictionary
literals over disjunctions to bind the elements together and
enable inference across elements and, as a consequence,
type pruning.
Resolves: rdar://119040159
Conditional and forced downcasts enter a constraint that almost
always succeeds; only when applying the solution do we evaluate
the feasability of the cast and determine if it always succeeds,
always fails, or conditionally succeeds. This changes how the
resulting AST is represented and can also emit diagnostics.
If the conditional cast is at this stage determined to always
succeed, we treat it as an unconditional cast, going through
ExprRewriter::coerceToType() to build the AST for the coercion.
However conditional cast constraints don't enter the same
restrictions into the solution as unconditional casts do, so
coerceToType() would fall over if casting a Swift type to a CF
type by first bridging the Swift type to Objective-C.
Get around this by checking for this case explicitly when
lowering a CoerceExpr.
It feels like there's a more fundamental issue here with how
casts are modeled in the constraint solver, but I'm not going
to try understanding that now.
Fixes <rdar://problem/32227571>.
where we type check the destination first, then apply its type to the source.
This allows us to get diagnostics for assignments that are as good as PBD
initializers and other cases.
Swift SVN r31404
The case where this comes up is when people name their app and framework
targets the same thing, or when they've renamed their test target module
in an attempt to avoid issues with NSClassFromString and differing
runtime names. We currently do various wrong things when this happens,
so just emit an error instead.
I left a hole for our overlays, which use '@exported import <the-current-module>'
to get at their Clang modules. The previous commit means this can be
replaced by -import-underlying-module, but that doesn't help our tests,
which use -enable-source-import for their overlays. Which we should stop doing.
rdar://problem/21254367
Swift SVN r29440
