Analyzer does not report an error when `new` is used in a non-constructor position with constructor tearoffs enabled

[leafpetersen]

With constructor tearoffs enabled, the analyzer correctly emits an error on the definition of the field in C in the code below, but issues no errors on the access of new on an instance of C and on foo in main. I believe that all of those should be an error. This should cause a failure in co19/Language/Expressions/Instance_Creation/New/type_t05 (source here) when constructor tearoffs are enabled. See logs here but note that the analyzer run failed with an infrastructure issue . CL turning on the flag is here.

cc @eernstg @lrhn @srawlins @scheglov @devoncarew

class C {
  int new = 42;
}

main() {
  new C().new is int;
  dynamic foo;
  foo.new;
  foo.new();
}

[lrhn]

They should all be compile-time errors. They all use .new on something which does not denote a class, which is not valid.

For the foo.news, it's an error during resolution or static type checking, not parsing, because the grammar is potentially a constructor tearoff/invocation.

For new C().new I don't think our grammar allows it at all, but @eernstg would know for sure. (Is .new a selector, where we then reject if the receiver does not denote a class, or is it special syntax which requires the prior terms to be (prefix.)?className(<typeArgs>)??)

It doesn't really matter how the parser/compiler gets to rejecting the program, they can optimize for recovery and good error message, as long as all valid programs, and only valid programs, get through the process.

[eernstg]

I believe the grammar in Dart.g, in particular the updates in 6facd6d, can be considered to specify the new syntax added by the constructor-tearoffs feature bundle. With that, we have two syntax errors (int new and new C().new), but it is of course not required for an implementation to label any error as a syntax error. I believe the behavior of dart and dartanalyzer from commit a6cc772 (a fresh one) is fine for int new, but they fail to report new C().new as an error (of any kind).

foo.new and foo.new() should be reported as compile-time errors, because foo fails to be a statically resolved reference to a class (it should be a class, and that class should have a constructor named foo, but we don't even get to step two).

Cf. dart-lang/language#1837.

[leafpetersen]

Tests affected:

• https://github.com/dart-lang/co19/blob/cc4df792d0f02f15bfe04911c1f856b90cb7cbf4/Language/Reference/Lexical_Rules/Reserved_Words/new_t04.dart