Sdk: unexpected token 'Function'

[zoechi]

'package:code_builder/dart/core.dart': error: line 114 pos 26: unexpected token 'Function'
  final ReferenceBuilder Function = _ref('Function');
                         ^

Dart VM version: 1.23.0-edge.b27f5f910078d8a53cbfdb33663a50fa96812e5f (Thu Feb  2 00:04:28 2017) on "linux_x64"

[zoechi]

https://github.com/dart-lang/code_builder/blob/master/lib/dart/core.dart#L114

Is this a bug? Is Function used as a type becoming invalid? Is there a workaround how to prepare for the future?

[eernstg]

Function has always been the core library type that marked a type as being a function type. After a large amount of discussion we decided on a syntax for specifying specific function types using that same identifier, e.g., a function that receives an int and returns an int can be written as int Function(int). The intuition is that you just declare a function header, then replace the name by Function, and (optionally) drop the names of parameters (except named ones, if any), so this offers a way to write function types in many locations and in a reasonably readable format, in addition to the ability to use the same syntax in typedefs (where you previously couldn't declare a generic method type).

For more details about this feature, please check out https://github.com/dart-lang/sdk/issues/27527.

We are currently working with this feature and the breakage that it causes, in particular because it will be similar to a built-in identifier (i.e., it cannot be the name of a type, except for the one in core). The parser is allowed to disambiguate declarations based on having seen Function in a specific context, but I think that shouldn't cause the error message that you have seen (so it may indeed be a bug).

However, you won't be able to use Function as a user-defined identifier in many contexts. The rule of thumb would be to not declare anything to have the name Function. Hope you can adjust your code (or code generators!) to follow that rule without too much hassle.

[zoechi]

@eernstg thanks a lot for your explanation.
The code is in the code_builder package in the dart-lang repo (see link above).

I also created https://github.com/dart-lang/code_builder/issues/69 recently.
Perhaps you can post a comment, if you think the code should be changed.
If the code is supposed to work, and just caused by a bug in the bleeding edge VM, then there is nothing to do of course.

I'm totally fine with bugs caused by using bleeding edge builds not being fixed.
My intention is just to point out issues ahead of time if possible, so they can be fixed before a new release is published and stuff breaks in stable.

[eernstg]

The parser is allowed to disambiguate and commit to seeing an inline function type (as opposed to a typedef'd function type) when it has seen type 'Function' ('(' | '<'), but there is no '(' and no '<' following 'Function' here. So the vm parser should not make any attempts to parse any part of final ReferenceBuilder Function = _ref('Function'); as a function type, and hence it is a bug in the vm parser (at commit b27f5f910078d8a53cbfdb33663a50fa96812e5f). Thanks for catching this so early!

[zoechi]

@eernstg Thanks for clarification. Wasn't entirely sure from your previous comment.

[crelier]

Agreed, this is my bug in the VM parser. I first had it right and then tried to improve error messages, totally forgetting that locals and members are allowed to be named "Function". A fix is under review: https://codereview.chromium.org/2673893002/

Thanks for the report.

Note however that it will be tricky to use such locals and members, especially to call a closure named "Function". I would recommend using a different name, e.g. "Function_".

[a-siva]

We should probably cherry pick this fix to 1.22

[whesse]

This issue is not in 1.22, because the function syntax only starts being accepted in 1.23, I think.
Do we need to cherry-pick all the relevant CLs, or none of them?

[crelier]

I'd say none of them.

On Mon, Feb 6, 2017 at 9:16 AM, William Hesse [e-mail]
wrote:

This issue is not in 1.22, because the function syntax only starts being
accepted in 1.23, I think.
Do we need to cherry-pick all the relevant CLs, or none of them?

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[eernstg]

Right, milestone 1.23 was indicated for #27527 when this comment was written, confirming what Bill said.

[a-siva]

Agree, my bad I thought it went into 1.22

On Mon, Feb 6, 2017 at 12:28 AM, Erik Ernst [e-mail]
wrote:

Right, milestone 1.23 was indicated for #27527
https://github.com/dart-lang/sdk/issues/27527 when this comment
https://github.com/dart-lang/sdk/issues/27527#issuecomment-273707746
was written, confirming what Bill said.

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