This fixes the following tests which are now crashing due to hitting
unreachable "no buffer containing location found" in
`SourceManager::findBufferContainingLoc`:
- attr/attr_dynamic_member_lookup.swift
- AutoDiff/Sema/DerivativeRegistrationCrossModule/main.swift
- Constraints/construction.swift
- Constraints/members.swift
- NameLookup/accessibility.swift
- Sema/call_as_function_simple.swift
The root cause of the crash is as follows. All the tests involve
emitting `InaccessibleMemberFailure` error diagnostic (see
`InaccessibleMemberFailure::diagnoseAsError`). When `DeclNameLoc
nameLoc` is initialized via default constructor and is not re-assigned
with smth meaningful later, the check `nameLoc.isValid()` returns `true`
even though it should be `false`. It turns out that we treat `const void
*LocationInfo` as `SourceLoc` and hope that if `LocationInfo` is
`nullptr`, casting this to `SourceLoc` would produce a "default"
`SourceLoc` with `Pointer` member set to `nullptr`. But such a cast (see
`getSourceLocs()` member of `DeclNameLoc`) is undefined behavior. So,
the compiler assumes that `Pointer` member of `SourceLoc` we try to cast
to is not `nullptr` (due to strict aliasing rule), which leads to
`nameLoc.isValid()` being mistakenly computed as `true`.
This patch resolves the issue by handling this special case separately.
When referencing a function in the type checker, drop argument labels
when we don't need them to type-check an immediate call to that
function. This provides the semantic behavior of SE-0111, e.g.,
references to functions as values produce unlabeled function types,
without the representational change of actually dropping argument
labels from the type system.
At the moment, this only works for bare references to functions. It
still needs to be pushed through more of the type checker and more AST
nodes to work in the general case.
Keep this work behind the frontend flag
-suppress-argument-labels-in-types for now.
When one spells a compound declaration name in the source (e.g.,
insertSubview(_:aboveSubview:), keep track of the locations of the
base name, parentheses, and argument labels.
