Assert in initializers experiment

[lrhn]

We are experimenting with allowing asserts in initializer lists.
See the design document.

For this experiment, we need (behind the flag --assert-initializer):

• the VM to implement the assertions (Committed: 99439a3)
• the analyzer to parse the assertions (but not necessarily analyze them yet). (The analyzer should parse asserts in initializer lists. #27142)
• the formatter to parse the assertions. (Formatter should handle asserts in initializer list. dart_style#522)

That should be sufficient for the people behind issue #24841 to test out the implementation and see if it covers their needs.

[a14n]

Could the design document be made public?

[lrhn]

My docs-fu is too weak, so I converted the design document it to a gist.

[a14n]

thanks

[bwilkerson]

The doc defines the assert statement as being assert(expression), but the analyzer accepts an optional second argument. Is the omission an oversight, or should asserts in constructor initializers not allow a message?

[lrhn]

We are going to add the second "argument" to assert, so keep it for now.

[dgrove]

@lrhn can you please provide an update?

[dgrove]

@lrhn can you provide an update?

[jmesserly]

FYI DDC issue #27809

[munificent]

This is not a 1.50 feature, so kicking out of the milestone. (I think we accidentally got it confused with assert messages, which are in 1.50).

[sethladd]

This is done, right? flutter has this turned on now.

[munificent]

I'm not sure if this tracking issue is for the experiment or the feature. If the former, I guess it's closable? If the latter, no, because we haven't decided if we want to commit to it, remove the flag, etc.

[jmesserly]

oh gosh, yeah. Also DDC doesn't implement it yet, which I think nowadays we want for new language features? (it's not hard to implement btw)

[lrhn]

This is a Flutter-only experiment (which is why it's VM+analyzer only so far, and should perhaps also include the formatter). That is all it is at this point. There is no decision to make it a language feature yet, it's not implemented by DDC or dart2js, and unless the experiment is a success, it will eventually be removed again.
The exact conditions for considering it a success isn't set in stone, but it should add non-negligible value for the Flutter developers. If it isn't, then it's just not worth its own weight.

[munificent]

The experiment has graduated to a feature. Closing out this bug in favor of #30968.

[sethladd]

Thanks for the help!