Clarify which language violations result in errors versus warnings in the language specification

[DartBot]

This issue was originally filed by mmendez@google.com

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What steps will reproduce the problem?

1. As an example, comment out the "ClassOverrideNegativeTest: Fail" line in test/language/language.status file (only applies to dartc).
2. From the compiler directory run "../tools/build.py --mode debug --arch dartc" then run "../tools/test.py --mode debug --arch dartc".

What is the expected output? What do you see instead?
Dartc generates a warning to stdout about the method override problem. However, it treats it as a warning and produces JS code. For the same file, the VM tries to load the file, reports an error and stops. Effectively, it is as if dartc should have generated a compilation error instead of a warning.

I'd like to get clarity on which violations of the language specification should be errors and which should be warnings.

Please use labels and text to provide additional information.

[gbracha]

The spec states:

It is a static warning if an instance method m1 overrides an instance member m2 and the type of m1 is not a subtype of the type of m2.

Hence:

a. The situation is unambiguously specified and there is no spec issue.
b. dartC is behaving correctly.
c. The VM is not in compliance with the specification.

I discussed this with members of the VM team last week, so I'm sure it will be resolved soon.

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Set owner to @iposva-google.
Removed Priority-High, Area-Language, Area-Compiler labels.
Added Priority-Medium, Area-VM labels.

[iposva-google]

Set owner to @crelier.

[crelier]

Fixed in r489.

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Added Fixed label.