Use it to provide an idealized API for the VarDecl case in validateDecl.
In reality, a lot of work is needed to rationalize the dependency
structure of this request. To start, the callers of
typeCheckPatternBinding must be eliminated piecemeal. Once that is
done, the AST should introduce pattern binding decls along all the
places where getParentStmt() used to apply.
This is an amalgam of simplifications to the way VarDecls are checked
and assigned interface types.
First, remove TypeCheckPattern's ability to assign the interface and
contextual types for a given var decl. Instead, replace it with the
notion of a "naming pattern". This is the pattern that semantically
binds a given VarDecl into scope, and whose type will be used to compute
the interface type. Note that not all VarDecls have a naming pattern
because they may not be canonical.
Second, remove VarDecl's separate contextual type member, and force the
contextual type to be computed the way it always was: by mapping the
interface type into the parent decl context.
Third, introduce a catch-all diagnostic to properly handle the change in
the way that circularity checking occurs. This is also motivated by
TypeCheckPattern not being principled about which parts of the AST it
chooses to invalidate, especially the parent pattern and naming patterns
for a given VarDecl. Once VarDecls are invalidated along with their
parent patterns, a large amount of this diagnostic churn can disappear.
Unfortunately, if this isn't here, we will fail to catch a number of
obviously circular cases and fail to emit a diagnostic.
And provide better semantic background by surrounding 'nil' in ticks when it is referred to as a value
Added missing tests for certain cases involving nil capitalization
<stdin>:1:16: error: nil cannot initialize specified type 'Int'
var foo: Int = nil
^
<stdin>:1:10: note: add '?' to form the optional type 'Int?'
var foo: Int = nil
^
?
