Dart VM: Cascaded calls do not work in class initializer lists

[larsbak]

The following code exposes a bug in the VM parser.
Cascaded calls are legal in class initializer expressions.
//Lars

class X {
 Stopwatch p;
 X() : p = new Stopwatch()..start();
}
main() => new X();

'Bug.dart': Error: line 3 pos 27: unexpected token '..'
 X() : p = new Stopwatch()..start();
                          ^

[DartBot]

This comment was originally written by @mhausner

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Cascaded calls are not legal in field initializer expressions. The language spec says the initializer expression is a conditionalExpression, which does not include cascade sections.

If you want cascades in initializer expressions, the grammar has to be changed. Or you can simply write

p = (new Stopwatch()..start)

[DartBot]

This comment was originally written by @mhausner

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Added Invalid label.

[larsbak]

I'm surprised a cascaded call cannot exist as a class initializer expression.
dart2js and dart_analyzer DO both handle the above case and I do not see any valid reason why the VM should reject the program.
Should be grammar be changed?

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Set owner to @gbracha.
Added Triaged label.

[lrhn]

I see no immediate reason why the RHS of an initializer assignment can't be 'expression', just as for normal assignment.

[iposva-google]

Removed Area-VM label.
Added Area-Language label.

[gbracha]

Possibly the grammar needs to be changed. We'll see.

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Added Accepted label.

[gbracha]

The grammar has required a conditionalExpression in that position until now. Even then, there is an ad hoc restriction on function expressions because

C(): x = (y) => 3;

is ambiguous. If you now support full expressions you need to make sure that

C(): x = z = y() => 3;

is flagged correctly. I don't think this is worthwhile.

We can do something more ad hoc, such as allowing

conditionalExpression cascadeSection*

in an initializer. Or just use parentheses.

[gbracha]

Removed this from the M1 milestone.
Added this to the M2 milestone.

[gbracha]

Per comment 7, changed the grammar so that cascadeExpressions are also allowed in the initializer.

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Added Done label.

[gbracha]

Bugs:

dart2js: issue #6953.
VM: issue #6954.
Analyzer: issue #6955