Following on from updating regular member completion, this hooks up unresolved
member completion (i.e. .<complete here>) to the typeCheckForCodeCompletion API
to generate completions from all solutions the constraint solver produces (even
those requiring fixes), rather than relying on a single solution being applied
to the AST (if any). This lets us produce unresolved member completions even
when the contextual type is ambiguous or involves errors.
Whenever typeCheckExpression is called on an expression containing a code
completion expression and a CompletionCallback has been set, each solution
formed is passed to the callback so the type of the completion expression can
be extracted and used to lookup up the members to return.
Since the user can now write additional member accesses off of an UnresolvedMemberExpr, we should offer all available completions rather than just those that match the contextual type.
For exmaple:
func foo(_: Int, _: IntOption)
func foo(_: Float, _: FloatOption)
foo(intVal, .<HERE>)
Previously code completion suggests static member from 'IntOption' and
'FloatOption' without any prioritization. Prioritize members from
'IntOption' because the user probably wants to input them.
In such cases, 'CodeCompletionExpr' at the cursor position is
pre-typechecked to 'IntOption'. So mark results with matching type with
'ExprSpecific'.
rdar://problem/62121221
PatternBindingInitializer may not be attached to any
PatternBindingDecl. e.g.
struct S {
@CustomAttr(something)
}
In this case DeclContext for 'something' is PatternBindingInitializer,
but it doesn't have PatternBindingDecl because it's not written yet.
Fixes a crash in code-completion.
rdar://problem/53034550
