Implement adjusted member conflict rules

[eernstg]

(Edit May 31st by eernstg: The member conflicts rules have been simplified considerably, which is reflected in the simpler text below. E.g., many rows in the table are now justified by the same line number in the specification.)

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Cf. issue #33077, CL 54410, and commits e8bb129816f75f6e0b38f7fbff32e3b3d919027c and 08c893d55bfe7e2d4b0d217ca45b238ee081b746, the Dart 2 rules for which pairs of member declarations constitute a conflict have changed slightly, and expressed in a significantly simpler form. This issue is concerned with the implementation and testing of the updated rules.

For instance, it is now an error if a class declares a setter named v= and has a method named v, which will make the two declarations of m here a conflict. Here is a complete table showing the member declaration conflicts with the new ruleset:

Member1                       Member2                       Conflict Reason
-----------------------------------------------------------------------------
declares constructor `C.n`    declares static getter `n`    2449
declares constructor `C.n`    declares static method `n`    2449
declares constructor `C.n`    declares static setter `n=`   2449
declares static getter `n`    declares static method `n`    346, 2450, and 2451
declares static getter `n`    has instance getter `n`       2452
declares static getter `n`    has instance method `n`       2452
declares static getter `n`    has instance setter `n=`      2452
declares static method `n`    has instance getter `n`       2452
declares static method `n`    has instance method `n`       2452
declares static method `n`    has instance setter `n=`      2452
declares static setter `n=`   declares static method `n`    2450 and 2451
declares static setter `n=`   has instance getter `n`       2452
declares static setter `n=`   has instance method `n`       2452
declares static setter `n=`   has instance setter `n=`      2452
has instance getter `n`       has instance method `n`       2450 or 2451, possibly 346
has instance setter `n=`      has instance method `n`       2450 or 2451

The number in the third column is the line number in dartLangSpec.tex as of c6129f768eaee60822d0ab98b909b0a509fb22bf where the given situation is specified to be a conflict (that is, a compile-time error or a static warning (which is also an error in Dart 2)).

The conflicts listed above are concerned with conflicts among member declarations that are beyond the simple name clash where two declarations introduce the same name into the same scope, that is, the names may be different, and they may be in different scopes.

In particular, the above list says nothing about overriding (because overriding is always concerned with two declarations of the same kind, and the list does not mention any such case).

It may be useful to consider certain cases where there is no conflict:

Member1                       Member2
---------------------------------------------------------
declares static setter `n=`   declares static getter `n`
has instance getter `n`       has instance setter `n=`
declares constructor `C.n`    has instance method `n`
declares constructor `C.n`    has instance getter `n`
declares constructor `C.n`    has instance setter `n=`

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Subtasks.

• [x] front end (#33237).
• [ ] analyzer (#33236).
• [ ] tests (#33238).

[mit-mit]

@eernstg how important is this for Dart 2 stable? Is this a breaking change or not? Do we have tests?

We are asking as this one is not in the Dart 2 milestone, but the CFE specific issue (https://github.com/dart-lang/sdk/issues/32613) is.

[eernstg]

It is breaking because it makes m in https://github.com/dart-lang/sdk/issues/33077#issue-321323537 an error, and also because it introduces a conflict between a named constructor and certain static members.

Almost all combinations of methods (static or instance) with the same base name (a method/getter named n has base name n, a setter named n= has base name n) were already an error, so anyone who knew that would probably not try to exploit that missing case (has method, declares setter), which means that it is expected to cause very little breakage.

I'm not aware of a concrete presubmit experiment which would reveal the breakage more precisely.

Note that #33237 (the Fasta subtask) was closed 10 days ago, which should imply that bleeding edge based usages would already have seen the breakage.

[eernstg]

I just noticed that issue #32613 is not closed, although #33237 is closed, and also that #33237 was closed based on a commit with message 'Check for conflicts between a static setter and a constructor or static method', which does not mention the case in #33077.

Issue #32613 is not exactly the CFE subtask for this issue, it is a broader task which is concerned with the implementation of conflict checking for members (at all, they used to be completely missing), not just the changes which were introduced as of 08c893d55bfe7e2d4b0d217ca45b238ee081b746. At this point, however, resolving issue #32613 should imply that #33237 is also resolved, because a full implementation should include the latest updates.

My current interpretation of the situation is that #33237 was closed too early (unless the remaining cases including "declares instance setter, has instance method" have been implemented in some other commit), and also that #33237 and #32613 should be consolidated (such that they do not overlap, or at least such that the overlap is known and is being managed).