Using let with attributes

[cueckoo]

Originally opened by @PierreR in cuelang/cue#938

It looks like let cannot be used with attributes ?

let Version = *"0.0.0" | string @tag(version)

version: "\(Version)"

would fail with the following error (using https://tip.cuelang.org/play/?id=kTgiOQPmiqe):

failed to load: missing ',' in struct literal (and 1 more errors)

The following works:

_version = *"0.0.0"  | string @tag(version)

version: "\(_version)"

but I would like to restrain the scope of _version to local (ensuring it is not set somewhere else). In that regard, a let seems more appropriate.

Alias would kind of work:

Version= "dummy" : *"0.0.0" | string @tag(version)

version: "\(Version)"

but does not seem to what I want because the "dummy" label is useless and if re-use somewhere else possibly damaging.

Thanks for your help.

[cueckoo]

Original reply by @PierreR in cuelang/cue#938 (comment)

The usecase might still be a valid one but as far as I am concerned this is not blocking or a big deal.
At the end, I have defined what I expect from a version down the file hierarchy in a common place as a definition.

[cueckoo]

Original reply by @mpvl in cuelang/cue#938 (comment)

Attributes are indeed not allowed on let. I would be quite a substantial change to support, as let is not something that is visible in the API, for instance, and which is the only place were attributes are used.

Am I guessing correctly that you are envisioning picking up the attribute in the cue AST rather than the API?

[cueckoo]

Original reply by @PierreR in cuelang/cue#938 (comment)

Yes, I don't expect using the API soon (just plain CUE for now).
Thanks for the feedback.

[cueckoo]

Original reply by @mpvl in cuelang/cue#938 (comment)

I see your point in how it could be useful, though. Feel free to open a feature request. This will allow tracking if this is a more widely desired feature. Haven’t thought about the implications yet, but barring any issues I could see this work for the tag use case, for example.