Using malformed types should produce a static warning in dartc

[DartBot]

This issue was originally filed by ms...@unipro.ru

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Section 10.29 (Type test): "It is a static warning if T does not denote a type available in the current lexical scope.".

However, the following test:

class C<T> {}

main() {
  var o = null;
  o is MalformedType;
  o is C<int, int>;
  o is C<MalformedType>;
}

produces a message on dartc (r8030), which does not look like a warning:
'no such type "MalformedType"
C<C.T>: wrong number of type arguments (2). Expected 1
no such type "MalformedType"
Compilation failed with 3 problems.'
 

[kasperl]

Added Area-Analyzer, Triaged labels.

[danrubel]

Added this to the M1 milestone.

[scheglov]

1. "o is MalformedType" - should be warning. "It is a static warning if T does not denote a type available in the current lexical scope."

 Hm..

"13.8 Parameterized Types".
"Let G < A1; : : : ; An > be a parameterized type.
It is a static type warning if G is not an accessible generic type declaration
with n type parameters. It is a static type warning if Ai
; i 2 1::n does not
denote a type in the enclosing lexical scope."

But in "10.29 Type Test"
"It is a compile-time error if T is a parameterized type of the form G < T1; : : : ; Tn > and G is not a generic type with n type parameters."

1. "o is C<int, int>" - not sure, conflict between "13.8" and "10.29"

2. "o is C<MalformedType>" - not sure. "13.8" say that this should be warning, but because of conflict I'm not sure if we should follow "13.8" of something else.

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   Set owner to @gbracha.
   Added NeedsInfo label.

[scheglov]

According to Gilad (I've asked for clarification during handling related issue):
"The distinction is based on whether G is being used at run time. Both instance creation and type testing (and now type casting) involve actually passing type parameters at run time. Type annotations do not."

Me: So, using not existing type for check is OK (warning), but using existing type incorrectly is error?
Gilad: Yes. I've explained why this is the case.

So, I conclude that for this code DartC works as intendent.

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Set owner to @scheglov.
Added AsDesigned label.