Unlike in Swift, Obj-C allows method overrides to be declared in extensions
(categories), even outside of the module that defines the type that is being
extended. When MemberImportVisibility is enabled, these overrides must be
filtered out to prevent them from hijacking name lookup and causing the
compiler to insist that the module that defines the extension be imported.
Resolves rdar://145329988.
`recordObjCOverride()` records semantic overrides for imported Obj-C methods.
Since these methods are imported from a different language, it doesn't make
sense to enforce Swift's member import visibility rules when performing lookups
to find overridden methods. Doing so caused the Constrain Solver to lack
important information needed to eliminate overloads, resulting in erroneous
ambiguities.
Resolves rdar://141636723.
Create some test cases that demonstrate MemberImportVisibility behavior with respect referencing inherited members. There are already tests that demonstrate overrides, but nothing seemed to show the behavior when referencing an inherted member through a derived type. I wanted to verify this behavior so I wrote a test to demonstrate it. It seems reasonable to check-in the test to ensure the behavior remains consistent.
Previously, the constraint solver would first attempt member lookup that
excluded members from transitively imported modules. If there were no viable
candidates, it would perform a second lookup that included the previously
excluded members, treating any candidates as unviable. This meant that if the
member reference did resolve to one of the unviable candidates the resulting
AST would be broken, which could cause unwanted knock-on diagnostics.
Now, members from transitively imported modules are always returned in the set
of viable candidates. However, scoring will always prioritize candidates from
directly imported modules over members from transitive imports. This solves the
ambiguities that `MemberImportVisibility` is designed to prevent. If the only
viable candidates are from transitively imported modules, though, then the
reference will be resolved successfully and diagnosed later in
`MiscDiagnostics.cpp`. The resulting AST will not contain any errors, which
ensures that necessary access levels can be computed correctly for the imports
suggested by `MemberImportVisibility` fix-its.
Resolves rdar://126637855.
In existing Swift, an `@_exported import` in any source file makes the
declarations from the imported module visible in all source files. It's unclear
whether this is an explicit decision or is simply and unintended consequence of
effectively adding an implicit import to each source file for the module being
compiled.
Although it's not clear whether this behavior is desirable, the behavior of
member lookup when the MemberImportVisibility feature is enabled should align
with it in order to avoid causing unnecessary churn in required imports.
Resolves rdar://132525152.
